Introduce a proper screen property in Toplevel

Instead of calculating the screen number each time screen() is invoked,
the screen number gets stored in a private member variable and evaluated
whenever either the screen count changes or the Toplevel's geometry
changes. During move/resize the screen property doesn't get updated. The
update is delayed till the end of the move/resize operation.

REVIEW: 109715

client.cpp

@@ -219,6 +219,8 @@ Client::Client(Workspace* ws)
     connect(this, SIGNAL(clientStepUserMovedResized(KWin::Client*,QRect)), SIGNAL(geometryChanged()));
     connect(this, SIGNAL(clientStartUserMovedResized(KWin::Client*)), SIGNAL(moveResizedChanged()));
     connect(this, SIGNAL(clientFinishUserMovedResized(KWin::Client*)), SIGNAL(moveResizedChanged()));
+    connect(this, SIGNAL(clientStartUserMovedResized(KWin::Client*)), SLOT(removeCheckScreenConnection()));
+    connect(this, SIGNAL(clientFinishUserMovedResized(KWin::Client*)), SLOT(setupCheckScreenConnection()));
 
     connect(clientMachine(), SIGNAL(localhostChanged()), SLOT(updateCaption()));
     connect(options, SIGNAL(condensedTitleChanged()), SLOT(updateCaption()));

geometry.cpp

@@ -2064,6 +2064,7 @@ void Client::move(int x, int y, ForceGeometry_t force)
     // Update states of all other windows in this group
     if (tabGroup())
         tabGroup()->updateStates(this, TabGroup::Geometry);
+    emit geometryChanged();
 }
 
 void Client::blockGeometryUpdates(bool block)

toplevel.cpp

@@ -29,6 +29,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "shadow.h"
 #include "xcbutils.h"
 
+#include <QDesktopWidget>
+
 namespace KWin
 {
 
@@ -49,8 +51,12 @@ Toplevel::Toplevel(Workspace* ws)
     , unredirect(false)
     , unredirectSuspend(false)
     , m_damageReplyPending(false)
+    , m_screen(0)
 {
     connect(this, SIGNAL(damaged(KWin::Toplevel*,QRect)), SIGNAL(needsRepaint()));
+    connect(QApplication::desktop(), SIGNAL(screenCountChanged(int)), SLOT(checkScreen()));
+    connect(QApplication::desktop(), SIGNAL(resized(int)), SLOT(checkScreen()));
+    setupCheckScreenConnection();
 }
 
 Toplevel::~Toplevel()
@@ -140,6 +146,7 @@ void Toplevel::copyToDeleted(Toplevel* c)
     wmClientLeaderWin = c->wmClientLeader();
     window_role = c->windowRole();
     opaque_region = c->opaqueRegion();
+    m_screen = c->m_screen;
     // this needs to be done already here, otherwise 'c' could very likely
     // call discardWindowPixmap() in something called during cleanup
     c->window_pix = None;
@@ -324,14 +331,38 @@ void Toplevel::deleteEffectWindow()
     effect_window = NULL;
 }
 
+void Toplevel::checkScreen()
+{
+    if (Workspace::self()->numScreens() == 1) {
+        if (m_screen != 0) {
+            m_screen = 0;
+            emit screenChanged();
+        }
+        return;
+    }
+    const int s = Workspace::self()->screenNumber(geometry().center());
+    if (s != m_screen) {
+        m_screen = s;
+        emit screenChanged();
+    }
+}
+
+void Toplevel::setupCheckScreenConnection()
+{
+    connect(this, SIGNAL(geometryShapeChanged(KWin::Toplevel*,QRect)), SLOT(checkScreen()));
+    connect(this, SIGNAL(geometryChanged()), SLOT(checkScreen()));
+    checkScreen();
+}
+
+void Toplevel::removeCheckScreenConnection()
+{
+    disconnect(this, SIGNAL(geometryShapeChanged(KWin::Toplevel*,QRect)), this, SLOT(checkScreen()));
+    disconnect(this, SIGNAL(geometryChanged()), this, SLOT(checkScreen()));
+}
+
 int Toplevel::screen() const
 {
-    int s = workspace()->screenNumber(geometry().center());
-    if (s < 0) {
-        kDebug(1212) << "Invalid screen: Center" << geometry().center() << ", screen" << s;
-        return 0;
-    }
-    return s;
+    return m_screen;
 }
 
 bool Toplevel::isOnScreen(int screen) const

toplevel.h

@@ -57,7 +57,7 @@ class Toplevel
     Q_PROPERTY(int height READ height)
     Q_PROPERTY(qreal opacity READ opacity WRITE setOpacity NOTIFY opacityChanged)
     Q_PROPERTY(QPoint pos READ pos)
-    Q_PROPERTY(int screen READ screen)
+    Q_PROPERTY(int screen READ screen NOTIFY screenChanged)
     Q_PROPERTY(QSize size READ size)
     Q_PROPERTY(int width READ width)
     Q_PROPERTY(qulonglong windowId READ window CONSTANT)
@@ -326,6 +326,21 @@ signals:
      **/
     void needsRepaint();
     void activitiesChanged(KWin::Toplevel* toplevel);
+    /**
+     * Emitted whenever the Toplevel's screen changes. This can happen either in consequence to
+     * a screen being removed/added or if the Toplevel's geometry changes.
+     * @since 4.11
+     **/
+    void screenChanged();
+
+protected Q_SLOTS:
+    /**
+     * Checks whether the screen number for this Toplevel changed and updates if needed.
+     * Any method changing the geometry of the Toplevel should call this method.
+     **/
+    void checkScreen();
+    void setupCheckScreenConnection();
+    void removeCheckScreenConnection();
 
 protected:
     virtual ~Toplevel();
@@ -394,6 +409,7 @@ private:
     bool m_damageReplyPending;
     QRegion opaque_region;
     xcb_xfixes_fetch_region_cookie_t m_regionCookie;
+    int m_screen;
     // when adding new data members, check also copyToDeleted()
 };
 

unmanaged.cpp

@@ -55,6 +55,7 @@ bool Unmanaged::track(Window w)
     setWindowHandles(w, w);   // the window is also the frame
     XSelectInput(display(), w, attr.your_event_mask | StructureNotifyMask | PropertyChangeMask);
     geom = QRect(attr.x, attr.y, attr.width, attr.height);
+    checkScreen();
     vis = attr.visual;
     bit_depth = attr.depth;
     unsigned long properties[ 2 ];