5 files changed, 76 insertions, 2 deletions

diff --git a/src/gui/kernel/qwidget.cpp b/src/gui/kernel/qwidget.cpp
index eb2e9f7..f612601 100644
--- a/src/gui/kernel/qwidget.cpp
+++ b/src/gui/kernel/qwidget.cpp
@@ -183,6 +183,7 @@ QWidgetPrivate::QWidgetPrivate(int version) :
         ,inDirtyList(0)
         ,isScrolled(0)
         ,isMoved(0)
+        ,usesDoubleBufferedGLContext(0)
 #ifdef Q_WS_WIN
         ,noPaintOnScreen(0)
 #endif
diff --git a/src/gui/kernel/qwidget_p.h b/src/gui/kernel/qwidget_p.h
index 423e833..db78682 100644
--- a/src/gui/kernel/qwidget_p.h
+++ b/src/gui/kernel/qwidget_p.h
@@ -536,6 +536,7 @@ public:
     uint inDirtyList : 1;
     uint isScrolled : 1;
     uint isMoved : 1;
+    uint usesDoubleBufferedGLContext : 1;
 
 #ifdef Q_WS_WIN
     uint noPaintOnScreen : 1; // see qwidget_win.cpp ::paintEngine()
diff --git a/src/gui/painting/qbackingstore.cpp b/src/gui/painting/qbackingstore.cpp
index fbac811a..34df6c9 100644
--- a/src/gui/painting/qbackingstore.cpp
+++ b/src/gui/painting/qbackingstore.cpp
@@ -1517,13 +1517,20 @@ void QWidgetPrivate::repaint_sys(const QRegion &rgn)
         extra->staticContentsSize = data.crect.size();
     }
 
+    QPaintEngine *engine = q->paintEngine();
+    // QGLWidget does not support partial updates if:
+    // 1) The context is double buffered
+    // 2) The context is single buffered and auto-fill background is enabled.
+    const bool noPartialUpdateSupport = (engine && engine->type() == QPaintEngine::OpenGL)
+                                        && (usesDoubleBufferedGLContext || q->autoFillBackground());
+    QRegion toBePainted(noPartialUpdateSupport ? q->rect() : rgn);
+
 #ifdef Q_WS_MAC
     // No difference between update() and repaint() on the Mac.
-    update_sys(rgn);
+    update_sys(toBePainted);
     return;
 #endif
 
-    QRegion toBePainted(rgn);
     toBePainted &= clipRect();
     clipToEffectiveMask(toBePainted);
     if (toBePainted.isEmpty())
diff --git a/src/opengl/qgl.cpp b/src/opengl/qgl.cpp
index b4a0e5c..8ffee87 100644
--- a/src/opengl/qgl.cpp
+++ b/src/opengl/qgl.cpp
@@ -2398,6 +2398,10 @@ bool QGLContext::create(const QGLContext* shareContext)
         return false;
     reset();
     d->valid = chooseContext(shareContext);
+    if (d->valid && d->paintDevice->devType() == QInternal::Widget) {
+        QWidgetPrivate *wd = qt_widget_private(static_cast<QWidget *>(d->paintDevice));
+        wd->usesDoubleBufferedGLContext = d->glFormat.doubleBuffer();
+    }
     if (d->sharing)  // ok, we managed to share
         qgl_share_reg()->addShare(this, shareContext);
     return d->valid;
diff --git a/tests/auto/qgl/tst_qgl.cpp b/tests/auto/qgl/tst_qgl.cpp
index a64dfc4..f982e6d 100644
--- a/tests/auto/qgl/tst_qgl.cpp
+++ b/tests/auto/qgl/tst_qgl.cpp
@@ -66,6 +66,8 @@ private slots:
     void getSetCheck();
     void openGLVersionCheck();
     void graphicsViewClipping();
+    void partialGLWidgetUpdates_data();
+    void partialGLWidgetUpdates();
 };
 
 tst_QGL::tst_QGL()
@@ -404,5 +406,64 @@ void tst_QGL::graphicsViewClipping()
 #endif
 }
 
+void tst_QGL::partialGLWidgetUpdates_data()
+{
+    QTest::addColumn<bool>("doubleBufferedContext");
+    QTest::addColumn<bool>("autoFillBackground");
+    QTest::addColumn<bool>("supportsPartialUpdates");
+
+    QTest::newRow("Double buffered context") << true << true << false;
+    QTest::newRow("Double buffered context without auto-fill background") << true << false << false;
+    QTest::newRow("Single buffered context") << false << true << false;
+    QTest::newRow("Single buffered context without auto-fill background") << false << false << true;
+}
+
+void tst_QGL::partialGLWidgetUpdates()
+{
+#ifdef QT_NO_OPENGL
+    QSKIP("QGL not yet supported", SkipAll);
+#else
+    if (!QGLFormat::hasOpenGL())
+        QSKIP("QGL not supported on this platform", SkipAll);
+
+    QFETCH(bool, doubleBufferedContext);
+    QFETCH(bool, autoFillBackground);
+    QFETCH(bool, supportsPartialUpdates);
+
+    class MyGLWidget : public QGLWidget
+    {
+        public:
+            QRegion paintEventRegion;
+            void paintEvent(QPaintEvent *e)
+            {
+                paintEventRegion = e->region();
+            }
+    };
+
+    QGLFormat format = QGLFormat::defaultFormat();
+    format.setDoubleBuffer(doubleBufferedContext);
+    QGLFormat::setDefaultFormat(format);
+
+    MyGLWidget widget;
+    widget.setFixedSize(150, 150);
+    widget.setAutoFillBackground(autoFillBackground);
+    widget.show();
+#ifdef Q_WS_X11
+    qt_x11_wait_for_window_manager(&widget);
+#endif
+    QTest::qWait(200);
+
+    if (widget.format().doubleBuffer() != doubleBufferedContext)
+        QSKIP("Platform does not support requested format", SkipAll);
+
+    widget.paintEventRegion = QRegion();
+    widget.repaint(50, 50, 50, 50);
+    if (supportsPartialUpdates)
+        QCOMPARE(widget.paintEventRegion, QRegion(50, 50, 50, 50));
+    else
+        QCOMPARE(widget.paintEventRegion, QRegion(widget.rect()));
+#endif
+}
+
 QTEST_MAIN(tst_QGL)
 #include "tst_qgl.moc"