[Bug 79685] New: Varying passed from gs->fs corrupted if not first similar draw.

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=79685

          Priority: medium
            Bug ID: 79685
          Assignee: idr at freedesktop.org
           Summary: Varying passed from gs->fs corrupted if not first
                    similar draw.
        QA Contact: intel-3d-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: Linux (All)
          Reporter: david at ingeniumdigital.com
          Hardware: x86-64 (AMD64)
            Status: NEW
           Version: 10.1
         Component: Drivers/DRI/i965
           Product: Mesa

This is a strange one.

I've got a bunch of simple objects being rendered (rectangles and ellipses),
using different gs+fs, but the same vs. One of the gs+fs pairs passes a vec2
varying from the gs->fs. If this object is the first (nonempty) drawcall in the
frame, it renders correctly as a circle (the varying being "texture
coordinates" as it were). If another gs+fs combination runs first, the varying
is not passed through correctly.

Example apitrace: http://davidgow.net/stuff/gs-fs-var.trace.bz2
- At call #180, we should see an ellipse, but see a rectangle.
  http://davidgow.net/stuff/gs-fs-var-bad.png
- If we change the glUseProgram in call #175 to use program 13, we see the
ellipse at call #180.
  http://davidgow.net/stuff/gs-fs-var-good.png

The source for program 13 is located here:
http://davidgow.net/stuff/gs-fs-var.glsldump

This code correctly displays the ellipse on both the nvidia and fglrx drivers,
but fails on both Mesa 10.1 (Ubuntu 14.04) and Mesa git (2211696-) IVB.

Am I doing anything obviously wrong?

Thanks,
— David

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