Improve raster graphics system performance on Mac (second try).

This fixes the qmlviewer "sluggish animations and lost
mouse events" issue by making sure we don't block and
wait for for the screen refresh when flushing the
backing store to the screen.

NB: This commit fixes build issues found in f5f62c0bed.

Review: msorvig

Details:

- Don't force repaints, flush the backingstore in response
  to a Cocoa paint/display events only.
- Flush once per window.
- Get the CGContext from the window (don't create a new one)
- Don't call CGContextiFlush on the context.

1 files changed, 1 insertions, 3 deletions

diff --git a/src/gui/painting/qwindowsurface_raster.cpp b/src/gui/painting/qwindowsurface_raster.cpp
index a0d2b9bd3a..eee6befe87 100644
--- a/src/gui/painting/qwindowsurface_raster.cpp
+++ b/src/gui/painting/qwindowsurface_raster.cpp
@@ -295,10 +295,8 @@ void QRasterWindowSurface::flush(QWidget *widget, const QRegion &rgn, const QPoi
     CGContextRestoreGState(context);
 #ifndef QT_MAC_USE_COCOA
     QDEndCGContext(port, &context);
-#else
-    CGContextFlush(context);
-#endif
 #endif
+#endif // Q_WS_MAC
 
 #ifdef Q_OS_SYMBIAN
     Q_UNUSED(widget);