Performance fix for OpenGL drawing

Excessive calling of glFlush() was causing a performance problem when
QML application was being run in the OpenGL graphics mode. There was an
unnecessary call to glFlush() in the function
QGLWindowSurfaceGLPaintDevice::endPaint(). This function gets called
each time a QPainter instance is destroyed, which may happen several
times per each painted screen frame (at least 4 times per frame can
easily happen). Calling glFlush() from endPaint() is not necessary at
all since it will be anyway called from QGLWindowSurface::flush()
(either directly if single-buffered context is used or indirectly by
swapping buffers if double-buffered context is used).

Task-number: ou1cimx1#957423
Change-Id: I89509d8935ad31cc47bfed41a1900b6bb76c2af8
Reviewed-by: Gunnar Sletta <[email protected]>
Reviewed-by: Pasi Pentikäinen <[email protected]>
(cherry picked from commit a56ff23)

Author: Pauli Jarvinen

src/opengl/qwindowsurface_gl.cpp

@@ -321,12 +321,6 @@ struct QGLWindowSurfacePrivate
 QGLFormat QGLWindowSurface::surfaceFormat;
 QGLWindowSurface::SwapMode QGLWindowSurface::swapBehavior = QGLWindowSurface::AutomaticSwap;
 
-void QGLWindowSurfaceGLPaintDevice::endPaint()
-{
-    glFlush();
-    QGLPaintDevice::endPaint();
-}
-
 QSize QGLWindowSurfaceGLPaintDevice::size() const
 {
     return d->size;

src/opengl/qwindowsurface_gl_p.h

@@ -74,7 +74,6 @@ class QGLWindowSurfaceGLPaintDevice : public QGLPaintDevice
 {
 public:
     QPaintEngine* paintEngine() const;
-    void endPaint();
     QSize size() const;
     int metric(PaintDeviceMetric m) const;
     QGLContext* context() const;