[Bug 45901] New: Avoid GPU synchronization due to GPU-CPU transfer ( Overwatch)

https://bugs.winehq.org/show_bug.cgi?id=45901

Bug ID: 45901
           Summary: Avoid GPU synchronization due to GPU-CPU transfer
                    (Overwatch)
           Product: Wine
           Version: unspecified
          Hardware: x86-64
                OS: Linux
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: directx-d3d
          Assignee: [e-mail]
          Reporter: [e-mail]
      Distribution: ---

Created attachment 62422
  --> https://bugs.winehq.org/attachment.cgi?id=62422
Patch to avoid GPU synchronization

One performance gap with Overwatch on Wine + AMD + Mesa is GPU synchronization
due to transfers from GPU texture to CPU texture. By using PBOs and
glReadPixels with GL_PIXEL_PACK_BUFFER, we can avoid this synchronization
leading to improved performance.

The attached patch is one approach to resolve the performance issue, but I am
not sure that it is the best way. Feedback is appreciated.

Also attached is before and after screenshots with Mesa's HUD. You can observe
that the buffer wait time decreases with the patched version. Both the before
and after screenshots are on wine-staging master plus my patch for 45723.