Add an option to share between TLWs

Task-number: QTBUG-41191
Change-Id: I510d1631926ed0d9e371703d22229aed92432aa6
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>

src/corelib/global/qnamespace.h

@@ -527,6 +527,7 @@ public:
         AA_UseDesktopOpenGL = 15,
         AA_UseOpenGLES = 16,
         AA_UseSoftwareOpenGL = 17,
+        AA_ShareOpenGLContexts = 18,
 
         // Add new attributes before this line
         AA_AttributeCount

src/corelib/global/qnamespace.qdoc

@@ -188,6 +188,11 @@
            instance \l{Qt for Windows}, for more information.  This value has
            been added in Qt 5.4.
 
+    \value AA_ShareOpenGLContexts Enables resource sharing between the OpenGL
+           contexts used by classes like QOpenGLWidget and QQuickWidget. This
+           allows sharing OpenGL resources, like textures, between QOpenGLWidget
+           instances that belong to different top-level windows.
+
     The following values are obsolete:
 
     \value AA_ImmediateWidgetCreation This attribute is no longer fully

src/gui/kernel/qguiapplication.cpp

@@ -82,6 +82,7 @@
 #include <qpa/qwindowsysteminterface_p.h>
 #include "private/qwindow_p.h"
 #include "private/qcursor_p.h"
+#include "private/qopenglcontext_p.h"
 
 #include "private/qdnd_p.h"
 #include <qpa/qplatformthemefactory_p.h>
@@ -604,7 +605,8 @@ QGuiApplicationPrivate::QGuiApplicationPrivate(int &argc, char **argv, int flags
     : QCoreApplicationPrivate(argc, argv, flags),
       styleHints(0),
       inputMethod(0),
-      lastTouchType(QEvent::TouchEnd)
+      lastTouchType(QEvent::TouchEnd),
+      ownGlobalShareContext(false)
 {
     self = this;
     application_type = QCoreApplicationPrivate::Gui;
@@ -1313,6 +1315,17 @@ void QGuiApplicationPrivate::init()
     // trigger registering of animation interpolators
     qRegisterGuiGetInterpolator();
 
+    // 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;
@@ -1374,6 +1387,13 @@ QGuiApplicationPrivate::~QGuiApplicationPrivate()
 
     QPixmapCache::clear();
 
+#ifndef QT_NO_OPENGL
+    if (ownGlobalShareContext) {
+        delete qt_gl_global_share_context();
+        qt_gl_set_global_share_context(0);
+    }
+#endif
+
     delete platform_theme;
     platform_theme = 0;
     delete platform_integration;

src/gui/kernel/qguiapplication_p.h

@@ -307,6 +307,8 @@ private:
     static QTouchDevice *m_fakeTouchDevice;
     static int m_fakeMouseSourcePointId;
     QAtomicPointer<QDrawHelperGammaTables> m_gammaTables;
+
+    bool ownGlobalShareContext;
 };
 
 Q_GUI_EXPORT uint qHash(const QGuiApplicationPrivate::ActiveTouchPointsKey &k);

src/gui/kernel/qopenglcontext.cpp

@@ -245,8 +245,9 @@ QMutex QOpenGLContextPrivate::makeCurrentTrackerMutex;
 /*!
     \internal
 
-    This function is used by the Qt WebEngine to set up context sharing
-    across multiple windows. Do not use it for any other purpose.
+    This function is used by Qt::AA_ShareOpenGLContexts and the Qt
+    WebEngine to set up context sharing across multiple windows. Do
+    not use it for any other purpose.
 
     Please maintain the binary compatibility of these functions.
 */

src/widgets/kernel/qopenglwidget.cpp

@@ -297,6 +297,18 @@ QT_BEGIN_NAMESPACE
   sharable resources, like textures, and there is no need for an extra "global
   share" context, as was the case with QGLWidget.
 
+  To set up sharing between QOpenGLWidget instances belonging to different
+  windows, set the Qt::AA_ShareOpenGLContexts application attribute before
+  instantiating QApplication. This will trigger sharing between all
+  QOpenGLWidget instances without any further steps.
+
+  Creating extra QOpenGLContext instances that share resources like textures
+  with the QOpenGLWidget's context is also possible. Simply pass the pointer
+  returned from context() to QOpenGLContext::setShareContext() before calling
+  QOpenGLContext::create(). The resulting context can also be used on a
+  different thread, allowing threaded generation of textures and asynchronous
+  texture uploads.
+
   Note that QOpenGLWidget expects a standard conformant implementation of
   resource sharing when it comes to the underlying graphics drivers. For
   example, some drivers, in particular for mobile and embedded hardware, have
@@ -359,11 +371,12 @@ QT_BEGIN_NAMESPACE
   each QOpenGLWidget's associated context is destroyed together with the
   QOpenGLWidget, the sharable resources in that context, like textures, will
   stay valid until the top-level window, in which the QOpenGLWidget lived, is
-  destroyed. Additionally, some Qt modules may trigger an even wider scope for
-  sharing contexts, potentially leading to keeping the resources in question
-  alive for the entire lifetime of the application. Therefore the safest and
-  most robust is always to perform explicit cleanup for all resources and
-  resource wrappers used in the QOpenGLWidget.
+  destroyed. Additionally, settings like Qt::AA_ShareOpenGLContexts and some Qt
+  modules may trigger an even wider scope for sharing contexts, potentially
+  leading to keeping the resources in question alive for the entire lifetime of
+  the application. Therefore the safest and most robust is always to perform
+  explicit cleanup for all resources and resource wrappers used in the
+  QOpenGLWidget.
 
   \section1 Limitations
 
@@ -388,7 +401,7 @@ QT_BEGIN_NAMESPACE
   \e{OpenGL is a trademark of Silicon Graphics, Inc. in the United States and other
   countries.}
 
-  \sa QOpenGLFunctions, QOpenGLWindow
+  \sa QOpenGLFunctions, QOpenGLWindow, Qt::AA_ShareOpenGLContexts
 */
 
 /*!

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

@@ -53,6 +53,8 @@
 #include <QOpenGLContext>
 #endif
 
+#include <QtGui/private/qopenglcontext_p.h>
+
 #include <QDebug>
 
 #include "tst_qcoreapplication.h"
@@ -79,6 +81,7 @@ private slots:
     void quitOnLastWindowClosed();
     void genericPluginsAndWindowSystemEvents();
     void layoutDirection();
+    void globalShareContext();
 };
 
 void tst_QGuiApplication::cleanup()
@@ -915,4 +918,28 @@ void tst_QGuiApplication::layoutDirection()
     QCOMPARE(signalSpy.count(), 1);
 }
 
+void tst_QGuiApplication::globalShareContext()
+{
+#ifndef QT_NO_OPENGL
+    // Test that there is a global share context when requested.
+    QCoreApplication::setAttribute(Qt::AA_ShareOpenGLContexts);
+    int argc = 1;
+    char *argv[] = { const_cast<char*>("tst_qguiapplication") };
+    QScopedPointer<QGuiApplication> app(new QGuiApplication(argc, argv));
+    QOpenGLContext *ctx = qt_gl_global_share_context();
+    QVERIFY(ctx);
+    app.reset();
+    ctx = qt_gl_global_share_context();
+    QVERIFY(!ctx);
+
+    // 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();
+    QVERIFY(!ctx);
+#else
+    QSKIP("No OpenGL support");
+#endif
+}
+
 QTEST_APPLESS_MAIN(tst_QGuiApplication)