I'm using Windows 7.

I suddenly detected that I didn't have to repaint the content of a win32 window when it got obscured, neither by some other window nor when the window got outside the screen. I only had to repainted it when it got resized.

So in principle I only had to repaint on WM_SIZE, not on WM_PAINT. I seemed like Windows 7 kept the window updated anyway.

Then I had to reinstall Windows 7 (due to problems with Explorer probably caused by Parallel Nsight from nVidia). Afterwards this effect was gone. Now when the win32 window is obscured the content becomes messed up and I have to repaint from WM_PAINT.

Is there some setting which makes Windows 7 keep win32 windows automatically updated when obscured so applications don't have to repain them, or was it just a dream?