diff --git a/abstract_client.cpp b/abstract_client.cpp
index 64e6cec193..363e4fa508 100644
--- a/abstract_client.cpp
+++ b/abstract_client.cpp
@@ -211,7 +211,7 @@ void AbstractClient::setActive(bool act)
                              ? rules()->checkOpacityActive(qRound(opacity() * 100.0))
                              : rules()->checkOpacityInactive(qRound(opacity() * 100.0));
     setOpacity(ruledOpacity / 100.0);
-    workspace()->setActiveClient(act ? this : NULL);
+    workspace()->setActiveClient(act ? this : nullptr);
 
     if (!m_active)
         cancelAutoRaise();
diff --git a/activation.cpp b/activation.cpp
index 9ffe34450f..0c9a3af72d 100644
--- a/activation.cpp
+++ b/activation.cpp
@@ -239,12 +239,12 @@ void Workspace::setActiveClient(AbstractClient* c)
     StackingUpdatesBlocker blocker(this);
     ++set_active_client_recursion;
     updateFocusMousePosition(Cursor::pos());
-    if (active_client != NULL) {
+    if (active_client != nullptr) {
         // note that this may call setActiveClient( NULL ), therefore the recursion counter
         active_client->setActive(false);
     }
     active_client = c;
-    Q_ASSERT(c == NULL || c->isActive());
+    Q_ASSERT(c == nullptr || c->isActive());
 
     if (active_client) {
         last_active_client = active_client;
@@ -291,9 +291,9 @@ void Workspace::setActiveClient(AbstractClient* c)
  */
 void Workspace::activateClient(AbstractClient* c, bool force)
 {
-    if (c == NULL) {
+    if (c == nullptr) {
         focusToNull();
-        setActiveClient(NULL);
+        setActiveClient(nullptr);
         return;
     }
     raiseClient(c);
@@ -358,7 +358,7 @@ void Workspace::takeActivity(AbstractClient* c, ActivityFlags flags)
 
     if (flags & ActivityFocus) {
         AbstractClient* modal = c->findModal();
-        if (modal != NULL && modal != c) {
+        if (modal != nullptr && modal != c) {
             if (!modal->isOnDesktop(c->desktop()))
                 modal->setDesktop(c->desktop());
             if (!modal->isShown(true) && !modal->isMinimized())  // forced desktop or utility window
@@ -434,7 +434,7 @@ AbstractClient *Workspace::clientUnderMouse(int screen) const
             return client;
         }
     }
-    return 0;
+    return nullptr;
 }
 
 // deactivates 'c' and activates next client
@@ -446,9 +446,9 @@ bool Workspace::activateNextClient(AbstractClient* c)
 
     closeActivePopup();
 
-    if (c != NULL) {
+    if (c != nullptr) {
         if (c == active_client)
-            setActiveClient(NULL);
+            setActiveClient(nullptr);
         should_get_focus.removeAll(c);
     }
 
@@ -462,7 +462,7 @@ bool Workspace::activateNextClient(AbstractClient* c)
     if (!options->focusPolicyIsReasonable())
         return false;
 
-    AbstractClient* get_focus = NULL;
+    AbstractClient* get_focus = nullptr;
 
     const int desktop = VirtualDesktopManager::self()->current();
 
@@ -473,7 +473,7 @@ bool Workspace::activateNextClient(AbstractClient* c)
         get_focus = clientUnderMouse(c ? c->screen() : screens()->current());
         if (get_focus && (get_focus == c || get_focus->isDesktop())) {
             // should rather not happen, but it cannot get the focus. rest of usability is tested above
-            get_focus = NULL;
+            get_focus = nullptr;
         }
     }
 
@@ -492,10 +492,10 @@ bool Workspace::activateNextClient(AbstractClient* c)
         }
     }
 
-    if (get_focus == NULL)   // last chance: focus the desktop
+    if (get_focus == nullptr)   // last chance: focus the desktop
         get_focus = findDesktop(true, desktop);
 
-    if (get_focus != NULL)
+    if (get_focus != nullptr)
         requestFocus(get_focus);
     else
         focusToNull();
@@ -513,9 +513,9 @@ void Workspace::setCurrentScreen(int new_screen)
     closeActivePopup();
     const int desktop = VirtualDesktopManager::self()->current();
     AbstractClient *get_focus = FocusChain::self()->getForActivation(desktop, new_screen);
-    if (get_focus == NULL)
+    if (get_focus == nullptr)
         get_focus = findDesktop(true, desktop);
-    if (get_focus != NULL && get_focus != mostRecentlyActivatedClient())
+    if (get_focus != nullptr && get_focus != mostRecentlyActivatedClient())
         requestFocus(get_focus);
     screens()->setCurrent(new_screen);
 }
@@ -589,7 +589,7 @@ bool Workspace::allowClientActivation(const KWin::AbstractClient *c, xcb_timesta
 
     // No active client, it's ok to pass focus
     // NOTICE that extreme protection needs to be handled before to allow protection on unmanged windows
-    if (ac == NULL || ac->isDesktop()) {
+    if (ac == nullptr || ac->isDesktop()) {
         qCDebug(KWIN_CORE) << "Activation: No client active, allowing";
         return true; // no active client -> always allow
     }
@@ -643,7 +643,7 @@ bool Workspace::allowFullClientRaising(const KWin::AbstractClient *c, xcb_timest
         return true;
     if (level == 4)   // extreme
         return false;
-    if (ac == NULL || ac->isDesktop()) {
+    if (ac == nullptr || ac->isDesktop()) {
         qCDebug(KWIN_CORE) << "Raising: No client active, allowing";
         return true; // no active client -> always allow
     }
@@ -706,7 +706,7 @@ void Client::updateUserTime(xcb_timestamp_t time)
             && (m_userTime == XCB_TIME_CURRENT_TIME
                 || NET::timestampCompare(time, m_userTime) > 0)) {    // time > user_time
         m_userTime = time;
-        shade_below = NULL; // do not hover re-shade a window after it got interaction
+        shade_below = nullptr; // do not hover re-shade a window after it got interaction
     }
     group()->updateUserTime(m_userTime);
 }
@@ -726,7 +726,7 @@ xcb_timestamp_t Client::readUserTimeMapTimestamp(const KStartupInfoId *asn_id, c
 
     // newer ASN timestamp always replaces user timestamp, unless user timestamp is 0
     // helps e.g. with konqy reusing
-    if (asn_data != NULL && time != 0) {
+    if (asn_data != nullptr && time != 0) {
         if (asn_id->timestamp() != 0
                 && (time == -1U || NET::timestampCompare(asn_id->timestamp(), time) > 0)) {
             time = asn_id->timestamp();
@@ -742,7 +742,7 @@ xcb_timestamp_t Client::readUserTimeMapTimestamp(const KStartupInfoId *asn_id, c
         // from already running application if this application
         // is not the active one (unless focus stealing prevention is turned off).
         Client* act = dynamic_cast<Client*>(workspace()->mostRecentlyActivatedClient());
-        if (act != NULL && !belongToSameApplication(act, this, SameApplicationCheck::RelaxedForActive)) {
+        if (act != nullptr && !belongToSameApplication(act, this, SameApplicationCheck::RelaxedForActive)) {
             bool first_window = true;
             auto sameApplicationActiveHackPredicate = [this](const Client *cl) {
                 // ignore already existing splashes, toolbars, utilities and menus,
@@ -765,7 +765,7 @@ xcb_timestamp_t Client::readUserTimeMapTimestamp(const KStartupInfoId *asn_id, c
                     ; // is transient for currently active window, even though it's not
                 // the same app (e.g. kcookiejar dialog) -> allow activation
                 else if (groupTransient() &&
-                        findInList<Client, Client>(clientMainClients(), sameApplicationActiveHackPredicate) == NULL)
+                        findInList<Client, Client>(clientMainClients(), sameApplicationActiveHackPredicate) == nullptr)
                     ; // standalone transient
                 else
                     first_window = false;
@@ -801,7 +801,7 @@ xcb_timestamp_t Client::userTime() const
     xcb_timestamp_t time = m_userTime;
     if (time == 0)   // doesn't want focus after showing
         return 0;
-    Q_ASSERT(group() != NULL);
+    Q_ASSERT(group() != nullptr);
     if (time == -1U
             || (group()->userTime() != -1U
                 && NET::timestampCompare(group()->userTime(), time) > 0))
diff --git a/activities.cpp b/activities.cpp
index 42c5db8019..262cd54bb1 100644
--- a/activities.cpp
+++ b/activities.cpp
@@ -47,7 +47,7 @@ Activities::Activities(QObject *parent)
 
 Activities::~Activities()
 {
-    s_self = NULL;
+    s_self = nullptr;
 }
 
 KActivities::Consumer::ServiceStatus Activities::serviceStatus() const
diff --git a/client.cpp b/client.cpp
index 2be0103539..873522efe0 100644
--- a/client.cpp
+++ b/client.cpp
@@ -106,17 +106,17 @@ Client::Client()
     , m_managed(false)
     , m_transientForId(XCB_WINDOW_NONE)
     , m_originalTransientForId(XCB_WINDOW_NONE)
-    , shade_below(NULL)
+    , shade_below(nullptr)
     , m_motif(atoms->motif_wm_hints)
     , blocks_compositing(false)
-    , shadeHoverTimer(NULL)
+    , shadeHoverTimer(nullptr)
     , m_colormap(XCB_COLORMAP_NONE)
-    , in_group(NULL)
-    , ping_timer(NULL)
+    , in_group(nullptr)
+    , ping_timer(nullptr)
     , m_killHelperPID(0)
     , m_pingTimestamp(XCB_TIME_CURRENT_TIME)
     , m_userTime(XCB_TIME_CURRENT_TIME)   // Not known yet
-    , allowed_actions(0)
+    , allowed_actions(nullptr)
     , shade_geometry_change(false)
     , sm_stacking_order(-1)
     , activitiesDefined(false)
@@ -128,14 +128,14 @@ Client::Client()
 {
     // TODO: Do all as initialization
     syncRequest.counter = syncRequest.alarm = XCB_NONE;
-    syncRequest.timeout = syncRequest.failsafeTimeout = NULL;
+    syncRequest.timeout = syncRequest.failsafeTimeout = nullptr;
     syncRequest.lastTimestamp = xTime();
     syncRequest.isPending = false;
 
     // Set the initial mapping state
     mapping_state = Withdrawn;
 
-    info = NULL;
+    info = nullptr;
 
     shade_mode = ShadeNone;
     deleting = false;
@@ -214,7 +214,7 @@ void Client::releaseWindow(bool on_shutdown)
     }
 #endif
     destroyWindowManagementInterface();
-    Deleted* del = NULL;
+    Deleted* del = nullptr;
     if (!on_shutdown) {
         del = Deleted::create(this);
     }
@@ -856,7 +856,7 @@ void Client::setShade(ShadeMode mode)
         if (shade_mode == ShadeHover) {
             ToplevelList order = workspace()->stackingOrder();
             // invalidate, since "this" could be the topmost toplevel and shade_below dangeling
-            shade_below = NULL;
+            shade_below = nullptr;
             // this is likely related to the index parameter?!
             for (int idx = order.indexOf(this) + 1; idx < order.count(); ++idx) {
                 shade_below = qobject_cast<Client*>(order.at(idx));
@@ -867,7 +867,7 @@ void Client::setShade(ShadeMode mode)
             if (shade_below && shade_below->isNormalWindow())
                 workspace()->raiseClient(this);
             else
-                shade_below = NULL;
+                shade_below = nullptr;
         }
         m_wrapper.map();
         m_client.map();
@@ -900,7 +900,7 @@ void Client::shadeUnhover()
 void Client::cancelShadeHoverTimer()
 {
     delete shadeHoverTimer;
-    shadeHoverTimer = 0;
+    shadeHoverTimer = nullptr;
 }
 
 void Client::toggleShade()
@@ -1077,7 +1077,7 @@ void Client::updateHiddenPreview()
         workspace()->forceRestacking();
         if (Xcb::Extensions::self()->isShapeInputAvailable()) {
             xcb_shape_rectangles(connection(), XCB_SHAPE_SO_SET, XCB_SHAPE_SK_INPUT,
-                                 XCB_CLIP_ORDERING_UNSORTED, frameId(), 0, 0, 0, NULL);
+                                 XCB_CLIP_ORDERING_UNSORTED, frameId(), 0, 0, 0, nullptr);
         }
     } else {
         workspace()->forceRestacking();
@@ -1155,7 +1155,7 @@ void Client::pingWindow()
         return; // Can't ping :(
     if (options->killPingTimeout() == 0)
         return; // Turned off
-    if (ping_timer != NULL)
+    if (ping_timer != nullptr)
         return; // Pinging already
     ping_timer = new QTimer(this);
     connect(ping_timer, &QTimer::timeout, this,
@@ -1188,7 +1188,7 @@ void Client::gotPing(xcb_timestamp_t timestamp)
     if (NET::timestampCompare(timestamp, m_pingTimestamp) != 0)
         return;
     delete ping_timer;
-    ping_timer = NULL;
+    ping_timer = nullptr;
 
     setUnresponsive(false);
 
@@ -1759,7 +1759,7 @@ void Client::setBlockingCompositing(bool block)
     const bool usedToBlock = blocks_compositing;
     blocks_compositing = rules()->checkBlockCompositing(block && options->windowsBlockCompositing());
     if (usedToBlock != blocks_compositing) {
-        emit blockingCompositingChanged(blocks_compositing ? this : 0);
+        emit blockingCompositingChanged(blocks_compositing ? this : nullptr);
     }
 }
 
@@ -1768,7 +1768,7 @@ void Client::updateAllowedActions(bool force)
     if (!isManaged() && !force)
         return;
     NET::Actions old_allowed_actions = NET::Actions(allowed_actions);
-    allowed_actions = 0;
+    allowed_actions = nullptr;
     if (isMovable())
         allowed_actions |= NET::ActionMove;
     if (isResizable())
diff --git a/client.h b/client.h
index 0bf24baa11..2b4b46474b 100644
--- a/client.h
+++ b/client.h
@@ -100,7 +100,7 @@ public:
     AbstractClient* findModal(bool allow_itself = false) override;
     const Group* group() const override;
     Group* group() override;
-    void checkGroup(Group* gr = NULL, bool force = false);
+    void checkGroup(Group* gr = nullptr, bool force = false);
     void changeClientLeaderGroup(Group* gr);
     void updateWindowRules(Rules::Types selection) override;
     void updateFullscreenMonitors(NETFullscreenMonitors topology);
diff --git a/client_machine.cpp b/client_machine.cpp
index 764b137138..f6c29bf5bf 100644
--- a/client_machine.cpp
+++ b/client_machine.cpp
@@ -54,8 +54,8 @@ GetAddrInfo::GetAddrInfo(const QByteArray &hostName, QObject *parent)
     , m_ownResolved(false)
     , m_hostName(hostName)
     , m_addressHints(new addrinfo)
-    , m_address(NULL)
-    , m_ownAddress(NULL)
+    , m_address(nullptr)
+    , m_ownAddress(nullptr)
     , m_watcher(new QFutureWatcher<int>(this))
     , m_ownAddressWatcher(new QFutureWatcher<int>(this))
 {
diff --git a/client_machine.h b/client_machine.h
index a3fc1f5a3d..63c3b7c00a 100644
--- a/client_machine.h
+++ b/client_machine.h
@@ -34,7 +34,7 @@ class GetAddrInfo : public QObject
 {
     Q_OBJECT
 public:
-    explicit GetAddrInfo(const QByteArray &hostName, QObject *parent = NULL);
+    explicit GetAddrInfo(const QByteArray &hostName, QObject *parent = nullptr);
     ~GetAddrInfo() override;
 
     void resolve();
@@ -64,7 +64,7 @@ class ClientMachine : public QObject
 {
     Q_OBJECT
 public:
-    explicit ClientMachine(QObject *parent = NULL);
+    explicit ClientMachine(QObject *parent = nullptr);
     ~ClientMachine() override;
 
     void resolve(xcb_window_t window, xcb_window_t clientLeader);
diff --git a/colorcorrection/manager.cpp b/colorcorrection/manager.cpp
index 70580500d0..cb91faa11f 100644
--- a/colorcorrection/manager.cpp
+++ b/colorcorrection/manager.cpp
@@ -94,7 +94,7 @@ void Manager::init()
 
     // Monitor for the time changing (flags == TFD_TIMER_ABSTIME | TFD_TIMER_CANCEL_ON_SET).
     // However these are not exposed in glibc so value is hardcoded:
-    ::timerfd_settime(timeChangedFd, 3, &timespec, 0);
+    ::timerfd_settime(timeChangedFd, 3, &timespec, nullptr);
 
     connect(this, &QObject::destroyed, [timeChangedFd]() {
         ::close(timeChangedFd);
diff --git a/composite.cpp b/composite.cpp
index fd7f93069e..3bc79a28c4 100644
--- a/composite.cpp
+++ b/composite.cpp
@@ -121,11 +121,11 @@ static inline qint64 nanoToMilli(int nano) { return nano / (1000*1000); }
 Compositor::Compositor(QObject* workspace)
     : QObject(workspace)
     , m_state(State::Off)
-    , m_selectionOwner(NULL)
+    , m_selectionOwner(nullptr)
     , vBlankInterval(0)
     , fpsInterval(0)
     , m_timeSinceLastVBlank(0)
-    , m_scene(NULL)
+    , m_scene(nullptr)
     , m_bufferSwapPending(false)
     , m_composeAtSwapCompletion(false)
 {
@@ -176,7 +176,7 @@ Compositor::~Compositor()
     stop();
     deleteUnusedSupportProperties();
     destroyCompositorSelection();
-    s_compositor = NULL;
+    s_compositor = nullptr;
 }
 
 bool Compositor::setupStart()
@@ -250,12 +250,12 @@ bool Compositor::setupStart()
         }
     }
 
-    if (m_scene == NULL || m_scene->initFailed()) {
+    if (m_scene == nullptr || m_scene->initFailed()) {
         qCCritical(KWIN_CORE) << "Failed to initialize compositing, compositing disabled";
         m_state = State::Off;
 
         delete m_scene;
-        m_scene = NULL;
+        m_scene = nullptr;
 
         if (m_selectionOwner) {
             m_selectionOwner->setOwning(false);
@@ -449,7 +449,7 @@ void Compositor::stop()
     }
 
     delete m_scene;
-    m_scene = NULL;
+    m_scene = nullptr;
     compositeTimer.stop();
     repaints_region = QRegion();
 
diff --git a/composite.h b/composite.h
index 9f9e52d7e5..0dc0d8d0dc 100644
--- a/composite.h
+++ b/composite.h
@@ -102,7 +102,7 @@ public:
      * @return bool @c true if there is a Compositor and it is active, @c false otherwise
      */
     static bool compositing() {
-        return s_compositor != NULL && s_compositor->isActive();
+        return s_compositor != nullptr && s_compositor->isActive();
     }
 
     // for delayed supportproperty management of effects
diff --git a/cursor.cpp b/cursor.cpp
index 47e60e05b8..7576690061 100644
--- a/cursor.cpp
+++ b/cursor.cpp
@@ -56,7 +56,7 @@ Cursor::Cursor(QObject *parent)
 
 Cursor::~Cursor()
 {
-    s_self = NULL;
+    s_self = nullptr;
 }
 
 void Cursor::loadThemeSettings()
diff --git a/deleted.cpp b/deleted.cpp
index 1713efc5f7..9cf4d49fce 100644
--- a/deleted.cpp
+++ b/deleted.cpp
@@ -92,7 +92,7 @@ void Deleted::discard()
 
 void Deleted::copyToDeleted(Toplevel* c)
 {
-    Q_ASSERT(dynamic_cast< Deleted* >(c) == NULL);
+    Q_ASSERT(dynamic_cast< Deleted* >(c) == nullptr);
     Toplevel::copyToDeleted(c);
     desk = c->desktop();
     m_desktops = c->desktops();
diff --git a/effects.cpp b/effects.cpp
index 1d3083eb9a..65b8036e2f 100644
--- a/effects.cpp
+++ b/effects.cpp
@@ -102,7 +102,7 @@ static xcb_atom_t registerSupportProperty(const QByteArray &propertyName)
     // get the atom for the propertyName
     ScopedCPointer<xcb_intern_atom_reply_t> atomReply(xcb_intern_atom_reply(c,
         xcb_intern_atom_unchecked(c, false, propertyName.size(), propertyName.constData()),
-        NULL));
+        nullptr));
     if (atomReply.isNull()) {
         return XCB_ATOM_NONE;
     }
@@ -117,8 +117,8 @@ static xcb_atom_t registerSupportProperty(const QByteArray &propertyName)
 
 EffectsHandlerImpl::EffectsHandlerImpl(Compositor *compositor, Scene *scene)
     : EffectsHandler(scene->compositingType())
-    , keyboard_grab_effect(NULL)
-    , fullscreen_effect(0)
+    , keyboard_grab_effect(nullptr)
+    , fullscreen_effect(nullptr)
     , next_window_quad_type(EFFECT_QUAD_TYPE_START)
     , m_compositor(compositor)
     , m_scene(scene)
@@ -150,7 +150,7 @@ EffectsHandlerImpl::EffectsHandlerImpl(Compositor *compositor, Scene *scene)
         [this](int old, AbstractClient *c) {
             const int newDesktop = VirtualDesktopManager::self()->current();
             if (old != 0 && newDesktop != old) {
-                emit desktopChanged(old, newDesktop, c ? c->effectWindow() : 0);
+                emit desktopChanged(old, newDesktop, c ? c->effectWindow() : nullptr);
                 // TODO: remove in 4.10
                 emit desktopChanged(old, newDesktop);
             }
@@ -464,7 +464,7 @@ Effect *EffectsHandlerImpl::provides(Effect::Feature ef)
     for (int i = 0; i < loaded_effects.size(); ++i)
         if (loaded_effects.at(i).second->provides(ef))
             return loaded_effects.at(i).second;
-    return NULL;
+    return nullptr;
 }
 
 void EffectsHandlerImpl::drawWindow(EffectWindow* w, int mask, QRegion region, WindowPaintData& data)
@@ -620,7 +620,7 @@ void EffectsHandlerImpl::slotGeometryShapeChanged(Toplevel* t, const QRect& old)
 {
     // during late cleanup effectWindow() may be already NULL
     // in some functions that may still call this
-    if (t == NULL || t->effectWindow() == NULL)
+    if (t == nullptr || t->effectWindow() == nullptr)
         return;
     emit windowGeometryShapeChanged(t->effectWindow(), old);
 }
@@ -629,7 +629,7 @@ void EffectsHandlerImpl::slotPaddingChanged(Toplevel* t, const QRect& old)
 {
     // during late cleanup effectWindow() may be already NULL
     // in some functions that may still call this
-    if (t == NULL || t->effectWindow() == NULL)
+    if (t == nullptr || t->effectWindow() == nullptr)
         return;
     emit windowPaddingChanged(t->effectWindow(), old);
 }
@@ -659,7 +659,7 @@ bool EffectsHandlerImpl::hasActiveFullScreenEffect() const
 
 bool EffectsHandlerImpl::grabKeyboard(Effect* effect)
 {
-    if (keyboard_grab_effect != NULL)
+    if (keyboard_grab_effect != nullptr)
         return false;
     if (!doGrabKeyboard()) {
         return false;
@@ -675,9 +675,9 @@ bool EffectsHandlerImpl::doGrabKeyboard()
 
 void EffectsHandlerImpl::ungrabKeyboard()
 {
-    Q_ASSERT(keyboard_grab_effect != NULL);
+    Q_ASSERT(keyboard_grab_effect != nullptr);
     doUngrabKeyboard();
-    keyboard_grab_effect = NULL;
+    keyboard_grab_effect = nullptr;
 }
 
 void EffectsHandlerImpl::doUngrabKeyboard()
@@ -686,7 +686,7 @@ void EffectsHandlerImpl::doUngrabKeyboard()
 
 void EffectsHandlerImpl::grabbedKeyboardEvent(QKeyEvent* e)
 {
-    if (keyboard_grab_effect != NULL)
+    if (keyboard_grab_effect != nullptr)
         keyboard_grab_effect->grabbedKeyboardEvent(e);
 }
 
@@ -788,7 +788,7 @@ void* EffectsHandlerImpl::getProxy(QString name)
         if ((*it).first == name)
             return (*it).second->proxy();
 
-    return NULL;
+    return nullptr;
 }
 
 void EffectsHandlerImpl::startMousePolling()
@@ -805,7 +805,7 @@ void EffectsHandlerImpl::stopMousePolling()
 
 bool EffectsHandlerImpl::hasKeyboardGrab() const
 {
-    return keyboard_grab_effect != NULL;
+    return keyboard_grab_effect != nullptr;
 }
 
 void EffectsHandlerImpl::desktopResized(const QSize &size)
@@ -885,7 +885,7 @@ void EffectsHandlerImpl::activateWindow(EffectWindow* c)
 
 EffectWindow* EffectsHandlerImpl::activeWindow() const
 {
-    return Workspace::self()->activeClient() ? Workspace::self()->activeClient()->effectWindow() : NULL;
+    return Workspace::self()->activeClient() ? Workspace::self()->activeClient()->effectWindow() : nullptr;
 }
 
 void EffectsHandlerImpl::moveWindow(EffectWindow* w, const QPoint& pos, bool snap, double snapAdjust)
@@ -1072,7 +1072,7 @@ EffectWindow* EffectsHandlerImpl::findWindow(WId id) const
             return w->effectWindow();
         }
     }
-    return NULL;
+    return nullptr;
 }
 
 EffectWindow* EffectsHandlerImpl::findWindow(KWayland::Server::SurfaceInterface *surf) const
@@ -1207,7 +1207,7 @@ EffectWindow* EffectsHandlerImpl::currentTabBoxWindow() const
     if (auto c = TabBox::TabBox::self()->currentClient())
         return c->effectWindow();
 #endif
-    return NULL;
+    return nullptr;
 }
 
 void EffectsHandlerImpl::addRepaintFull()
@@ -2149,13 +2149,13 @@ EffectWindowList EffectWindowGroupImpl::members() const
 //****************************************
 
 EffectFrameImpl::EffectFrameImpl(EffectFrameStyle style, bool staticSize, QPoint position, Qt::Alignment alignment)
-    : QObject(0)
+    : QObject(nullptr)
     , EffectFrame()
     , m_style(style)
     , m_static(staticSize)
     , m_point(position)
     , m_alignment(alignment)
-    , m_shader(NULL)
+    , m_shader(nullptr)
     , m_theme(new Plasma::Theme(this))
 {
     if (m_style == EffectFrameStyled) {
@@ -2271,7 +2271,7 @@ void EffectFrameImpl::render(QRegion region, double opacity, double frameOpacity
     if (m_geometry.isEmpty()) {
         return; // Nothing to display
     }
-    m_shader = NULL;
+    m_shader = nullptr;
     setScreenProjectionMatrix(static_cast<EffectsHandlerImpl*>(effects)->scene()->screenProjectionMatrix());
     effects->paintEffectFrame(this, region, opacity, frameOpacity);
 }
diff --git a/effects/backgroundcontrast/contrastshader.cpp b/effects/backgroundcontrast/contrastshader.cpp
index 64a708768f..936a88e697 100644
--- a/effects/backgroundcontrast/contrastshader.cpp
+++ b/effects/backgroundcontrast/contrastshader.cpp
@@ -34,7 +34,7 @@ using namespace KWin;
 
 
 ContrastShader::ContrastShader()
-    : mValid(false), shader(NULL), m_opacity(1)
+    : mValid(false), shader(nullptr), m_opacity(1)
 {
 }
 
@@ -51,7 +51,7 @@ ContrastShader *ContrastShader::create()
 void ContrastShader::reset()
 {
     delete shader;
-    shader = NULL;
+    shader = nullptr;
 
     setIsValid(false);
 }
diff --git a/effects/blur/blur_config.h b/effects/blur/blur_config.h
index a766eec68c..60edd08efd 100644
--- a/effects/blur/blur_config.h
+++ b/effects/blur/blur_config.h
@@ -31,7 +31,7 @@ class BlurEffectConfig : public KCModule
     Q_OBJECT
 
 public:
-    explicit BlurEffectConfig(QWidget *parent = 0, const QVariantList& args = QVariantList());
+    explicit BlurEffectConfig(QWidget *parent = nullptr, const QVariantList& args = QVariantList());
     ~BlurEffectConfig() override;
 
     void save() override;
diff --git a/effects/coverswitch/coverswitch.cpp b/effects/coverswitch/coverswitch.cpp
index 29b7009c46..3776366771 100644
--- a/effects/coverswitch/coverswitch.cpp
+++ b/effects/coverswitch/coverswitch.cpp
@@ -50,8 +50,8 @@ CoverSwitchEffect::CoverSwitchEffect()
     , zPosition(900.0)
     , scaleFactor(0.0)
     , direction(Left)
-    , selected_window(0)
-    , captionFrame(NULL)
+    , selected_window(nullptr)
+    , captionFrame(nullptr)
     , primaryTabBox(false)
     , secondaryTabBox(false)
 {
@@ -65,7 +65,7 @@ CoverSwitchEffect::CoverSwitchEffect()
     if (effects->compositingType() == OpenGL2Compositing) {
         m_reflectionShader = ShaderManager::instance()->generateShaderFromResources(ShaderTrait::MapTexture, QString(), QStringLiteral("coverswitch-reflection.glsl"));
     } else {
-        m_reflectionShader = NULL;
+        m_reflectionShader = nullptr;
     }
     connect(effects, &EffectsHandler::windowClosed, this, &CoverSwitchEffect::slotWindowClosed);
     connect(effects, &EffectsHandler::tabBoxAdded, this, &CoverSwitchEffect::slotTabBoxAdded);
@@ -123,7 +123,7 @@ void CoverSwitchEffect::prePaintScreen(ScreenPrePaintData& data, int time)
         if (animation || start || stop) {
             timeLine.update(std::chrono::milliseconds(time));
         }
-        if (selected_window == NULL)
+        if (selected_window == nullptr)
             abort();
     }
     effects->prePaintScreen(data, time);
@@ -292,7 +292,7 @@ void CoverSwitchEffect::postPaintScreen()
             timeLine.reset();
             if (stop) {
                 stop = false;
-                effects->setActiveFullScreenEffect(0);
+                effects->setActiveFullScreenEffect(nullptr);
                 foreach (EffectWindow * window, referrencedWindows) {
                     window->unrefWindow();
                 }
@@ -547,7 +547,7 @@ void CoverSwitchEffect::slotTabBoxClosed()
                 stopRequested = true;
             }
         } else {
-            effects->setActiveFullScreenEffect(0);
+            effects->setActiveFullScreenEffect(nullptr);
             start = false;
             animation = false;
             timeLine.reset();
@@ -565,7 +565,7 @@ void CoverSwitchEffect::slotTabBoxUpdated()
         if (animateSwitch && currentWindowList.count() > 1) {
             // determine the switch direction
             if (selected_window != effects->currentTabBoxWindow()) {
-                if (selected_window != NULL) {
+                if (selected_window != nullptr) {
                     int old_index = currentWindowList.indexOf(selected_window);
                     int new_index = effects->currentTabBoxWindowList().indexOf(effects->currentTabBoxWindow());
                     Direction new_direction;
@@ -701,7 +701,7 @@ void CoverSwitchEffect::paintWindowCover(EffectWindow* w, bool reflectedWindow,
 
 void CoverSwitchEffect::paintFrontWindow(EffectWindow* frontWindow, int width, int leftWindows, int rightWindows, bool reflectedWindow)
 {
-    if (frontWindow == NULL)
+    if (frontWindow == nullptr)
         return;
     bool specialHandlingForward = false;
     WindowPaintData data(frontWindow);
@@ -764,7 +764,7 @@ void CoverSwitchEffect::paintWindows(const EffectWindowList& windows, bool left,
         xTranslate = ((float)screenSize.width() * 0.5 * scaleFactor) - (float)width * 0.5f;
     // handling for additional window from other side
     // has to appear on this side after half of the time
-    if (animation && timeLine.value() >= 0.5 && additionalWindow != NULL) {
+    if (animation && timeLine.value() >= 0.5 && additionalWindow != nullptr) {
         WindowPaintData data(additionalWindow);
         if (effects->numScreens() > 1) {
             data.setProjectionMatrix(m_projectionMatrix);
@@ -786,7 +786,7 @@ void CoverSwitchEffect::paintWindows(const EffectWindowList& windows, bool left,
     // normal behaviour
     for (int i = 0; i < windows.count(); i++) {
         window = windows.at(i);
-        if (window == NULL || window->isDeleted()) {
+        if (window == nullptr || window->isDeleted()) {
             continue;
         }
         WindowPaintData data(window);
@@ -918,7 +918,7 @@ void CoverSwitchEffect::abort()
         effects->unrefTabBox();
         effects->stopMouseInterception(this);
     }
-    effects->setActiveFullScreenEffect(0);
+    effects->setActiveFullScreenEffect(nullptr);
     timeLine.reset();
     mActivated = false;
     stop = false;
@@ -930,7 +930,7 @@ void CoverSwitchEffect::abort()
 void CoverSwitchEffect::slotWindowClosed(EffectWindow* c)
 {
     if (c == selected_window)
-        selected_window = 0;
+        selected_window = nullptr;
     // if the list is not empty, the effect is active
     if (!currentWindowList.isEmpty()) {
         c->refWindow();
diff --git a/effects/coverswitch/coverswitch.h b/effects/coverswitch/coverswitch.h
index 7b071b987b..2629e90b23 100644
--- a/effects/coverswitch/coverswitch.h
+++ b/effects/coverswitch/coverswitch.h
@@ -107,7 +107,7 @@ private:
                     bool reflectedWindows = false);
     void paintWindowCover(EffectWindow* w, bool reflectedWindow, WindowPaintData& data);
     void paintFrontWindow(EffectWindow* frontWindow, int width, int leftWindows, int rightWindows, bool reflectedWindow);
-    void paintWindows(const EffectWindowList& windows, bool left, bool reflectedWindows, EffectWindow* additionalWindow = NULL);
+    void paintWindows(const EffectWindowList& windows, bool left, bool reflectedWindows, EffectWindow* additionalWindow = nullptr);
     void selectNextOrPreviousWindow(bool forward);
     inline void selectNextWindow() { selectNextOrPreviousWindow(true); }
     inline void selectPreviousWindow() { selectNextOrPreviousWindow(false); }
diff --git a/effects/coverswitch/coverswitch_config.h b/effects/coverswitch/coverswitch_config.h
index f6986a5dbe..c82b76b83e 100644
--- a/effects/coverswitch/coverswitch_config.h
+++ b/effects/coverswitch/coverswitch_config.h
@@ -40,7 +40,7 @@ class CoverSwitchEffectConfig : public KCModule
 {
     Q_OBJECT
 public:
-    explicit CoverSwitchEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit CoverSwitchEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
 
 public Q_SLOTS:
     void save() override;
diff --git a/effects/cube/cube.cpp b/effects/cube/cube.cpp
index 6430ad9e21..f6d48c3978 100644
--- a/effects/cube/cube.cpp
+++ b/effects/cube/cube.cpp
@@ -56,13 +56,13 @@ CubeEffect::CubeEffect()
     , cubeOpacity(1.0)
     , opacityDesktopOnly(true)
     , displayDesktopName(false)
-    , desktopNameFrame(NULL)
+    , desktopNameFrame(nullptr)
     , reflection(true)
     , desktopChangedWhileRotating(false)
     , paintCaps(true)
-    , wallpaper(NULL)
+    , wallpaper(nullptr)
     , texturedCaps(true)
-    , capTexture(NULL)
+    , capTexture(nullptr)
     , reflectionPainting(false)
     , activeScreen(0)
     , bottomCap(false)
@@ -74,12 +74,12 @@ CubeEffect::CubeEffect()
     , shortcutsRegistered(false)
     , mode(Cube)
     , useShaders(false)
-    , cylinderShader(0)
-    , sphereShader(0)
+    , cylinderShader(nullptr)
+    , sphereShader(nullptr)
     , zOrderingFactor(0.0f)
     , mAddedHeightCoeff1(0.0f)
     , mAddedHeightCoeff2(0.0f)
-    , m_cubeCapBuffer(NULL)
+    , m_cubeCapBuffer(nullptr)
     , m_proxy(this)
     , m_cubeAction(new QAction(this))
     , m_cylinderAction(new QAction(this))
@@ -93,8 +93,8 @@ CubeEffect::CubeEffect()
         m_reflectionShader = ShaderManager::instance()->generateShaderFromResources(ShaderTrait::MapTexture, QString(), QStringLiteral("cube-reflection.glsl"));
         m_capShader = ShaderManager::instance()->generateShaderFromResources(ShaderTrait::MapTexture, QString(), QStringLiteral("cube-cap.glsl"));
     } else {
-        m_reflectionShader = NULL;
-        m_capShader = NULL;
+        m_reflectionShader = nullptr;
+        m_capShader = nullptr;
     }
     m_textureMirrorMatrix.scale(1.0, -1.0, 1.0);
     m_textureMirrorMatrix.translate(0.0, -1.0, 0.0);
@@ -179,9 +179,9 @@ void CubeEffect::reconfigure(ReconfigureFlags)
     capDeformationFactor = (float)CubeConfig::capDeformation() / 100.0f;
     useZOrdering = CubeConfig::zOrdering();
     delete wallpaper;
-    wallpaper = NULL;
+    wallpaper = nullptr;
     delete capTexture;
-    capTexture = NULL;
+    capTexture = nullptr;
     texturedCaps = CubeConfig::texturedCaps();
 
     timeLine.setEasingCurve(QEasingCurve::InOutSine);
@@ -282,7 +282,7 @@ void CubeEffect::slotCubeCapLoaded()
         }
         // need to recreate the VBO for the cube cap
         delete m_cubeCapBuffer;
-        m_cubeCapBuffer = NULL;
+        m_cubeCapBuffer = nullptr;
         effects->addRepaintFull();
     }
     watcher->deleteLater();
@@ -844,7 +844,7 @@ void CubeEffect::paintCubeCap()
     }
     delete m_cubeCapBuffer;
     m_cubeCapBuffer = new GLVertexBuffer(GLVertexBuffer::Static);
-    m_cubeCapBuffer->setData(verts.count() / 3, 3, verts.constData(), texture ? texCoords.constData() : NULL);
+    m_cubeCapBuffer->setData(verts.count() / 3, 3, verts.constData(), texture ? texCoords.constData() : nullptr);
 }
 
 void CubeEffect::paintCylinderCap()
@@ -899,7 +899,7 @@ void CubeEffect::paintCylinderCap()
     }
     delete m_cubeCapBuffer;
     m_cubeCapBuffer = new GLVertexBuffer(GLVertexBuffer::Static);
-    m_cubeCapBuffer->setData(verts.count() / 3, 3, verts.constData(), texture ? texCoords.constData() : NULL);
+    m_cubeCapBuffer->setData(verts.count() / 3, 3, verts.constData(), texture ? texCoords.constData() : nullptr);
 }
 
 void CubeEffect::paintSphereCap()
@@ -956,7 +956,7 @@ void CubeEffect::paintSphereCap()
     }
     delete m_cubeCapBuffer;
     m_cubeCapBuffer = new GLVertexBuffer(GLVertexBuffer::Static);
-    m_cubeCapBuffer->setData(verts.count() / 3, 3, verts.constData(), texture ? texCoords.constData() : NULL);
+    m_cubeCapBuffer->setData(verts.count() / 3, 3, verts.constData(), texture ? texCoords.constData() : nullptr);
 }
 
 void CubeEffect::postPaintScreen()
@@ -975,9 +975,9 @@ void CubeEffect::postPaintScreen()
             keyboard_grab = false;
             effects->stopMouseInterception(this);
             effects->setCurrentDesktop(frontDesktop);
-            effects->setActiveFullScreenEffect(0);
+            effects->setActiveFullScreenEffect(nullptr);
             delete m_cubeCapBuffer;
-            m_cubeCapBuffer = NULL;
+            m_cubeCapBuffer = nullptr;
             if (desktopNameFrame)
                 desktopNameFrame->free();
             activated = false;
@@ -1314,7 +1314,7 @@ void CubeEffect::paintWindow(EffectWindow* w, int mask, QRegion region, WindowPa
                 QColor color = capColor;
                 capColor.setAlphaF(cubeOpacity);
                 vbo->setColor(color);
-                vbo->setData(verts.size() / 2, 2, verts.constData(), NULL);
+                vbo->setData(verts.size() / 2, 2, verts.constData(), nullptr);
                 if (!capShader || mode == Cube) {
                     // TODO: use sphere and cylinder shaders
                     vbo->render(GL_TRIANGLES);
diff --git a/effects/cube/cube_config.h b/effects/cube/cube_config.h
index 1cb151ab49..e3964e4f97 100644
--- a/effects/cube/cube_config.h
+++ b/effects/cube/cube_config.h
@@ -40,7 +40,7 @@ class CubeEffectConfig : public KCModule
 {
     Q_OBJECT
 public:
-    explicit CubeEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit CubeEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
 
 public Q_SLOTS:
     void save() override;
diff --git a/effects/cubeslide/cubeslide.cpp b/effects/cubeslide/cubeslide.cpp
index d3e86eb19e..79c75b0a26 100644
--- a/effects/cubeslide/cubeslide.cpp
+++ b/effects/cubeslide/cubeslide.cpp
@@ -387,7 +387,7 @@ void CubeSlideEffect::postPaintScreen()
                     w->setData(WindowForceBackgroundContrastRole, QVariant());
                 }
                 staticWindows.clear();
-                effects->setActiveFullScreenEffect(0);
+                effects->setActiveFullScreenEffect(nullptr);
             }
         }
         effects->addRepaintFull();
@@ -586,7 +586,7 @@ void CubeSlideEffect::slotWindowStepUserMovedResized(EffectWindow* w)
         timeLine.setCurrentTime(0);
         if (!slideRotations.isEmpty())
             slideRotations.clear();
-        effects->setActiveFullScreenEffect(0);
+        effects->setActiveFullScreenEffect(nullptr);
         effects->addRepaintFull();
     }
 }
diff --git a/effects/cubeslide/cubeslide_config.h b/effects/cubeslide/cubeslide_config.h
index 647a2621c3..bb032b1dce 100644
--- a/effects/cubeslide/cubeslide_config.h
+++ b/effects/cubeslide/cubeslide_config.h
@@ -40,7 +40,7 @@ class CubeSlideEffectConfig : public KCModule
 {
     Q_OBJECT
 public:
-    explicit CubeSlideEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit CubeSlideEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
 
 public Q_SLOTS:
     void save() override;
diff --git a/effects/desktopgrid/desktopgrid.cpp b/effects/desktopgrid/desktopgrid.cpp
index 95f6eba596..03925f959f 100644
--- a/effects/desktopgrid/desktopgrid.cpp
+++ b/effects/desktopgrid/desktopgrid.cpp
@@ -57,7 +57,7 @@ DesktopGridEffect::DesktopGridEffect()
     , wasWindowCopy(false)
     , wasDesktopMove(false)
     , isValidMove(false)
-    , windowMove(NULL)
+    , windowMove(nullptr)
     , windowMoveDiff()
     , gridSize()
     , orientation(Qt::Horizontal)
@@ -66,7 +66,7 @@ DesktopGridEffect::DesktopGridEffect()
     , unscaledBorder()
     , scaledSize()
     , scaledOffset()
-    , m_proxy(0)
+    , m_proxy(nullptr)
     , m_activateAction(new QAction(this))
 {
     initConfig<DesktopGridConfig>();
@@ -428,7 +428,7 @@ void DesktopGridEffect::slotWindowClosed(EffectWindow* w)
         return;
     if (w == windowMove) {
         effects->setElevatedWindow(windowMove, false);
-        windowMove = NULL;
+        windowMove = nullptr;
     }
     if (isUsingPresentWindows()) {
         foreach (const int i, desktopList(w)) {
@@ -443,7 +443,7 @@ void DesktopGridEffect::slotWindowClosed(EffectWindow* w)
 void DesktopGridEffect::slotWindowDeleted(EffectWindow* w)
 {
     if (w == windowMove)
-        windowMove = 0;
+        windowMove = nullptr;
     foreach (DesktopButtonsView *view, m_desktopButtonsViews) {
         if (view->effectWindow && view->effectWindow == w) {
             view->effectWindow = nullptr;
@@ -494,7 +494,7 @@ void DesktopGridEffect::windowInputMouseEvent(QEvent* e)
 
     if (e->type() == QEvent::MouseMove) {
         int d = posToDesktop(me->pos());
-        if (windowMove != NULL &&
+        if (windowMove != nullptr &&
                 (me->pos() - dragStartPos).manhattanLength() > QApplication::startDragDistance()) {
             // Handle window moving
             if (!wasWindowMove) { // Activate on move
@@ -522,7 +522,7 @@ void DesktopGridEffect::windowInputMouseEvent(QEvent* e)
             if (windowMove->isMovable() && !isUsingPresentWindows()) {
                 wasWindowMove = true;
                 int screen = effects->screenNumber(me->pos());
-                effects->moveWindow(windowMove, unscalePos(me->pos(), NULL) + windowMoveDiff, true, 1.0 / scale[screen]);
+                effects->moveWindow(windowMove, unscalePos(me->pos(), nullptr) + windowMoveDiff, true, 1.0 / scale[screen]);
             }
             if (wasWindowMove) {
                 if (effects->waylandDisplay() && (me->modifiers() & Qt::ControlModifier)) {
@@ -603,25 +603,25 @@ void DesktopGridEffect::windowInputMouseEvent(QEvent* e)
             dragStartPos = me->pos();
             sourceDesktop = posToDesktop(me->pos());
             bool isDesktop = (me->modifiers() & Qt::ShiftModifier);
-            EffectWindow* w = isDesktop ? NULL : windowAt(me->pos());
-            if (w != NULL)
+            EffectWindow* w = isDesktop ? nullptr : windowAt(me->pos());
+            if (w != nullptr)
                 isDesktop = w->isDesktop();
             if (isDesktop)
                 m_originalMovingDesktop = posToDesktop(me->pos());
             else
                 m_originalMovingDesktop = 0;
-            if (w != NULL && !w->isDesktop() && (w->isMovable() || w->isMovableAcrossScreens() || isUsingPresentWindows())) {
+            if (w != nullptr && !w->isDesktop() && (w->isMovable() || w->isMovableAcrossScreens() || isUsingPresentWindows())) {
                 // Prepare it for moving
-                windowMoveDiff = w->pos() - unscalePos(me->pos(), NULL);
+                windowMoveDiff = w->pos() - unscalePos(me->pos(), nullptr);
                 windowMove = w;
                 effects->setElevatedWindow(windowMove, true);
             }
-        } else if ((me->buttons() == Qt::MidButton || me->buttons() == Qt::RightButton) && windowMove == NULL) {
+        } else if ((me->buttons() == Qt::MidButton || me->buttons() == Qt::RightButton) && windowMove == nullptr) {
             EffectWindow* w = windowAt(me->pos());
             if (w && w->isDesktop()) {
                 w = nullptr;
             }
-            if (w != NULL) {
+            if (w != nullptr) {
                 const int desktop = posToDesktop(me->pos());
                 if (w->isOnAllDesktops()) {
                     effects->windowToDesktop(w, desktop);
@@ -675,7 +675,7 @@ void DesktopGridEffect::windowInputMouseEvent(QEvent* e)
                 effects->addRepaintFull();
             }
             effects->setElevatedWindow(windowMove, false);
-            windowMove = NULL;
+            windowMove = nullptr;
         }
         wasWindowMove = false;
         wasWindowCopy = false;
@@ -687,7 +687,7 @@ void DesktopGridEffect::grabbedKeyboardEvent(QKeyEvent* e)
 {
     if (timeline.currentValue() != 1)   // Block user input during animations
         return;
-    if (windowMove != NULL)
+    if (windowMove != nullptr)
         return;
     if (e->type() == QEvent::KeyPress) {
         // check for global shortcuts
@@ -823,7 +823,7 @@ QPoint DesktopGridEffect::unscalePos(const QPoint& pos, int* desktop) const
     int gy = qBound(0, int(scaledY), gridSize.height() - 1);
     scaledX -= gx;
     scaledY -= gy;
-    if (desktop != NULL) {
+    if (desktop != nullptr) {
         if (orientation == Qt::Horizontal)
             *desktop = gy * gridSize.width() + gx + 1;
         else
@@ -879,7 +879,7 @@ EffectWindow* DesktopGridEffect::windowAt(QPoint pos) const
     int desktop;
     pos = unscalePos(pos, &desktop);
     if (desktop > effects->numberOfDesktops())
-        return NULL;
+        return nullptr;
     if (isUsingPresentWindows()) {
         const int screen = effects->screenNumber(pos);
         EffectWindow *w =
@@ -896,7 +896,7 @@ EffectWindow* DesktopGridEffect::windowAt(QPoint pos) const
                 return w;
         }
     }
-    return NULL;
+    return nullptr;
 }
 
 void DesktopGridEffect::setCurrentDesktop(int desktop)
@@ -1223,13 +1223,13 @@ void DesktopGridEffect::finish()
         effects->ungrabKeyboard();
     keyboardGrab = false;
     effects->stopMouseInterception(this);
-    effects->setActiveFullScreenEffect(0);
+    effects->setActiveFullScreenEffect(nullptr);
     if (isUsingPresentWindows()) {
         while (!m_managers.isEmpty()) {
             m_managers.first().unmanageAll();
             m_managers.removeFirst();
         }
-        m_proxy = 0;
+        m_proxy = nullptr;
     }
 }
 
@@ -1256,7 +1256,7 @@ bool DesktopGridEffect::isMotionManagerMovingWindows() const
 
 bool DesktopGridEffect::isUsingPresentWindows() const
 {
-    return (m_proxy != NULL);
+    return (m_proxy != nullptr);
 }
 
 // transforms the geometry of the moved window to a geometry on the desktop
diff --git a/effects/desktopgrid/desktopgrid.h b/effects/desktopgrid/desktopgrid.h
index abcf98d508..4d6c8df56c 100644
--- a/effects/desktopgrid/desktopgrid.h
+++ b/effects/desktopgrid/desktopgrid.h
@@ -36,7 +36,7 @@ class DesktopButtonsView : public QQuickView
 {
     Q_OBJECT
 public:
-    explicit DesktopButtonsView(QWindow *parent = 0);
+    explicit DesktopButtonsView(QWindow *parent = nullptr);
     void windowInputMouseEvent(QMouseEvent* e);
     void setAddDesktopEnabled(bool enable);
     void setRemoveDesktopEnabled(bool enable);
@@ -119,7 +119,7 @@ private Q_SLOTS:
 
 private:
     QPointF scalePos(const QPoint& pos, int desktop, int screen = -1) const;
-    QPoint unscalePos(const QPoint& pos, int* desktop = NULL) const;
+    QPoint unscalePos(const QPoint& pos, int* desktop = nullptr) const;
     int posToDesktop(const QPoint& pos) const;
     EffectWindow* windowAt(QPoint pos) const;
     void setCurrentDesktop(int desktop);
diff --git a/effects/desktopgrid/desktopgrid_config.cpp b/effects/desktopgrid/desktopgrid_config.cpp
index 2d8e917a97..ab5525d8fe 100644
--- a/effects/desktopgrid/desktopgrid_config.cpp
+++ b/effects/desktopgrid/desktopgrid_config.cpp
@@ -73,7 +73,7 @@ DesktopGridEffectConfig::DesktopGridEffectConfig(QWidget* parent, const QVariant
     m_ui->shortcutEditor->addCollection(m_actionCollection);
 
 
-    m_ui->desktopNameAlignmentCombo->addItem(i18nc("Desktop name alignment:", "Disabled"), QVariant(Qt::Alignment(0)));
+    m_ui->desktopNameAlignmentCombo->addItem(i18nc("Desktop name alignment:", "Disabled"), QVariant(Qt::Alignment(nullptr)));
     m_ui->desktopNameAlignmentCombo->addItem(i18n("Top"), QVariant(Qt::AlignHCenter | Qt::AlignTop));
     m_ui->desktopNameAlignmentCombo->addItem(i18n("Top-Right"), QVariant(Qt::AlignRight | Qt::AlignTop));
     m_ui->desktopNameAlignmentCombo->addItem(i18n("Right"), QVariant(Qt::AlignRight | Qt::AlignVCenter));
diff --git a/effects/desktopgrid/desktopgrid_config.h b/effects/desktopgrid/desktopgrid_config.h
index 1654d36234..6167293881 100644
--- a/effects/desktopgrid/desktopgrid_config.h
+++ b/effects/desktopgrid/desktopgrid_config.h
@@ -41,7 +41,7 @@ class DesktopGridEffectConfig : public KCModule
 {
     Q_OBJECT
 public:
-    explicit DesktopGridEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit DesktopGridEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~DesktopGridEffectConfig() override;
 
 public Q_SLOTS:
diff --git a/effects/flipswitch/flipswitch.cpp b/effects/flipswitch/flipswitch.cpp
index 15b7446fd3..38aedd98dd 100644
--- a/effects/flipswitch/flipswitch.cpp
+++ b/effects/flipswitch/flipswitch.cpp
@@ -45,7 +45,7 @@ FlipSwitchEffect::FlipSwitchEffect()
     , m_stop(false)
     , m_animation(false)
     , m_hasKeyboardGrab(false)
-    , m_captionFrame(NULL)
+    , m_captionFrame(nullptr)
 {
     initConfig<FlipSwitchConfig>();
     reconfigure(ReconfigureAll);
@@ -153,7 +153,7 @@ void FlipSwitchEffect::paintScreen(int mask, QRegion region, ScreenPaintData& da
                     index = index % tempList.count();
             }
             tabIndex = index;
-            EffectWindow* w = NULL;
+            EffectWindow* w = nullptr;
             if (!m_scheduledDirections.isEmpty() && m_scheduledDirections.head() == DirectionBackward) {
                 index--;
                 if (index < 0)
@@ -180,7 +180,7 @@ void FlipSwitchEffect::paintScreen(int mask, QRegion region, ScreenPaintData& da
                     index = 0;
             }
             tabIndex = index;
-            EffectWindow* w = NULL;
+            EffectWindow* w = nullptr;
             if (!m_scheduledDirections.isEmpty() && m_scheduledDirections.head() == DirectionBackward) {
                 index++;
                 if (index >= tempList.count())
@@ -331,7 +331,7 @@ void FlipSwitchEffect::postPaintScreen()
             m_stop = false;
             m_active = false;
             m_captionFrame->free();
-            effects->setActiveFullScreenEffect(0);
+            effects->setActiveFullScreenEffect(nullptr);
             effects->addRepaintFull();
             qDeleteAll(m_windows);
             m_windows.clear();
@@ -437,7 +437,7 @@ void FlipSwitchEffect::slotTabBoxUpdated()
         if (!effects->currentTabBoxWindowList().isEmpty()) {
             // determine the switch direction
             if (m_selectedWindow != effects->currentTabBoxWindow()) {
-                if (m_selectedWindow != NULL) {
+                if (m_selectedWindow != nullptr) {
                     int old_index = effects->currentTabBoxWindowList().indexOf(m_selectedWindow);
                     int new_index = effects->currentTabBoxWindowList().indexOf(effects->currentTabBoxWindow());
                     SwitchingDirection new_direction;
@@ -485,7 +485,7 @@ void FlipSwitchEffect::slotWindowAdded(EffectWindow* w)
 void FlipSwitchEffect::slotWindowClosed(EffectWindow* w)
 {
     if (m_selectedWindow == w)
-        m_selectedWindow = 0;
+        m_selectedWindow = nullptr;
     if (m_active) {
         QHash< const EffectWindow*, ItemInfo* >::iterator it = m_windows.find(w);
         if (it != m_windows.end()) {
diff --git a/effects/flipswitch/flipswitch_config.h b/effects/flipswitch/flipswitch_config.h
index 27252e4746..317763730e 100644
--- a/effects/flipswitch/flipswitch_config.h
+++ b/effects/flipswitch/flipswitch_config.h
@@ -41,7 +41,7 @@ class FlipSwitchEffectConfig : public KCModule
 {
     Q_OBJECT
 public:
-    explicit FlipSwitchEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit FlipSwitchEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~FlipSwitchEffectConfig() override;
 
 public Q_SLOTS:
diff --git a/effects/highlightwindow/highlightwindow.cpp b/effects/highlightwindow/highlightwindow.cpp
index 9fa28120ca..9de3c1785a 100644
--- a/effects/highlightwindow/highlightwindow.cpp
+++ b/effects/highlightwindow/highlightwindow.cpp
@@ -26,7 +26,7 @@ namespace KWin
 HighlightWindowEffect::HighlightWindowEffect()
     : m_finishing(false)
     , m_fadeDuration(float(animationTime(150)))
-    , m_monitorWindow(NULL)
+    , m_monitorWindow(nullptr)
 {
     m_atom = effects->announceSupportProperty("_KDE_WINDOW_HIGHLIGHT", this);
     connect(effects, &EffectsHandler::windowAdded, this, &HighlightWindowEffect::slotWindowAdded);
@@ -259,7 +259,7 @@ void HighlightWindowEffect::prepareHighlighting()
 void HighlightWindowEffect::finishHighlighting()
 {
     m_finishing = true;
-    m_monitorWindow = NULL;
+    m_monitorWindow = nullptr;
     m_highlightedWindows.clear();
     if (!m_windowOpacity.isEmpty())
         m_windowOpacity.constBegin().key()->addRepaintFull();
diff --git a/effects/highlightwindow/highlightwindow.h b/effects/highlightwindow/highlightwindow.h
index 58158813c5..dc3a6d92b2 100644
--- a/effects/highlightwindow/highlightwindow.h
+++ b/effects/highlightwindow/highlightwindow.h
@@ -49,7 +49,7 @@ public Q_SLOTS:
     void slotWindowAdded(KWin::EffectWindow* w);
     void slotWindowClosed(KWin::EffectWindow *w);
     void slotWindowDeleted(KWin::EffectWindow *w);
-    void slotPropertyNotify(KWin::EffectWindow* w, long atom, EffectWindow *addedWindow = NULL);
+    void slotPropertyNotify(KWin::EffectWindow* w, long atom, EffectWindow *addedWindow = nullptr);
 
 private:
     void prepareHighlighting();
diff --git a/effects/invert/invert.cpp b/effects/invert/invert.cpp
index be1e1f6a32..b8b907017b 100644
--- a/effects/invert/invert.cpp
+++ b/effects/invert/invert.cpp
@@ -37,7 +37,7 @@ namespace KWin
 InvertEffect::InvertEffect()
     :   m_inited(false),
         m_valid(true),
-        m_shader(NULL),
+        m_shader(nullptr),
         m_allWindows(false)
 {
     QAction* a = new QAction(this);
diff --git a/effects/invert/invert_config.h b/effects/invert/invert_config.h
index b4269a19b5..e5237bca6a 100644
--- a/effects/invert/invert_config.h
+++ b/effects/invert/invert_config.h
@@ -32,7 +32,7 @@ class InvertEffectConfig : public KCModule
 {
     Q_OBJECT
 public:
-    explicit InvertEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit InvertEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~InvertEffectConfig() override;
 
 public Q_SLOTS:
diff --git a/effects/lookingglass/lookingglass.cpp b/effects/lookingglass/lookingglass.cpp
index dd806a9f6d..a08fa59806 100644
--- a/effects/lookingglass/lookingglass.cpp
+++ b/effects/lookingglass/lookingglass.cpp
@@ -45,10 +45,10 @@ LookingGlassEffect::LookingGlassEffect()
     : zoom(1.0f)
     , target_zoom(1.0f)
     , polling(false)
-    , m_texture(NULL)
-    , m_fbo(NULL)
-    , m_vbo(NULL)
-    , m_shader(NULL)
+    , m_texture(nullptr)
+    , m_fbo(nullptr)
+    , m_vbo(nullptr)
+    , m_shader(nullptr)
     , m_enabled(false)
     , m_valid(false)
 {
diff --git a/effects/lookingglass/lookingglass_config.h b/effects/lookingglass/lookingglass_config.h
index 22adf1b10f..21619ee5f5 100644
--- a/effects/lookingglass/lookingglass_config.h
+++ b/effects/lookingglass/lookingglass_config.h
@@ -41,7 +41,7 @@ class LookingGlassEffectConfig : public KCModule
 {
     Q_OBJECT
 public:
-    explicit LookingGlassEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit LookingGlassEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~LookingGlassEffectConfig() override;
 
     void save() override;
diff --git a/effects/magiclamp/magiclamp.cpp b/effects/magiclamp/magiclamp.cpp
index 76513b7105..155ccf39ee 100644
--- a/effects/magiclamp/magiclamp.cpp
+++ b/effects/magiclamp/magiclamp.cpp
@@ -134,7 +134,7 @@ void MagicLampEffect::paintWindow(EffectWindow* w, int mask, QRegion region, Win
             icon = QRect(pt, QSize(0, 0));
         } else {
             // Assumption: there is a panel containing the icon position
-            EffectWindow* panel = NULL;
+            EffectWindow* panel = nullptr;
             foreach (EffectWindow * window, effects->stackingOrder()) {
                 if (!window->isDock())
                     continue;
diff --git a/effects/magiclamp/magiclamp_config.h b/effects/magiclamp/magiclamp_config.h
index 2f074c07d6..c4b838d96a 100644
--- a/effects/magiclamp/magiclamp_config.h
+++ b/effects/magiclamp/magiclamp_config.h
@@ -40,7 +40,7 @@ class MagicLampEffectConfig : public KCModule
 {
     Q_OBJECT
 public:
-    explicit MagicLampEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit MagicLampEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
 
 public Q_SLOTS:
     void save() override;
diff --git a/effects/magnifier/magnifier.cpp b/effects/magnifier/magnifier.cpp
index 9a22b3806d..d800ef4f87 100644
--- a/effects/magnifier/magnifier.cpp
+++ b/effects/magnifier/magnifier.cpp
@@ -44,8 +44,8 @@ MagnifierEffect::MagnifierEffect()
     : zoom(1)
     , target_zoom(1)
     , polling(false)
-    , m_texture(0)
-    , m_fbo(0)
+    , m_texture(nullptr)
+    , m_fbo(nullptr)
 #ifdef KWIN_HAVE_XRENDER_COMPOSITING
     , m_pixmap(XCB_PIXMAP_NONE)
 #endif
@@ -127,8 +127,8 @@ void MagnifierEffect::prePaintScreen(ScreenPrePaintData& data, int time)
                 // zoom ended - delete FBO and texture
                 delete m_fbo;
                 delete m_texture;
-                m_fbo = NULL;
-                m_texture = NULL;
+                m_fbo = nullptr;
+                m_texture = nullptr;
                 destroyPixmap();
             }
         }
@@ -195,7 +195,7 @@ void MagnifierEffect::paintScreen(int mask, QRegion region, ScreenPaintData& dat
             verts << areaF.left() - FRAME_WIDTH << areaF.bottom() + FRAME_WIDTH;
             verts << areaF.right() + FRAME_WIDTH << areaF.bottom() + FRAME_WIDTH;
             verts << areaF.right() + FRAME_WIDTH << areaF.bottom();
-            vbo->setData(verts.size() / 2, 2, verts.constData(), NULL);
+            vbo->setData(verts.size() / 2, 2, verts.constData(), nullptr);
 
             ShaderBinder binder(ShaderTrait::UniformColor);
             binder.shader()->setUniform(GLShader::ModelViewProjectionMatrix, data.projectionMatrix());
@@ -228,10 +228,10 @@ void MagnifierEffect::paintScreen(int mask, QRegion region, ScreenPaintData& dat
             xform.matrix22 = DOUBLE_TO_FIXED(1.0/zoom);
 #undef DOUBLE_TO_FIXED
             xcb_render_set_picture_transform(xcbConnection(), *m_picture, xform);
-            xcb_render_set_picture_filter(xcbConnection(), *m_picture, 4, const_cast<char*>("good"), 0, NULL);
+            xcb_render_set_picture_filter(xcbConnection(), *m_picture, 4, const_cast<char*>("good"), 0, nullptr);
             xcb_render_composite(xcbConnection(), XCB_RENDER_PICT_OP_SRC, *m_picture, 0, effects->xrenderBufferPicture(),
                                  0, 0, 0, 0, area.x(), area.y(), area.width(), area.height() );
-            xcb_render_set_picture_filter(xcbConnection(), *m_picture, 4, const_cast<char*>("fast"), 0, NULL);
+            xcb_render_set_picture_filter(xcbConnection(), *m_picture, 4, const_cast<char*>("fast"), 0, nullptr);
             xcb_render_set_picture_transform(xcbConnection(), *m_picture, identity);
             const xcb_rectangle_t rects[4] = {
                 { int16_t(area.x()+FRAME_WIDTH), int16_t(area.y()), uint16_t(area.width()-FRAME_WIDTH), uint16_t(FRAME_WIDTH)},
@@ -290,8 +290,8 @@ void MagnifierEffect::zoomOut()
             effects->makeOpenGLContextCurrent();
             delete m_fbo;
             delete m_texture;
-            m_fbo = NULL;
-            m_texture = NULL;
+            m_fbo = nullptr;
+            m_texture = nullptr;
             destroyPixmap();
         }
     }
diff --git a/effects/magnifier/magnifier_config.h b/effects/magnifier/magnifier_config.h
index 6dafd4f877..6b7ec1a920 100644
--- a/effects/magnifier/magnifier_config.h
+++ b/effects/magnifier/magnifier_config.h
@@ -41,7 +41,7 @@ class MagnifierEffectConfig : public KCModule
 {
     Q_OBJECT
 public:
-    explicit MagnifierEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit MagnifierEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~MagnifierEffectConfig() override;
 
     void save() override;
diff --git a/effects/mouseclick/mouseclick.cpp b/effects/mouseclick/mouseclick.cpp
index baa53f5913..a735b14199 100644
--- a/effects/mouseclick/mouseclick.cpp
+++ b/effects/mouseclick/mouseclick.cpp
@@ -164,7 +164,7 @@ void MouseClickEffect::slotMouseChanged(const QPoint& pos, const QPoint&,
     if (buttons == oldButtons)
         return;
 
-    MouseEvent* m = NULL;
+    MouseEvent* m = nullptr;
     int i = BUTTON_COUNT;
     while (--i >= 0) {
         MouseButton* b = m_buttons[i];
@@ -187,7 +187,7 @@ void MouseClickEffect::slotMouseChanged(const QPoint& pos, const QPoint&,
 
 EffectFrame* MouseClickEffect::createEffectFrame(const QPoint& pos, const QString& text) {
     if (!m_showText) {
-        return NULL;
+        return nullptr;
     }
     QPoint point(pos.x() + m_ringMaxSize, pos.y());
     EffectFrame* frame = effects->effectFrame(EffectFrameStyled, false, point, Qt::AlignLeft);
@@ -295,7 +295,7 @@ void MouseClickEffect::drawCircleGl(const QColor& color, float cx, float cy, flo
         x = c * x - s * y;
         y = s * t + c * y;
     }
-    vbo->setData(verts.size() / 2, 2, verts.data(), NULL);
+    vbo->setData(verts.size() / 2, 2, verts.data(), nullptr);
     vbo->render(GL_LINE_LOOP);
 }
 
diff --git a/effects/mouseclick/mouseclick_config.h b/effects/mouseclick/mouseclick_config.h
index 9e8ef375c1..52713c9330 100644
--- a/effects/mouseclick/mouseclick_config.h
+++ b/effects/mouseclick/mouseclick_config.h
@@ -41,7 +41,7 @@ class MouseClickEffectConfig : public KCModule
 {
     Q_OBJECT
 public:
-    explicit MouseClickEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit MouseClickEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~MouseClickEffectConfig() override;
 
     void save() override;
diff --git a/effects/mousemark/mousemark.cpp b/effects/mousemark/mousemark.cpp
index a205ea13c8..d135b04af0 100644
--- a/effects/mousemark/mousemark.cpp
+++ b/effects/mousemark/mousemark.cpp
@@ -138,7 +138,7 @@ void MouseMarkEffect::paintScreen(int mask, QRegion region, ScreenPaintData& dat
             foreach (const QPoint & p, mark) {
                 verts << p.x() << p.y();
             }
-            vbo->setData(verts.size() / 2, 2, verts.data(), NULL);
+            vbo->setData(verts.size() / 2, 2, verts.data(), nullptr);
             vbo->render(GL_LINE_STRIP);
         }
         if (!drawing.isEmpty()) {
@@ -147,7 +147,7 @@ void MouseMarkEffect::paintScreen(int mask, QRegion region, ScreenPaintData& dat
             foreach (const QPoint & p, drawing) {
                 verts << p.x() << p.y();
             }
-            vbo->setData(verts.size() / 2, 2, verts.data(), NULL);
+            vbo->setData(verts.size() / 2, 2, verts.data(), nullptr);
             vbo->render(GL_LINE_STRIP);
         }
         glLineWidth(1.0);
diff --git a/effects/mousemark/mousemark_config.h b/effects/mousemark/mousemark_config.h
index aea63f0c03..20bd754cfd 100644
--- a/effects/mousemark/mousemark_config.h
+++ b/effects/mousemark/mousemark_config.h
@@ -41,7 +41,7 @@ class MouseMarkEffectConfig : public KCModule
 {
     Q_OBJECT
 public:
-    explicit MouseMarkEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit MouseMarkEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~MouseMarkEffectConfig() override;
 
     void save() override;
diff --git a/effects/presentwindows/presentwindows.cpp b/effects/presentwindows/presentwindows.cpp
index 35a29fdadf..b1238e9dc7 100644
--- a/effects/presentwindows/presentwindows.cpp
+++ b/effects/presentwindows/presentwindows.cpp
@@ -55,12 +55,12 @@ PresentWindowsEffect::PresentWindowsEffect()
     , m_decalOpacity(0.0)
     , m_hasKeyboardGrab(false)
     , m_mode(ModeCurrentDesktop)
-    , m_managerWindow(NULL)
+    , m_managerWindow(nullptr)
     , m_needInitialSelection(false)
-    , m_highlightedWindow(NULL)
-    , m_filterFrame(NULL)
-    , m_closeView(NULL)
-    , m_closeWindow(NULL)
+    , m_highlightedWindow(nullptr)
+    , m_filterFrame(nullptr)
+    , m_closeView(nullptr)
+    , m_closeWindow(nullptr)
     , m_exposeAction(new QAction(this))
     , m_exposeAllAction(new QAction(this))
     , m_exposeClassAction(new QAction(this))
@@ -250,7 +250,7 @@ void PresentWindowsEffect::postPaintScreen()
             w->setData(WindowForceBlurRole, QVariant());
             w->setData(WindowForceBackgroundContrastRole, QVariant());
         }
-        effects->setActiveFullScreenEffect(NULL);
+        effects->setActiveFullScreenEffect(nullptr);
         effects->addRepaintFull();
     } else if (m_activated && m_needInitialSelection) {
         m_needInitialSelection = false;
@@ -325,7 +325,7 @@ void PresentWindowsEffect::prePaintWindow(EffectWindow *w, WindowPrePaintData &d
                 winData->referenced = false;
                 w->unrefWindow();
                 if (w == m_closeWindow) {
-                    m_closeWindow = NULL;
+                    m_closeWindow = nullptr;
                 }
             } else
                 w->enablePainting(EffectWindow::PAINT_DISABLED_BY_DELETE);
@@ -487,7 +487,7 @@ void PresentWindowsEffect::slotWindowAdded(EffectWindow *w)
 void PresentWindowsEffect::slotWindowClosed(EffectWindow *w)
 {
     if (m_managerWindow == w)
-        m_managerWindow = NULL;
+        m_managerWindow = nullptr;
     DataHash::iterator winData = m_windowData.find(w);
     if (winData == m_windowData.end())
         return;
@@ -589,7 +589,7 @@ void PresentWindowsEffect::inputEventUpdate(const QPoint &pos, QEvent::Type type
     // We cannot use m_motionManager.windowAtPoint() as the window might not be visible
     EffectWindowList windows = m_motionManager.managedWindows();
     bool hovering = false;
-    EffectWindow *highlightCandidate = NULL;
+    EffectWindow *highlightCandidate = nullptr;
     for (int i = 0; i < windows.size(); ++i) {
         DataHash::const_iterator winData = m_windowData.constFind(windows.at(i));
         if (winData == m_windowData.constEnd())
@@ -603,7 +603,7 @@ void PresentWindowsEffect::inputEventUpdate(const QPoint &pos, QEvent::Type type
         }
     }
     if (!hovering)
-        setHighlightedWindow(NULL);
+        setHighlightedWindow(nullptr);
     if (m_highlightedWindow && m_motionManager.transformedGeometry(m_highlightedWindow).contains(pos))
         updateCloseWindow();
     else if (m_closeView)
@@ -951,7 +951,7 @@ void PresentWindowsEffect::rearrangeWindows()
         }
     }
     if (windowlist.isEmpty()) {
-        setHighlightedWindow(NULL);
+        setHighlightedWindow(nullptr);
         return;
     }
 
@@ -986,7 +986,7 @@ void PresentWindowsEffect::rearrangeWindows()
     }
 
     // Resize text frames if required
-    QFontMetrics* metrics = NULL; // All fonts are the same
+    QFontMetrics* metrics = nullptr; // All fonts are the same
     foreach (EffectWindow * w, m_motionManager.managedWindows()) {
         DataHash::iterator winData = m_windowData.find(w);
         if (winData == m_windowData.end())
@@ -1534,7 +1534,7 @@ void PresentWindowsEffect::setActive(bool active)
         m_needInitialSelection = true;
         m_closeButtonCorner = (Qt::Corner)effects->kwinOption(KWin::CloseButtonCorner).toInt();
         m_decalOpacity = 0.0;
-        m_highlightedWindow = NULL;
+        m_highlightedWindow = nullptr;
         m_windowFilter.clear();
 
         if (!(m_doNotCloseWindows || m_closeView)) {
@@ -1643,7 +1643,7 @@ void PresentWindowsEffect::setActive(bool active)
                 m_managerWindow->deleteProperty(m_atomDesktop);
             else if (m_mode == ModeWindowGroup && m_atomWindows != XCB_ATOM_NONE)
                 m_managerWindow->deleteProperty(m_atomWindows);
-            m_managerWindow = NULL;
+            m_managerWindow = nullptr;
         }
     }
     effects->addRepaintFull(); // Trigger the first repaint
@@ -1709,7 +1709,7 @@ bool PresentWindowsEffect::isVisibleWindow(EffectWindow *w)
 
 void PresentWindowsEffect::setHighlightedWindow(EffectWindow *w)
 {
-    if (w == m_highlightedWindow || (w != NULL && !m_motionManager.isManaging(w)))
+    if (w == m_highlightedWindow || (w != nullptr && !m_motionManager.isManaging(w)))
         return;
 
     if (m_closeView)
@@ -1800,7 +1800,7 @@ EffectWindow* PresentWindowsEffect::relativeWindow(EffectWindow *w, int xdiff, i
             for (int i = 0; i < xdiff; i++) {
                 QRectF wArea = m_motionManager.transformedGeometry(w);
                 detectRect = QRect(0, wArea.y(), area.width(), wArea.height());
-                next = NULL;
+                next = nullptr;
                 foreach (EffectWindow * e, m_motionManager.managedWindows()) {
                     DataHash::const_iterator winData = m_windowData.find(e);
                     if (winData == m_windowData.end() || !winData->visible)
@@ -1808,7 +1808,7 @@ EffectWindow* PresentWindowsEffect::relativeWindow(EffectWindow *w, int xdiff, i
                     QRectF eArea = m_motionManager.transformedGeometry(e);
                     if (eArea.intersects(detectRect) &&
                             eArea.x() > wArea.x()) {
-                        if (next == NULL)
+                        if (next == nullptr)
                             next = e;
                         else {
                             QRectF nArea = m_motionManager.transformedGeometry(next);
@@ -1817,7 +1817,7 @@ EffectWindow* PresentWindowsEffect::relativeWindow(EffectWindow *w, int xdiff, i
                         }
                     }
                 }
-                if (next == NULL) {
+                if (next == nullptr) {
                     if (wrap)   // We are at the right-most window, now get the left-most one to wrap
                         return relativeWindow(w, -1000, 0, false);
                     break; // No more windows to the right
@@ -1830,7 +1830,7 @@ EffectWindow* PresentWindowsEffect::relativeWindow(EffectWindow *w, int xdiff, i
             for (int i = 0; i < -xdiff; i++) {
                 QRectF wArea = m_motionManager.transformedGeometry(w);
                 detectRect = QRect(0, wArea.y(), area.width(), wArea.height());
-                next = NULL;
+                next = nullptr;
                 foreach (EffectWindow * e, m_motionManager.managedWindows()) {
                     DataHash::const_iterator winData = m_windowData.find(e);
                     if (winData == m_windowData.end() || !winData->visible)
@@ -1838,7 +1838,7 @@ EffectWindow* PresentWindowsEffect::relativeWindow(EffectWindow *w, int xdiff, i
                     QRectF eArea = m_motionManager.transformedGeometry(e);
                     if (eArea.intersects(detectRect) &&
                             eArea.x() + eArea.width() < wArea.x() + wArea.width()) {
-                        if (next == NULL)
+                        if (next == nullptr)
                             next = e;
                         else {
                             QRectF nArea = m_motionManager.transformedGeometry(next);
@@ -1847,7 +1847,7 @@ EffectWindow* PresentWindowsEffect::relativeWindow(EffectWindow *w, int xdiff, i
                         }
                     }
                 }
-                if (next == NULL) {
+                if (next == nullptr) {
                     if (wrap)   // We are at the left-most window, now get the right-most one to wrap
                         return relativeWindow(w, 1000, 0, false);
                     break; // No more windows to the left
@@ -1865,7 +1865,7 @@ EffectWindow* PresentWindowsEffect::relativeWindow(EffectWindow *w, int xdiff, i
             for (int i = 0; i < ydiff; i++) {
                 QRectF wArea = m_motionManager.transformedGeometry(w);
                 detectRect = QRect(wArea.x(), 0, wArea.width(), area.height());
-                next = NULL;
+                next = nullptr;
                 foreach (EffectWindow * e, m_motionManager.managedWindows()) {
                     DataHash::const_iterator winData = m_windowData.find(e);
                     if (winData == m_windowData.end() || !winData->visible)
@@ -1873,7 +1873,7 @@ EffectWindow* PresentWindowsEffect::relativeWindow(EffectWindow *w, int xdiff, i
                     QRectF eArea = m_motionManager.transformedGeometry(e);
                     if (eArea.intersects(detectRect) &&
                             eArea.y() > wArea.y()) {
-                        if (next == NULL)
+                        if (next == nullptr)
                             next = e;
                         else {
                             QRectF nArea = m_motionManager.transformedGeometry(next);
@@ -1882,7 +1882,7 @@ EffectWindow* PresentWindowsEffect::relativeWindow(EffectWindow *w, int xdiff, i
                         }
                     }
                 }
-                if (next == NULL) {
+                if (next == nullptr) {
                     if (wrap)   // We are at the bottom-most window, now get the top-most one to wrap
                         return relativeWindow(w, 0, -1000, false);
                     break; // No more windows to the bottom
@@ -1895,7 +1895,7 @@ EffectWindow* PresentWindowsEffect::relativeWindow(EffectWindow *w, int xdiff, i
             for (int i = 0; i < -ydiff; i++) {
                 QRectF wArea = m_motionManager.transformedGeometry(w);
                 detectRect = QRect(wArea.x(), 0, wArea.width(), area.height());
-                next = NULL;
+                next = nullptr;
                 foreach (EffectWindow * e, m_motionManager.managedWindows()) {
                     DataHash::const_iterator winData = m_windowData.find(e);
                     if (winData == m_windowData.end() || !winData->visible)
@@ -1903,7 +1903,7 @@ EffectWindow* PresentWindowsEffect::relativeWindow(EffectWindow *w, int xdiff, i
                     QRectF eArea = m_motionManager.transformedGeometry(e);
                     if (eArea.intersects(detectRect) &&
                             eArea.y() + eArea.height() < wArea.y() + wArea.height()) {
-                        if (next == NULL)
+                        if (next == nullptr)
                             next = e;
                         else {
                             QRectF nArea = m_motionManager.transformedGeometry(next);
@@ -1912,7 +1912,7 @@ EffectWindow* PresentWindowsEffect::relativeWindow(EffectWindow *w, int xdiff, i
                         }
                     }
                 }
-                if (next == NULL) {
+                if (next == nullptr) {
                     if (wrap)   // We are at the top-most window, now get the bottom-most one to wrap
                         return relativeWindow(w, 0, 1000, false);
                     break; // No more windows to the top
@@ -1928,7 +1928,7 @@ EffectWindow* PresentWindowsEffect::relativeWindow(EffectWindow *w, int xdiff, i
 
 EffectWindow* PresentWindowsEffect::findFirstWindow() const
 {
-    EffectWindow *topLeft = NULL;
+    EffectWindow *topLeft = nullptr;
     QRectF topLeftGeometry;
     foreach (EffectWindow * w, m_motionManager.managedWindows()) {
         DataHash::const_iterator winData = m_windowData.find(w);
@@ -1939,7 +1939,7 @@ EffectWindow* PresentWindowsEffect::findFirstWindow() const
             continue; // Not visible
         if (winData->deleted)
             continue; // Window has been closed
-        if (topLeft == NULL) {
+        if (topLeft == nullptr) {
             topLeft = w;
             topLeftGeometry = geometry;
         } else if (geometry.x() < topLeftGeometry.x() || geometry.y() < topLeftGeometry.y()) {
diff --git a/effects/presentwindows/presentwindows.h b/effects/presentwindows/presentwindows.h
index 7d94136a71..8b7c259a40 100644
--- a/effects/presentwindows/presentwindows.h
+++ b/effects/presentwindows/presentwindows.h
@@ -36,7 +36,7 @@ class CloseWindowView : public QObject
 {
     Q_OBJECT
 public:
-    explicit CloseWindowView(QObject *parent = 0);
+    explicit CloseWindowView(QObject *parent = nullptr);
     void windowInputMouseEvent(QMouseEvent* e);
     void disarm();
 
diff --git a/effects/presentwindows/presentwindows_config.h b/effects/presentwindows/presentwindows_config.h
index 4607be00b9..bc15ea7624 100644
--- a/effects/presentwindows/presentwindows_config.h
+++ b/effects/presentwindows/presentwindows_config.h
@@ -40,7 +40,7 @@ class PresentWindowsEffectConfig : public KCModule
 {
     Q_OBJECT
 public:
-    explicit PresentWindowsEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit PresentWindowsEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~PresentWindowsEffectConfig() override;
 
 public Q_SLOTS:
diff --git a/effects/resize/resize.cpp b/effects/resize/resize.cpp
index 2b4e51428f..4cdbb90493 100644
--- a/effects/resize/resize.cpp
+++ b/effects/resize/resize.cpp
@@ -38,7 +38,7 @@ namespace KWin
 ResizeEffect::ResizeEffect()
     : AnimationEffect()
     , m_active(false)
-    , m_resizeWindow(0)
+    , m_resizeWindow(nullptr)
 {
     initConfig<ResizeConfig>();
     reconfigure(ReconfigureAll);
@@ -102,7 +102,7 @@ void ResizeEffect::paintWindow(EffectWindow* w, int mask, QRegion region, Window
                     verts << r.x() + r.width() << r.y() + r.height();
                     verts << r.x() + r.width() << r.y();
                 }
-                vbo->setData(verts.count() / 2, 2, verts.data(), NULL);
+                vbo->setData(verts.count() / 2, 2, verts.data(), nullptr);
                 vbo->render(GL_TRIANGLES);
                 glDisable(GL_BLEND);
             }
@@ -159,7 +159,7 @@ void ResizeEffect::slotWindowFinishUserMovedResized(EffectWindow *w)
 {
     if (m_active && w == m_resizeWindow) {
         m_active = false;
-        m_resizeWindow = NULL;
+        m_resizeWindow = nullptr;
         if (m_features & TextureScale)
             animate(w, CrossFadePrevious, 0, 150, FPx2(1.0));
         effects->addRepaintFull();
diff --git a/effects/resize/resize_config.h b/effects/resize/resize_config.h
index e02e596e38..7c07c23acc 100644
--- a/effects/resize/resize_config.h
+++ b/effects/resize/resize_config.h
@@ -33,14 +33,14 @@ class ResizeEffectConfigForm : public QWidget, public Ui::ResizeEffectConfigForm
 {
     Q_OBJECT
 public:
-    explicit ResizeEffectConfigForm(QWidget* parent = 0);
+    explicit ResizeEffectConfigForm(QWidget* parent = nullptr);
 };
 
 class ResizeEffectConfig : public KCModule
 {
     Q_OBJECT
 public:
-    explicit ResizeEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit ResizeEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
 
 public Q_SLOTS:
     void save() override;
diff --git a/effects/screenedge/screenedgeeffect.cpp b/effects/screenedge/screenedgeeffect.cpp
index 3c0810eb10..88654bb627 100644
--- a/effects/screenedge/screenedgeeffect.cpp
+++ b/effects/screenedge/screenedgeeffect.cpp
@@ -233,7 +233,7 @@ Glow *ScreenEdgeEffect::createGlow(ElectricBorder border, qreal factor, const QR
         }
         if (glow->texture.isNull()) {
             delete glow;
-            return NULL;
+            return nullptr;
         }
     } else if (effects->compositingType() == XRenderCompositing) {
 #ifdef KWIN_HAVE_XRENDER_COMPOSITING
@@ -246,7 +246,7 @@ Glow *ScreenEdgeEffect::createGlow(ElectricBorder border, qreal factor, const QR
         }
         if (glow->picture.isNull()) {
             delete glow;
-            return NULL;
+            return nullptr;
         }
 #endif
     } else if (effects->compositingType() == QPainterCompositing) {
@@ -259,7 +259,7 @@ Glow *ScreenEdgeEffect::createGlow(ElectricBorder border, qreal factor, const QR
         }
         if (glow->image.isNull()) {
             delete glow;
-            return NULL;
+            return nullptr;
         }
     }
 
@@ -281,7 +281,7 @@ T *ScreenEdgeEffect::createCornerGlow(ElectricBorder border)
     case ElectricBottomLeft:
         return new T(m_glow->pixmap(QStringLiteral("topright")).toImage());
     default:
-        return NULL;
+        return nullptr;
     }
 }
 
@@ -336,7 +336,7 @@ T *ScreenEdgeEffect::createEdgeGlow(ElectricBorder border, const QSize &size)
         pixmapPosition = QPoint(size.width() - c.width(), 0);
         break;
     default:
-        return NULL;
+        return nullptr;
     }
     QPixmap image(size);
     image.fill(Qt::transparent);
diff --git a/effects/screenshot/screenshot.cpp b/effects/screenshot/screenshot.cpp
index 35a64cbeb4..a37b684f25 100644
--- a/effects/screenshot/screenshot.cpp
+++ b/effects/screenshot/screenshot.cpp
@@ -58,7 +58,7 @@ bool ScreenShotEffect::supported()
 }
 
 ScreenShotEffect::ScreenShotEffect()
-    : m_scheduledScreenshot(0)
+    : m_scheduledScreenshot(nullptr)
 {
     connect(effects, &EffectsHandler::windowClosed, this, &ScreenShotEffect::windowClosed);
     QDBusConnection::sessionBus().registerObject(QStringLiteral("/Screenshot"), this, QDBusConnection::ExportScriptableContents);
@@ -234,7 +234,7 @@ void ScreenShotEffect::postPaintScreen()
                 ScreenShotEffect::convertFromGLImage(img, width, height);
             }
 #ifdef KWIN_HAVE_XRENDER_COMPOSITING
-            xcb_image_t *xImage = NULL;
+            xcb_image_t *xImage = nullptr;
             if (effects->compositingType() == XRenderCompositing) {
                 setXRenderOffscreen(true);
                 effects->drawWindow(m_scheduledScreenshot, mask, QRegion(0, 0, width, height), d);
@@ -276,7 +276,7 @@ void ScreenShotEffect::postPaintScreen()
             }
 #endif
         }
-        m_scheduledScreenshot = NULL;
+        m_scheduledScreenshot = nullptr;
     }
 
     if (!m_scheduledGeometry.isNull()) {
@@ -373,7 +373,7 @@ void ScreenShotEffect::screenshotWindowUnderCursor(int mask)
             !m_scheduledScreenshot->isMinimized() && !m_scheduledScreenshot->isDeleted() &&
             m_scheduledScreenshot->geometry().contains(cursor))
             break;
-        m_scheduledScreenshot = 0;
+        m_scheduledScreenshot = nullptr;
     }
     if (m_scheduledScreenshot) {
         m_windowMode = WindowMode::Xpixmap;
@@ -626,7 +626,7 @@ QImage ScreenShotEffect::blitScreenshot(const QRect &geometry)
 
 #ifdef KWIN_HAVE_XRENDER_COMPOSITING
     if (effects->compositingType() == XRenderCompositing) {
-    xcb_image_t *xImage = NULL;
+    xcb_image_t *xImage = nullptr;
         img = xPictureToImage(effects->xrenderBufferPicture(), geometry, &xImage);
         if (xImage) {
             xcb_image_destroy(xImage);
@@ -684,13 +684,13 @@ void ScreenShotEffect::convertFromGLImage(QImage &img, int w, int h)
 
 bool ScreenShotEffect::isActive() const
 {
-    return (m_scheduledScreenshot != NULL || !m_scheduledGeometry.isNull()) && !effects->isScreenLocked();
+    return (m_scheduledScreenshot != nullptr || !m_scheduledGeometry.isNull()) && !effects->isScreenLocked();
 }
 
 void ScreenShotEffect::windowClosed( EffectWindow* w )
 {
     if (w == m_scheduledScreenshot) {
-        m_scheduledScreenshot = NULL;
+        m_scheduledScreenshot = nullptr;
         screenshotWindowUnderCursor(m_type);
     }
 }
diff --git a/effects/showfps/showfps.cpp b/effects/showfps/showfps.cpp
index ad7f707305..b02ca1eef5 100644
--- a/effects/showfps/showfps.cpp
+++ b/effects/showfps/showfps.cpp
@@ -201,7 +201,7 @@ void ShowFpsEffect::paintGL(int fps, const QMatrix4x4 &projectionMatrix)
     verts << x << y + MAX_TIME;
     verts << x + 2 * NUM_PAINTS + FPS_WIDTH << y + MAX_TIME;
     verts << x + 2 * NUM_PAINTS + FPS_WIDTH << y;
-    vbo->setData(6, 2, verts.constData(), NULL);
+    vbo->setData(6, 2, verts.constData(), nullptr);
     vbo->render(GL_TRIANGLES);
     y += MAX_TIME; // paint up from the bottom
     color.setRed(0);
@@ -214,7 +214,7 @@ void ShowFpsEffect::paintGL(int fps, const QMatrix4x4 &projectionMatrix)
     verts << x << y;
     verts << x + FPS_WIDTH << y;
     verts << x + FPS_WIDTH << y - fps;
-    vbo->setData(6, 2, verts.constData(), NULL);
+    vbo->setData(6, 2, verts.constData(), nullptr);
     vbo->render(GL_TRIANGLES);
 
 
@@ -227,7 +227,7 @@ void ShowFpsEffect::paintGL(int fps, const QMatrix4x4 &projectionMatrix)
         vertices << x << y - i;
         vertices << x + FPS_WIDTH << y - i;
     }
-    vbo->setData(vertices.size() / 2, 2, vertices.constData(), NULL);
+    vbo->setData(vertices.size() / 2, 2, vertices.constData(), nullptr);
     vbo->render(GL_LINES);
     x += FPS_WIDTH;
 
@@ -406,7 +406,7 @@ void ShowFpsEffect::paintGraph(int x, int y, QList<int> values, QList<int> lines
             verts << x << y - h;
             verts << x + values.count() << y - h;
         }
-        vbo->setData(verts.size() / 2, 2, verts.constData(), NULL);
+        vbo->setData(verts.size() / 2, 2, verts.constData(), nullptr);
         vbo->render(GL_LINES);
         // Then the graph values
         int lastValue = 0;
@@ -415,7 +415,7 @@ void ShowFpsEffect::paintGraph(int x, int y, QList<int> values, QList<int> lines
             int value = values[ i ];
             if (colorize && value != lastValue) {
                 if (!verts.isEmpty()) {
-                    vbo->setData(verts.size() / 2, 2, verts.constData(), NULL);
+                    vbo->setData(verts.size() / 2, 2, verts.constData(), nullptr);
                     vbo->render(GL_LINES);
                 }
                 verts.clear();
@@ -435,7 +435,7 @@ void ShowFpsEffect::paintGraph(int x, int y, QList<int> values, QList<int> lines
             lastValue = value;
         }
         if (!verts.isEmpty()) {
-            vbo->setData(verts.size() / 2, 2, verts.constData(), NULL);
+            vbo->setData(verts.size() / 2, 2, verts.constData(), nullptr);
             vbo->render(GL_LINES);
         }
     }
diff --git a/effects/showfps/showfps_config.h b/effects/showfps/showfps_config.h
index 7ac264d08d..7d79a07fcf 100644
--- a/effects/showfps/showfps_config.h
+++ b/effects/showfps/showfps_config.h
@@ -32,7 +32,7 @@ class ShowFpsEffectConfig : public KCModule
 {
     Q_OBJECT
 public:
-    explicit ShowFpsEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit ShowFpsEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~ShowFpsEffectConfig() override;
 
 public Q_SLOTS:
diff --git a/effects/slideback/slideback.cpp b/effects/slideback/slideback.cpp
index 67970ecd43..00356e8baf 100644
--- a/effects/slideback/slideback.cpp
+++ b/effects/slideback/slideback.cpp
@@ -26,7 +26,7 @@ namespace KWin
 SlideBackEffect::SlideBackEffect()
 {
     m_tabboxActive = 0;
-    m_justMapped = m_upmostWindow = NULL;
+    m_justMapped = m_upmostWindow = nullptr;
     connect(effects, &EffectsHandler::windowAdded, this, &SlideBackEffect::slotWindowAdded);
     connect(effects, &EffectsHandler::windowDeleted, this, &SlideBackEffect::slotWindowDeleted);
     connect(effects, &EffectsHandler::windowUnminimized, this, &SlideBackEffect::slotWindowUnminimized);
@@ -54,7 +54,7 @@ void SlideBackEffect::slotStackingOrderChanged()
     m_upmostWindow = usableNewStackingOrder.last();
 
     if (m_upmostWindow == m_justMapped ) // a window was added, got on top, stacking changed. Nothing impressive
-        m_justMapped = 0;
+        m_justMapped = nullptr;
     else if (!usableOldStackingOrder.isEmpty() && m_upmostWindow != usableOldStackingOrder.last())
         windowRaised(m_upmostWindow);
 
@@ -259,9 +259,9 @@ void SlideBackEffect::postPaintWindow(EffectWindow* w)
 void SlideBackEffect::slotWindowDeleted(EffectWindow* w)
 {
     if (w == m_upmostWindow)
-        m_upmostWindow = 0;
+        m_upmostWindow = nullptr;
     if (w == m_justMapped)
-        m_justMapped = 0;
+        m_justMapped = nullptr;
     usableOldStackingOrder.removeAll(w);
     oldStackingOrder.removeAll(w);
     coveringWindows.removeAll(w);
diff --git a/effects/startupfeedback/startupfeedback.cpp b/effects/startupfeedback/startupfeedback.cpp
index 01f0ae23df..6864d65d98 100644
--- a/effects/startupfeedback/startupfeedback.cpp
+++ b/effects/startupfeedback/startupfeedback.cpp
@@ -78,13 +78,13 @@ StartupFeedbackEffect::StartupFeedbackEffect()
     , m_active(false)
     , m_frame(0)
     , m_progress(0)
-    , m_texture(0)
+    , m_texture(nullptr)
     , m_type(BouncingFeedback)
-    , m_blinkingShader(0)
+    , m_blinkingShader(nullptr)
     , m_cursorSize(0)
 {
     for (int i = 0; i < 5; ++i) {
-        m_bouncingTextures[i] = 0;
+        m_bouncingTextures[i] = nullptr;
     }
     if (KWindowSystem::isPlatformX11()) {
         m_selection = new KSelectionOwner("_KDE_STARTUP_FEEDBACK", xcbConnection(), x11RootWindow(), this);
@@ -276,7 +276,7 @@ void StartupFeedbackEffect::start(const QString& icon)
     if (m_type == BouncingFeedback)
         m_bounceSizesRatio = IconSize(KIconLoader::Small) / 16.0;
     QPixmap iconPixmap = KIconLoader::global()->loadIcon(icon, KIconLoader::Small, 0,
-                         KIconLoader::DefaultState, QStringList(), 0, true);  // return null pixmap if not found
+                         KIconLoader::DefaultState, QStringList(), nullptr, true);  // return null pixmap if not found
     if (iconPixmap.isNull())
         iconPixmap = SmallIcon(QStringLiteral("system-run"));
     prepareTextures(iconPixmap);
@@ -307,13 +307,13 @@ void StartupFeedbackEffect::stop()
     case BouncingFeedback:
         for (int i = 0; i < 5; ++i) {
             delete m_bouncingTextures[i];
-            m_bouncingTextures[i] = 0;
+            m_bouncingTextures[i] = nullptr;
         }
         break;
     case BlinkingFeedback:
     case PassiveFeedback:
         delete m_texture;
-        m_texture = 0;
+        m_texture = nullptr;
         break;
     case NoFeedback:
         return; // don't want the full repaint
@@ -371,7 +371,7 @@ QRect StartupFeedbackEffect::feedbackRect() const
     else
         xDiff = 32 + 7;
     int yDiff = xDiff;
-    GLTexture* texture = 0;
+    GLTexture* texture = nullptr;
     int yOffset = 0;
     switch(m_type) {
     case BouncingFeedback:
diff --git a/effects/thumbnailaside/thumbnailaside.cpp b/effects/thumbnailaside/thumbnailaside.cpp
index 66ce377703..9bca3c6a78 100644
--- a/effects/thumbnailaside/thumbnailaside.cpp
+++ b/effects/thumbnailaside/thumbnailaside.cpp
@@ -113,7 +113,7 @@ void ThumbnailAsideEffect::slotWindowClosed(EffectWindow* w)
 void ThumbnailAsideEffect::toggleCurrentThumbnail()
 {
     EffectWindow* active = effects->activeWindow();
-    if (active == NULL)
+    if (active == nullptr)
         return;
     if (windows.contains(active))
         removeThumbnail(active);
diff --git a/effects/thumbnailaside/thumbnailaside_config.h b/effects/thumbnailaside/thumbnailaside_config.h
index 88973b8328..4055892652 100644
--- a/effects/thumbnailaside/thumbnailaside_config.h
+++ b/effects/thumbnailaside/thumbnailaside_config.h
@@ -41,7 +41,7 @@ class ThumbnailAsideEffectConfig : public KCModule
 {
     Q_OBJECT
 public:
-    explicit ThumbnailAsideEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit ThumbnailAsideEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~ThumbnailAsideEffectConfig() override;
 
     void save() override;
diff --git a/effects/touchpoints/touchpoints.cpp b/effects/touchpoints/touchpoints.cpp
index 5c358831c2..52e9e95212 100644
--- a/effects/touchpoints/touchpoints.cpp
+++ b/effects/touchpoints/touchpoints.cpp
@@ -231,7 +231,7 @@ void TouchPointsEffect::drawCircleGl(const QColor& color, float cx, float cy, fl
         x = c * x - s * y;
         y = s * t + c * y;
     }
-    vbo->setData(verts.size() / 2, 2, verts.data(), NULL);
+    vbo->setData(verts.size() / 2, 2, verts.data(), nullptr);
     vbo->render(GL_LINE_LOOP);
 }
 
diff --git a/effects/trackmouse/trackmouse.cpp b/effects/trackmouse/trackmouse.cpp
index 534b98f240..e84728d98b 100644
--- a/effects/trackmouse/trackmouse.cpp
+++ b/effects/trackmouse/trackmouse.cpp
@@ -46,9 +46,9 @@ TrackMouseEffect::TrackMouseEffect()
     : m_angle(0)
 {
     initConfig<TrackMouseConfig>();
-    m_texture[0] = m_texture[1] = 0;
+    m_texture[0] = m_texture[1] = nullptr;
 #ifdef KWIN_HAVE_XRENDER_COMPOSITING
-    m_picture[0] = m_picture[1] = 0;
+    m_picture[0] = m_picture[1] = nullptr;
     if ( effects->compositingType() == XRenderCompositing)
         m_angleBase = 1.57079632679489661923; // Pi/2
 #endif
@@ -74,16 +74,16 @@ TrackMouseEffect::~TrackMouseEffect()
     if (m_mousePolling)
         effects->stopMousePolling();
     for (int i = 0; i < 2; ++i) {
-        delete m_texture[i]; m_texture[i] = 0;
+        delete m_texture[i]; m_texture[i] = nullptr;
 #ifdef KWIN_HAVE_XRENDER_COMPOSITING
-        delete m_picture[i]; m_picture[i] = 0;
+        delete m_picture[i]; m_picture[i] = nullptr;
 #endif
     }
 }
 
 void TrackMouseEffect::reconfigure(ReconfigureFlags)
 {
-    m_modifiers = 0;
+    m_modifiers = nullptr;
     TrackMouseConfig::self()->read();
     if (TrackMouseConfig::shift())
         m_modifiers |= Qt::ShiftModifier;
@@ -161,7 +161,7 @@ void TrackMouseEffect::paintScreen(int mask, QRegion region, ScreenPaintData& da
             };
 #undef DOUBLE_TO_FIXED
             xcb_render_set_picture_transform(xcbConnection(), picture, xform);
-            xcb_render_set_picture_filter(xcbConnection(), picture, 8, "bilinear", 0, NULL);
+            xcb_render_set_picture_filter(xcbConnection(), picture, 8, "bilinear", 0, nullptr);
             const QRect &rect = m_lastRect[i];
             xcb_render_composite(xcbConnection(), XCB_RENDER_PICT_OP_OVER, picture, XCB_RENDER_PICTURE_NONE,
                                  effects->xrenderBufferPicture(), 0, 0, 0, 0,
diff --git a/effects/trackmouse/trackmouse_config.h b/effects/trackmouse/trackmouse_config.h
index 7a6a8d3f1c..a3bdc4b258 100644
--- a/effects/trackmouse/trackmouse_config.h
+++ b/effects/trackmouse/trackmouse_config.h
@@ -42,7 +42,7 @@ class TrackMouseEffectConfig : public KCModule
 {
     Q_OBJECT
 public:
-    explicit TrackMouseEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit TrackMouseEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~TrackMouseEffectConfig() override;
 
 public Q_SLOTS:
diff --git a/effects/windowgeometry/windowgeometry.cpp b/effects/windowgeometry/windowgeometry.cpp
index e976d664ba..c77af6efb3 100644
--- a/effects/windowgeometry/windowgeometry.cpp
+++ b/effects/windowgeometry/windowgeometry.cpp
@@ -37,7 +37,7 @@ WindowGeometry::WindowGeometry()
     initConfig<WindowGeometryConfiguration>();
     iAmActivated = true;
     iAmActive = false;
-    myResizeWindow = 0L;
+    myResizeWindow = nullptr;
 #define myResizeString "Window geometry display, %1 and %2 are the new size," \
                        " %3 and %4 are pixel increments - avoid reformatting or suffixes like 'px'", \
                        "Width: %1 (%3)\nHeight: %2 (%4)"
@@ -128,7 +128,7 @@ void WindowGeometry::slotWindowFinishUserMovedResized(EffectWindow *w)
 {
     if (iAmActive && w == myResizeWindow) {
         iAmActive = false;
-        myResizeWindow = 0L;
+        myResizeWindow = nullptr;
         w->addRepaintFull();
         if (myExtraDirtyArea.isValid())
             w->addLayerRepaint(myExtraDirtyArea);
diff --git a/effects/windowgeometry/windowgeometry_config.h b/effects/windowgeometry/windowgeometry_config.h
index b45d302753..247f47c56f 100644
--- a/effects/windowgeometry/windowgeometry_config.h
+++ b/effects/windowgeometry/windowgeometry_config.h
@@ -40,7 +40,7 @@ class WindowGeometryConfig : public KCModule
 {
     Q_OBJECT
 public:
-    explicit WindowGeometryConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit WindowGeometryConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~WindowGeometryConfig() override;
 
 public Q_SLOTS:
diff --git a/effects/wobblywindows/wobblywindows_config.h b/effects/wobblywindows/wobblywindows_config.h
index 3dadb60fb8..f423c9a19f 100644
--- a/effects/wobblywindows/wobblywindows_config.h
+++ b/effects/wobblywindows/wobblywindows_config.h
@@ -34,7 +34,7 @@ class WobblyWindowsEffectConfig : public KCModule
 {
     Q_OBJECT
 public:
-    explicit WobblyWindowsEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit WobblyWindowsEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~WobblyWindowsEffectConfig() override;
 
 public Q_SLOTS:
diff --git a/effects/zoom/zoom.cpp b/effects/zoom/zoom.cpp
index d239c9e4f2..413d0261c6 100644
--- a/effects/zoom/zoom.cpp
+++ b/effects/zoom/zoom.cpp
@@ -61,7 +61,7 @@ ZoomEffect::ZoomEffect()
     , moveFactor(20.0)
 {
     initConfig<ZoomConfig>();
-    QAction* a = 0;
+    QAction* a = nullptr;
     a = KStandardAction::zoomIn(this, SLOT(zoomIn()), this);
     KGlobalAccel::self()->setDefaultShortcut(a, QList<QKeySequence>() << Qt::META + Qt::Key_Equal);
     KGlobalAccel::self()->setShortcut(a, QList<QKeySequence>() << Qt::META + Qt::Key_Equal);
@@ -369,7 +369,7 @@ void ZoomEffect::paintScreen(int mask, QRegion region, ScreenPaintData& data)
                 DOUBLE_TO_FIXED(0), DOUBLE_TO_FIXED(0), DOUBLE_TO_FIXED(1)
             };
             if (mousePointer == MousePointerScale) {
-                xcb_render_set_picture_filter(xcbConnection(), *xrenderPicture, 4, const_cast<char*>("good"), 0, NULL);
+                xcb_render_set_picture_filter(xcbConnection(), *xrenderPicture, 4, const_cast<char*>("good"), 0, nullptr);
                 const xcb_render_transform_t xform = {
                     DOUBLE_TO_FIXED(1.0 / zoom), DOUBLE_TO_FIXED(0), DOUBLE_TO_FIXED(0),
                     DOUBLE_TO_FIXED(0), DOUBLE_TO_FIXED(1.0 / zoom), DOUBLE_TO_FIXED(0),
diff --git a/effects/zoom/zoom_config.h b/effects/zoom/zoom_config.h
index c40c8be975..72fe20ddba 100644
--- a/effects/zoom/zoom_config.h
+++ b/effects/zoom/zoom_config.h
@@ -34,14 +34,14 @@ class ZoomEffectConfigForm : public QWidget, public Ui::ZoomEffectConfigForm
 {
     Q_OBJECT
 public:
-    explicit ZoomEffectConfigForm(QWidget* parent = 0);
+    explicit ZoomEffectConfigForm(QWidget* parent = nullptr);
 };
 
 class ZoomEffectConfig : public KCModule
 {
     Q_OBJECT
 public:
-    explicit ZoomEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit ZoomEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~ZoomEffectConfig() override;
 
 public Q_SLOTS:
diff --git a/events.cpp b/events.cpp
index b0fe982c87..54d812c511 100644
--- a/events.cpp
+++ b/events.cpp
@@ -326,7 +326,7 @@ bool Workspace::workspaceEvent(xcb_generic_event_t *e)
         const auto *event = reinterpret_cast<xcb_map_notify_event_t*>(e);
         if (event->override_redirect) {
             Unmanaged* c = findUnmanaged(event->window);
-            if (c == NULL)
+            if (c == nullptr)
                 c = createUnmanaged(event->window);
             if (c)
                 return c->windowEvent(e);
@@ -373,9 +373,9 @@ bool Workspace::workspaceEvent(xcb_generic_event_t *e)
             if (!currentInput.isNull() && (currentInput->focus == XCB_WINDOW_NONE || currentInput->focus == XCB_INPUT_FOCUS_POINTER_ROOT || lostFocusPointerToRoot)) {
                 //kWarning( 1212 ) << "X focus set to None/PointerRoot, reseting focus" ;
                 AbstractClient *c = mostRecentlyActivatedClient();
-                if (c != NULL)
+                if (c != nullptr)
                     requestFocus(c, true);
-                else if (activateNextClient(NULL))
+                else if (activateNextClient(nullptr))
                     ; // ok, activated
                 else
                     focusToNull();
@@ -444,7 +444,7 @@ bool Client::windowEvent(xcb_generic_event_t *e)
                 emit opacityChanged(this, old_opacity);
             } else {
                 // forward to the frame if there's possibly another compositing manager running
-                NETWinInfo i(connection(), frameId(), rootWindow(), 0, 0);
+                NETWinInfo i(connection(), frameId(), rootWindow(), nullptr, nullptr);
                 i.setOpacity(info->opacity());
             }
         }
@@ -821,7 +821,7 @@ void Client::leaveNotifyEvent(xcb_leave_notify_event_t *e)
             }
         }
         if (options->focusPolicy() == Options::FocusStrictlyUnderMouse && isActive() && lostMouse) {
-            workspace()->requestDelayFocus(0);
+            workspace()->requestDelayFocus(nullptr);
         }
         return;
     }
diff --git a/focuschain.cpp b/focuschain.cpp
index 1054d69a55..229314968c 100644
--- a/focuschain.cpp
+++ b/focuschain.cpp
@@ -29,14 +29,14 @@ KWIN_SINGLETON_FACTORY_VARIABLE(FocusChain, s_manager)
 FocusChain::FocusChain(QObject *parent)
     : QObject(parent)
     , m_separateScreenFocus(false)
-    , m_activeClient(NULL)
+    , m_activeClient(nullptr)
     , m_currentDesktop(0)
 {
 }
 
 FocusChain::~FocusChain()
 {
-    s_manager = NULL;
+    s_manager = nullptr;
 }
 
 void FocusChain::remove(AbstractClient *client)
@@ -68,7 +68,7 @@ AbstractClient *FocusChain::getForActivation(uint desktop, int screen) const
 {
     auto it = m_desktopFocusChains.constFind(desktop);
     if (it == m_desktopFocusChains.constEnd()) {
-        return NULL;
+        return nullptr;
     }
     const auto &chain = it.value();
     for (int i = chain.size() - 1; i >= 0; --i) {
@@ -79,7 +79,7 @@ AbstractClient *FocusChain::getForActivation(uint desktop, int screen) const
             return tmp;
         }
     }
-    return NULL;
+    return nullptr;
 }
 
 void FocusChain::update(AbstractClient *client, FocusChain::Change change)
@@ -191,7 +191,7 @@ void FocusChain::moveAfterClientInChain(AbstractClient *client, AbstractClient *
 AbstractClient *FocusChain::firstMostRecentlyUsed() const
 {
     if (m_mostRecentlyUsed.isEmpty()) {
-        return NULL;
+        return nullptr;
     }
     return m_mostRecentlyUsed.first();
 }
@@ -199,7 +199,7 @@ AbstractClient *FocusChain::firstMostRecentlyUsed() const
 AbstractClient *FocusChain::nextMostRecentlyUsed(AbstractClient *reference) const
 {
     if (m_mostRecentlyUsed.isEmpty()) {
-        return NULL;
+        return nullptr;
     }
     const int index = m_mostRecentlyUsed.indexOf(reference);
     if (index == -1) {
@@ -223,7 +223,7 @@ AbstractClient *FocusChain::nextForDesktop(AbstractClient *reference, uint deskt
 {
     auto it = m_desktopFocusChains.constFind(desktop);
     if (it == m_desktopFocusChains.constEnd()) {
-        return NULL;
+        return nullptr;
     }
     const auto &chain = it.value();
     for (int i = chain.size() - 1; i >= 0; --i) {
@@ -232,7 +232,7 @@ AbstractClient *FocusChain::nextForDesktop(AbstractClient *reference, uint deskt
             return client;
         }
     }
-    return NULL;
+    return nullptr;
 }
 
 void FocusChain::makeFirstInChain(AbstractClient *client, Chain &chain)
diff --git a/geometry.cpp b/geometry.cpp
index ab6cceb852..7164e6b4f8 100644
--- a/geometry.cpp
+++ b/geometry.cpp
@@ -894,7 +894,7 @@ void Workspace::setMoveResizeClient(AbstractClient *c)
 // (the property with the size of the frame remains on the window after the crash).
 void Workspace::fixPositionAfterCrash(xcb_window_t w, const xcb_get_geometry_reply_t *geometry)
 {
-    NETWinInfo i(connection(), w, rootWindow(), NET::WMFrameExtents, 0);
+    NETWinInfo i(connection(), w, rootWindow(), NET::WMFrameExtents, nullptr);
     NETStrut frame = i.frameExtents();
 
     if (frame.left != 0 || frame.top != 0) {
@@ -2511,7 +2511,7 @@ QRect Client::fullscreenMonitorsArea(NETFullscreenMonitors requestedTopology) co
     return total;
 }
 
-static GeometryTip* geometryTip    = 0;
+static GeometryTip* geometryTip    = nullptr;
 
 void Client::positionGeometryTip()
 {
@@ -2538,10 +2538,10 @@ void Client::positionGeometryTip()
 bool AbstractClient::startMoveResize()
 {
     Q_ASSERT(!isMoveResize());
-    Q_ASSERT(QWidget::keyboardGrabber() == NULL);
-    Q_ASSERT(QWidget::mouseGrabber() == NULL);
+    Q_ASSERT(QWidget::keyboardGrabber() == nullptr);
+    Q_ASSERT(QWidget::mouseGrabber() == nullptr);
     stopDelayedMoveResize();
-    if (QApplication::activePopupWidget() != NULL)
+    if (QApplication::activePopupWidget() != nullptr)
         return false; // popups have grab
     if (isFullScreen() && (screens()->count() < 2 || !isMovableAcrossScreens()))
         return false;
@@ -2585,7 +2585,7 @@ bool Client::doStartMoveResize()
     // something with Enter/LeaveNotify events, looks like XFree performance problem or something *shrug*
     // (https://lists.kde.org/?t=107302193400001&r=1&w=2)
     QRect r = workspace()->clientArea(FullArea, this);
-    m_moveResizeGrabWindow.create(r, XCB_WINDOW_CLASS_INPUT_ONLY, 0, NULL, rootWindow());
+    m_moveResizeGrabWindow.create(r, XCB_WINDOW_CLASS_INPUT_ONLY, 0, nullptr, rootWindow());
     m_moveResizeGrabWindow.map();
     m_moveResizeGrabWindow.raise();
     updateXTime();
@@ -2593,7 +2593,7 @@ bool Client::doStartMoveResize()
         XCB_EVENT_MASK_BUTTON_PRESS | XCB_EVENT_MASK_BUTTON_RELEASE | XCB_EVENT_MASK_POINTER_MOTION |
         XCB_EVENT_MASK_ENTER_WINDOW | XCB_EVENT_MASK_LEAVE_WINDOW,
         XCB_GRAB_MODE_ASYNC, XCB_GRAB_MODE_ASYNC, m_moveResizeGrabWindow, Cursor::x11Cursor(cursor()), xTime());
-    ScopedCPointer<xcb_grab_pointer_reply_t> pointerGrab(xcb_grab_pointer_reply(connection(), cookie, NULL));
+    ScopedCPointer<xcb_grab_pointer_reply_t> pointerGrab(xcb_grab_pointer_reply(connection(), cookie, nullptr));
     if (!pointerGrab.isNull() && pointerGrab->status == XCB_GRAB_STATUS_SUCCESS) {
         has_grab = true;
     }
@@ -2666,7 +2666,7 @@ void Client::leaveMoveResize()
     if (geometryTip) {
         geometryTip->hide();
         delete geometryTip;
-        geometryTip = NULL;
+        geometryTip = nullptr;
     }
     if (move_resize_has_keyboard_grab)
         ungrabXKeyboard();
@@ -2676,7 +2676,7 @@ void Client::leaveMoveResize()
     if (syncRequest.counter == XCB_NONE) // don't forget to sanitize since the timeout will no more fire
         syncRequest.isPending = false;
     delete syncRequest.timeout;
-    syncRequest.timeout = NULL;
+    syncRequest.timeout = nullptr;
     AbstractClient::leaveMoveResize();
 }
 
diff --git a/geometrytip.cpp b/geometrytip.cpp
index 237f3644f3..0395213644 100644
--- a/geometrytip.cpp
+++ b/geometrytip.cpp
@@ -24,7 +24,7 @@ namespace KWin
 {
 
 GeometryTip::GeometryTip(const Xcb::GeometryHints* xSizeHints):
-    QLabel(0)
+    QLabel(nullptr)
 {
     setObjectName(QLatin1String("kwingeometry"));
     setMargin(1);
diff --git a/group.cpp b/group.cpp
index 0fea1fdbb8..44d3821c8e 100644
--- a/group.cpp
+++ b/group.cpp
@@ -51,16 +51,16 @@ namespace KWin
 //********************************************
 
 Group::Group(xcb_window_t leader_P)
-    :   leader_client(NULL),
+    :   leader_client(nullptr),
         leader_wid(leader_P),
-        leader_info(NULL),
+        leader_info(nullptr),
         user_time(-1U),
         refcount(0)
 {
     if (leader_P != XCB_WINDOW_NONE) {
         leader_client = workspace()->findClient(Predicate::WindowMatch, leader_P);
         leader_info = new NETWinInfo(connection(), leader_P, rootWindow(),
-                                      0, NET::WM2StartupId);
+                                      nullptr, NET::WM2StartupId);
     }
     effect_group = new EffectWindowGroupImpl(this);
     workspace()->addGroup(this);
@@ -74,7 +74,7 @@ Group::~Group()
 
 QIcon Group::icon() const
 {
-    if (leader_client != NULL)
+    if (leader_client != nullptr)
         return leader_client->icon();
     else if (leader_wid != XCB_WINDOW_NONE) {
         QIcon ic;
@@ -140,7 +140,7 @@ void Group::gotLeader(Client* leader_P)
 void Group::lostLeader()
 {
     Q_ASSERT(!_members.contains(leader_client));
-    leader_client = NULL;
+    leader_client = nullptr;
     if (_members.isEmpty()) {
         workspace()->removeGroup(this);
         delete this;
@@ -159,21 +159,21 @@ Group* Workspace::findGroup(xcb_window_t leader) const
             ++it)
         if ((*it)->leader() == leader)
             return *it;
-    return NULL;
+    return nullptr;
 }
 
 // Client is group transient, but has no group set. Try to find
 // group with windows with the same client leader.
 Group* Workspace::findClientLeaderGroup(const Client* c) const
 {
-    Group* ret = NULL;
+    Group* ret = nullptr;
     for (ClientList::ConstIterator it = clients.constBegin();
             it != clients.constEnd();
             ++it) {
         if (*it == c)
             continue;
         if ((*it)->wmClientLeader() == c->wmClientLeader()) {
-            if (ret == NULL || ret == (*it)->group())
+            if (ret == nullptr || ret == (*it)->group())
                 ret = (*it)->group();
             else {
                 // There are already two groups with the same client leader.
@@ -436,11 +436,11 @@ void Client::setTransient(xcb_window_t new_transient_for_id)
         m_transientForId = new_transient_for_id;
         if (m_transientForId != XCB_WINDOW_NONE && !groupTransient()) {
             transient_for = workspace()->findClient(Predicate::WindowMatch, m_transientForId);
-            Q_ASSERT(transient_for != NULL);   // verifyTransient() had to check this
+            Q_ASSERT(transient_for != nullptr);   // verifyTransient() had to check this
             transient_for->addTransient(this);
         } // checkGroup() will check 'check_active_modal'
         setTransientFor(transient_for);
-        checkGroup(NULL, true);   // force, because transiency has changed
+        checkGroup(nullptr, true);   // force, because transiency has changed
         workspace()->updateClientLayer(this);
         workspace()->resetUpdateToolWindowsTimer();
         emit transientChanged();
@@ -513,7 +513,7 @@ void Client::cleanGrouping()
     // added 'this' to those transient lists :(
     ClientList group_members = group()->members();
     group()->removeMember(this);
-    in_group = NULL;
+    in_group = nullptr;
     for (ClientList::ConstIterator it = group_members.constBegin();
             it != group_members.constEnd();
             ++it)
@@ -544,7 +544,7 @@ void Client::checkGroupTransients()
             if (*it1 == *it2)
                 continue;
             for (AbstractClient* cl = (*it2)->transientFor();
-                    cl != NULL;
+                    cl != nullptr;
                     cl = cl->transientFor()) {
                 if (cl == *it1) {
                     // don't use removeTransient(), that would modify *it2 too
@@ -628,7 +628,7 @@ xcb_window_t Client::verifyTransientFor(xcb_window_t new_transient_for, bool set
     xcb_window_t loop_pos = new_transient_for;
     while (loop_pos != XCB_WINDOW_NONE && loop_pos != rootWindow()) {
         Client* pos = workspace()->findClient(Predicate::WindowMatch, loop_pos);
-        if (pos == NULL)
+        if (pos == nullptr)
             break;
         loop_pos = pos->m_transientForId;
         if (--count == 0 || pos == this) {
@@ -637,7 +637,7 @@ xcb_window_t Client::verifyTransientFor(xcb_window_t new_transient_for, bool set
         }
     }
     if (new_transient_for != rootWindow()
-            && workspace()->findClient(Predicate::WindowMatch, new_transient_for) == NULL) {
+            && workspace()->findClient(Predicate::WindowMatch, new_transient_for) == nullptr) {
         // it's transient for a specific window, but that window is not mapped
         new_transient_for = rootWindow();
     }
@@ -759,7 +759,7 @@ AbstractClient* Client::findModal(bool allow_itself)
             return ret;
     if (isModal() && allow_itself)
         return this;
-    return NULL;
+    return nullptr;
 }
 
 // Client::window_group only holds the contents of the hint,
@@ -768,11 +768,11 @@ AbstractClient* Client::findModal(bool allow_itself)
 void Client::checkGroup(Group* set_group, bool force)
 {
     Group* old_group = in_group;
-    if (old_group != NULL)
+    if (old_group != nullptr)
         old_group->ref(); // turn off automatic deleting
-    if (set_group != NULL) {
+    if (set_group != nullptr) {
         if (set_group != in_group) {
-            if (in_group != NULL)
+            if (in_group != nullptr)
                 in_group->removeMember(this);
             in_group = set_group;
             in_group->addMember(this);
@@ -780,15 +780,15 @@ void Client::checkGroup(Group* set_group, bool force)
     } else if (info->groupLeader() != XCB_WINDOW_NONE) {
         Group* new_group = workspace()->findGroup(info->groupLeader());
         Client *t = qobject_cast<Client*>(transientFor());
-        if (t != NULL && t->group() != new_group) {
+        if (t != nullptr && t->group() != new_group) {
             // move the window to the right group (e.g. a dialog provided
             // by different app, but transient for this one, so make it part of that group)
             new_group = t->group();
         }
-        if (new_group == NULL)   // doesn't exist yet
+        if (new_group == nullptr)   // doesn't exist yet
             new_group = new Group(info->groupLeader());
         if (new_group != in_group) {
-            if (in_group != NULL)
+            if (in_group != nullptr)
                 in_group->removeMember(this);
             in_group = new_group;
             in_group->addMember(this);
@@ -799,7 +799,7 @@ void Client::checkGroup(Group* set_group, bool force)
             // so make it part of that group
             Group* new_group = t->group();
             if (new_group != in_group) {
-                if (in_group != NULL)
+                if (in_group != nullptr)
                     in_group->removeMember(this);
                 in_group = t->group();
                 in_group->addMember(this);
@@ -808,10 +808,10 @@ void Client::checkGroup(Group* set_group, bool force)
             // group transient which actually doesn't have a group :(
             // try creating group with other windows with the same client leader
             Group* new_group = workspace()->findClientLeaderGroup(this);
-            if (new_group == NULL)
+            if (new_group == nullptr)
                 new_group = new Group(XCB_WINDOW_NONE);
             if (new_group != in_group) {
-                if (in_group != NULL)
+                if (in_group != nullptr)
                     in_group->removeMember(this);
                 in_group = new_group;
                 in_group->addMember(this);
@@ -821,11 +821,11 @@ void Client::checkGroup(Group* set_group, bool force)
             // or minimizing together the whole group, but as long as it is used
             // only for dialogs it's better to keep windows from one app in one group.
             Group* new_group = workspace()->findClientLeaderGroup(this);
-            if (in_group != NULL && in_group != new_group) {
+            if (in_group != nullptr && in_group != new_group) {
                 in_group->removeMember(this);
-                in_group = NULL;
+                in_group = nullptr;
             }
-            if (new_group == NULL)
+            if (new_group == nullptr)
                 new_group = new Group(XCB_WINDOW_NONE);
             if (in_group != new_group) {
                 in_group = new_group;
@@ -847,7 +847,7 @@ void Client::checkGroup(Group* set_group, bool force)
         }
         if (groupTransient()) {
             // no longer transient for ones in the old group
-            if (old_group != NULL) {
+            if (old_group != nullptr) {
                 for (ClientList::ConstIterator it = old_group->members().constBegin();
                         it != old_group->members().constEnd();
                         ++it)
@@ -876,7 +876,7 @@ void Client::checkGroup(Group* set_group, bool force)
             addTransient(*it);
         }
     }
-    if (old_group != NULL)
+    if (old_group != nullptr)
         old_group->deref(); // can be now deleted if empty
     checkGroupTransients();
     checkActiveModal();
@@ -887,7 +887,7 @@ void Client::checkGroup(Group* set_group, bool force)
 void Client::changeClientLeaderGroup(Group* gr)
 {
     // transientFor() != NULL are in the group of their mainwindow, so keep them there
-    if (transientFor() != NULL)
+    if (transientFor() != nullptr)
         return;
     // also don't change the group for window which have group set
     if (info->groupLeader())
@@ -903,9 +903,9 @@ void Client::checkActiveModal()
     // cannot be done in AddTransient(), because there may temporarily
     // exist loops, breaking findModal
     Client* check_modal = dynamic_cast<Client*>(workspace()->mostRecentlyActivatedClient());
-    if (check_modal != NULL && check_modal->check_active_modal) {
+    if (check_modal != nullptr && check_modal->check_active_modal) {
         Client* new_modal = dynamic_cast<Client*>(check_modal->findModal());
-        if (new_modal != NULL && new_modal != check_modal) {
+        if (new_modal != nullptr && new_modal != check_modal) {
             if (!new_modal->isManaged())
                 return; // postpone check until end of manage()
             workspace()->activateClient(new_modal);
diff --git a/input.cpp b/input.cpp
index 627da7b352..839e24db2b 100644
--- a/input.cpp
+++ b/input.cpp
@@ -1647,7 +1647,7 @@ InputRedirection::InputRedirection(QObject *parent)
 
 InputRedirection::~InputRedirection()
 {
-    s_self = NULL;
+    s_self = nullptr;
     qDeleteAll(m_filters);
     qDeleteAll(m_spies);
 }
@@ -2129,7 +2129,7 @@ Toplevel *InputRedirection::findManagedToplevel(const QPoint &pos)
     const bool isScreenLocked = waylandServer() && waylandServer()->isScreenLocked();
     const ToplevelList &stacking = Workspace::self()->stackingOrder();
     if (stacking.isEmpty()) {
-        return NULL;
+        return nullptr;
     }
     auto it = stacking.end();
     do {
@@ -2156,7 +2156,7 @@ Toplevel *InputRedirection::findManagedToplevel(const QPoint &pos)
             return t;
         }
     } while (it != stacking.begin());
-    return NULL;
+    return nullptr;
 }
 
 Qt::KeyboardModifiers InputRedirection::keyboardModifiers() const
diff --git a/kcmkwin/kwincompositing/compositing.h b/kcmkwin/kwincompositing/compositing.h
index 0439e81b5d..902dd64fea 100644
--- a/kcmkwin/kwincompositing/compositing.h
+++ b/kcmkwin/kwincompositing/compositing.h
@@ -48,7 +48,7 @@ class Compositing : public QObject
     Q_PROPERTY(bool windowsBlockCompositing READ windowsBlockCompositing WRITE setWindowsBlockCompositing NOTIFY windowsBlockCompositingChanged)
     Q_PROPERTY(bool compositingRequired READ compositingRequired CONSTANT)
 public:
-    explicit Compositing(QObject *parent = 0);
+    explicit Compositing(QObject *parent = nullptr);
 
     Q_INVOKABLE bool OpenGLIsUnsafe() const;
     Q_INVOKABLE bool OpenGLIsBroken();
@@ -132,7 +132,7 @@ public:
         TypeRole = Qt::UserRole +2
     };
 
-    explicit CompositingType(QObject *parent = 0);
+    explicit CompositingType(QObject *parent = nullptr);
 
     QModelIndex index(int row, int column, const QModelIndex &parent = QModelIndex()) const override;
     QModelIndex parent(const QModelIndex &child) const override;
diff --git a/kcmkwin/kwincompositing/main.cpp b/kcmkwin/kwincompositing/main.cpp
index 81f38ac92a..1412776a5c 100644
--- a/kcmkwin/kwincompositing/main.cpp
+++ b/kcmkwin/kwincompositing/main.cpp
@@ -33,7 +33,7 @@ class KWinCompositingSettings : public KCModule
 {
     Q_OBJECT
 public:
-    explicit KWinCompositingSettings(QWidget *parent = 0, const QVariantList &args = QVariantList());
+    explicit KWinCompositingSettings(QWidget *parent = nullptr, const QVariantList &args = QVariantList());
 
 public Q_SLOTS:
     void load() override;
diff --git a/kcmkwin/kwindecoration/declarative-plugin/buttonsmodel.h b/kcmkwin/kwindecoration/declarative-plugin/buttonsmodel.h
index 9c19faf5f2..ae0a1c2afd 100644
--- a/kcmkwin/kwindecoration/declarative-plugin/buttonsmodel.h
+++ b/kcmkwin/kwindecoration/declarative-plugin/buttonsmodel.h
@@ -34,7 +34,7 @@ class ButtonsModel : public QAbstractListModel
 {
     Q_OBJECT
 public:
-    explicit ButtonsModel(const QVector< DecorationButtonType > &buttons, QObject *parent = 0);
+    explicit ButtonsModel(const QVector< DecorationButtonType > &buttons, QObject *parent = nullptr);
     explicit ButtonsModel(QObject *parent = nullptr);
     ~ButtonsModel() override;
     QVariant data(const QModelIndex& index, int role = Qt::DisplayRole) const override;
diff --git a/kcmkwin/kwindecoration/declarative-plugin/previewitem.cpp b/kcmkwin/kwindecoration/declarative-plugin/previewitem.cpp
index d31c4dd3b0..616b88ae2d 100644
--- a/kcmkwin/kwindecoration/declarative-plugin/previewitem.cpp
+++ b/kcmkwin/kwindecoration/declarative-plugin/previewitem.cpp
@@ -78,7 +78,7 @@ void PreviewItem::createDecoration()
     if (m_bridge.isNull() || m_settings.isNull() || m_decoration) {
         return;
     }
-    Decoration *decoration = m_bridge->createDecoration(0);
+    Decoration *decoration = m_bridge->createDecoration(nullptr);
     m_client = m_bridge->lastCreatedClient();
     setDecoration(decoration);
 }
diff --git a/kcmkwin/kwindecoration/declarative-plugin/previewsettings.h b/kcmkwin/kwindecoration/declarative-plugin/previewsettings.h
index f206e79ff2..abace01eb3 100644
--- a/kcmkwin/kwindecoration/declarative-plugin/previewsettings.h
+++ b/kcmkwin/kwindecoration/declarative-plugin/previewsettings.h
@@ -37,7 +37,7 @@ class BorderSizesModel : public QAbstractListModel
 {
     Q_OBJECT
 public:
-    explicit BorderSizesModel(QObject *parent = 0);
+    explicit BorderSizesModel(QObject *parent = nullptr);
     ~BorderSizesModel() override;
     QVariant data(const QModelIndex& index, int role = Qt::DisplayRole) const override;
     int rowCount(const QModelIndex& parent = QModelIndex()) const override;
diff --git a/kcmkwin/kwinoptions/mouse.cpp b/kcmkwin/kwinoptions/mouse.cpp
index 90ac7faa4f..10626f88b3 100644
--- a/kcmkwin/kwinoptions/mouse.cpp
+++ b/kcmkwin/kwinoptions/mouse.cpp
@@ -64,7 +64,7 @@ void createMaxButtonPixmaps()
 {
     char const * maxButtonXpms[][3 + 13] = {
         {
-            0, 0, 0,
+            nullptr, nullptr, nullptr,
             "...............",
             ".......#.......",
             "......###......",
@@ -80,7 +80,7 @@ void createMaxButtonPixmaps()
             "..............."
         },
         {
-            0, 0, 0,
+            nullptr, nullptr, nullptr,
             "...............",
             ".......#.......",
             "......###......",
@@ -96,7 +96,7 @@ void createMaxButtonPixmaps()
             "..............."
         },
         {
-            0, 0, 0,
+            nullptr, nullptr, nullptr,
             "...............",
             "...............",
             "...............",
diff --git a/kcmkwin/kwinrules/ruleswidget.cpp b/kcmkwin/kwinrules/ruleswidget.cpp
index 1ff550093d..b6029a9e78 100644
--- a/kcmkwin/kwinrules/ruleswidget.cpp
+++ b/kcmkwin/kwinrules/ruleswidget.cpp
@@ -586,7 +586,7 @@ Rules* RulesWidget::rules() const
     rules->wmclassmatch = static_cast< Rules::StringMatch >(wmclass_match->currentIndex());
     rules->windowrole = role->text().toUtf8();
     rules->windowrolematch = static_cast< Rules::StringMatch >(role_match->currentIndex());
-    rules->types = 0;
+    rules->types = nullptr;
     bool all_types = true;
     for (int i = 0;
             i < types->count();
diff --git a/kcmkwin/kwinscreenedges/monitor.h b/kcmkwin/kwinscreenedges/monitor.h
index 300305815f..aa50dcd076 100644
--- a/kcmkwin/kwinscreenedges/monitor.h
+++ b/kcmkwin/kwinscreenedges/monitor.h
@@ -100,7 +100,7 @@ protected:
     void mousePressEvent(QGraphicsSceneMouseEvent* e) override;
     void hoverEnterEvent(QGraphicsSceneHoverEvent * e) override;
     void hoverLeaveEvent(QGraphicsSceneHoverEvent * e) override;
-    void paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget = 0) override;
+    void paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget = nullptr) override;
 private:
     Monitor* monitor;
     Plasma::FrameSvg *button;
diff --git a/kcmkwin/kwintabbox/thumbnailitem.cpp b/kcmkwin/kwintabbox/thumbnailitem.cpp
index 8c8edb488b..4d8f5762f9 100644
--- a/kcmkwin/kwintabbox/thumbnailitem.cpp
+++ b/kcmkwin/kwintabbox/thumbnailitem.cpp
@@ -69,7 +69,7 @@ const char *BrightnessSaturationShader::fragmentShader() const
 
 const char* const *BrightnessSaturationShader::attributeNames() const
 {
-    static char const *const names[] = { "vertex", "texCoord", 0 };
+    static char const *const names[] = { "vertex", "texCoord", nullptr };
     return names;
 }
 
diff --git a/layers.cpp b/layers.cpp
index fb41bfe9ae..e871819bc9 100644
--- a/layers.cpp
+++ b/layers.cpp
@@ -265,7 +265,7 @@ AbstractClient* Workspace::topClientOnDesktop(int desktop, int screen, bool unco
                 return c;
         }
     }
-    return 0;
+    return nullptr;
 }
 
 AbstractClient* Workspace::findDesktop(bool topmost, int desktop) const
@@ -286,13 +286,13 @@ AbstractClient* Workspace::findDesktop(bool topmost, int desktop) const
                 return client;
         }
     }
-    return NULL;
+    return nullptr;
 }
 
 void Workspace::raiseOrLowerClient(AbstractClient *c)
 {
     if (!c) return;
-    AbstractClient* topmost = NULL;
+    AbstractClient* topmost = nullptr;
 // TODO    Q_ASSERT( block_stacking_updates == 0 );
     if (most_recently_raised && stacking_order.contains(most_recently_raised) &&
             most_recently_raised->isShown(true) && c->isOnCurrentDesktop())
@@ -334,7 +334,7 @@ void Workspace::lowerClient(AbstractClient* c, bool nogroup)
     }
 
     if (c == most_recently_raised)
-        most_recently_raised = 0;
+        most_recently_raised = nullptr;
 }
 
 void Workspace::lowerClientWithinApplication(AbstractClient* c)
@@ -454,7 +454,7 @@ void Workspace::restack(AbstractClient* c, AbstractClient* under, bool force)
         for (int i = 0; i < unconstrained_stacking_order.size(); ++i) {
             AbstractClient *other = qobject_cast<AbstractClient*>(unconstrained_stacking_order.at(i));
             if (other && other->layer() == c->layer() && AbstractClient::belongToSameApplication(under, other)) {
-                under = (c == other) ? 0 : other;
+                under = (c == other) ? nullptr : other;
                 break;
             }
         }
@@ -514,7 +514,7 @@ ToplevelList Workspace::constrainedStackingOrder()
 
         const int screen = (*it)->screen();
         Client *c = qobject_cast<Client*>(*it);
-        QMap< Group*, Layer >::iterator mLayer = minimum_layer[screen].find(c ? c->group() : NULL);
+        QMap< Group*, Layer >::iterator mLayer = minimum_layer[screen].find(c ? c->group() : nullptr);
         if (mLayer != minimum_layer[screen].end()) {
             // If a window is raised above some other window in the same window group
             // which is in the ActiveLayer (i.e. it's fulscreened), make sure it stays
@@ -778,7 +778,7 @@ void Workspace::updateXStackingOrder()
 
 void Client::restackWindow(xcb_window_t above, int detail, NET::RequestSource src, xcb_timestamp_t timestamp, bool send_event)
 {
-    Client *other = 0;
+    Client *other = nullptr;
     if (detail == XCB_STACK_MODE_OPPOSITE) {
         other = workspace()->findClient(Predicate::WindowMatch, above);
         if (!other) {
@@ -837,7 +837,7 @@ void Client::restackWindow(xcb_window_t above, int detail, NET::RequestSource sr
         if (it != begin && (*(it - 1) == other))
             other = qobject_cast<Client*>(*it);
         else
-            other = 0;
+            other = nullptr;
     }
 
     if (other)
diff --git a/libkwineffects/kwinglplatform.cpp b/libkwineffects/kwinglplatform.cpp
index d3c91b75f7..9c80bc4c3d 100644
--- a/libkwineffects/kwinglplatform.cpp
+++ b/libkwineffects/kwinglplatform.cpp
@@ -38,7 +38,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 namespace KWin
 {
 
-GLPlatform *GLPlatform::s_platform = 0;
+GLPlatform *GLPlatform::s_platform = nullptr;
 
 static qint64 parseVersionString(const QByteArray &version)
 {
@@ -293,7 +293,7 @@ static ChipClass detectNVidiaClass(const QString &chipset)
 {
     QString name = extract(chipset, QStringLiteral("\\bNV[0-9,A-F]{2}\\b")); // NV followed by two hexadecimal digits
     if (!name.isEmpty()) {
-        const int id = chipset.midRef(2, -1).toInt(0, 16); // Strip the 'NV' from the id
+        const int id = chipset.midRef(2, -1).toInt(nullptr, 16); // Strip the 'NV' from the id
 
         switch(id & 0xf0) {
         case 0x00:
diff --git a/libkwineffects/kwinglutils.cpp b/libkwineffects/kwinglutils.cpp
index be0843348a..fcd885128d 100644
--- a/libkwineffects/kwinglutils.cpp
+++ b/libkwineffects/kwinglutils.cpp
@@ -1968,7 +1968,7 @@ void GLVertexBufferPrivate::reallocateBuffer(size_t size)
     const size_t minSize = 32768; // Minimum size for streaming buffers
     const size_t alloc = usage != GL_STATIC_DRAW ? align(qMax(size, minSize), 4096) : size;
 
-    glBufferData(GL_ARRAY_BUFFER, alloc, 0, usage);
+    glBufferData(GL_ARRAY_BUFFER, alloc, nullptr, usage);
 
     bufferSize = alloc;
 }
diff --git a/manage.cpp b/manage.cpp
index b801fe93bb..31cc30910a 100644
--- a/manage.cpp
+++ b/manage.cpp
@@ -223,7 +223,7 @@ bool Client::manage(xcb_window_t w, bool isMapped)
                 desk = NET::OnAllDesktops;
             else if (on_current)
                 desk = VirtualDesktopManager::self()->current();
-            else if (maincl != NULL)
+            else if (maincl != nullptr)
                 desk = maincl->desktop();
 
             if (maincl)
@@ -517,7 +517,7 @@ bool Client::manage(xcb_window_t w, bool isMapped)
     updateAllowedActions(true);
 
     // Set initial user time directly
-    m_userTime = readUserTimeMapTimestamp(asn_valid ? &asn_id : NULL, asn_valid ? &asn_data : NULL, session);
+    m_userTime = readUserTimeMapTimestamp(asn_valid ? &asn_id : nullptr, asn_valid ? &asn_data : nullptr, session);
     group()->updateUserTime(m_userTime);   // And do what Client::updateUserTime() does
 
     // This should avoid flicker, because real restacking is done
@@ -539,7 +539,7 @@ bool Client::manage(xcb_window_t w, bool isMapped)
         bool allow;
         if (session)
             allow = session->active &&
-                    (!workspace()->wasUserInteraction() || workspace()->activeClient() == NULL ||
+                    (!workspace()->wasUserInteraction() || workspace()->activeClient() == nullptr ||
                      workspace()->activeClient()->isDesktop());
         else
             allow = workspace()->allowClientActivation(this, userTime(), false);
@@ -606,7 +606,7 @@ bool Client::manage(xcb_window_t w, bool isMapped)
             if (opacity() == 1.0) {
                 return;
             }
-            NETWinInfo info(connection(), frameId(), rootWindow(), 0, 0);
+            NETWinInfo info(connection(), frameId(), rootWindow(), nullptr, nullptr);
             info.setOpacity(static_cast<unsigned long>(opacity() * 0xffffffff));
         }
     );
diff --git a/netinfo.cpp b/netinfo.cpp
index fc40245443..1f09c1818a 100644
--- a/netinfo.cpp
+++ b/netinfo.cpp
@@ -33,7 +33,7 @@ namespace KWin
 {
 extern int screen_number;
 
-RootInfo *RootInfo::s_self = NULL;
+RootInfo *RootInfo::s_self = nullptr;
 
 RootInfo *RootInfo::create()
 {
@@ -136,7 +136,7 @@ void RootInfo::destroy()
     }
     xcb_window_t supportWindow = s_self->supportWindow();
     delete s_self;
-    s_self = NULL;
+    s_self = nullptr;
     xcb_destroy_window(connection(), supportWindow);
 }
 
@@ -176,7 +176,7 @@ void RootInfo::changeActiveWindow(xcb_window_t w, NET::RequestSource src, xcb_ti
                 workspace->activateClient(c);
             // if activation of the requestor's window would be allowed, allow activation too
             else if (active_window != XCB_WINDOW_NONE
-                    && (c2 = workspace->findClient(Predicate::WindowMatch, active_window)) != NULL
+                    && (c2 = workspace->findClient(Predicate::WindowMatch, active_window)) != nullptr
                     && workspace->allowClientActivation(c2,
                             timestampCompare(timestamp, c2->userTime() > 0 ? timestamp : c2->userTime()), false, true)) {
                 workspace->activateClient(c);
@@ -299,7 +299,7 @@ void WinInfo::changeState(NET::States state, NET::States mask)
 
 void WinInfo::disable()
 {
-    m_client = NULL; // only used when the object is passed to Deleted
+    m_client = nullptr; // only used when the object is passed to Deleted
 }
 
 } // namespace
diff --git a/options.h b/options.h
index 7f0996eed5..8d92f09a83 100644
--- a/options.h
+++ b/options.h
@@ -184,7 +184,7 @@ class KWIN_EXPORT Options : public QObject
     Q_PROPERTY(bool windowsBlockCompositing READ windowsBlockCompositing WRITE setWindowsBlockCompositing NOTIFY windowsBlockCompositingChanged)
 public:
 
-    explicit Options(QObject *parent = NULL);
+    explicit Options(QObject *parent = nullptr);
     ~Options() override;
 
     void updateSettings();
diff --git a/placement.cpp b/placement.cpp
index fb40c20f77..d617046131 100644
--- a/placement.cpp
+++ b/placement.cpp
@@ -48,7 +48,7 @@ Placement::Placement(QObject*)
 
 Placement::~Placement()
 {
-    s_self = NULL;
+    s_self = nullptr;
 }
 
 /**
@@ -562,7 +562,7 @@ void Placement::placeOnMainWindow(AbstractClient *c, const QRect &area, Policy n
         ++mains_count;
         place_on2 = *it;
         if ((*it)->isOnCurrentDesktop()) {
-            if (place_on == NULL)
+            if (place_on == nullptr)
                 place_on = *it;
             else {
                 // two or more on current desktop -> center
@@ -576,7 +576,7 @@ void Placement::placeOnMainWindow(AbstractClient *c, const QRect &area, Policy n
             }
         }
     }
-    if (place_on == NULL) {
+    if (place_on == nullptr) {
         // 'mains_count' is used because it doesn't include ignored mainwindows
         if (mains_count != 1) {
             place(c, area, Centered);
diff --git a/platformsupport/scenes/opengl/backend.cpp b/platformsupport/scenes/opengl/backend.cpp
index 5e6c3e6260..45b6fbd30a 100644
--- a/platformsupport/scenes/opengl/backend.cpp
+++ b/platformsupport/scenes/opengl/backend.cpp
@@ -82,7 +82,7 @@ QRegion OpenGLBackend::accumulatedDamageHistory(int bufferAge) const
 
 OverlayWindow* OpenGLBackend::overlayWindow() const
 {
-    return NULL;
+    return nullptr;
 }
 
 QRegion OpenGLBackend::prepareRenderingForScreen(int screenId)
diff --git a/platformsupport/scenes/opengl/linux_dmabuf.cpp b/platformsupport/scenes/opengl/linux_dmabuf.cpp
index c9dd2de334..56941e9b58 100644
--- a/platformsupport/scenes/opengl/linux_dmabuf.cpp
+++ b/platformsupport/scenes/opengl/linux_dmabuf.cpp
@@ -461,7 +461,7 @@ void LinuxDmabuf::setSupportedFormatsAndModifiers()
 {
     const EGLDisplay eglDisplay = m_backend->eglDisplay();
     EGLint count = 0;
-    EGLBoolean success = eglQueryDmaBufFormatsEXT(eglDisplay, 0, NULL, &count);
+    EGLBoolean success = eglQueryDmaBufFormatsEXT(eglDisplay, 0, nullptr, &count);
 
     if (!success || count == 0) {
         return;
@@ -479,13 +479,13 @@ void LinuxDmabuf::setSupportedFormatsAndModifiers()
     for (auto format : qAsConst(formats)) {
         if (eglQueryDmaBufModifiersEXT != nullptr) {
             count = 0;
-            success = eglQueryDmaBufModifiersEXT(eglDisplay, format, 0, NULL, NULL, &count);
+            success = eglQueryDmaBufModifiersEXT(eglDisplay, format, 0, nullptr, nullptr, &count);
 
             if (success && count > 0) {
                 QVector<uint64_t> modifiers(count);
                 if (eglQueryDmaBufModifiersEXT(eglDisplay,
                                                format, count, modifiers.data(),
-                                               NULL, &count)) {
+                                               nullptr, &count)) {
                     QSet<uint64_t> modifiersSet;
                     for (auto mod : qAsConst(modifiers)) {
                         modifiersSet.insert(mod);
diff --git a/plugins/idletime/poller.h b/plugins/idletime/poller.h
index 62e6e88ae5..7b51275f32 100644
--- a/plugins/idletime/poller.h
+++ b/plugins/idletime/poller.h
@@ -41,7 +41,7 @@ class Poller : public AbstractSystemPoller
     Q_INTERFACES(AbstractSystemPoller)
 
 public:
-    Poller(QObject *parent = 0);
+    Poller(QObject *parent = nullptr);
     ~Poller() override;
 
     bool isAvailable() override;
diff --git a/plugins/kglobalaccel/kglobalaccel_plugin.h b/plugins/kglobalaccel/kglobalaccel_plugin.h
index 2b72b6d3e2..ac594e6bd2 100644
--- a/plugins/kglobalaccel/kglobalaccel_plugin.h
+++ b/plugins/kglobalaccel/kglobalaccel_plugin.h
@@ -31,7 +31,7 @@ class KGlobalAccelImpl : public KGlobalAccelInterface
     Q_INTERFACES(KGlobalAccelInterface)
 
 public:
-    KGlobalAccelImpl(QObject *parent = 0);
+    KGlobalAccelImpl(QObject *parent = nullptr);
     ~KGlobalAccelImpl() override;
 
     bool grabKey(int key, bool grab) override;
diff --git a/plugins/platforms/wayland/wayland_backend.cpp b/plugins/platforms/wayland/wayland_backend.cpp
index 0b10029d0e..e0e3b6f399 100644
--- a/plugins/platforms/wayland/wayland_backend.cpp
+++ b/plugins/platforms/wayland/wayland_backend.cpp
@@ -209,10 +209,10 @@ void WaylandSubSurfaceCursor::move(const QPointF &globalPosition)
 }
 
 WaylandSeat::WaylandSeat(wl_seat *seat, WaylandBackend *backend)
-    : QObject(NULL)
+    : QObject(nullptr)
     , m_seat(new Seat(this))
-    , m_pointer(NULL)
-    , m_keyboard(NULL)
+    , m_pointer(nullptr)
+    , m_keyboard(nullptr)
     , m_touch(nullptr)
     , m_enteredSerial(0)
     , m_backend(backend)
diff --git a/plugins/platforms/x11/standalone/glxbackend.cpp b/plugins/platforms/x11/standalone/glxbackend.cpp
index d2bbc666a9..1ae6ccd9ae 100644
--- a/plugins/platforms/x11/standalone/glxbackend.cpp
+++ b/plugins/platforms/x11/standalone/glxbackend.cpp
@@ -107,7 +107,7 @@ GlxBackend::GlxBackend(Display *display)
     : OpenGLBackend()
     , m_overlayWindow(kwinApp()->platform()->createOverlayWindow())
     , window(None)
-    , fbconfig(NULL)
+    , fbconfig(nullptr)
     , glxWindow(None)
     , ctx(nullptr)
     , m_bufferAge(0)
@@ -270,7 +270,7 @@ void GlxBackend::init()
         // VirtualBox does not support glxQueryDrawable
         // this should actually be in kwinglutils_funcs, but QueryDrawable seems not to be provided by an extension
         // and the GLPlatform has not been initialized at the moment when initGLX() is called.
-        glXQueryDrawable = NULL;
+        glXQueryDrawable = nullptr;
     }
 
     setIsDirectRendering(bool(glXIsDirect(display(), ctx)));
@@ -336,7 +336,7 @@ bool GlxBackend::initRenderingContext()
         }
         for (auto it = candidates.begin(); it != candidates.end(); it++) {
             const auto attribs = it->build();
-            ctx = glXCreateContextAttribsARB(display(), fbconfig, 0, true, attribs.data());
+            ctx = glXCreateContextAttribsARB(display(), fbconfig, nullptr, true, attribs.data());
             if (ctx) {
                 qCDebug(KWIN_X11STANDALONE) << "Created GLX context with attributes:" << &(*it);
                 break;
@@ -345,7 +345,7 @@ bool GlxBackend::initRenderingContext()
     }
 
     if (!ctx)
-        ctx = glXCreateNewContext(display(), fbconfig, GLX_RGBA_TYPE, NULL, direct);
+        ctx = glXCreateNewContext(display(), fbconfig, GLX_RGBA_TYPE, nullptr, direct);
 
     if (!ctx) {
         qCDebug(KWIN_X11STANDALONE) << "Failed to create an OpenGL context.";
@@ -355,7 +355,7 @@ bool GlxBackend::initRenderingContext()
     if (!glXMakeCurrent(display(), glxWindow, ctx)) {
         qCDebug(KWIN_X11STANDALONE) << "Failed to make the OpenGL context current.";
         glXDestroyContext(display(), ctx);
-        ctx = 0;
+        ctx = nullptr;
         return false;
     }
 
@@ -389,7 +389,7 @@ bool GlxBackend::initBuffer()
                           0, 0, size.width(), size.height(), 0, XCB_WINDOW_CLASS_INPUT_OUTPUT,
                           visual, XCB_CW_COLORMAP, &colormap);
 
-        glxWindow = glXCreateWindow(display(), fbconfig, window, NULL);
+        glxWindow = glXCreateWindow(display(), fbconfig, window, nullptr);
         overlayWindow()->setup(window);
     } else {
         qCCritical(KWIN_X11STANDALONE) << "Failed to create overlay window";
@@ -884,7 +884,7 @@ void GlxTexture::onDamage()
 {
     if (options->isGlStrictBinding() && m_glxpixmap) {
         glXReleaseTexImageEXT(display(), m_glxpixmap, GLX_FRONT_LEFT_EXT);
-        glXBindTexImageEXT(display(), m_glxpixmap, GLX_FRONT_LEFT_EXT, NULL);
+        glXBindTexImageEXT(display(), m_glxpixmap, GLX_FRONT_LEFT_EXT, nullptr);
     }
     GLTexturePrivate::onDamage();
 }
diff --git a/plugins/platforms/x11/standalone/overlaywindow_x11.cpp b/plugins/platforms/x11/standalone/overlaywindow_x11.cpp
index 05e70a5396..3bd2281806 100644
--- a/plugins/platforms/x11/standalone/overlaywindow_x11.cpp
+++ b/plugins/platforms/x11/standalone/overlaywindow_x11.cpp
@@ -88,7 +88,7 @@ void OverlayWindowX11::setup(xcb_window_t window)
 
 void OverlayWindowX11::setupInputShape(xcb_window_t window)
 {
-    xcb_shape_rectangles(connection(), XCB_SHAPE_SO_SET, XCB_SHAPE_SK_INPUT, XCB_CLIP_ORDERING_UNSORTED, window, 0, 0, 0, NULL);
+    xcb_shape_rectangles(connection(), XCB_SHAPE_SO_SET, XCB_SHAPE_SK_INPUT, XCB_CLIP_ORDERING_UNSORTED, window, 0, 0, 0, nullptr);
 }
 
 void OverlayWindowX11::setNoneBackgroundPixmap(xcb_window_t window)
diff --git a/plugins/platforms/x11/standalone/windowselector.cpp b/plugins/platforms/x11/standalone/windowselector.cpp
index 4f7d39e5e8..aa4412e972 100644
--- a/plugins/platforms/x11/standalone/windowselector.cpp
+++ b/plugins/platforms/x11/standalone/windowselector.cpp
@@ -94,7 +94,7 @@ bool WindowSelector::activate(const QByteArray &cursorName)
         XCB_EVENT_MASK_POINTER_MOTION |
         XCB_EVENT_MASK_ENTER_WINDOW | XCB_EVENT_MASK_LEAVE_WINDOW,
         XCB_GRAB_MODE_ASYNC, XCB_GRAB_MODE_ASYNC, XCB_WINDOW_NONE,
-        cursor, XCB_TIME_CURRENT_TIME), NULL));
+        cursor, XCB_TIME_CURRENT_TIME), nullptr));
     if (grabPointer.isNull() || grabPointer->status != XCB_GRAB_STATUS_SUCCESS) {
         return false;
     }
@@ -241,7 +241,7 @@ void WindowSelector::selectWindowId(xcb_window_t window_to_select)
         return;
     }
     xcb_window_t window = window_to_select;
-    Client* client = NULL;
+    Client* client = nullptr;
     while (true) {
         client = Workspace::self()->findClient(Predicate::FrameIdMatch, window);
         if (client) {
diff --git a/plugins/scenes/opengl/lanczosfilter.cpp b/plugins/scenes/opengl/lanczosfilter.cpp
index f70c2c12a5..6b4cae1003 100644
--- a/plugins/scenes/opengl/lanczosfilter.cpp
+++ b/plugins/scenes/opengl/lanczosfilter.cpp
@@ -45,10 +45,10 @@ namespace KWin
 
 LanczosFilter::LanczosFilter(QObject* parent)
     : QObject(parent)
-    , m_offscreenTex(0)
-    , m_offscreenTarget(0)
+    , m_offscreenTex(nullptr)
+    , m_offscreenTarget(nullptr)
     , m_inited(false)
-    , m_shader(0)
+    , m_shader(nullptr)
     , m_uOffsets(0)
     , m_uKernel(0)
 {
@@ -240,7 +240,7 @@ void LanczosFilter::performPaint(EffectWindowImpl* w, int mask, QRegion region,
                 } else {
                     // offscreen texture not matching - delete
                     delete cachedTexture;
-                    cachedTexture = 0;
+                    cachedTexture = nullptr;
                     w->setData(LanczosCacheRole, QVariant());
                 }
             }
@@ -392,8 +392,8 @@ void LanczosFilter::timerEvent(QTimerEvent *event)
 
         delete m_offscreenTarget;
         delete m_offscreenTex;
-        m_offscreenTarget = 0;
-        m_offscreenTex = 0;
+        m_offscreenTarget = nullptr;
+        m_offscreenTex = nullptr;
         foreach (Client *c, Workspace::self()->clientList()) {
             discardCacheTexture(c->effectWindow());
         }
diff --git a/plugins/scenes/opengl/lanczosfilter.h b/plugins/scenes/opengl/lanczosfilter.h
index bb11a6e1fa..f05872db38 100644
--- a/plugins/scenes/opengl/lanczosfilter.h
+++ b/plugins/scenes/opengl/lanczosfilter.h
@@ -43,7 +43,7 @@ class LanczosFilter : public QObject
     Q_OBJECT
 
 public:
-    explicit LanczosFilter(QObject* parent = 0);
+    explicit LanczosFilter(QObject* parent = nullptr);
     ~LanczosFilter() override;
     void performPaint(EffectWindowImpl* w, int mask, QRegion region, WindowPaintData& data);
 
diff --git a/plugins/scenes/opengl/scene_opengl.cpp b/plugins/scenes/opengl/scene_opengl.cpp
index e7460375b1..b253ee9c9d 100644
--- a/plugins/scenes/opengl/scene_opengl.cpp
+++ b/plugins/scenes/opengl/scene_opengl.cpp
@@ -494,15 +494,15 @@ SceneOpenGL *SceneOpenGL::createScene(QObject *parent)
     }
     if (backend->isFailed()) {
         delete backend;
-        return NULL;
+        return nullptr;
     }
-    SceneOpenGL *scene = NULL;
+    SceneOpenGL *scene = nullptr;
     // first let's try an OpenGL 2 scene
     if (SceneOpenGL2::supported(backend)) {
         scene = new SceneOpenGL2(backend, parent);
         if (scene->initFailed()) {
             delete scene;
-            scene = NULL;
+            scene = nullptr;
         } else {
             return scene;
         }
@@ -918,7 +918,7 @@ bool SceneOpenGL2::supported(OpenGLBackend *backend)
 
 SceneOpenGL2::SceneOpenGL2(OpenGLBackend *backend, QObject *parent)
     : SceneOpenGL(backend, parent)
-    , m_lanczosFilter(NULL)
+    , m_lanczosFilter(nullptr)
 {
     if (!init_ok) {
         // base ctor already failed
@@ -1027,7 +1027,7 @@ void SceneOpenGL2::doPaintBackground(const QVector< float >& vertices)
     GLVertexBuffer *vbo = GLVertexBuffer::streamingBuffer();
     vbo->reset();
     vbo->setUseColor(true);
-    vbo->setData(vertices.count() / 2, 2, vertices.data(), NULL);
+    vbo->setData(vertices.count() / 2, 2, vertices.data(), nullptr);
 
     ShaderBinder binder(ShaderTrait::UniformColor);
     binder.shader()->setUniform(GLShader::ModelViewProjectionMatrix, m_projectionMatrix);
@@ -1060,7 +1060,7 @@ void SceneOpenGL2::performPaintWindow(EffectWindowImpl* w, int mask, QRegion reg
             connect(screens(), &Screens::changed, this, [this]() {
                 makeOpenGLContextCurrent();
                 delete m_lanczosFilter;
-                m_lanczosFilter = NULL;
+                m_lanczosFilter = nullptr;
             });
         }
         m_lanczosFilter->performPaint(w, mask, region, data);
@@ -1074,7 +1074,7 @@ void SceneOpenGL2::performPaintWindow(EffectWindowImpl* w, int mask, QRegion reg
 
 SceneOpenGL::Window::Window(Toplevel* c)
     : Scene::Window(c)
-    , m_scene(NULL)
+    , m_scene(nullptr)
 {
 }
 
@@ -1082,11 +1082,11 @@ SceneOpenGL::Window::~Window()
 {
 }
 
-static SceneOpenGLTexture *s_frameTexture = NULL;
+static SceneOpenGLTexture *s_frameTexture = nullptr;
 // Bind the window pixmap to an OpenGL texture.
 bool SceneOpenGL::Window::bindTexture()
 {
-    s_frameTexture = NULL;
+    s_frameTexture = nullptr;
     OpenGLWindowPixmap *pixmap = windowPixmap<OpenGLWindowPixmap>();
     if (!pixmap) {
         return false;
@@ -1293,7 +1293,7 @@ void SceneOpenGL2Window::setupLeafNodes(LeafNode *nodes, const WindowQuadList *q
 
     if (data.crossFadeProgress() != 1.0) {
         OpenGLWindowPixmap *previous = previousWindowPixmap<OpenGLWindowPixmap>();
-        nodes[PreviousContentLeaf].texture = previous ? previous->texture() : NULL;
+        nodes[PreviousContentLeaf].texture = previous ? previous->texture() : nullptr;
         nodes[PreviousContentLeaf].hasAlpha = !isOpaque();
         nodes[PreviousContentLeaf].opacity = data.opacity() * (1.0 - data.crossFadeProgress());
         nodes[PreviousContentLeaf].coordinateType = NormalizedCoordinates;
@@ -1596,19 +1596,19 @@ bool OpenGLWindowPixmap::isValid() const
 // SceneOpenGL::EffectFrame
 //****************************************
 
-GLTexture* SceneOpenGL::EffectFrame::m_unstyledTexture = NULL;
-QPixmap* SceneOpenGL::EffectFrame::m_unstyledPixmap = NULL;
+GLTexture* SceneOpenGL::EffectFrame::m_unstyledTexture = nullptr;
+QPixmap* SceneOpenGL::EffectFrame::m_unstyledPixmap = nullptr;
 
 SceneOpenGL::EffectFrame::EffectFrame(EffectFrameImpl* frame, SceneOpenGL *scene)
     : Scene::EffectFrame(frame)
-    , m_texture(NULL)
-    , m_textTexture(NULL)
-    , m_oldTextTexture(NULL)
-    , m_textPixmap(NULL)
-    , m_iconTexture(NULL)
-    , m_oldIconTexture(NULL)
-    , m_selectionTexture(NULL)
-    , m_unstyledVBO(NULL)
+    , m_texture(nullptr)
+    , m_textTexture(nullptr)
+    , m_oldTextTexture(nullptr)
+    , m_textPixmap(nullptr)
+    , m_iconTexture(nullptr)
+    , m_oldIconTexture(nullptr)
+    , m_selectionTexture(nullptr)
+    , m_unstyledVBO(nullptr)
     , m_scene(scene)
 {
     if (m_effectFrame->style() == EffectFrameUnstyled && !m_unstyledTexture) {
@@ -1632,55 +1632,55 @@ void SceneOpenGL::EffectFrame::free()
 {
     glFlush();
     delete m_texture;
-    m_texture = NULL;
+    m_texture = nullptr;
     delete m_textTexture;
-    m_textTexture = NULL;
+    m_textTexture = nullptr;
     delete m_textPixmap;
-    m_textPixmap = NULL;
+    m_textPixmap = nullptr;
     delete m_iconTexture;
-    m_iconTexture = NULL;
+    m_iconTexture = nullptr;
     delete m_selectionTexture;
-    m_selectionTexture = NULL;
+    m_selectionTexture = nullptr;
     delete m_unstyledVBO;
-    m_unstyledVBO = NULL;
+    m_unstyledVBO = nullptr;
     delete m_oldIconTexture;
-    m_oldIconTexture = NULL;
+    m_oldIconTexture = nullptr;
     delete m_oldTextTexture;
-    m_oldTextTexture = NULL;
+    m_oldTextTexture = nullptr;
 }
 
 void SceneOpenGL::EffectFrame::freeIconFrame()
 {
     delete m_iconTexture;
-    m_iconTexture = NULL;
+    m_iconTexture = nullptr;
 }
 
 void SceneOpenGL::EffectFrame::freeTextFrame()
 {
     delete m_textTexture;
-    m_textTexture = NULL;
+    m_textTexture = nullptr;
     delete m_textPixmap;
-    m_textPixmap = NULL;
+    m_textPixmap = nullptr;
 }
 
 void SceneOpenGL::EffectFrame::freeSelection()
 {
     delete m_selectionTexture;
-    m_selectionTexture = NULL;
+    m_selectionTexture = nullptr;
 }
 
 void SceneOpenGL::EffectFrame::crossFadeIcon()
 {
     delete m_oldIconTexture;
     m_oldIconTexture = m_iconTexture;
-    m_iconTexture = NULL;
+    m_iconTexture = nullptr;
 }
 
 void SceneOpenGL::EffectFrame::crossFadeText()
 {
     delete m_oldTextTexture;
     m_oldTextTexture = m_textTexture;
-    m_textTexture = NULL;
+    m_textTexture = nullptr;
 }
 
 void SceneOpenGL::EffectFrame::render(QRegion region, double opacity, double frameOpacity)
@@ -1951,7 +1951,7 @@ void SceneOpenGL::EffectFrame::render(QRegion region, double opacity, double fra
 void SceneOpenGL::EffectFrame::updateTexture()
 {
     delete m_texture;
-    m_texture = 0L;
+    m_texture = nullptr;
     if (m_effectFrame->style() == EffectFrameStyled) {
         QPixmap pixmap = m_effectFrame->frame().framePixmap();
         m_texture = new GLTexture(pixmap);
@@ -1961,9 +1961,9 @@ void SceneOpenGL::EffectFrame::updateTexture()
 void SceneOpenGL::EffectFrame::updateTextTexture()
 {
     delete m_textTexture;
-    m_textTexture = 0L;
+    m_textTexture = nullptr;
     delete m_textPixmap;
-    m_textPixmap = 0L;
+    m_textPixmap = nullptr;
 
     if (m_effectFrame->text().isEmpty())
         return;
@@ -1996,9 +1996,9 @@ void SceneOpenGL::EffectFrame::updateTextTexture()
 void SceneOpenGL::EffectFrame::updateUnstyledTexture()
 {
     delete m_unstyledTexture;
-    m_unstyledTexture = 0L;
+    m_unstyledTexture = nullptr;
     delete m_unstyledPixmap;
-    m_unstyledPixmap = 0L;
+    m_unstyledPixmap = nullptr;
     // Based off circle() from kwinxrenderutils.cpp
 #define CS 8
     m_unstyledPixmap = new QPixmap(2 * CS, 2 * CS);
@@ -2016,9 +2016,9 @@ void SceneOpenGL::EffectFrame::updateUnstyledTexture()
 void SceneOpenGL::EffectFrame::cleanup()
 {
     delete m_unstyledTexture;
-    m_unstyledTexture = NULL;
+    m_unstyledTexture = nullptr;
     delete m_unstyledPixmap;
-    m_unstyledPixmap = NULL;
+    m_unstyledPixmap = nullptr;
 }
 
 //****************************************
diff --git a/plugins/scenes/opengl/scene_opengl.h b/plugins/scenes/opengl/scene_opengl.h
index 3c0d54b871..b2eea05f68 100644
--- a/plugins/scenes/opengl/scene_opengl.h
+++ b/plugins/scenes/opengl/scene_opengl.h
@@ -183,7 +183,7 @@ public:
     struct LeafNode
     {
         LeafNode()
-            : texture(0),
+            : texture(nullptr),
               firstVertex(0),
               vertexCount(0),
               opacity(1.0),
diff --git a/plugins/scenes/qpainter/scene_qpainter.cpp b/plugins/scenes/qpainter/scene_qpainter.cpp
index bf462071e6..0fffdfc39b 100644
--- a/plugins/scenes/qpainter/scene_qpainter.cpp
+++ b/plugins/scenes/qpainter/scene_qpainter.cpp
@@ -53,7 +53,7 @@ SceneQPainter *SceneQPainter::createScene(QObject *parent)
         return nullptr;
     }
     if (backend->isFailed()) {
-        return NULL;
+        return nullptr;
     }
     return new SceneQPainter(backend.take(), parent);
 }
diff --git a/plugins/scenes/xrender/scene_xrender.cpp b/plugins/scenes/xrender/scene_xrender.cpp
index 24ad72bb2c..633cc0b1eb 100644
--- a/plugins/scenes/xrender/scene_xrender.cpp
+++ b/plugins/scenes/xrender/scene_xrender.cpp
@@ -80,7 +80,7 @@ XRenderBackend::~XRenderBackend()
 
 OverlayWindow* XRenderBackend::overlayWindow()
 {
-    return NULL;
+    return nullptr;
 }
 
 void XRenderBackend::showOverlay()
@@ -146,7 +146,7 @@ void X11XRenderBackend::init(bool createOverlay)
     if (haveOverlay) {
         m_overlayWindow->setup(XCB_WINDOW_NONE);
         ScopedCPointer<xcb_get_window_attributes_reply_t> attribs(xcb_get_window_attributes_reply(connection(),
-            xcb_get_window_attributes_unchecked(connection(), m_overlayWindow->window()), NULL));
+            xcb_get_window_attributes_unchecked(connection(), m_overlayWindow->window()), nullptr));
         if (!attribs) {
             setFailed("Failed getting window attributes for overlay window");
             return;
@@ -157,7 +157,7 @@ void X11XRenderBackend::init(bool createOverlay)
             return;
         }
         m_front = xcb_generate_id(connection());
-        xcb_render_create_picture(connection(), m_front, m_overlayWindow->window(), m_format, 0, NULL);
+        xcb_render_create_picture(connection(), m_front, m_overlayWindow->window(), m_format, 0, nullptr);
     } else {
         // create XRender picture for the root window
         m_format = XRenderUtils::findPictFormat(defaultScreen()->root_visual);
@@ -178,7 +178,7 @@ void X11XRenderBackend::createBuffer()
     const auto displaySize = screens()->displaySize();
     xcb_create_pixmap(connection(), Xcb::defaultDepth(), pixmap, rootWindow(), displaySize.width(), displaySize.height());
     xcb_render_picture_t b = xcb_generate_id(connection());
-    xcb_render_create_picture(connection(), b, pixmap, m_format, 0, NULL);
+    xcb_render_create_picture(connection(), b, pixmap, m_format, 0, nullptr);
     xcb_free_pixmap(connection(), pixmap);   // The picture owns the pixmap now
     setBuffer(b);
 }
@@ -224,7 +224,7 @@ SceneXrender* SceneXrender::createScene(QObject *parent)
     QScopedPointer<XRenderBackend> backend;
     backend.reset(new X11XRenderBackend);
     if (backend->isFailed()) {
-        return NULL;
+        return nullptr;
     }
     return new SceneXrender(backend.take(), parent);
 }
@@ -312,7 +312,7 @@ Decoration::Renderer *SceneXrender::createDecorationRenderer(Decoration::Decorat
 // SceneXrender::Window
 //****************************************
 
-XRenderPicture *SceneXrender::Window::s_tempPicture = 0;
+XRenderPicture *SceneXrender::Window::s_tempPicture = nullptr;
 QRect SceneXrender::Window::temp_visibleRect;
 XRenderPicture *SceneXrender::Window::s_fadeAlphaPicture = nullptr;
 
@@ -331,7 +331,7 @@ SceneXrender::Window::~Window()
 void SceneXrender::Window::cleanup()
 {
     delete s_tempPicture;
-    s_tempPicture = NULL;
+    s_tempPicture = nullptr;
     delete s_fadeAlphaPicture;
     s_fadeAlphaPicture = nullptr;
 }
@@ -392,7 +392,7 @@ void SceneXrender::Window::prepareTempPixmap()
     temp_visibleRect = toplevel->visibleRect().translated(-toplevel->pos());
     if (s_tempPicture && (oldSize.width() < temp_visibleRect.width() || oldSize.height() < temp_visibleRect.height())) {
         delete s_tempPicture;
-        s_tempPicture = NULL;
+        s_tempPicture = nullptr;
         scene_setXRenderOffscreenTarget(0); // invalidate, better crash than cause weird results for developers
     }
     if (!s_tempPicture) {
@@ -768,7 +768,7 @@ void SceneXrender::Window::setPictureFilter(xcb_render_picture_t pic, Scene::Ima
         filterName = QByteArray("good");
         break;
     }
-    xcb_render_set_picture_filter(connection(), pic, filterName.length(), filterName.constData(), 0, NULL);
+    xcb_render_set_picture_filter(connection(), pic, filterName.length(), filterName.constData(), 0, nullptr);
 }
 
 WindowPixmap* SceneXrender::Window::createWindowPixmap()
@@ -810,22 +810,22 @@ void XRenderWindowPixmap::create()
         return;
     }
     m_picture = xcb_generate_id(connection());
-    xcb_render_create_picture(connection(), m_picture, pixmap(), m_format, 0, NULL);
+    xcb_render_create_picture(connection(), m_picture, pixmap(), m_format, 0, nullptr);
 }
 
 //****************************************
 // SceneXrender::EffectFrame
 //****************************************
 
-XRenderPicture *SceneXrender::EffectFrame::s_effectFrameCircle = NULL;
+XRenderPicture *SceneXrender::EffectFrame::s_effectFrameCircle = nullptr;
 
 SceneXrender::EffectFrame::EffectFrame(EffectFrameImpl* frame)
     : Scene::EffectFrame(frame)
 {
-    m_picture = NULL;
-    m_textPicture = NULL;
-    m_iconPicture = NULL;
-    m_selectionPicture = NULL;
+    m_picture = nullptr;
+    m_textPicture = nullptr;
+    m_iconPicture = nullptr;
+    m_selectionPicture = nullptr;
 }
 
 SceneXrender::EffectFrame::~EffectFrame()
@@ -839,37 +839,37 @@ SceneXrender::EffectFrame::~EffectFrame()
 void SceneXrender::EffectFrame::cleanup()
 {
     delete s_effectFrameCircle;
-    s_effectFrameCircle = NULL;
+    s_effectFrameCircle = nullptr;
 }
 
 void SceneXrender::EffectFrame::free()
 {
     delete m_picture;
-    m_picture = NULL;
+    m_picture = nullptr;
     delete m_textPicture;
-    m_textPicture = NULL;
+    m_textPicture = nullptr;
     delete m_iconPicture;
-    m_iconPicture = NULL;
+    m_iconPicture = nullptr;
     delete m_selectionPicture;
-    m_selectionPicture = NULL;
+    m_selectionPicture = nullptr;
 }
 
 void SceneXrender::EffectFrame::freeIconFrame()
 {
     delete m_iconPicture;
-    m_iconPicture = NULL;
+    m_iconPicture = nullptr;
 }
 
 void SceneXrender::EffectFrame::freeTextFrame()
 {
     delete m_textPicture;
-    m_textPicture = NULL;
+    m_textPicture = nullptr;
 }
 
 void SceneXrender::EffectFrame::freeSelection()
 {
     delete m_selectionPicture;
-    m_selectionPicture = NULL;
+    m_selectionPicture = nullptr;
 }
 
 void SceneXrender::EffectFrame::crossFadeIcon()
@@ -1038,7 +1038,7 @@ xcb_render_composite(connection(), XCB_RENDER_PICT_OP_OVER, *s_effectFrameCircle
 void SceneXrender::EffectFrame::updatePicture()
 {
     delete m_picture;
-    m_picture = 0L;
+    m_picture = nullptr;
     if (m_effectFrame->style() == EffectFrameStyled) {
         const QPixmap pix = m_effectFrame->frame().framePixmap();
         if (!pix.isNull())
@@ -1050,7 +1050,7 @@ void SceneXrender::EffectFrame::updateTextPicture()
 {
     // Mostly copied from SceneOpenGL::EffectFrame::updateTextTexture() above
     delete m_textPicture;
-    m_textPicture = 0L;
+    m_textPicture = nullptr;
 
     if (m_effectFrame->text().isEmpty()) {
         return;
@@ -1088,7 +1088,7 @@ SceneXRenderShadow::SceneXRenderShadow(Toplevel *toplevel)
     :Shadow(toplevel)
 {
     for (int i=0; i<ShadowElementsCount; ++i) {
-        m_pictures[i] = NULL;
+        m_pictures[i] = nullptr;
     }
 }
 
diff --git a/scene.cpp b/scene.cpp
index 55c0a2d14f..4d5a273b0a 100644
--- a/scene.cpp
+++ b/scene.cpp
@@ -461,7 +461,7 @@ void Scene::clearStackingOrder()
     stacking_order.clear();
 }
 
-static Scene::Window *s_recursionCheck = NULL;
+static Scene::Window *s_recursionCheck = nullptr;
 
 void Scene::paintWindow(Window* w, int mask, QRegion region, WindowQuadList quads)
 {
@@ -597,7 +597,7 @@ void Scene::paintDesktopThumbnails(Scene::Window *w)
         data += QPointF(x, y);
         const int desktopMask = PAINT_SCREEN_TRANSFORMED | PAINT_WINDOW_TRANSFORMED | PAINT_SCREEN_BACKGROUND_FIRST;
         paintDesktop(item->desktop(), desktopMask, clippingRegion, data);
-        s_recursionCheck = NULL;
+        s_recursionCheck = nullptr;
     }
 }
 
@@ -690,13 +690,13 @@ QVector<QByteArray> Scene::openGLPlatformInterfaceExtensions() const
 Scene::Window::Window(Toplevel * c)
     : toplevel(c)
     , filter(ImageFilterFast)
-    , m_shadow(NULL)
+    , m_shadow(nullptr)
     , m_currentPixmap()
     , m_previousPixmap()
     , m_referencePixmapCounter(0)
     , disable_painting(0)
     , shape_valid(false)
-    , cached_quad_list(NULL)
+    , cached_quad_list(nullptr)
 {
 }
 
@@ -841,7 +841,7 @@ void Scene::Window::disablePainting(int reason)
 
 WindowQuadList Scene::Window::buildQuads(bool force) const
 {
-    if (cached_quad_list != NULL && !force)
+    if (cached_quad_list != nullptr && !force)
         return *cached_quad_list;
     WindowQuadList ret;
     qreal scale = 1.0;
diff --git a/screenedge.cpp b/screenedge.cpp
index dce70ab81e..4dd6adf501 100644
--- a/screenedge.cpp
+++ b/screenedge.cpp
@@ -716,7 +716,7 @@ ScreenEdges::ScreenEdges(QObject *parent)
     , m_desktopSwitchingMovingClients(false)
     , m_timeThreshold(0)
     , m_reactivateThreshold(0)
-    , m_virtualDesktopLayout(0)
+    , m_virtualDesktopLayout(nullptr)
     , m_actionTopLeft(ElectricActionNone)
     , m_actionTop(ElectricActionNone)
     , m_actionTopRight(ElectricActionNone)
@@ -735,7 +735,7 @@ ScreenEdges::ScreenEdges(QObject *parent)
 
 ScreenEdges::~ScreenEdges()
 {
-    s_self = NULL;
+    s_self = nullptr;
 }
 
 void ScreenEdges::init()
@@ -880,7 +880,7 @@ void ScreenEdges::setActionForTouchBorder(ElectricBorder border, ElectricBorderA
 void ScreenEdges::updateLayout()
 {
     const QSize desktopMatrix = VirtualDesktopManager::self()->grid().size();
-    Qt::Orientations newLayout = 0;
+    Qt::Orientations newLayout = nullptr;
     if (desktopMatrix.width() > 1) {
         newLayout |= Qt::Horizontal;
     }
diff --git a/screens.cpp b/screens.cpp
index e0cbb9d613..7b4e40415b 100644
--- a/screens.cpp
+++ b/screens.cpp
@@ -74,7 +74,7 @@ Screens::Screens(QObject *parent)
 
 Screens::~Screens()
 {
-    s_self = NULL;
+    s_self = nullptr;
 }
 
 void Screens::init()
diff --git a/scripting/dbuscall.h b/scripting/dbuscall.h
index 7b9391251b..53135ec086 100644
--- a/scripting/dbuscall.h
+++ b/scripting/dbuscall.h
@@ -81,7 +81,7 @@ class DBusCall : public QObject
     Q_PROPERTY(QString method READ method WRITE setMethod NOTIFY methodChanged)
     Q_PROPERTY(QVariantList arguments READ arguments WRITE setArguments NOTIFY argumentsChanged)
 public:
-    explicit DBusCall(QObject* parent = 0);
+    explicit DBusCall(QObject* parent = nullptr);
     ~DBusCall() override;
 
     const QString &service() const;
diff --git a/scripting/screenedgeitem.h b/scripting/screenedgeitem.h
index c5e10e85bb..64bbf16c33 100644
--- a/scripting/screenedgeitem.h
+++ b/scripting/screenedgeitem.h
@@ -80,7 +80,7 @@ public:
         Pointer,
         Touch
     };
-    explicit ScreenEdgeItem(QObject *parent = 0);
+    explicit ScreenEdgeItem(QObject *parent = nullptr);
     ~ScreenEdgeItem() override;
     bool isEnabled() const;
     Edge edge() const;
diff --git a/scripting/workspace_wrapper.cpp b/scripting/workspace_wrapper.cpp
index be48d6e9de..a9844e7bc0 100644
--- a/scripting/workspace_wrapper.cpp
+++ b/scripting/workspace_wrapper.cpp
@@ -357,7 +357,7 @@ QList<KWin::AbstractClient *> QtScriptWorkspaceWrapper::clientList() const
 
 QQmlListProperty<KWin::AbstractClient> DeclarativeScriptWorkspaceWrapper::clients()
 {
-    return QQmlListProperty<KWin::AbstractClient>(this, 0, &DeclarativeScriptWorkspaceWrapper::countClientList, &DeclarativeScriptWorkspaceWrapper::atClientList);
+    return QQmlListProperty<KWin::AbstractClient>(this, nullptr, &DeclarativeScriptWorkspaceWrapper::countClientList, &DeclarativeScriptWorkspaceWrapper::atClientList);
 }
 
 int DeclarativeScriptWorkspaceWrapper::countClientList(QQmlListProperty<KWin::AbstractClient> *clients)
diff --git a/shadow.cpp b/shadow.cpp
index 1699b837af..ad53ca5ca5 100644
--- a/shadow.cpp
+++ b/shadow.cpp
@@ -51,7 +51,7 @@ Shadow::~Shadow()
 Shadow *Shadow::createShadow(Toplevel *toplevel)
 {
     if (!effects) {
-        return NULL;
+        return nullptr;
     }
     Shadow *shadow = createShadowFromDecoration(toplevel);
     if (!shadow && waylandServer()) {
@@ -78,11 +78,11 @@ Shadow *Shadow::createShadowFromX11(Toplevel *toplevel)
 
         if (!shadow->init(data)) {
             delete shadow;
-            return NULL;
+            return nullptr;
         }
         return shadow;
     } else {
-        return NULL;
+        return nullptr;
     }
 }
 
diff --git a/sm.cpp b/sm.cpp
index 192ff33110..3cd48060d0 100644
--- a/sm.cpp
+++ b/sm.cpp
@@ -68,7 +68,7 @@ static const char* windowTypeToTxt(NET::WindowType type)
     if (type == -2)   // undefined (not really part of NET::WindowType)
         return "Undefined";
     qFatal("Unknown Window Type");
-    return NULL;
+    return nullptr;
 }
 
 static NET::WindowType txtToWindowType(const char* txt)
@@ -314,7 +314,7 @@ static bool sessionInfoWindowTypeMatch(Client* c, SessionInfo* info)
  */
 SessionInfo* Workspace::takeSessionInfo(Client* c)
 {
-    SessionInfo *realInfo = 0;
+    SessionInfo *realInfo = nullptr;
     QByteArray sessionId = c->sessionId();
     QByteArray windowRole = c->windowRole();
     QByteArray wmCommand = c->wmCommand();
@@ -430,14 +430,14 @@ SessionSaveDoneHelper::SessionSaveDoneHelper()
     calls.save_complete.client_data = reinterpret_cast< SmPointer >(this);
     calls.shutdown_cancelled.callback = shutdown_cancelled;
     calls.shutdown_cancelled.client_data = reinterpret_cast< SmPointer >(this);
-    char* id = NULL;
+    char* id = nullptr;
     char err[ 11 ];
-    conn = SmcOpenConnection(NULL, 0, 1, 0,
+    conn = SmcOpenConnection(nullptr, nullptr, 1, 0,
                              SmcSaveYourselfProcMask | SmcDieProcMask | SmcSaveCompleteProcMask
-                             | SmcShutdownCancelledProcMask, &calls, NULL, &id, 10, err);
-    if (id != NULL)
+                             | SmcShutdownCancelledProcMask, &calls, nullptr, &id, 10, err);
+    if (id != nullptr)
         free(id);
-    if (conn == NULL)
+    if (conn == nullptr)
         return; // no SM
 
     // detect ksmserver
@@ -456,8 +456,8 @@ SessionSaveDoneHelper::SessionSaveDoneHelper()
     props[ 0 ].num_vals = 1;
     props[ 0 ].vals = &propvalue[ 0 ];
     struct passwd* entry = getpwuid(geteuid());
-    propvalue[ 1 ].length = entry != NULL ? strlen(entry->pw_name) : 0;
-    propvalue[ 1 ].value = (SmPointer)(entry != NULL ? entry->pw_name : "");
+    propvalue[ 1 ].length = entry != nullptr ? strlen(entry->pw_name) : 0;
+    propvalue[ 1 ].value = (SmPointer)(entry != nullptr ? entry->pw_name : "");
     props[ 1 ].name = const_cast< char* >(SmUserID);
     props[ 1 ].type = const_cast< char* >(SmARRAY8);
     props[ 1 ].num_vals = 1;
@@ -494,17 +494,17 @@ SessionSaveDoneHelper::~SessionSaveDoneHelper()
 
 void SessionSaveDoneHelper::close()
 {
-    if (conn != NULL) {
+    if (conn != nullptr) {
         delete notifier;
-        SmcCloseConnection(conn, 0, NULL);
+        SmcCloseConnection(conn, 0, nullptr);
     }
-    conn = NULL;
+    conn = nullptr;
 }
 
 void SessionSaveDoneHelper::processData()
 {
-    if (conn != NULL)
-        IceProcessMessages(SmcGetIceConnection(conn), 0, 0);
+    if (conn != nullptr)
+        IceProcessMessages(SmcGetIceConnection(conn), nullptr, nullptr);
 }
 
 void Workspace::sessionSaveDone()
diff --git a/tabbox/tabbox.cpp b/tabbox/tabbox.cpp
index 1175eb0bf7..9736ee21b5 100644
--- a/tabbox/tabbox.cpp
+++ b/tabbox/tabbox.cpp
@@ -1475,7 +1475,7 @@ AbstractClient* TabBox::nextClientStatic(AbstractClient* c) const
 {
     const auto &list = Workspace::self()->allClientList();
     if (!c || list.isEmpty())
-        return 0;
+        return nullptr;
     int pos = list.indexOf(c);
     if (pos == -1)
         return list.first();
@@ -1493,7 +1493,7 @@ AbstractClient* TabBox::previousClientStatic(AbstractClient* c) const
 {
     const auto &list = Workspace::self()->allClientList();
     if (!c || list.isEmpty())
-        return 0;
+        return nullptr;
     int pos = list.indexOf(c);
     if (pos == -1)
         return list.last();
diff --git a/tests/pointerconstraintstest.cpp b/tests/pointerconstraintstest.cpp
index 8334d3b1a7..66722fda59 100644
--- a/tests/pointerconstraintstest.cpp
+++ b/tests/pointerconstraintstest.cpp
@@ -260,7 +260,7 @@ XBackend::XBackend(QObject *parent)
 void XBackend::init(QQuickView *view)
 {
     Backend::init(view);
-    m_xcbConn = xcb_connect(NULL, NULL);
+    m_xcbConn = xcb_connect(nullptr, nullptr);
     if (!m_xcbConn) {
         qDebug() << "Could not open XCB connection.";
     }
diff --git a/thumbnailitem.cpp b/thumbnailitem.cpp
index b3cf84cadb..662512a859 100644
--- a/thumbnailitem.cpp
+++ b/thumbnailitem.cpp
@@ -121,8 +121,8 @@ void AbstractThumbnailItem::setClipTo(QQuickItem *clip)
 
 WindowThumbnailItem::WindowThumbnailItem(QQuickItem* parent)
     : AbstractThumbnailItem(parent)
-    , m_wId(0)
-    , m_client(NULL)
+    , m_wId(nullptr)
+    , m_client(nullptr)
 {
 }
 
@@ -136,10 +136,10 @@ void WindowThumbnailItem::setWId(const QUuid &wId)
         return;
     }
     m_wId = wId;
-    if (m_wId != 0) {
+    if (m_wId != nullptr) {
         setClient(workspace()->findAbstractClient([this] (const AbstractClient *c) { return c->internalId() == m_wId; }));
     } else if (m_client) {
-        m_client = NULL;
+        m_client = nullptr;
         emit clientChanged();
     }
     emit wIdChanged(wId);
diff --git a/thumbnailitem.h b/thumbnailitem.h
index 2c2cc065a8..4c23d7a1ab 100644
--- a/thumbnailitem.h
+++ b/thumbnailitem.h
@@ -56,7 +56,7 @@ Q_SIGNALS:
     void clipToChanged();
 
 protected:
-    explicit AbstractThumbnailItem(QQuickItem *parent = 0);
+    explicit AbstractThumbnailItem(QQuickItem *parent = nullptr);
 
 protected Q_SLOTS:
     virtual void repaint(KWin::EffectWindow* w) = 0;
@@ -80,7 +80,7 @@ class WindowThumbnailItem : public AbstractThumbnailItem
     Q_PROPERTY(QUuid wId READ wId WRITE setWId NOTIFY wIdChanged SCRIPTABLE true)
     Q_PROPERTY(KWin::AbstractClient *client READ client WRITE setClient NOTIFY clientChanged)
 public:
-    explicit WindowThumbnailItem(QQuickItem *parent = 0);
+    explicit WindowThumbnailItem(QQuickItem *parent = nullptr);
     ~WindowThumbnailItem() override;
 
     QUuid wId() const {
@@ -105,7 +105,7 @@ class DesktopThumbnailItem : public AbstractThumbnailItem
     Q_OBJECT
     Q_PROPERTY(int desktop READ desktop WRITE setDesktop NOTIFY desktopChanged)
 public:
-    DesktopThumbnailItem(QQuickItem *parent = 0);
+    DesktopThumbnailItem(QQuickItem *parent = nullptr);
     ~DesktopThumbnailItem() override;
 
     int desktop() const {
diff --git a/toplevel.cpp b/toplevel.cpp
index ec23d754f8..88cee2fb76 100644
--- a/toplevel.cpp
+++ b/toplevel.cpp
@@ -42,14 +42,14 @@ namespace KWin
 Toplevel::Toplevel()
     : m_visual(XCB_NONE)
     , bit_depth(24)
-    , info(NULL)
+    , info(nullptr)
     , ready_for_painting(true)
     , m_isDamaged(false)
     , m_internalId(QUuid::createUuid())
     , m_client()
     , damage_handle(XCB_NONE)
     , is_shape(false)
-    , effect_window(NULL)
+    , effect_window(nullptr)
     , m_clientMachine(new ClientMachine(this))
     , m_wmClientLeader(XCB_WINDOW_NONE)
     , m_damageReplyPending(false)
@@ -70,7 +70,7 @@ Toplevel::~Toplevel()
 
 QDebug& operator<<(QDebug& stream, const Toplevel* cl)
 {
-    if (cl == NULL)
+    if (cl == nullptr)
         return stream << "\'NULL\'";
     cl->debug(stream);
     return stream;
@@ -122,7 +122,7 @@ void Toplevel::copyToDeleted(Toplevel* c)
     layer_repaints_region = c->layer_repaints_region;
     is_shape = c->is_shape;
     effect_window = c->effect_window;
-    if (effect_window != NULL)
+    if (effect_window != nullptr)
         effect_window->setWindow(this);
     resource_name = c->resourceName();
     resource_class = c->resourceClass();
@@ -139,7 +139,7 @@ void Toplevel::copyToDeleted(Toplevel* c)
 // owner by Deleted
 void Toplevel::disownDataPassedToDeleted()
 {
-    info = NULL;
+    info = nullptr;
 }
 
 QRect Toplevel::visibleRect() const
@@ -298,13 +298,13 @@ void Toplevel::finishCompositing(ReleaseReason releaseReason)
     damage_handle = XCB_NONE;
     damage_region = QRegion();
     repaints_region = QRegion();
-    effect_window = NULL;
+    effect_window = nullptr;
 }
 
 void Toplevel::discardWindowPixmap()
 {
     addDamageFull();
-    if (effectWindow() != NULL && effectWindow()->sceneWindow() != NULL)
+    if (effectWindow() != nullptr && effectWindow()->sceneWindow() != nullptr)
         effectWindow()->sceneWindow()->pixmapDiscarded();
 }
 
@@ -359,7 +359,7 @@ bool Toplevel::resetAndFetchDamage()
     // Create a new region and copy the damage region to it,
     // resetting the damaged state.
     xcb_xfixes_region_t region = xcb_generate_id(conn);
-    xcb_xfixes_create_region(conn, region, 0, 0);
+    xcb_xfixes_create_region(conn, region, 0, nullptr);
     xcb_damage_subtract(conn, damage_handle, 0, region);
 
     // Send a fetch-region request and destroy the region
@@ -381,7 +381,7 @@ void Toplevel::getDamageRegionReply()
 
     // Get the fetch-region reply
     xcb_xfixes_fetch_region_reply_t *reply =
-            xcb_xfixes_fetch_region_reply(connection(), m_regionCookie, 0);
+            xcb_xfixes_fetch_region_reply(connection(), m_regionCookie, nullptr);
 
     if (!reply)
         return;
@@ -511,7 +511,7 @@ void Toplevel::setReadyForPainting()
 void Toplevel::deleteEffectWindow()
 {
     delete effect_window;
-    effect_window = NULL;
+    effect_window = nullptr;
 }
 
 void Toplevel::checkScreen()
@@ -594,7 +594,7 @@ void Toplevel::getShadow()
 bool Toplevel::hasShadow() const
 {
     if (effectWindow() && effectWindow()->sceneWindow()) {
-        return effectWindow()->sceneWindow()->shadow() != NULL;
+        return effectWindow()->sceneWindow()->shadow() != nullptr;
     }
     return false;
 }
@@ -604,7 +604,7 @@ Shadow *Toplevel::shadow()
     if (effectWindow() && effectWindow()->sceneWindow()) {
         return effectWindow()->sceneWindow()->shadow();
     } else {
-        return NULL;
+        return nullptr;
     }
 }
 
@@ -613,7 +613,7 @@ const Shadow *Toplevel::shadow() const
     if (effectWindow() && effectWindow()->sceneWindow()) {
         return effectWindow()->sceneWindow()->shadow();
     } else {
-        return NULL;
+        return nullptr;
     }
 }
 
diff --git a/unmanaged.cpp b/unmanaged.cpp
index 393b1363ff..1e5b6231f9 100644
--- a/unmanaged.cpp
+++ b/unmanaged.cpp
@@ -92,7 +92,7 @@ bool Unmanaged::track(xcb_window_t w)
 
 void Unmanaged::release(ReleaseReason releaseReason)
 {
-    Deleted* del = NULL;
+    Deleted* del = nullptr;
     if (releaseReason != ReleaseReason::KWinShutsDown) {
         del = Deleted::create(this);
     }
diff --git a/useractions.cpp b/useractions.cpp
index aa998c2875..d57674fabb 100644
--- a/useractions.cpp
+++ b/useractions.cpp
@@ -79,21 +79,21 @@ namespace KWin
 
 UserActionsMenu::UserActionsMenu(QObject *parent)
     : QObject(parent)
-    , m_menu(NULL)
-    , m_desktopMenu(NULL)
-    , m_screenMenu(NULL)
-    , m_activityMenu(NULL)
-    , m_scriptsMenu(NULL)
-    , m_resizeOperation(NULL)
-    , m_moveOperation(NULL)
-    , m_maximizeOperation(NULL)
-    , m_shadeOperation(NULL)
-    , m_keepAboveOperation(NULL)
-    , m_keepBelowOperation(NULL)
-    , m_fullScreenOperation(NULL)
-    , m_noBorderOperation(NULL)
-    , m_minimizeOperation(NULL)
-    , m_closeOperation(NULL)
+    , m_menu(nullptr)
+    , m_desktopMenu(nullptr)
+    , m_screenMenu(nullptr)
+    , m_activityMenu(nullptr)
+    , m_scriptsMenu(nullptr)
+    , m_resizeOperation(nullptr)
+    , m_moveOperation(nullptr)
+    , m_maximizeOperation(nullptr)
+    , m_shadeOperation(nullptr)
+    , m_keepAboveOperation(nullptr)
+    , m_keepBelowOperation(nullptr)
+    , m_fullScreenOperation(nullptr)
+    , m_noBorderOperation(nullptr)
+    , m_minimizeOperation(nullptr)
+    , m_closeOperation(nullptr)
 {
 }
 
@@ -169,7 +169,7 @@ void UserActionsMenu::helperDialog(const QString& message, AbstractClient* clien
     QString type;
     auto shortcut = [](const QString &name) {
         QAction* action = Workspace::self()->findChild<QAction*>(name);
-        Q_ASSERT(action != NULL);
+        Q_ASSERT(action != nullptr);
         const auto shortcuts = KGlobalAccel::self()->shortcut(action);
         return QStringLiteral("%1 (%2)").arg(action->text())
                              .arg(shortcuts.isEmpty() ? QString() : shortcuts.first().toString(QKeySequence::NativeText));
@@ -363,12 +363,12 @@ void UserActionsMenu::init()
 void UserActionsMenu::discard()
 {
     delete m_menu;
-    m_menu = NULL;
-    m_desktopMenu = NULL;
+    m_menu = nullptr;
+    m_desktopMenu = nullptr;
     m_multipleDesktopsMenu = nullptr;
-    m_screenMenu = NULL;
-    m_activityMenu = NULL;
-    m_scriptsMenu = NULL;
+    m_screenMenu = nullptr;
+    m_activityMenu = nullptr;
+    m_scriptsMenu = nullptr;
 }
 
 void UserActionsMenu::menuAboutToShow()
@@ -378,7 +378,7 @@ void UserActionsMenu::menuAboutToShow()
 
     if (VirtualDesktopManager::self()->count() == 1) {
         delete m_desktopMenu;
-        m_desktopMenu = 0;
+        m_desktopMenu = nullptr;
         delete m_multipleDesktopsMenu;
         m_multipleDesktopsMenu = nullptr;
     } else {
@@ -386,7 +386,7 @@ void UserActionsMenu::menuAboutToShow()
     }
     if (screens()->count() == 1 || (!m_client->isMovable() && !m_client->isMovableAcrossScreens())) {
         delete m_screenMenu;
-        m_screenMenu = NULL;
+        m_screenMenu = nullptr;
     } else {
         initScreenPopup();
     }
@@ -440,7 +440,7 @@ void UserActionsMenu::showHideActivityMenu()
     qCDebug(KWIN_CORE) << "activities:" << openActivities_.size();
     if (openActivities_.size() < 2) {
         delete m_activityMenu;
-        m_activityMenu = 0;
+        m_activityMenu = nullptr;
     } else {
         initActivityPopup();
     }
@@ -941,8 +941,8 @@ void Workspace::closeActivePopup()
 {
     if (active_popup) {
         active_popup->close();
-        active_popup = NULL;
-        active_popup_client = NULL;
+        active_popup = nullptr;
+        active_popup_client = nullptr;
     }
     m_userActionsMenu->close();
 }
@@ -986,7 +986,7 @@ void Workspace::initShortcuts()
 
 void Workspace::setupWindowShortcut(AbstractClient* c)
 {
-    Q_ASSERT(client_keys_dialog == NULL);
+    Q_ASSERT(client_keys_dialog == nullptr);
     // TODO: PORT ME (KGlobalAccel related)
     //keys->setEnabled( false );
     //disable_shortcuts_keys->setEnabled( false );
@@ -1016,8 +1016,8 @@ void Workspace::setupWindowShortcutDone(bool ok)
         client_keys_client->setShortcut(client_keys_dialog->shortcut().toString());
     closeActivePopup();
     client_keys_dialog->deleteLater();
-    client_keys_dialog = NULL;
-    client_keys_client = NULL;
+    client_keys_dialog = nullptr;
+    client_keys_client = nullptr;
     if (active_client)
         active_client->takeFocus();
 }
@@ -1027,7 +1027,7 @@ void Workspace::clientShortcutUpdated(AbstractClient* c)
     QString key = QStringLiteral("_k_session:%1").arg(c->window());
     QAction* action = findChild<QAction*>(key);
     if (!c->shortcut().isEmpty()) {
-        if (action == NULL) { // new shortcut
+        if (action == nullptr) { // new shortcut
             action = new QAction(this);
             kwinApp()->platform()->setupActionForGlobalAccel(action);
             action->setProperty("componentName", QStringLiteral(KWIN_NAME));
diff --git a/useractions.h b/useractions.h
index af93bcc0a5..2de1804821 100644
--- a/useractions.h
+++ b/useractions.h
@@ -59,7 +59,7 @@ class KWIN_EXPORT UserActionsMenu : public QObject
 {
     Q_OBJECT
 public:
-    explicit UserActionsMenu(QObject *parent = 0);
+    explicit UserActionsMenu(QObject *parent = nullptr);
     ~UserActionsMenu() override;
     /**
      * Discards the constructed menu, so that it gets recreates
diff --git a/utils.cpp b/utils.cpp
index 3c63c91dc2..b28330fbbe 100644
--- a/utils.cpp
+++ b/utils.cpp
@@ -104,17 +104,17 @@ static bool keyboard_grabbed = false;
 
 bool grabXKeyboard(xcb_window_t w)
 {
-    if (QWidget::keyboardGrabber() != NULL)
+    if (QWidget::keyboardGrabber() != nullptr)
         return false;
     if (keyboard_grabbed)
         return false;
-    if (qApp->activePopupWidget() != NULL)
+    if (qApp->activePopupWidget() != nullptr)
         return false;
     if (w == XCB_WINDOW_NONE)
         w = rootWindow();
     const xcb_grab_keyboard_cookie_t c = xcb_grab_keyboard_unchecked(connection(), false, w, xTime(),
                                                                      XCB_GRAB_MODE_ASYNC, XCB_GRAB_MODE_ASYNC);
-    ScopedCPointer<xcb_grab_keyboard_reply_t> grab(xcb_grab_keyboard_reply(connection(), c, NULL));
+    ScopedCPointer<xcb_grab_keyboard_reply_t> grab(xcb_grab_keyboard_reply(connection(), c, nullptr));
     if (grab.isNull()) {
         return false;
     }
@@ -172,7 +172,7 @@ Qt::MouseButton x11ToQtMouseButton(int button)
 
 Qt::MouseButtons x11ToQtMouseButtons(int state)
 {
-    Qt::MouseButtons ret = 0;
+    Qt::MouseButtons ret = nullptr;
     if (state & XCB_KEY_BUT_MASK_BUTTON_1)
         ret |= Qt::LeftButton;
     if (state & XCB_KEY_BUT_MASK_BUTTON_2)
@@ -188,7 +188,7 @@ Qt::MouseButtons x11ToQtMouseButtons(int state)
 
 Qt::KeyboardModifiers x11ToQtKeyboardModifiers(int state)
 {
-    Qt::KeyboardModifiers ret = 0;
+    Qt::KeyboardModifiers ret = nullptr;
     if (state & XCB_KEY_BUT_MASK_SHIFT)
         ret |= Qt::ShiftModifier;
     if (state & XCB_KEY_BUT_MASK_CONTROL)
diff --git a/virtualdesktops.cpp b/virtualdesktops.cpp
index 76ed4819fa..31b64badc4 100644
--- a/virtualdesktops.cpp
+++ b/virtualdesktops.cpp
@@ -232,13 +232,13 @@ KWIN_SINGLETON_FACTORY_VARIABLE(VirtualDesktopManager, s_manager)
 VirtualDesktopManager::VirtualDesktopManager(QObject *parent)
     : QObject(parent)
     , m_navigationWrapsAround(false)
-    , m_rootInfo(NULL)
+    , m_rootInfo(nullptr)
 {
 }
 
 VirtualDesktopManager::~VirtualDesktopManager()
 {
-    s_manager = NULL;
+    s_manager = nullptr;
 }
 
 void VirtualDesktopManager::setRootInfo(NETRootInfo *info)
diff --git a/workspace.cpp b/workspace.cpp
index 6d4309b447..298f72653d 100644
--- a/workspace.cpp
+++ b/workspace.cpp
@@ -99,31 +99,31 @@ void ColorMapper::update()
     }
 }
 
-Workspace* Workspace::_self = 0;
+Workspace* Workspace::_self = nullptr;
 
 Workspace::Workspace(const QString &sessionKey)
-    : QObject(0)
-    , m_compositor(NULL)
+    : QObject(nullptr)
+    , m_compositor(nullptr)
     // Unsorted
-    , active_popup(NULL)
-    , active_popup_client(NULL)
+    , active_popup(nullptr)
+    , active_popup_client(nullptr)
     , m_initialDesktop(1)
-    , active_client(0)
-    , last_active_client(0)
-    , most_recently_raised(0)
-    , movingClient(0)
-    , delayfocus_client(0)
+    , active_client(nullptr)
+    , last_active_client(nullptr)
+    , most_recently_raised(nullptr)
+    , movingClient(nullptr)
+    , delayfocus_client(nullptr)
     , force_restacking(false)
     , showing_desktop(false)
     , was_user_interaction(false)
     , session_saving(false)
     , block_focus(0)
     , m_userActionsMenu(new UserActionsMenu(this))
-    , client_keys_dialog(NULL)
-    , client_keys_client(NULL)
+    , client_keys_dialog(nullptr)
+    , client_keys_client(nullptr)
     , global_shortcuts_disabled_for_client(false)
     , workspaceInit(true)
-    , startup(0)
+    , startup(nullptr)
     , set_active_client_recursion(0)
     , block_stacking_updates(0)
 {
@@ -150,7 +150,7 @@ Workspace::Workspace(const QString &sessionKey)
     options->loadConfig();
     options->loadCompositingConfig(false);
 
-    delayFocusTimer = 0;
+    delayFocusTimer = nullptr;
 
     if (!sessionKey.isEmpty())
         loadSessionInfo(sessionKey);
@@ -281,7 +281,7 @@ void Workspace::init()
                                           QStringLiteral("refreshFonts"),
                                           this, SLOT(reconfigure()));
 
-    active_client = NULL;
+    active_client = nullptr;
 
     initWithX11();
 
@@ -517,15 +517,15 @@ void Workspace::initWithX11()
         --block_focus;
         new_active_client = findClient(Predicate::WindowMatch, client_info.activeWindow());
     }
-    if (new_active_client == NULL
-            && activeClient() == NULL && should_get_focus.count() == 0) {
+    if (new_active_client == nullptr
+            && activeClient() == nullptr && should_get_focus.count() == 0) {
         // No client activated in manage()
-        if (new_active_client == NULL)
+        if (new_active_client == nullptr)
             new_active_client = topClientOnDesktop(VirtualDesktopManager::self()->current(), -1);
-        if (new_active_client == NULL && !desktops.isEmpty())
+        if (new_active_client == nullptr && !desktops.isEmpty())
             new_active_client = findDesktop(true, VirtualDesktopManager::self()->current());
     }
-    if (new_active_client != NULL)
+    if (new_active_client != nullptr)
         activateClient(new_active_client);
 }
 
@@ -594,7 +594,7 @@ Workspace::~Workspace()
     // TODO: ungrabXServer();
 
     Xcb::Extensions::destroy();
-    _self = 0;
+    _self = nullptr;
 }
 
 void Workspace::setupClientConnections(AbstractClient *c)
@@ -615,7 +615,7 @@ Client* Workspace::createClient(xcb_window_t w, bool is_mapped)
     connect(c, SIGNAL(clientFullScreenSet(KWin::Client*,bool,bool)), ScreenEdges::self(), SIGNAL(checkBlocking()));
     if (!c->manage(w, is_mapped)) {
         Client::deleteClient(c);
-        return NULL;
+        return nullptr;
     }
     addClient(c);
     return c;
@@ -631,7 +631,7 @@ Unmanaged* Workspace::createUnmanaged(xcb_window_t w)
     Unmanaged* c = new Unmanaged();
     if (!c->track(w)) {
         Unmanaged::deleteUnmanaged(c);
-        return NULL;
+        return nullptr;
     }
     connect(c, &Unmanaged::needsRepaint, m_compositor, &Compositor::scheduleRepaint);
     addUnmanaged(c);
@@ -645,12 +645,12 @@ void Workspace::addClient(Client* c)
 
     emit clientAdded(c);
 
-    if (grp != NULL)
+    if (grp != nullptr)
         grp->gotLeader(c);
 
     if (c->isDesktop()) {
         desktops.append(c);
-        if (active_client == NULL && should_get_focus.isEmpty() && c->isOnCurrentDesktop())
+        if (active_client == nullptr && should_get_focus.isEmpty() && c->isOnCurrentDesktop())
             requestFocus(c);   // TODO: Make sure desktop is active after startup if there's no other window active
     } else {
         FocusChain::self()->update(c, FocusChain::Update);
@@ -667,7 +667,7 @@ void Workspace::addClient(Client* c)
     if (c->isDesktop()) {
         raiseClient(c);
         // If there's no active client, make this desktop the active one
-        if (activeClient() == NULL && should_get_focus.count() == 0)
+        if (activeClient() == nullptr && should_get_focus.count() == 0)
             activateClient(findDesktop(true, VirtualDesktopManager::self()->current()));
     }
     c->checkActiveModal();
@@ -710,15 +710,15 @@ void Workspace::removeClient(Client* c)
     markXStackingOrderAsDirty();
     attention_chain.removeAll(c);
     Group* group = findGroup(c->window());
-    if (group != NULL)
+    if (group != nullptr)
         group->lostLeader();
 
     if (c == most_recently_raised)
-        most_recently_raised = 0;
+        most_recently_raised = nullptr;
     should_get_focus.removeAll(c);
     Q_ASSERT(c != active_client);
     if (c == last_active_client)
-        last_active_client = 0;
+        last_active_client = nullptr;
     if (c == delayfocus_client)
         cancelDelayFocus();
 
@@ -811,14 +811,14 @@ void Workspace::updateToolWindows(bool also_hide)
             if (!c->isTransient()) {
                 if (!c->group() || c->group()->members().count() == 1)   // Has its own group, keep always visible
                     show = true;
-                else if (client != NULL && c->group() == client->group())
+                else if (client != nullptr && c->group() == client->group())
                     show = true;
                 else
                     show = false;
             } else {
-                if (group != NULL && c->group() == group)
+                if (group != nullptr && c->group() == group)
                     show = true;
-                else if (client != NULL && client->hasTransient(c, true))
+                else if (client != nullptr && client->hasTransient(c, true))
                     show = true;
                 else
                     show = false;
@@ -968,7 +968,7 @@ void Workspace::updateClientVisibilityOnDesktopChange(uint newDesktop)
 
 void Workspace::activateClientOnNewDesktop(uint desktop)
 {
-    AbstractClient* c = NULL;
+    AbstractClient* c = nullptr;
     if (options->focusPolicyIsReasonable()) {
         c = findClientToActivateOnDesktop(desktop);
     }
@@ -978,11 +978,11 @@ void Workspace::activateClientOnNewDesktop(uint desktop)
     else if (active_client && active_client->isShown(true) && active_client->isOnCurrentDesktop())
         c = active_client;
 
-    if (c == NULL && !desktops.isEmpty())
+    if (c == nullptr && !desktops.isEmpty())
         c = findDesktop(true, desktop);
 
     if (c != active_client)
-        setActiveClient(NULL);
+        setActiveClient(nullptr);
 
     if (c)
         requestFocus(c);
@@ -994,7 +994,7 @@ void Workspace::activateClientOnNewDesktop(uint desktop)
 
 AbstractClient *Workspace::findClientToActivateOnDesktop(uint desktop)
 {
-    if (movingClient != NULL && active_client == movingClient &&
+    if (movingClient != nullptr && active_client == movingClient &&
         FocusChain::self()->contains(active_client, desktop) &&
         active_client->isShown(true) && active_client->isOnCurrentDesktop()) {
         // A requestFocus call will fail, as the client is already active
@@ -1081,7 +1081,7 @@ void Workspace::updateCurrentActivity(const QString &new_activity)
 
     // Restore the focus on this desktop
     --block_focus;
-    AbstractClient* c = 0;
+    AbstractClient* c = nullptr;
 
     //FIXME below here is a lot of focuschain stuff, probably all wrong now
     if (options->focusPolicyIsReasonable()) {
@@ -1094,11 +1094,11 @@ void Workspace::updateCurrentActivity(const QString &new_activity)
     else if (active_client && active_client->isShown(true) && active_client->isOnCurrentDesktop() && active_client->isOnCurrentActivity())
         c = active_client;
 
-    if (c == NULL && !desktops.isEmpty())
+    if (c == nullptr && !desktops.isEmpty())
         c = findDesktop(true, VirtualDesktopManager::self()->current());
 
     if (c != active_client)
-        setActiveClient(NULL);
+        setActiveClient(nullptr);
 
     if (c)
         requestFocus(c);
@@ -1256,7 +1256,7 @@ void Workspace::requestDelayFocus(AbstractClient* c)
 void Workspace::cancelDelayFocus()
 {
     delete delayFocusTimer;
-    delayFocusTimer = 0;
+    delayFocusTimer = nullptr;
 }
 
 bool Workspace::checkStartupNotification(xcb_window_t w, KStartupInfoId &id, KStartupInfoData &data)
diff --git a/workspace.h b/workspace.h
index 1aff18e2ea..12a3b15e13 100644
--- a/workspace.h
+++ b/workspace.h
@@ -331,7 +331,7 @@ public:
     void focusToNull(); // SELI TODO: Public?
 
     void clientShortcutUpdated(AbstractClient* c);
-    bool shortcutAvailable(const QKeySequence &cut, AbstractClient* ignore = NULL) const;
+    bool shortcutAvailable(const QKeySequence &cut, AbstractClient* ignore = nullptr) const;
     bool globalShortcutsDisabled() const;
     void disableGlobalShortcutsForClient(bool disable);
 
diff --git a/xcbutils.cpp b/xcbutils.cpp
index fa9f5936e6..1c873205d4 100644
--- a/xcbutils.cpp
+++ b/xcbutils.cpp
@@ -343,11 +343,11 @@ ExtensionData::ExtensionData()
 template<typename reply, typename T, typename F>
 void Extensions::initVersion(T cookie, F f, ExtensionData *dataToFill)
 {
-    ScopedCPointer<reply> version(f(connection(), cookie, NULL));
+    ScopedCPointer<reply> version(f(connection(), cookie, nullptr));
     dataToFill->version = version->major_version * 0x10 + version->minor_version;
 }
 
-Extensions *Extensions::s_self = NULL;
+Extensions *Extensions::s_self = nullptr;
 
 Extensions *Extensions::self()
 {
@@ -360,7 +360,7 @@ Extensions *Extensions::self()
 void Extensions::destroy()
 {
     delete s_self;
-    s_self = NULL;
+    s_self = nullptr;
 }
 
 Extensions::Extensions()
@@ -499,7 +499,7 @@ bool Extensions::hasShape(xcb_window_t w) const
         return false;
     }
     ScopedCPointer<xcb_shape_query_extents_reply_t> extents(xcb_shape_query_extents_reply(
-        connection(), xcb_shape_query_extents_unchecked(connection(), w), NULL));
+        connection(), xcb_shape_query_extents_unchecked(connection(), w), nullptr));
     if (extents.isNull()) {
         return false;
     }
@@ -560,7 +560,7 @@ QVector<ExtensionData> Extensions::extensions() const
 //****************************************
 Shm::Shm()
     : m_shmId(-1)
-    , m_buffer(NULL)
+    , m_buffer(nullptr)
     , m_segment(XCB_NONE)
     , m_valid(false)
     , m_pixmapFormat(XCB_IMAGE_FORMAT_XY_BITMAP)
@@ -584,7 +584,7 @@ bool Shm::init()
         return false;
     }
     ScopedCPointer<xcb_shm_query_version_reply_t> version(xcb_shm_query_version_reply(connection(),
-        xcb_shm_query_version_unchecked(connection()), NULL));
+        xcb_shm_query_version_unchecked(connection()), nullptr));
     if (version.isNull()) {
         qCDebug(KWIN_CORE) << "Failed to get SHM extension version information";
         return false;
@@ -596,13 +596,13 @@ bool Shm::init()
         qCDebug(KWIN_CORE) << "Failed to allocate SHM segment";
         return false;
     }
-    m_buffer = shmat(m_shmId, NULL, 0 /*read/write*/);
+    m_buffer = shmat(m_shmId, nullptr, 0 /*read/write*/);
     if (-1 == reinterpret_cast<long>(m_buffer)) {
         qCDebug(KWIN_CORE) << "Failed to attach SHM segment";
-        shmctl(m_shmId, IPC_RMID, NULL);
+        shmctl(m_shmId, IPC_RMID, nullptr);
         return false;
     }
-    shmctl(m_shmId, IPC_RMID, NULL);
+    shmctl(m_shmId, IPC_RMID, nullptr);
 
     m_segment = xcb_generate_id(connection());
     const xcb_void_cookie_t cookie = xcb_shm_attach_checked(connection(), m_segment, m_shmId, false);
diff --git a/xcbutils.h b/xcbutils.h
index d446297860..827d92498a 100644
--- a/xcbutils.h
+++ b/xcbutils.h
@@ -263,7 +263,7 @@ public:
     }
     inline bool isNull() {
         getReply();
-        return m_reply == NULL;
+        return m_reply == nullptr;
     }
     inline bool isNull() const {
         const_cast<AbstractWrapper*>(this)->getReply();
@@ -299,7 +299,7 @@ public:
     inline Reply *take() {
         getReply();
         Reply *ret = m_reply;
-        m_reply = NULL;
+        m_reply = nullptr;
         m_window = XCB_WINDOW_NONE;
         return ret;
     }
@@ -308,7 +308,7 @@ protected:
     AbstractWrapper()
         : m_retrieved(false)
         , m_window(XCB_WINDOW_NONE)
-        , m_reply(NULL)
+        , m_reply(nullptr)
     {
         m_cookie.sequence = 0;
     }
@@ -316,14 +316,14 @@ protected:
         : m_retrieved(false)
         , m_cookie(cookie)
         , m_window(window)
-        , m_reply(NULL)
+        , m_reply(nullptr)
     {
     }
     explicit AbstractWrapper(const AbstractWrapper &other)
         : m_retrieved(other.m_retrieved)
         , m_cookie(other.m_cookie)
         , m_window(other.m_window)
-        , m_reply(NULL)
+        , m_reply(nullptr)
     {
         takeFromOther(const_cast<AbstractWrapper&>(other));
     }
@@ -1332,7 +1332,7 @@ public:
      * @param values The values to be passed to xcb_create_window
      * @param parent The parent window
      */
-    Window(const QRect &geometry, uint32_t mask = 0, const uint32_t *values = NULL, xcb_window_t parent = rootWindow());
+    Window(const QRect &geometry, uint32_t mask = 0, const uint32_t *values = nullptr, xcb_window_t parent = rootWindow());
     /**
      * Creates an xcb_window_t and manages it. It's a convenient method to create a window with
      * depth and visual being copied from parent and border being @c 0.
@@ -1342,7 +1342,7 @@ public:
      * @param values The values to be passed to xcb_create_window
      * @param parent The parent window
      */
-    Window(const QRect &geometry, uint16_t windowClass, uint32_t mask = 0, const uint32_t *values = NULL, xcb_window_t parent = rootWindow());
+    Window(const QRect &geometry, uint16_t windowClass, uint32_t mask = 0, const uint32_t *values = nullptr, xcb_window_t parent = rootWindow());
     Window(const Window &other) = delete;
     ~Window();
 
@@ -1356,7 +1356,7 @@ public:
      * @param values The values to be passed to xcb_create_window
      * @param parent The parent window
      */
-    void create(const QRect &geometry, uint32_t mask = 0, const uint32_t *values = NULL, xcb_window_t parent = rootWindow());
+    void create(const QRect &geometry, uint32_t mask = 0, const uint32_t *values = nullptr, xcb_window_t parent = rootWindow());
     /**
      * Creates a new window for which the responsibility is taken over. If a window had been managed
      * before it is freed.
@@ -1368,7 +1368,7 @@ public:
      * @param values The values to be passed to xcb_create_window
      * @param parent The parent window
      */
-    void create(const QRect &geometry, uint16_t windowClass, uint32_t mask = 0, const uint32_t *values = NULL, xcb_window_t parent = rootWindow());
+    void create(const QRect &geometry, uint16_t windowClass, uint32_t mask = 0, const uint32_t *values = nullptr, xcb_window_t parent = rootWindow());
     /**
      * Frees the existing window and starts to manage the new @p window.
      * If @p destroy is @c true the new managed window will be destroyed together with this
@@ -1419,7 +1419,7 @@ public:
     void kill();
     operator xcb_window_t() const;
 private:
-    xcb_window_t doCreate(const QRect &geometry, uint16_t windowClass, uint32_t mask = 0, const uint32_t *values = NULL, xcb_window_t parent = rootWindow());
+    xcb_window_t doCreate(const QRect &geometry, uint16_t windowClass, uint32_t mask = 0, const uint32_t *values = nullptr, xcb_window_t parent = rootWindow());
     void destroy();
     xcb_window_t m_window;
     bool m_destroy;
diff --git a/xkb.cpp b/xkb.cpp
index d334b1ebbc..4b99630f84 100644
--- a/xkb.cpp
+++ b/xkb.cpp
@@ -69,8 +69,8 @@ static void xkbLogHandler(xkb_context *context, xkb_log_level priority, const ch
 Xkb::Xkb(QObject *parent)
     : QObject(parent)
     , m_context(xkb_context_new(XKB_CONTEXT_NO_FLAGS))
-    , m_keymap(NULL)
-    , m_state(NULL)
+    , m_keymap(nullptr)
+    , m_state(nullptr)
     , m_shiftModifier(0)
     , m_capsModifier(0)
     , m_controlModifier(0)
@@ -206,7 +206,7 @@ void Xkb::installKeymap(int fd, uint32_t size)
     if (!m_context) {
         return;
     }
-    char *map = reinterpret_cast<char*>(mmap(NULL, size, PROT_READ, MAP_SHARED, fd, 0));
+    char *map = reinterpret_cast<char*>(mmap(nullptr, size, PROT_READ, MAP_SHARED, fd, 0));
     if (map == MAP_FAILED) {
         return;
     }
diff --git a/xwl/drag_x.cpp b/xwl/drag_x.cpp
index a0e50f715d..b108c07be1 100644
--- a/xwl/drag_x.cpp
+++ b/xwl/drag_x.cpp
@@ -408,8 +408,8 @@ void WlVisit::getMimesFromWinProperty(Mimes &offers)
                                    XCB_GET_PROPERTY_TYPE_ANY,
                                    0, 0x1fffffff);
 
-    auto *reply = xcb_get_property_reply(xcbConn, cookie, NULL);
-    if (reply == NULL) {
+    auto *reply = xcb_get_property_reply(xcbConn, cookie, nullptr);
+    if (reply == nullptr) {
         return;
     }
     if (reply->type != XCB_ATOM_ATOM || reply->value_len == 0) {
diff --git a/xwl/transfer.cpp b/xwl/transfer.cpp
index e2a8f4dd77..8f4945a273 100644
--- a/xwl/transfer.cpp
+++ b/xwl/transfer.cpp
@@ -265,7 +265,7 @@ void TransferWltoX::handlePropertyDelete()
                                 m_request->requestor,
                                 m_request->property,
                                 m_request->target,
-                                8, 0, NULL);
+                                8, 0, nullptr);
             xcb_flush(xcbConn);
             m_flushPropertyOnDelete = false;
             endTransfer();
@@ -375,8 +375,8 @@ void TransferXtoWl::startTransfer()
                                    0x1fffffff
                                    );
 
-    auto *reply = xcb_get_property_reply(xcbConn, cookie, NULL);
-    if (reply == NULL) {
+    auto *reply = xcb_get_property_reply(xcbConn, cookie, nullptr);
+    if (reply == nullptr) {
         qCWarning(KWIN_XWL) << "Can't get selection property.";
         endTransfer();
         return;