http://bugs.winehq.org/show_bug.cgi?id=11203
--- Comment #41 from Henri Verbeet hverbeet@gmail.com 2009-08-16 12:23:30 --- (In reply to comment #34)
The reason why games usually check for 32 bpp is:
*) Because they're stupid and don't know what they're doing *) OpenGL and D3D can use the 8 fill bytes for backbuffer alpha, allowing additional blend modes. There are better ways to check for support for that, so it comes down to "games are stupid" again.
Not entirely. Having 32bpp screen depth also implies alpha channel support for DIBs and DDBs. Current winex11.drv doesn't always handle that correctly, but Roderick's XRender patches might eventually fix that.