Some clients such as QOpenGLWidget will end up drawing and flushing during the resize event, which for GL will result in an immediate update on the screen. The problem is that the underlying Core Animation layer, and the window's frame, has not been visually updated yet to the new size, so we end up drawing "ahead" of what the window server is showing the user. Ideally we'd be able to present the GL drawing in a transaction, in sync with the drawing of the window frame, but this API is only available for CAMetalLayer and CAEAGLLayer. As a workaround we detect when the exposed size is out of sync with the window geometry, and skip the flush until the exposed size has caught up. We know this will happen eventually as AppKit will always ask us to display after a resize. Change-Id: I1739ac8878b3fc6820a55dd017ddd170fd5f55d6 Fixes: QTBUG-79139 Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>