[Bug 15232] Button in simple OpenGL application gets overdrawn

http://bugs.winehq.org/show_bug.cgi?id=15232

--- Comment #9 from Henri Verbeet   2010-04-06 11:07:58 ---
I don't know if there are issues with the basic approach of using a clipmask,
but I can't think of any. As for the specific implementation, it forces gl_copy
for cases where it isn't needed, and recalculates the clipmask on every
SwapBuffers() call. Both aren't going to help performance. The gl_copy path
should be limited to the cases where there are actual child windows to clip by,
and updating the clip mask should only happen when those child windows are
created / destroyed / moved / etc.