From Roni Zanolli,Added use of Qt's new devicePixelRatio() method to assist with handling the upscalling of resolution on iPhone for "retina" displays.

From Robert Osfield, changed Roni's code to use a #define GETDEVICEPIXELRATIO to access the versioned Qt devicePixelRatio() method to avoid duplication of the Qt version checking.

include/osgQt/GraphicsWindowQt

@@ -109,6 +109,7 @@ protected:
     QSet<QEvent::Type> _eventCompressor;
 
     bool _forwardKeyEvents;
+    qreal _devicePixelRatio;
 
     virtual void resizeEvent( QResizeEvent* event );
     virtual void moveEvent( QMoveEvent* event );