the 2 screenshots show the correct result and wrong result.
problem seems to be that, some part of the screen is not updated, but reverse to older buffered image. when i rotate the camera, part of image is jumping back and forth. the size of unupdated part is not constant.
my app has the machanism that the main scene is rendered into texture then blit the texture on screen. if this is on. AA works correctly. if the scene is rendered directly on screen. AA causes problem.
it is also related to my cloud effect. if the clouds are not drawn, no problem. the clouds are drawn with several passes at different time points and there are some gl state changes, it's quite complicated.