[iOS] Why empty QOpenGLWidget update/repaint() uses about 20%-50% cpu?

[vitaliynet]

I am guessing that this is the cause of your problem. You should not have to call update(), repaint(), or anything else in a mouse event. Qt takes care of whatever needs to be done in response to mouse move events to keep the window updated.

Thanks for response. but sorry I'm unclear. If I'll insert some code to draw for example simple rectangle (0, 0, mouse_y, 100). Then Nothing happens if I NOT call update(); Please note that I use iOS/Android devices, not the windows in MacOS/Windows OS.

But ok... Let's not use mouse. Even with a QTimer for 100-200 ms (i.e. if I call update() each 100ms). I see 30-40% cpu load and GPU 70-80% load. On the iOS with a basic 4000 CALayers and changing their frame/bounds at the same time - I see just 5-7% cpu load and gpu load is about 0-1%. I tried Juce framework, but they have 60-70% cpu and very very critical GPU load. about 80-90%. Again I'm asking only about iPad/iPhone. Not tested a lot android.