You should get two rects. First one is for your app and the second one is for the tray. The second one is a bit tricky since taskbar can be positioned on all 4 sides of the screen. I'll try to find a code that does this...

Then:

1. Hide your main window
2. call BOOL WINAPI DrawAnimatedRects(HWND hwnd, int idAni, CONST RECT *lprcFrom, CONST RECT *lprcTo);