https://bugs.winehq.org/show_bug.cgi?id=45277
--- Comment #16 from Roderick Colenbrander thunderbird2k@gmail.com --- (In reply to Ken Thomases from comment #15)
There's another possibility: change the X11 driver back to using actual X11 child windows for the Win32 child windows. Then, child window rendering for OpenGL and Vulkan just falls out for free. This is what the Mac driver does.
I believe that handling of clipping with siblings and parent windows (for GDI drawing, not necessarily OpenGL/D3D) was the reason that the X11 driver switched away from X11 child windows in the first place. But that was before client side rendering via the DIB engine. With that, it may be OK to switch back. On the other hand, I may not have the full story there.
That would be interesting, but I thought the issue had to do with X11 events confusing win32 applications. I mean events the applications were not expecting.