1 files changed, 15 insertions, 0 deletions
diff --git a/src/plugins/platforms/cocoa/qcocoawindow.mm b/src/plugins/platforms/cocoa/qcocoawindow.mm
index af44564968..d1f19f2de9 100644
--- a/src/plugins/platforms/cocoa/qcocoawindow.mm
+++ b/src/plugins/platforms/cocoa/qcocoawindow.mm
@@ -1442,6 +1442,21 @@ QCocoaNSWindow *QCocoaWindow::createNSWindow(bool shouldBePanel)
 
     applyContentBorderThickness(nsWindow);
 
+    // Prevent CoreGraphics RGB32 -> RGB64 backing store conversions on deep color
+    // displays by forcing 8-bit components, unless a deep color format has been
+    // requested. This conversion uses significant CPU time.
+    QSurface::SurfaceType surfaceType = QPlatformWindow::window()->surfaceType();
+    bool usesCoreGraphics = surfaceType == QSurface::RasterSurface || surfaceType == QSurface::RasterGLSurface;
+    QSurfaceFormat surfaceFormat = QPlatformWindow::window()->format();
+    bool usesDeepColor = surfaceFormat.redBufferSize() > 8 ||
+                         surfaceFormat.greenBufferSize() > 8 ||
+                         surfaceFormat.blueBufferSize() > 8;
+    bool usesLayer = view().layer;
+    if (usesCoreGraphics && !usesDeepColor && !usesLayer) {
+        [nsWindow setDynamicDepthLimit:NO];
+        [nsWindow setDepthLimit:NSWindowDepthTwentyfourBitRGB];
+    }
+
     return nsWindow;
 }