[Bug 34166] Fullscreen flickering on Mac

https://bugs.winehq.org/show_bug.cgi?id=34166

--- Comment #103 from Ken Thomases  ---
Created attachment 61513
  --> https://bugs.winehq.org/attachment.cgi?id=61513
Patch to add a registry key to force preservation of the OpenGL backing store

We don't want to force the preservation of the backing store all the time,
because it hurts performance for apps which use a double buffer.

The attached patch adds support for a registry key to control whether it's
forced or not (default to not forced).  To test it, apply the patch, build
Wine, and set the following registry key in your prefix:

[HKCU\Software\Wine\Mac Driver]
"ForceOpenGLBackingStore"="y"

If this works for folks, I'm willing to submit it for inclusion in Wine.