xcb: Initialize OpenGL integration only when required

In some cases OpenGL integration may be unnecessary, e.g.
an application may set Qt::AA_ForceRasterWidgets attribute
and don't use OpenGL in any other way. In addition OpenGL
initialization can take noticeable time on some configurations.
So do it on demand only.

Change-Id: If88953f8d5c826bc96fd49eb397b5e1ad693546d
Reviewed-by: Gatis Paeglis <gatis.paeglis@qt.io>

src/plugins/platforms/xcb/qxcbconnection.cpp

@@ -654,34 +654,6 @@ QXcbConnection::QXcbConnection(xcb_connection_t *c, int primaryScreenNumber,
     if (!m_startupId.isNull())
         qunsetenv("DESKTOP_STARTUP_ID");
 
-
-    QStringList glIntegrationNames;
-    glIntegrationNames << QStringLiteral("xcb_glx") << QStringLiteral("xcb_egl");
-    QString glIntegrationName = QString::fromLocal8Bit(qgetenv("QT_XCB_GL_INTEGRATION"));
-    if (!glIntegrationName.isEmpty()) {
-        qCDebug(lcQpaGl) << "QT_XCB_GL_INTEGRATION is set to" << glIntegrationName;
-        if (glIntegrationName != QLatin1String("none")) {
-            glIntegrationNames.removeAll(glIntegrationName);
-            glIntegrationNames.prepend(glIntegrationName);
-        } else {
-            glIntegrationNames.clear();
-        }
-    }
-
-    if (!glIntegrationNames.isEmpty()) {
-        qCDebug(lcQpaGl) << "Choosing xcb gl-integration based on following priority\n" << glIntegrationNames;
-        for (int i = 0; i < glIntegrationNames.size() && !m_glIntegration; i++) {
-            m_glIntegration = QXcbGlIntegrationFactory::create(glIntegrationNames.at(i));
-            if (m_glIntegration && !m_glIntegration->initialize(this)) {
-                qCDebug(lcQpaGl) << "Failed to initialize xcb gl-integration" << glIntegrationNames.at(i);
-                delete m_glIntegration;
-                m_glIntegration = nullptr;
-            }
-        }
-        if (!m_glIntegration)
-            qCDebug(lcQpaGl) << "Failed to create xcb gl-integration";
-    }
-
     sync();
 }
 
@@ -2304,6 +2276,42 @@ Qt::KeyboardModifiers QXcbConnection::queryKeyboardModifiers() const
     return keyboard()->translateModifiers(stateMask);
 }
 
+QXcbGlIntegration *QXcbConnection::glIntegration() const
+{
+    if (m_glIntegrationInitialized)
+        return m_glIntegration;
+
+    QStringList glIntegrationNames;
+    glIntegrationNames << QStringLiteral("xcb_glx") << QStringLiteral("xcb_egl");
+    QString glIntegrationName = QString::fromLocal8Bit(qgetenv("QT_XCB_GL_INTEGRATION"));
+    if (!glIntegrationName.isEmpty()) {
+        qCDebug(lcQpaGl) << "QT_XCB_GL_INTEGRATION is set to" << glIntegrationName;
+        if (glIntegrationName != QLatin1String("none")) {
+            glIntegrationNames.removeAll(glIntegrationName);
+            glIntegrationNames.prepend(glIntegrationName);
+        } else {
+            glIntegrationNames.clear();
+        }
+    }
+
+    if (!glIntegrationNames.isEmpty()) {
+        qCDebug(lcQpaGl) << "Choosing xcb gl-integration based on following priority\n" << glIntegrationNames;
+        for (int i = 0; i < glIntegrationNames.size() && !m_glIntegration; i++) {
+            m_glIntegration = QXcbGlIntegrationFactory::create(glIntegrationNames.at(i));
+            if (m_glIntegration && !m_glIntegration->initialize(const_cast<QXcbConnection *>(this))) {
+                qCDebug(lcQpaGl) << "Failed to initialize xcb gl-integration" << glIntegrationNames.at(i);
+                delete m_glIntegration;
+                m_glIntegration = nullptr;
+            }
+        }
+        if (!m_glIntegration)
+            qCDebug(lcQpaGl) << "Failed to create xcb gl-integration";
+    }
+
+    m_glIntegrationInitialized = true;
+    return m_glIntegration;
+}
+
 bool QXcbConnection::event(QEvent *e)
 {
     if (e->type() == QEvent::User + 1) {

src/plugins/platforms/xcb/qxcbconnection.h

@@ -546,7 +546,7 @@ public:
 
     bool canGrab() const { return m_canGrabServer; }
 
-    QXcbGlIntegration *glIntegration() const { return m_glIntegration; }
+    QXcbGlIntegration *glIntegration() const;
 
 protected:
     bool event(QEvent *e) override;
@@ -727,7 +727,8 @@ private:
     xcb_window_t m_clientLeader = 0;
     QByteArray m_startupId;
     QXcbSystemTrayTracker *m_systemTrayTracker = nullptr;
-    QXcbGlIntegration *m_glIntegration = nullptr;
+    mutable QXcbGlIntegration *m_glIntegration = nullptr;
+    mutable bool m_glIntegrationInitialized = false;
     bool m_xiGrab = false;
     QVector<int> m_xiMasterPointerIds;
 

src/plugins/platforms/xcb/qxcbintegration.cpp

@@ -231,11 +231,11 @@ QPlatformPixmap *QXcbIntegration::createPlatformPixmap(QPlatformPixmap::PixelTyp
 
 QPlatformWindow *QXcbIntegration::createPlatformWindow(QWindow *window) const
 {
-    QXcbScreen *screen = static_cast<QXcbScreen *>(window->screen()->handle());
+    QXcbGlIntegration *glIntegration = nullptr;
-    QXcbGlIntegration *glIntegration = screen->connection()->glIntegration();
     const bool isTrayIconWindow = window->objectName() == QLatin1String("QSystemTrayIconSysWindow");
     if (window->type() != Qt::Desktop && !isTrayIconWindow) {
         if (window->supportsOpenGL()) {
+            glIntegration = defaultConnection()->glIntegration();
             if (glIntegration) {
                 QXcbWindow *xcbWindow = glIntegration->createWindow(window);
                 xcbWindow->create();

src/plugins/platforms/xcb/qxcbwindow.cpp

@@ -397,9 +397,12 @@ void QXcbWindow::create()
                  | XCB_CW_SAVE_UNDER
                  | XCB_CW_EVENT_MASK;
 
-    static const bool haveOpenGL = QGuiApplicationPrivate::platformIntegration()->hasCapability(QPlatformIntegration::OpenGL);
+    static auto haveOpenGL = []() {
+        static const bool result = QGuiApplicationPrivate::platformIntegration()->hasCapability(QPlatformIntegration::OpenGL);
+        return result;
+    };
 
-    if ((window()->supportsOpenGL() && haveOpenGL) || m_format.hasAlpha()) {
+    if ((window()->supportsOpenGL() && haveOpenGL()) || m_format.hasAlpha()) {
         m_cmap = xcb_generate_id(xcb_connection());
         xcb_create_colormap(xcb_connection(),
                             XCB_COLORMAP_ALLOC_NONE,