I have drawn QGraphicsItem in scene, and these QGraphicsItem have children(QGraphicsRectItem) above it as well.

My program provides the mouse action to resize or move the child items. During mouse dragging, if I drag the right-side edge of the rect to left side, which makes the rect invalid (minus width), the paiting of the rect starts blinking. It paints only during mouse-move, which means, if I stop moving the mouse but pressing the mouse, it will not show up. But if I release mouse, it shows correctly. This problem only happends in FullScreen mode, in normal window mode, no such problem.

I guess this comes from the zvalue of items. I set the parent zvalue: normal mode 2.0, Fullscreen mode 1.0. Child item is always 2.5.
To my knowledge, this makes sure the child item will be above the parent item, then I can easily grasp it. But I don't know what happens for the paiting in fullscreen mode.

Any one can give me a hint? Thanks.