Cocoa: Add drawBackingStoreUsingCoreGraphics

drawRect is a general “repaint now” function, which
we should handle also for OpenGL content. Make that
clearer by moving the implementation details of drawing
the raster backing store using CoreGraphics to a
separate function.

Behavior change: Call invalidateWindowShadowIfNeeded
also for the OpenGL case.

Change-Id: I158ebef548e063f826db2dc708c14ab1d784b095
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@theqtcompany.com>

src/plugins/platforms/cocoa/qnsview.h

@@ -101,6 +101,7 @@ Q_FORWARD_DECLARE_OBJC_CLASS(QT_MANGLE_NAMESPACE(QNSViewMouseMoveHelper));
 - (void)setMaskRegion:(const QRegion *)region;
 - (void)invalidateWindowShadowIfNeeded;
 - (void)drawRect:(NSRect)dirtyRect;
+- (void)drawBackingStoreUsingCoreGraphics:(NSRect)dirtyRect;
 - (void)updateGeometry;
 - (void)notifyWindowStateChanged:(Qt::WindowState)newState;
 - (void)windowNotification : (NSNotification *) windowNotification;

src/plugins/platforms/cocoa/qnsview.mm

@@ -569,6 +569,18 @@ static bool _q_dontOverrideCtrlLMB = false;
     if (m_platformWindow->m_drawContentBorderGradient)
         NSDrawWindowBackground(dirtyRect);
 
+    if (m_backingStore)
+        [self drawBackingStoreUsingCoreGraphics:dirtyRect];
+
+    [self invalidateWindowShadowIfNeeded];
+}
+
+// Draws the backing store content to the QNSView using Core Graphics.
+// This function assumes that the QNSView is in a configuration that
+// supports Core Graphics, such as "classic" mode or layer mode with
+// the default layer.
+- (void)drawBackingStoreUsingCoreGraphics:(NSRect)dirtyRect
+{
     if (!m_backingStore)
         return;
 
@@ -623,8 +635,6 @@ static bool _q_dontOverrideCtrlLMB = false;
     CGImageRelease(cleanImg);
     CGImageRelease(subMask);
     CGImageRelease(bsCGImage);
-
-    [self invalidateWindowShadowIfNeeded];
 }
 
 - (BOOL) isFlipped