Lazily create global share context when Qt::AA_ShareOpenGLContexts is set

The requirement to set Qt::AA_ShareOpenGLContexts before creating QGuiApp
was forcing users to also set the default surface format before QGuiApp,
which prevents us from initializing a default surface format based on
the platform integration.

By creating the global share context lazily when requested via the
Qt::AA_ShareOpenGLContext application attribute we open up this
possibility.

Change-Id: I958639c997e96321013b1080c31e2533a36c13ff
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

src/corelib/kernel/qcoreapplication.cpp

@@ -1013,7 +1013,6 @@ void QCoreApplication::setAttribute(Qt::ApplicationAttribute attribute, bool on)
             case Qt::AA_UseDesktopOpenGL:
             case Qt::AA_UseOpenGLES:
             case Qt::AA_UseSoftwareOpenGL:
-            case Qt::AA_ShareOpenGLContexts:
 #ifdef QT_BOOTSTRAPPED
                 qWarning("Attribute %d must be set before QCoreApplication is created.",
                          attribute);

src/gui/kernel/qguiapplication.cpp

@@ -727,8 +727,7 @@ QGuiApplication::~QGuiApplication()
 QGuiApplicationPrivate::QGuiApplicationPrivate(int &argc, char **argv)
     : QCoreApplicationPrivate(argc, argv),
       inputMethod(nullptr),
-      lastTouchType(QEvent::TouchEnd),
+      lastTouchType(QEvent::TouchEnd)
-      ownGlobalShareContext(false)
 {
     self = this;
     application_type = QCoreApplicationPrivate::Gui;
@@ -1740,17 +1739,6 @@ void Q_TRACE_INSTRUMENT(qtgui) QGuiApplicationPrivate::init()
     qRegisterGuiGetInterpolator();
 #endif
 
-    // set a global share context when enabled unless there is already one
-#ifndef QT_NO_OPENGL
-    if (qApp->testAttribute(Qt::AA_ShareOpenGLContexts) && !qt_gl_global_share_context()) {
-        QOpenGLContext *ctx = new QOpenGLContext;
-        ctx->setFormat(QSurfaceFormat::defaultFormat());
-        ctx->create();
-        qt_gl_set_global_share_context(ctx);
-        ownGlobalShareContext = true;
-    }
-#endif
-
     QWindowSystemInterfacePrivate::eventTime.start();
 
     is_app_running = true;

src/gui/kernel/qguiapplication_p.h

@@ -342,6 +342,10 @@ public:
 
     static QThreadPool *qtGuiThreadPool();
 
+#ifndef QT_NO_OPENGL
+    bool ownGlobalShareContext = false;
+#endif
+
 protected:
     virtual void handleThemeChanged();
 
@@ -366,8 +370,6 @@ private:
 #endif
     std::shared_ptr<QColorTrcLut> m_a32ColorProfile;
 
-    bool ownGlobalShareContext;
-
     static QInputDeviceManager *m_inputDeviceManager;
 
     // Cache the maximum device pixel ratio, to iterate through the screen list

src/gui/kernel/qopenglcontext.cpp

@@ -959,10 +959,6 @@ bool QOpenGLContext::supportsThreadedOpenGL()
     This is useful if you need to upload OpenGL objects (buffers, textures,
     etc.) before creating or showing a QOpenGLWidget or QQuickWidget.
 
-    \note You must set the Qt::AA_ShareOpenGLContexts flag on QGuiApplication
-    before creating the QGuiApplication object, otherwise Qt may not create a
-    global shared context.
-
     \warning Do not attempt to make the context returned by this function
     current on any surface. Instead, you can create a new context which shares
     with the global one, and then make the new context current.
@@ -972,6 +968,14 @@ bool QOpenGLContext::supportsThreadedOpenGL()
 QOpenGLContext *QOpenGLContext::globalShareContext()
 {
     Q_ASSERT(qGuiApp);
+    // Lazily create a global share context when enabled unless there is already one
+    if (!qt_gl_global_share_context() && qGuiApp->testAttribute(Qt::AA_ShareOpenGLContexts)) {
+        QOpenGLContext *ctx = new QOpenGLContext;
+        ctx->setFormat(QSurfaceFormat::defaultFormat());
+        ctx->create();
+        qt_gl_set_global_share_context(ctx);
+        QGuiApplicationPrivate::instance()->ownGlobalShareContext = true;
+    }
     return qt_gl_global_share_context();
 }
 

src/gui/kernel/qsurfaceformat.cpp

@@ -9,6 +9,10 @@
 #include <QtGui/qcolorspace.h>
 #include <QtGui/qguiapplication.h>
 
+#ifndef QT_NO_OPENGL
+#include <QtGui/private/qopenglcontext_p.h>
+#endif
+
 #ifdef major
 #undef major
 #endif
@@ -807,12 +811,6 @@ Q_GLOBAL_STATIC(QSurfaceFormat, qt_default_surface_format)
     and surfaces, even the ones created internally by Qt, will use the same
     format.
 
-    \note When setting Qt::AA_ShareOpenGLContexts, it is strongly recommended to
-    place the call to this function before the construction of the
-    QGuiApplication or QApplication. Otherwise \a format will not be applied to
-    the global share context and therefore issues may arise with context sharing
-    afterwards.
-
     \since 5.4
     \sa defaultFormat()
  */
@@ -820,7 +818,7 @@ void QSurfaceFormat::setDefaultFormat(const QSurfaceFormat &format)
 {
 #ifndef QT_NO_OPENGL
     if (qApp) {
-        QOpenGLContext *globalContext = QOpenGLContext::globalShareContext();
+        QOpenGLContext *globalContext = qt_gl_global_share_context();
         if (globalContext && globalContext->isValid()) {
             qWarning("Warning: Setting a new default format with a different version or profile "
                      "after the global shared context is created may cause issues with context "

src/gui/painting/qbackingstorerhisupport.cpp

@@ -74,7 +74,7 @@ bool QBackingStoreRhiSupport::create()
         params.fallbackSurface = surface;
         params.window = m_window;
         params.format = m_format;
-        params.shareContext = qt_gl_global_share_context();
+        params.shareContext = QOpenGLContext::globalShareContext();
         rhi = QRhi::create(QRhi::OpenGLES2, &params, flags);
     }
 #endif

src/gui/rhi/qrhigles2.cpp

@@ -771,7 +771,7 @@ bool QRhiGles2::create(QRhi::Flags flags)
         if (maybeShareContext) {
             ctx->setShareContext(maybeShareContext);
             ctx->setScreen(maybeShareContext->screen());
-        } else if (QOpenGLContext *shareContext = qt_gl_global_share_context()) {
+        } else if (QOpenGLContext *shareContext = QOpenGLContext::globalShareContext()) {
             ctx->setShareContext(shareContext);
             ctx->setScreen(shareContext->screen());
         } else if (maybeWindow) {

src/opengl/qopenglwindow.cpp

@@ -161,7 +161,7 @@ public:
         , shareContext(shareContext)
     {
         if (!shareContext)
-            this->shareContext = qt_gl_global_share_context();
+            this->shareContext = QOpenGLContext::globalShareContext();
     }
 
     ~QOpenGLWindowPrivate();

src/openglwidgets/qopenglwidget.cpp

@@ -856,7 +856,7 @@ void QOpenGLWidgetPrivate::initialize()
     context = new QOpenGLContext;
     context->setFormat(requestedFormat);
 
-    QOpenGLContext *shareContext = contextFromRhi ? contextFromRhi : qt_gl_global_share_context();
+    QOpenGLContext *shareContext = contextFromRhi ? contextFromRhi : QOpenGLContext::globalShareContext();
     if (shareContext) {
         context->setShareContext(shareContext);
         context->setScreen(shareContext->screen());

src/plugins/platforms/eglfs/api/qeglfswindow.cpp

@@ -108,14 +108,14 @@ void QEglFSWindow::setBackingStore(QOpenGLCompositorBackingStore *backingStore)
 #ifndef QT_NO_OPENGL
     if (!m_rasterCompositingContext) {
         m_rasterCompositingContext = new QOpenGLContext;
-        m_rasterCompositingContext->setShareContext(qt_gl_global_share_context());
+        m_rasterCompositingContext->setShareContext(QOpenGLContext::globalShareContext());
         m_rasterCompositingContext->setFormat(m_format);
         m_rasterCompositingContext->setScreen(window()->screen());
         if (Q_UNLIKELY(!m_rasterCompositingContext->create()))
             qFatal("EGLFS: Failed to create compositing context");
         // If there is a "root" window into which raster and QOpenGLWidget content is
         // composited, all other contexts must share with its context.
-        if (!qt_gl_global_share_context())
+        if (!QOpenGLContext::globalShareContext())
             qt_gl_set_global_share_context(m_rasterCompositingContext);
     }
     QOpenGLCompositor *compositor = QOpenGLCompositor::instance();
@@ -145,7 +145,7 @@ void QEglFSWindow::destroy()
 
         if (compositor->windows().isEmpty()) {
             compositor->destroy();
-            if (qt_gl_global_share_context() == m_rasterCompositingContext)
+            if (QOpenGLContext::globalShareContext() == m_rasterCompositingContext)
                 qt_gl_set_global_share_context(nullptr);
             delete m_rasterCompositingContext;
         } else {

tests/auto/gui/kernel/qguiapplication/tst_qguiapplication.cpp

@@ -1273,7 +1273,7 @@ void tst_QGuiApplication::globalShareContext()
     int argc = 1;
     char *argv[] = { const_cast<char*>("tst_qguiapplication") };
     QScopedPointer<QGuiApplication> app(new QGuiApplication(argc, argv));
-    QOpenGLContext *ctx = qt_gl_global_share_context();
+    QOpenGLContext *ctx = QOpenGLContext::globalShareContext();
     QVERIFY(ctx);
     app.reset();
     ctx = qt_gl_global_share_context();
@@ -1282,8 +1282,16 @@ void tst_QGuiApplication::globalShareContext()
     // Test that there is no global share context by default.
     QCoreApplication::setAttribute(Qt::AA_ShareOpenGLContexts, false);
     app.reset(new QGuiApplication(argc, argv));
-    ctx = qt_gl_global_share_context();
+    ctx = QOpenGLContext::globalShareContext();
     QVERIFY(!ctx);
+
+    // Test that setting AA_ShareOpenGLContexts can happen after creating
+    // QGuiApplication.
+    app.reset();
+    app.reset(new QGuiApplication(argc, argv));
+    QCoreApplication::setAttribute(Qt::AA_ShareOpenGLContexts, true);
+    ctx = QOpenGLContext::globalShareContext();
+    QVERIFY(ctx);
 #else
     QSKIP("No OpenGL support");
 #endif