[Bug 97477] i915g: gl_FragCoord is always (0.0, max_y)

[Bug 97477] i915g: gl_FragCoord is always (0.0, max_y)

[bugzilla-daemon]

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https://bugs.freedesktop.org/show_bug.cgi?id=97477

            Bug ID: 97477
           Summary: i915g: gl_FragCoord is always (0.0, max_y)
           Product: Mesa
           Version: git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/Gallium/i915g
          Assignee: dri-devel@lists.freedesktop.org
          Reporter: nicholasbishop@gmail.com
        QA Contact: dri-devel@lists.freedesktop.org

Created attachment 126029
  --> https://bugs.freedesktop.org/attachment.cgi?id=126029&action=edit
Patch: Handle I915_SEMANTIC_POS when setting texCoords for gl_FragCoord

On Intel Pineview M hardware, the i915 gallium driver doesn't output the
correct gl_FragCoord. It seems to always have an X coord of 0.0 and a Y coord
of the window's height in pixels, e.g. 600.0f or such.

I believe this is a regression caused in part by commit
afa035031ff9e0c07a2297d864e46c76f7bfff58
(https://lists.freedesktop.org/archives/mesa-commit/2016-January/061181.html)

The old behavior used output zero, while the new behavior uses actual zeroes.
In the case of gl_FragCoord output zero happened to be the correct one.

I've attached a patch that seems to fix the issue for me. I ran the piglit
"quick" tests and observed 17 new tests passing, and one regression. I suspect
the regression is unimportant since it involves derivatives that aren't
implemented for this driver anyway:

"fs-dfdy-accuracy" test failed ... in i915_fpc_translate.c:
case TGSI_OPCODE_DDY:
      /* XXX We just output 0 here */
      debug_printf("Punting DDX/DDX\n");

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[Bug 97477] i915g: gl_FragCoord is always (0.0, max_y)

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https://bugs.freedesktop.org/show_bug.cgi?id=97477

--- Comment #1 from Nicholas Bishop <nicholasbishop@gmail.com> ---
Posted the patch to the mailing list with a somewhat clearer commit message:
https://lists.freedesktop.org/archives/mesa-dev/2016-August/127065.html

FWIW, the process of submitting a patch via the mailing list is a really big
barrier to entry for someone new to the project.

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[Bug 97477] i915g: gl_FragCoord is always (0.0, max_y)

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https://bugs.freedesktop.org/show_bug.cgi?id=97477

GitLab Migration User <gitlab-migration@fdo.invalid> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |MOVED
             Status|NEW                         |RESOLVED

--- Comment #2 from GitLab Migration User <gitlab-migration@fdo.invalid> ---
-- GitLab Migration Automatic Message --

This bug has been migrated to freedesktop.org's GitLab instance and has been
closed from further activity.

You can subscribe and participate further through the new bug through this link
to our GitLab instance: https://gitlab.freedesktop.org/mesa/mesa/issues/668.

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