Prevent QPainter buffer swap

As the QGraphicsScene overlay does not work for all cards/drivers we disable the possible buffer swap of the qpainter, as this could be a potential source of the flickering. If the painter swaps buffers and we do it again the user will see first the correct picture (first swap) and then something uninitalized (second swap)

src/Gui/Quarter/QuarterWidget.cpp

@@ -126,6 +126,16 @@ using namespace SIM::Coin3D::Quarter;
 #ifndef GL_MULTISAMPLE_BIT_EXT
 #define GL_MULTISAMPLE_BIT_EXT 0x20000000
 #endif
+
+//We need to avoid buffer swaping when initializing a QPainter on this widget
+class QUARTER_DLL_API CustomGLWidget : public QGLWidget {
+public:
+    CustomGLWidget(const QGLFormat& fo, QWidget* parent = 0, const QGLWidget* shareWidget = 0, Qt::WindowFlags f = 0)
+     : QGLWidget(fo, parent, shareWidget, f) {
+
+         setAutoBufferSwap(false);
+     };    
+};
 
 /*! constructor */
 QuarterWidget::QuarterWidget(const QGLFormat & format, QWidget * parent, const QGLWidget * sharewidget, Qt::WindowFlags f)
@@ -153,7 +163,7 @@ QuarterWidget::constructor(const QGLFormat & format, const QGLWidget * sharewidg
 {
   QGraphicsScene* scene = new QGraphicsScene;
   setScene(scene);
-  setViewport(new QGLWidget(format, this, sharewidget)); 
+  setViewport(new CustomGLWidget(format, this, sharewidget)); 
 
   setFrameStyle(QFrame::NoFrame);
   setAutoFillBackground(false);
@@ -720,12 +730,8 @@ void QuarterWidget::paintEvent(QPaintEvent* event)
     //start the standard graphics view processing for all widgets and graphic items. As 
     //QGraphicsView initaliizes a QPainter which changes the Opengl context in an unpredictable 
     //manner we need to store the context and recreate it after Qt is done.
-    glPushAttrib(GL_ALL_ATTRIB_BITS);
     glPushAttrib(GL_MULTISAMPLE_BIT_EXT);
-
     inherited::paintEvent(event);
-
-    glPopAttrib();
     glPopAttrib();
 
     if (w->doubleBuffer()) { w->swapBuffers(); }