This seems to fix the flicker

examples/cube_qt.py

@@ -25,7 +25,7 @@
 from rendercanvas.utils.cube import setup_drawing_sync
 
 
-canvas = RenderCanvas(title=f"The wgpu cube example on {lib}", update_mode="continuous")
+canvas = RenderCanvas(title=f"The wgpu cube example on {lib}", update_mode="fastest", present_method='screen')
 draw_frame = setup_drawing_sync(canvas)
 canvas.request_draw(draw_frame)
 

rendercanvas/qt.py

@@ -327,7 +327,8 @@ def _get_surface_ids(self):
 
     def paintEngine(self):  # noqa: N802 - this is a Qt method
         # https://doc.qt.io/qt-5/qt.html#WidgetAttribute-enum  WA_PaintOnScreen
-        if self._present_to_screen:
+        print(f"paintEngine called, _present_to_screen is {self._present_to_screen} ")
+        if self._present_to_screen or self._present_to_screen is None:
             return None
         else:
             return super().paintEngine()
@@ -366,6 +367,8 @@ def _rc_get_present_info(self, present_methods):
         if the_method == "screen":
             surface_ids = self._get_surface_ids()
             if surface_ids:
+                # Now is a good time to set WA_PaintOnScreen. Note that it implies WA_NativeWindow.
+                self.setAttribute(WA_PaintOnScreen, True)
                 self._present_to_screen = True
                 return {"method": "screen", **surface_ids}
             elif "bitmap" in present_methods:

rendercanvas/utils/cube.py

@@ -14,7 +14,7 @@
 
 
 def setup_drawing_sync(
-    canvas, power_preference="high-performance", limits=None, format=None
+    canvas, power_preference="low-power", limits=None, format=None
 ) -> Callable[[], None]:
     """Setup to draw a rotating cube on the given canvas.