[Mesa-dev] [Bug 94280] Regression related to mesa/readpix

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=94280

            Bug ID: 94280
           Summary: Regression related to mesa/readpix
           Product: Mesa
           Version: git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Mesa core
          Assignee: mesa-dev at lists.freedesktop.org
          Reporter: kennethmorrismartin at gmail.com
        QA Contact: mesa-dev at lists.freedesktop.org

It appears there was a regression related to recent changes in mesa/readpix. It
could be that the changes exposed something bad in our code, but it works
everywhere else so ...

Specifically it happened with 

Last week this test started failing on hythloth's nightly Mesa builds
(along with a few other tests):

* OpenGL2: https://open.cdash.org/viewTest.php?onlyfailed&buildid=4229706
           https://open.cdash.org/testDetails.php?test=418931875&build=4229706

* OpenGL1: https://open.cdash.org/viewTest.php?onlyfailed&buildid=4230126
           https://open.cdash.org/testDetails.php?test=418952240&build=4230126

For now I've checked out a mesa that still works and stopped updating.

The problem bisects to:

 mesa/readpix: Clip ReadPixels() area to the ReadBuffer's

https://cgit.freedesktop.org/mesa/mesa/commit/?id=605832736a6d9427ad894d403cceeb74a5b18dc1

and still occurs after some related follow-up changes to Mesa:

 mesa/readpix: Don't clip in _mesa_readpixels()

https://cgit.freedesktop.org/mesa/mesa/commit/?id=b89a8a15c240418d1859947b5114993ecdf424fb

 mesa/readpix: Dedent former _mesa_readpixels() if block

https://cgit.freedesktop.org/mesa/mesa/commit/?id=c624241ef47c3a6ea2d1177969328bd4547e45a2

Valgrind reports that vtkImageDifference encounters uninitialized memory
after the change to Mesa but not before.  That looks consistent with the
messy corner of the test image seen in the above links.  Mesa is no longer
populating the full image with data.

I'll post an apitrace file run with an old mesa that hopefully will show the
problem for you should you not want to build VTK yourself.

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