[Bug 71760] New: [GLSL] Transformation of vertex position looks incorrect

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=71760

          Priority: medium
            Bug ID: 71760
          Assignee: idr at freedesktop.org
           Summary: [GLSL] Transformation of vertex position looks
                    incorrect
        QA Contact: intel-3d-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: Linux (All)
          Reporter: vluchits at gmail.com
          Hardware: x86-64 (AMD64)
            Status: NEW
           Version: 9.2
         Component: glsl-compiler
           Product: Mesa

Created attachment 89432
  --> https://bugs.freedesktop.org/attachment.cgi?id=89432&action=edit
test case

Hello,

I'm the lead programmer of game "Warsow" - an open source first person shooter.
We just tried running development version of the game with open source AMD
drivers shipped with Ubuntu 13.10 and custom-installed 3.12 Linux kernel. While
the performance was better than we had expected, there were a few visual
glitches.

In the game we use the so called "hardware skinning" for skeletal models to
transform vertex coordinates by the influencing bones on the GPU. The
transformation code is pretty complex and involves quaternion maths and
accessing uniform arrays by index read from vertex attribute.

Despite the fact that vertex shader compiles successfully, the end result looks
quite a bit off, meaning that sometimes meshes look deformed in unexpected
directions. Unfortunately I can't take a screenshot to demonstrate the bug
right now, but I managed to cook a somewhat minimal version of the shader. You
will find the aforementioned transformation code in function
QF_VertexDualQuatsTransform.

If you need to access our repository to be able to reproduce and observe the
bug, just let me know.

Best regards,
Victor

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