[Bug 90839] [10.5.5/10.6 regression, bisected] PBO glDrawPixels no longer using blit fastpath

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=90839

            Bug ID: 90839
           Summary: [10.5.5/10.6 regression, bisected] PBO glDrawPixels no
                    longer using blit fastpath
           Product: Mesa
           Version: unspecified
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/DRI/i965
          Assignee: idr at freedesktop.org
          Reporter: amonakov at gmail.com
        QA Contact: intel-3d-bugs at lists.freedesktop.org

Starting from commit
http://cgit.freedesktop.org/mesa/mesa/commit/?id=536003c11e4cb1172c540932ce3cce06f03bf44e
(i965: Add XRGB8888 format to intel_screen_make_configs), PBO-based
glDrawPixels may be unable to use the blitter "fast path" (apparently if the
application happens to get an XRGB window fbconfig).  It is rejected in
do_blit_drawpixels, because _mesa_format_matches_format_and_type returns false
for BGRX formats.  INTEL_DEBUG=perf,pix says:

do_blit_drawpixels
do_blit_drawpixels: bad format for blit
intelDrawPixels: fallback to generic code in PBO case

A repro is available at https://bugs.freedesktop.org/attachment.cgi?id=97258
(run as "./a.out 1000").

A possible workaround on the glx client side is to explicitely request
"GLX_ALPHA_BITS, 1" in the fbconfig, but is that really expected now?

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