kwin/xcbutils.cpp

/*
    KWin - the KDE window manager
    This file is part of the KDE project.

    SPDX-FileCopyrightText: 2006 Lubos Lunak <l.lunak@kde.org>
    SPDX-FileCopyrightText: 2012 Martin Gräßlin <mgraesslin@kde.org>

    SPDX-License-Identifier: GPL-2.0-or-later
*/
#include "xcbutils.h"
#include "utils.h"
// Qt
#include <QDebug>
// xcb
#include <xcb/composite.h>
#include <xcb/damage.h>
#include <xcb/randr.h>
#include <xcb/render.h>
#include <xcb/shape.h>
#include <xcb/sync.h>
#include <xcb/xfixes.h>
#include <xcb/glx.h>
// system
#include <sys/shm.h>
#include <sys/types.h>

namespace KWin {

namespace Xcb {

static const int COMPOSITE_MAX_MAJOR = 0;
static const int COMPOSITE_MAX_MINOR = 4;
static const int DAMAGE_MAX_MAJOR = 1;
static const int DAMAGE_MIN_MAJOR = 1;
static const int SYNC_MAX_MAJOR = 3;
static const int SYNC_MAX_MINOR = 0;
static const int RANDR_MAX_MAJOR = 1;
static const int RANDR_MAX_MINOR = 4;
static const int RENDER_MAX_MAJOR = 0;
static const int RENDER_MAX_MINOR = 11;
static const int XFIXES_MAX_MAJOR = 5;
static const int XFIXES_MAX_MINOR = 0;

QVector<QByteArray> shapeOpCodes()
{
    // see https://www.x.org/releases/X11R7.7/doc/xextproto/shape.html
    // extracted from <xcb/shape.h>
    return QVector<QByteArray>({QByteArrayLiteral("QueryVersion"),
                                QByteArrayLiteral("Rectangles"),
                                QByteArrayLiteral("Mask"),
                                QByteArrayLiteral("Combine"),
                                QByteArrayLiteral("Offset"),
                                QByteArrayLiteral("Extents"),
                                QByteArrayLiteral("Input"),
                                QByteArrayLiteral("InputSelected"),
                                QByteArrayLiteral("GetRectangles")});
}

QVector<QByteArray> randrOpCodes()
{
    // see https://www.x.org/releases/X11R7.7/doc/randrproto/randrproto.txt
    // extracted from <xcb/randr.h>
    return QVector<QByteArray>({QByteArrayLiteral("QueryVersion"),
                                QByteArray(""), // doesn't exist
                                QByteArrayLiteral("SetScreenConfig"),
                                QByteArray(""), // doesn't exits
                                QByteArrayLiteral("SelectInput"),
                                QByteArrayLiteral("GetScreenInfo"),
                                QByteArrayLiteral("GetScreenSizeRange"),
                                QByteArrayLiteral("SetScreenSize"),
                                QByteArrayLiteral("GetScreenResources"),
                                QByteArrayLiteral("GetOutputInfo"),
                                QByteArrayLiteral("ListOutputProperties"),
                                QByteArrayLiteral("QueryOutputProperty"),
                                QByteArrayLiteral("ConfigureOutputProperty"),
                                QByteArrayLiteral("ChangeOutputProperty"),
                                QByteArrayLiteral("DeleteOutputProperty"),
                                QByteArrayLiteral("GetOutputproperty"),
                                QByteArrayLiteral("CreateMode"),
                                QByteArrayLiteral("DestroyMode"),
                                QByteArrayLiteral("AddOutputMode"),
                                QByteArrayLiteral("DeleteOutputMode"),
                                QByteArrayLiteral("GetCrtcInfo"),
                                QByteArrayLiteral("SetCrtcConfig"),
                                QByteArrayLiteral("GetCrtcGammaSize"),
                                QByteArrayLiteral("GetCrtcGamma"),
                                QByteArrayLiteral("SetCrtcGamma"),
                                QByteArrayLiteral("GetScreenResourcesCurrent"),
                                QByteArrayLiteral("SetCrtcTransform"),
                                QByteArrayLiteral("GetCrtcTransform"),
                                QByteArrayLiteral("GetPanning"),
                                QByteArrayLiteral("SetPanning"),
                                QByteArrayLiteral("SetOutputPrimary"),
                                QByteArrayLiteral("GetOutputPrimary"),
                                QByteArrayLiteral("GetProviders"),
                                QByteArrayLiteral("GetProviderInfo"),
                                QByteArrayLiteral("SetProviderOffloadSink"),
                                QByteArrayLiteral("SetProviderOutputSource"),
                                QByteArrayLiteral("ListProviderProperties"),
                                QByteArrayLiteral("QueryProviderProperty"),
                                QByteArrayLiteral("ConfigureProviderroperty"),
                                QByteArrayLiteral("ChangeProviderProperty"),
                                QByteArrayLiteral("DeleteProviderProperty"),
                                QByteArrayLiteral("GetProviderProperty")});
}

QVector<QByteArray> randrErrorCodes()
{
    // see https://www.x.org/releases/X11R7.7/doc/randrproto/randrproto.txt
    // extracted from <xcb/randr.h>
    return QVector<QByteArray>({QByteArrayLiteral("BadOutput"),
                                QByteArrayLiteral("BadCrtc"),
                                QByteArrayLiteral("BadMode"),
                                QByteArrayLiteral("BadProvider")});
}

QVector<QByteArray> damageOpCodes()
{
    // see https://www.x.org/releases/X11R7.7/doc/damageproto/damageproto.txt
    // extracted from <xcb/damage.h>
    return QVector<QByteArray>({QByteArrayLiteral("QueryVersion"),
                                QByteArrayLiteral("Create"),
                                QByteArrayLiteral("Destroy"),
                                QByteArrayLiteral("Subtract"),
                                QByteArrayLiteral("Add")});
}

QVector<QByteArray> damageErrorCodes()
{
    // see https://www.x.org/releases/X11R7.7/doc/damageproto/damageproto.txt
    // extracted from <xcb/damage.h>
    return QVector<QByteArray>({QByteArrayLiteral("BadDamage")});
}

QVector<QByteArray> compositeOpCodes()
{
    // see https://www.x.org/releases/X11R7.7/doc/compositeproto/compositeproto.txt
    // extracted from <xcb/composite.h>
    return QVector<QByteArray>({QByteArrayLiteral("QueryVersion"),
                                QByteArrayLiteral("RedirectWindow"),
                                QByteArrayLiteral("RedirectSubwindows"),
                                QByteArrayLiteral("UnredirectWindow"),
                                QByteArrayLiteral("UnredirectSubwindows"),
                                QByteArrayLiteral("CreateRegionFromBorderClip"),
                                QByteArrayLiteral("NameWindowPixmap"),
                                QByteArrayLiteral("GetOverlayWindow"),
                                QByteArrayLiteral("ReleaseOverlayWindow")});
}

QVector<QByteArray> fixesOpCodes()
{
    // see https://www.x.org/releases/X11R7.7/doc/fixesproto/fixesproto.txt
    // extracted from <xcb/xfixes.h>
    return QVector<QByteArray>({QByteArrayLiteral("QueryVersion"),
                                QByteArrayLiteral("ChangeSaveSet"),
                                QByteArrayLiteral("SelectSelectionInput"),
                                QByteArrayLiteral("SelectCursorInput"),
                                QByteArrayLiteral("GetCursorImage"),
                                QByteArrayLiteral("CreateRegion"),
                                QByteArrayLiteral("CreateRegionFromBitmap"),
                                QByteArrayLiteral("CreateRegionFromWindow"),
                                QByteArrayLiteral("CreateRegionFromGc"),
                                QByteArrayLiteral("CreateRegionFromPicture"),
                                QByteArrayLiteral("DestroyRegion"),
                                QByteArrayLiteral("SetRegion"),
                                QByteArrayLiteral("CopyRegion"),
                                QByteArrayLiteral("UnionRegion"),
                                QByteArrayLiteral("IntersectRegion"),
                                QByteArrayLiteral("SubtractRegion"),
                                QByteArrayLiteral("InvertRegion"),
                                QByteArrayLiteral("TranslateRegion"),
                                QByteArrayLiteral("RegionExtents"),
                                QByteArrayLiteral("FetchRegion"),
                                QByteArrayLiteral("SetGcClipRegion"),
                                QByteArrayLiteral("SetWindowShapeRegion"),
                                QByteArrayLiteral("SetPictureClipRegion"),
                                QByteArrayLiteral("SetCursorName"),
                                QByteArrayLiteral("GetCursorName"),
                                QByteArrayLiteral("GetCursorImageAndName"),
                                QByteArrayLiteral("ChangeCursor"),
                                QByteArrayLiteral("ChangeCursorByName"),
                                QByteArrayLiteral("ExpandRegion"),
                                QByteArrayLiteral("HideCursor"),
                                QByteArrayLiteral("ShowCursor"),
                                QByteArrayLiteral("CreatePointerBarrier"),
                                QByteArrayLiteral("DeletePointerBarrier")});
}

QVector<QByteArray> fixesErrorCodes()
{
    // see https://www.x.org/releases/X11R7.7/doc/fixesproto/fixesproto.txt
    // extracted from <xcb/xfixes.h>
    return QVector<QByteArray>({QByteArrayLiteral("BadRegion")});
}

QVector<QByteArray> renderOpCodes()
{
    // see https://www.x.org/releases/X11R7.7/doc/renderproto/renderproto.txt
    // extracted from <xcb/render.h>
    return QVector<QByteArray>({QByteArrayLiteral("QueryVersion"),
                                QByteArrayLiteral("QueryPictFormats"),
                                QByteArrayLiteral("QueryPictIndexValues"),
                                QByteArrayLiteral("CreatePicture"),
                                QByteArrayLiteral("ChangePicture"),
                                QByteArrayLiteral("SetPictureClipRectangles"),
                                QByteArrayLiteral("FreePicture"),
                                QByteArrayLiteral("Composite"),
                                QByteArrayLiteral("Trapezoids"),
                                QByteArrayLiteral("Triangles"),
                                QByteArrayLiteral("TriStrip"),
                                QByteArrayLiteral("TriFan"),
                                QByteArrayLiteral("CreateGlyphSet"),
                                QByteArrayLiteral("ReferenceGlyphSet"),
                                QByteArrayLiteral("FreeGlyphSet"),
                                QByteArrayLiteral("AddGlyphs"),
                                QByteArrayLiteral("FreeGlyphs"),
                                QByteArrayLiteral("CompositeGlyphs8"),
                                QByteArrayLiteral("CompositeGlyphs16"),
                                QByteArrayLiteral("CompositeGlyphs32"),
                                QByteArrayLiteral("FillRectangles"),
                                QByteArrayLiteral("CreateCursor"),
                                QByteArrayLiteral("SetPictureTransform"),
                                QByteArrayLiteral("QueryFilters"),
                                QByteArrayLiteral("SetPictureFilter"),
                                QByteArrayLiteral("CreateAnimCursor"),
                                QByteArrayLiteral("AddTraps"),
                                QByteArrayLiteral("CreateSolidFill"),
                                QByteArrayLiteral("CreateLinearGradient"),
                                QByteArrayLiteral("CreateRadialGradient"),
                                QByteArrayLiteral("CreateConicalGradient")});
}

QVector<QByteArray> syncOpCodes()
{
    // see https://www.x.org/releases/X11R7.7/doc/xextproto/sync.html
    // extracted from <xcb/sync.h>
    return QVector<QByteArray>({QByteArrayLiteral("Initialize"),
                                QByteArrayLiteral("ListSystemCounters"),
                                QByteArrayLiteral("CreateCounter"),
                                QByteArrayLiteral("DestroyCounter"),
                                QByteArrayLiteral("QueryCounter"),
                                QByteArrayLiteral("Await"),
                                QByteArrayLiteral("ChangeCounter"),
                                QByteArrayLiteral("SetCounter"),
                                QByteArrayLiteral("CreateAlarm"),
                                QByteArrayLiteral("ChangeAlarm"),
                                QByteArrayLiteral("DestroyAlarm"),
                                QByteArrayLiteral("QueryAlarm"),
                                QByteArrayLiteral("SetPriority"),
                                QByteArrayLiteral("GetPriority"),
                                QByteArrayLiteral("CreateFence"),
                                QByteArrayLiteral("TriggerFence"),
                                QByteArrayLiteral("ResetFence"),
                                QByteArrayLiteral("DestroyFence"),
                                QByteArrayLiteral("QueryFence"),
                                QByteArrayLiteral("AwaitFence")});
}

static QVector<QByteArray> glxOpCodes()
{
    return QVector<QByteArray>{
        QByteArrayLiteral(""),
        QByteArrayLiteral("Render"),
        QByteArrayLiteral("RenderLarge"),
        QByteArrayLiteral("CreateContext"),
        QByteArrayLiteral("DestroyContext"),
        QByteArrayLiteral("MakeCurrent"),
        QByteArrayLiteral("IsDirect"),
        QByteArrayLiteral("QueryVersion"),
        QByteArrayLiteral("WaitGL"),
        QByteArrayLiteral("WaitX"),
        QByteArrayLiteral("CopyContext"),
        QByteArrayLiteral("SwapBuffers"),
        QByteArrayLiteral("UseXFont"),
        QByteArrayLiteral("CreateGLXPixmap"),
        QByteArrayLiteral("GetVisualConfigs"),
        QByteArrayLiteral("DestroyGLXPixmap"),
        QByteArrayLiteral("VendorPrivate"),
        QByteArrayLiteral("VendorPrivateWithReply"),
        QByteArrayLiteral("QueryExtensionsString"),
        QByteArrayLiteral("QueryServerString"),
        QByteArrayLiteral("ClientInfo"),
        QByteArrayLiteral("GetFBConfigs"),
        QByteArrayLiteral("CreatePixmap"),
        QByteArrayLiteral("DestroyPixmap"),
        QByteArrayLiteral("CreateNewContext"),
        QByteArrayLiteral("QueryContext"),
        QByteArrayLiteral("MakeContextCurrent"),
        QByteArrayLiteral("CreatePbuffer"),
        QByteArrayLiteral("DestroyPbuffer"),
        QByteArrayLiteral("GetDrawableAttributes"),
        QByteArrayLiteral("ChangeDrawableAttributes"),
        QByteArrayLiteral("CreateWindow"),
        QByteArrayLiteral("DeleteWindow"),
        QByteArrayLiteral("SetClientInfoARB"),
        QByteArrayLiteral("CreateContextAttribsARB"),
        QByteArrayLiteral("SetClientInfo2ARB")
        // Opcodes 36-100 are unused
        // The GL single commands begin at opcode 101
    };
}

static QVector<QByteArray> glxErrorCodes()
{
    return QVector<QByteArray>{
        QByteArrayLiteral("BadContext"),
        QByteArrayLiteral("BadContextState"),
        QByteArrayLiteral("BadDrawable"),
        QByteArrayLiteral("BadPixmap"),
        QByteArrayLiteral("BadContextTag"),
        QByteArrayLiteral("BadCurrentWindow"),
        QByteArrayLiteral("BadRenderRequest"),
        QByteArrayLiteral("BadLargeRequest"),
        QByteArrayLiteral("UnsupportedPrivateRequest"),
        QByteArrayLiteral("BadFBConfig"),
        QByteArrayLiteral("BadPbuffer"),
        QByteArrayLiteral("BadCurrentDrawable"),
        QByteArrayLiteral("BadWindow"),
        QByteArrayLiteral("GLXBadProfileARB")
    };
}

ExtensionData::ExtensionData()
    : version(0)
    , eventBase(0)
    , errorBase(0)
    , majorOpcode(0)
    , present(0)
{
}

template<typename reply, typename T, typename F>
void Extensions::initVersion(T cookie, F f, ExtensionData *dataToFill)
{
    ScopedCPointer<reply> version(f(connection(), cookie, nullptr));
    dataToFill->version = version->major_version * 0x10 + version->minor_version;
}

Extensions *Extensions::s_self = nullptr;

Extensions *Extensions::self()
{
    if (!s_self) {
        s_self = new Extensions();
    }
    return s_self;
}

void Extensions::destroy()
{
    delete s_self;
    s_self = nullptr;
}

Extensions::Extensions()
{
    init();
}

Extensions::~Extensions()
{
}

void Extensions::init()
{
    xcb_connection_t *c = connection();
    xcb_prefetch_extension_data(c, &xcb_shape_id);
    xcb_prefetch_extension_data(c, &xcb_randr_id);
    xcb_prefetch_extension_data(c, &xcb_damage_id);
    xcb_prefetch_extension_data(c, &xcb_composite_id);
    xcb_prefetch_extension_data(c, &xcb_xfixes_id);
    xcb_prefetch_extension_data(c, &xcb_render_id);
    xcb_prefetch_extension_data(c, &xcb_sync_id);
    xcb_prefetch_extension_data(c, &xcb_glx_id);

    m_shape.name     = QByteArray("SHAPE");
    m_randr.name     = QByteArray("RANDR");
    m_damage.name    = QByteArray("DAMAGE");
    m_composite.name = QByteArray("Composite");
    m_fixes.name     = QByteArray("XFIXES");
    m_render.name    = QByteArray("RENDER");
    m_sync.name      = QByteArray("SYNC");
    m_glx.name       = QByteArray("GLX");

    m_shape.opCodes     = shapeOpCodes();
    m_randr.opCodes     = randrOpCodes();
    m_damage.opCodes    = damageOpCodes();
    m_composite.opCodes = compositeOpCodes();
    m_fixes.opCodes     = fixesOpCodes();
    m_render.opCodes    = renderOpCodes();
    m_sync.opCodes      = syncOpCodes();
    m_glx.opCodes       = glxOpCodes();

    m_randr.errorCodes  = randrErrorCodes();
    m_damage.errorCodes = damageErrorCodes();
    m_fixes.errorCodes  = fixesErrorCodes();
    m_glx.errorCodes    = glxErrorCodes();

    extensionQueryReply(xcb_get_extension_data(c, &xcb_shape_id), &m_shape);
    extensionQueryReply(xcb_get_extension_data(c, &xcb_randr_id), &m_randr);
    extensionQueryReply(xcb_get_extension_data(c, &xcb_damage_id), &m_damage);
    extensionQueryReply(xcb_get_extension_data(c, &xcb_composite_id), &m_composite);
    extensionQueryReply(xcb_get_extension_data(c, &xcb_xfixes_id), &m_fixes);
    extensionQueryReply(xcb_get_extension_data(c, &xcb_render_id), &m_render);
    extensionQueryReply(xcb_get_extension_data(c, &xcb_sync_id), &m_sync);
    extensionQueryReply(xcb_get_extension_data(c, &xcb_glx_id), &m_glx);

    // extension specific queries
    xcb_shape_query_version_cookie_t shapeVersion;
    xcb_randr_query_version_cookie_t randrVersion;
    xcb_damage_query_version_cookie_t damageVersion;
    xcb_composite_query_version_cookie_t compositeVersion;
    xcb_xfixes_query_version_cookie_t xfixesVersion;
    xcb_render_query_version_cookie_t renderVersion;
    xcb_sync_initialize_cookie_t syncVersion;
    if (m_shape.present) {
        shapeVersion = xcb_shape_query_version_unchecked(c);
    }
    if (m_randr.present) {
        randrVersion = xcb_randr_query_version_unchecked(c, RANDR_MAX_MAJOR, RANDR_MAX_MINOR);
        xcb_randr_select_input(connection(), rootWindow(), XCB_RANDR_NOTIFY_MASK_SCREEN_CHANGE);
    }
    if (m_damage.present) {
        damageVersion = xcb_damage_query_version_unchecked(c, DAMAGE_MAX_MAJOR, DAMAGE_MIN_MAJOR);
    }
    if (m_composite.present) {
        compositeVersion = xcb_composite_query_version_unchecked(c, COMPOSITE_MAX_MAJOR, COMPOSITE_MAX_MINOR);
    }
    if (m_fixes.present) {
        xfixesVersion = xcb_xfixes_query_version_unchecked(c, XFIXES_MAX_MAJOR, XFIXES_MAX_MINOR);
    }
    if (m_render.present) {
        renderVersion = xcb_render_query_version_unchecked(c, RENDER_MAX_MAJOR, RENDER_MAX_MINOR);
    }
    if (m_sync.present) {
        syncVersion = xcb_sync_initialize(c, SYNC_MAX_MAJOR, SYNC_MAX_MINOR);
    }
    // handle replies
    if (m_shape.present) {
        initVersion<xcb_shape_query_version_reply_t>(shapeVersion, &xcb_shape_query_version_reply, &m_shape);
    }
    if (m_randr.present) {
        initVersion<xcb_randr_query_version_reply_t>(randrVersion, &xcb_randr_query_version_reply, &m_randr);
    }
    if (m_damage.present) {
        initVersion<xcb_damage_query_version_reply_t>(damageVersion, &xcb_damage_query_version_reply, &m_damage);
    }
    if (m_composite.present) {
        initVersion<xcb_composite_query_version_reply_t>(compositeVersion, &xcb_composite_query_version_reply, &m_composite);
    }
    if (m_fixes.present) {
        initVersion<xcb_xfixes_query_version_reply_t>(xfixesVersion, &xcb_xfixes_query_version_reply, &m_fixes);
    }
    if (m_render.present) {
        initVersion<xcb_render_query_version_reply_t>(renderVersion, &xcb_render_query_version_reply, &m_render);
    }
    if (m_sync.present) {
        initVersion<xcb_sync_initialize_reply_t>(syncVersion, &xcb_sync_initialize_reply, &m_sync);
    }
    qCDebug(KWIN_CORE) << "Extensions: shape: 0x" << QString::number(m_shape.version, 16)
                 << " composite: 0x" << QString::number(m_composite.version, 16)
                 << " render: 0x" << QString::number(m_render.version, 16)
                 << " fixes: 0x" << QString::number(m_fixes.version, 16)
                 << " randr: 0x" << QString::number(m_randr.version, 16)
                 << " sync: 0x" << QString::number(m_sync.version, 16)
                 << " damage: 0x " << QString::number(m_damage.version, 16);
}

void Extensions::extensionQueryReply(const xcb_query_extension_reply_t *extension, ExtensionData *dataToFill)
{
    if (!extension) {
        return;
    }
    dataToFill->present = extension->present;
    dataToFill->eventBase = extension->first_event;
    dataToFill->errorBase = extension->first_error;
    dataToFill->majorOpcode = extension->major_opcode;
}

int Extensions::damageNotifyEvent() const
{
    return m_damage.eventBase + XCB_DAMAGE_NOTIFY;
}

bool Extensions::hasShape(xcb_window_t w) const
{
    if (!isShapeAvailable()) {
        return false;
    }
    ScopedCPointer<xcb_shape_query_extents_reply_t> extents(xcb_shape_query_extents_reply(
        connection(), xcb_shape_query_extents_unchecked(connection(), w), nullptr));
    if (extents.isNull()) {
        return false;
    }
    return extents->bounding_shaped > 0;
}

bool Extensions::isCompositeOverlayAvailable() const
{
    return m_composite.version >= 0x03; // 0.3
}

bool Extensions::isFixesRegionAvailable() const
{
    return m_fixes.version >= 0x30; // 3
}

int Extensions::fixesCursorNotifyEvent() const
{
    return m_fixes.eventBase + XCB_XFIXES_CURSOR_NOTIFY;
}

int Extensions::fixesSelectionNotifyEvent() const
{
    return m_fixes.eventBase + XCB_XFIXES_SELECTION_NOTIFY;
}

bool Extensions::isShapeInputAvailable() const
{
    return m_shape.version >= 0x11; // 1.1
}

int Extensions::randrNotifyEvent() const
{
    return m_randr.eventBase + XCB_RANDR_SCREEN_CHANGE_NOTIFY;
}

int Extensions::shapeNotifyEvent() const
{
    return m_shape.eventBase + XCB_SHAPE_NOTIFY;
}

int Extensions::syncAlarmNotifyEvent() const
{
    return m_sync.eventBase + XCB_SYNC_ALARM_NOTIFY;
}

QVector<ExtensionData> Extensions::extensions() const
{
    return {
        m_shape,
        m_randr,
        m_damage,
        m_composite,
        m_render,
        m_fixes,
        m_sync,
        m_glx
    };
}

//****************************************
// Shm
//****************************************
Shm::Shm()
    : m_shmId(-1)
    , m_buffer(nullptr)
    , m_segment(XCB_NONE)
    , m_valid(false)
    , m_pixmapFormat(XCB_IMAGE_FORMAT_XY_BITMAP)
{
    m_valid = init();
}

Shm::~Shm()
{
    if (m_valid) {
        xcb_shm_detach(connection(), m_segment);
        shmdt(m_buffer);
    }
}

bool Shm::init()
{
    const xcb_query_extension_reply_t *ext = xcb_get_extension_data(connection(), &xcb_shm_id);
    if (!ext || !ext->present) {
        qCDebug(KWIN_CORE) << "SHM extension not available";
        return false;
    }
    ScopedCPointer<xcb_shm_query_version_reply_t> version(xcb_shm_query_version_reply(connection(),
        xcb_shm_query_version_unchecked(connection()), nullptr));
    if (version.isNull()) {
        qCDebug(KWIN_CORE) << "Failed to get SHM extension version information";
        return false;
    }
    m_pixmapFormat = version->pixmap_format;
    const int MAXSIZE = 4096 * 2048 * 4; // TODO check there are not larger windows
    m_shmId = shmget(IPC_PRIVATE, MAXSIZE, IPC_CREAT | 0600);
    if (m_shmId < 0) {
        qCDebug(KWIN_CORE) << "Failed to allocate SHM segment";
        return false;
    }
    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, nullptr);
        return false;
    }
    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);
    ScopedCPointer<xcb_generic_error_t> error(xcb_request_check(connection(), cookie));
    if (!error.isNull()) {
        qCDebug(KWIN_CORE) << "xcb_shm_attach error: " << error->error_code;
        shmdt(m_buffer);
        return false;
    }

    return true;
}

} // namespace Xcb
} // namespace KWin