Fixes wrong QPaintEvent::region() in QGLWidget::paintEvent.

QGLWidget does not support partial updates unless the context is
single buffered and auto-fill background is disabled. The problem
was that QPaintEvent::region() returned the requested update region
without taking into account the limitation of QGLWidget. If QGLWidget
doesn't support partial updates, it means everything has to be updated,
and QPaintEvent::region() must return the whole widget rect.

Auto test included.

Task-number: 241785
Reviewed-by: Trond

3 files changed, 11 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())