Added private API for enabling sharing between the QQuickwindow instances.

This API is primarily a hook which is needed by the Qt WebEngine to
set up sharing with the scene graph's OpenGL contexts.

Change-Id: I5bb03abd9ab99f502db8e413fe838a8b30365b8d
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>

src/quick/scenegraph/qsgcontext.cpp

@@ -117,8 +117,12 @@ public:
     QSGContext::AntialiasingMethod antialiasingMethod;
     bool distanceFieldDisabled;
     QSGDistanceFieldGlyphNode::AntialiasingMode distanceFieldAntialiasing;
+
+    static QOpenGLContext *sharedOpenGLContext;
 };
 
+QOpenGLContext *QSGContextPrivate::sharedOpenGLContext = 0;
+
 class QSGTextureCleanupEvent : public QEvent
 {
 public:
@@ -170,6 +174,20 @@ QSGContext::~QSGContext()
 {
 }
 
+/*!
+ * This function is used by the Qt WebEngine to set up context sharing
+ * across multiple windows. Do not use it for any other purpose.
+ */
+void QSGContext::setSharedOpenGLContext(QOpenGLContext *context)
+{
+    QSGContextPrivate::sharedOpenGLContext = context;
+}
+
+QOpenGLContext *QSGContext::sharedOpenGLContext()
+{
+    return QSGContextPrivate::sharedOpenGLContext;
+}
+
 void QSGContext::renderContextInitialized(QSGRenderContext *renderContext)
 {
     Q_D(QSGContext);

src/quick/scenegraph/qsgcontext_p.h

@@ -162,6 +162,9 @@ public:
     virtual QSize minimumFBOSize() const;
     virtual QSurfaceFormat defaultSurfaceFormat() const;
 
+    static void setSharedOpenGLContext(QOpenGLContext *context);
+    static QOpenGLContext *sharedOpenGLContext();
+
     void setDistanceFieldEnabled(bool enabled);
     bool isDistanceFieldEnabled() const;
 

src/quick/scenegraph/qsgrenderloop.cpp

@@ -264,6 +264,8 @@ void QSGGuiThreadRenderLoop::renderWindow(QQuickWindow *window)
     if (!gl) {
         gl = new QOpenGLContext();
         gl->setFormat(window->requestedFormat());
+        if (QSGContext::sharedOpenGLContext())
+            gl->setShareContext(QSGContext::sharedOpenGLContext());
         if (!gl->create()) {
             delete gl;
             gl = 0;

src/quick/scenegraph/qsgthreadedrenderloop.cpp

@@ -889,6 +889,8 @@ void QSGThreadedRenderLoop::handleExposure(Window *w)
 
         if (!w->thread->gl) {
             w->thread->gl = new QOpenGLContext();
+            if (QSGContext::sharedOpenGLContext())
+                w->thread->gl->setShareContext(QSGContext::sharedOpenGLContext());
             w->thread->gl->setFormat(w->window->requestedFormat());
             if (!w->thread->gl->create()) {
                 delete w->thread->gl;

src/quick/scenegraph/qsgwindowsrenderloop.cpp

@@ -178,6 +178,8 @@ void QSGWindowsRenderLoop::show(QQuickWindow *window)
         RLDEBUG(" - creating GL context");
         m_gl = new QOpenGLContext();
         m_gl->setFormat(window->requestedFormat());
+        if (QSGContext::sharedOpenGLContext())
+            m_gl->setShareContext(QSGContext::sharedOpenGLContext());
         m_gl->create();
         QSG_RENDER_TIMING_SAMPLE(time_created);
         RLDEBUG(" - making current");

tests/auto/quick/scenegraph/tst_scenegraph.cpp

@@ -42,8 +42,8 @@
 #include <qtest.h>
 
 #include <QtQuick>
-#include <private/qquickanimator_p.h>
 
+#include <private/qsgcontext_p.h>
 
 
 #include <QtQml>
@@ -99,9 +99,13 @@ bool containsSomethingOtherThanWhite(const QImage &image)
     return false;
 }
 
-// To compare images, we need a special function with a bit of error
-// as glyphs has an invisible, but measurable variance depending
-// on where in the glyph cache they end up.
+// When running on native Nvidia graphics cards on linux, the
+// distance field glyph pixels have a measurable, but not visible
+// pixel error. Use a custom compare function to avoid
+//
+// This was GT-216 with the ubuntu "nvidia-319" driver package.
+// llvmpipe does not show the same issue.
+//
 bool compareImages(const QImage &ia, const QImage &ib)
 {
     if (ia.size() != ib.size())
@@ -137,21 +141,44 @@ void tst_SceneGraph::manyWindows_data()
 {
     QTest::addColumn<QString>("file");
     QTest::addColumn<bool>("toplevel");
+    QTest::addColumn<bool>("shared");
 
-    QTest::newRow("image,toplevel") << QStringLiteral("manyWindows_image.qml") << true;
-    QTest::newRow("image,subwindow") << QStringLiteral("manyWindows_image.qml") << false;
-    QTest::newRow("dftext,toplevel") << QStringLiteral("manyWindows_dftext.qml") << true;
-    QTest::newRow("dftext,subwindow") << QStringLiteral("manyWindows_dftext.qml") << false;
-    QTest::newRow("ntext,toplevel") << QStringLiteral("manyWindows_ntext.qml") << true;
-    QTest::newRow("ntext,subwindow") << QStringLiteral("manyWindows_ntext.qml") << false;
-    QTest::newRow("rects,toplevel") << QStringLiteral("manyWindows_rects.qml") << true;
-    QTest::newRow("rects,subwindow") << QStringLiteral("manyWindows_rects.qml") << false;
+    QTest::newRow("image,toplevel") << QStringLiteral("manyWindows_image.qml") << true << false;
+    QTest::newRow("image,subwindow") << QStringLiteral("manyWindows_image.qml") << false << false;
+    QTest::newRow("dftext,toplevel") << QStringLiteral("manyWindows_dftext.qml") << true << false;
+    QTest::newRow("dftext,subwindow") << QStringLiteral("manyWindows_dftext.qml") << false << false;
+    QTest::newRow("ntext,toplevel") << QStringLiteral("manyWindows_ntext.qml") << true << false;
+    QTest::newRow("ntext,subwindow") << QStringLiteral("manyWindows_ntext.qml") << false << false;
+    QTest::newRow("rects,toplevel") << QStringLiteral("manyWindows_rects.qml") << true << false;
+    QTest::newRow("rects,subwindow") << QStringLiteral("manyWindows_rects.qml") << false << false;
+
+    QTest::newRow("image,toplevel,sharing") << QStringLiteral("manyWindows_image.qml") << true << true;
+    QTest::newRow("image,subwindow,sharing") << QStringLiteral("manyWindows_image.qml") << false << true;
+    QTest::newRow("dftext,toplevel,sharing") << QStringLiteral("manyWindows_dftext.qml") << true << true;
+    QTest::newRow("dftext,subwindow,sharing") << QStringLiteral("manyWindows_dftext.qml") << false << true;
+    QTest::newRow("ntext,toplevel,sharing") << QStringLiteral("manyWindows_ntext.qml") << true << true;
+    QTest::newRow("ntext,subwindow,sharing") << QStringLiteral("manyWindows_ntext.qml") << false << true;
+    QTest::newRow("rects,toplevel,sharing") << QStringLiteral("manyWindows_rects.qml") << true << true;
+    QTest::newRow("rects,subwindow,sharing") << QStringLiteral("manyWindows_rects.qml") << false << true;
 }
 
+struct ShareContextResetter {
+public:
+    ~ShareContextResetter() { QSGContext::setSharedOpenGLContext(0); }
+};
+
 void tst_SceneGraph::manyWindows()
 {
     QFETCH(QString, file);
     QFETCH(bool, toplevel);
+    QFETCH(bool, shared);
+
+    QOpenGLContext sharedGLContext;
+    ShareContextResetter cleanup; // To avoid dangling pointer in case of test-failure.
+    if (shared) {
+        sharedGLContext.create();
+        QSGContext::setSharedOpenGLContext(&sharedGLContext);
+    }
 
     QScopedPointer<QWindow> parent;
     if (!toplevel) {