This patch also fixes CPU-based rendering via LIBGL_ALWAYS_SOFTWARE that otherwise renders blackscreen: https://bugs.winehq.org/show_bug.cgi?id=45364#c23 I tried to test cpu_blit cases but unable to successfully force it by simply commenting out other blitters for `device_gl_create_primary_opengl_context_cs` because it seems to break things. CPU-based rendering with backbuffers > 1 seems very edge case but wanted to test all cases (LIBGL_ALWAYS_SOFTWARE is as slow as watching grass grow). Please let me know if there are older CPU-based rendering games/cases that this MR may impact. So far patches still seems to fix more than break. Thanks to @alesliehughes it is now part of staging for even wider testing. -- https://gitlab.winehq.org/wine/wine/-/merge_requests/10567#note_141802