Prevent double draw when alt-tabbing from fullscreen applications

[FrigoCoder]

We first construct our form, and only then switch from the fullscreen application to our form. This triggers a resolution change, which causes our form to be redrawn. Find a way to prevent this double draw.

[FrigoCoder]

I managed to solve the issue. Instead of trying to detect fullscreen applications, I simply send an inactivation message to the foreground application, which triggers an early resolution change:

SendMessage(GetForegroundWindow(), WM_ACTIVATEAPP, false, GetCurrentThreadId());

This exact same message is also sent during application switches, so I essentially emulate one before it actually happens. I have not encountered any side effects yet.

Mind you however, that this does not solve DWM issues. Windows 7 automatically disables DWM composition for compatibility launches, or when it detects direct access to the primary display surface. It does not allow you to re-enable, and I do not see an easy solution to this problem. Thankfully this issue will eventually go away since DWM composition is always enabled in Windows 8 and newer.

[FrigoCoder]

Issue arises again after changing SendMessage to PostMessage so we do not wait for the foreground window.