[Mesa-dev] [Bug 96853] gl_PrimitiveID is zero when rendering points of size > 1

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Thu Jul 7 21:10:12 UTC 2016


https://bugs.freedesktop.org/show_bug.cgi?id=96853

            Bug ID: 96853
           Summary: gl_PrimitiveID is zero when rendering points of size >
                    1
           Product: Mesa
           Version: git
          Hardware: Other
                OS: Linux (All)
            Status: NEW
          Severity: major
          Priority: medium
         Component: Mesa core
          Assignee: mesa-dev at lists.freedesktop.org
          Reporter: denis.fisseler at tu-dortmund.de
        QA Contact: mesa-dev at lists.freedesktop.org

Using Mesa3d 12.1.0-devel with Ubuntu 16.04 LTS in VMware, I stumbled upon a
bug regarding the contents of gl_PrimitiveID in the fragment shader.
I am using gl_PrimitiveID for color generation. When rendering a VAO as
GL_POINTS and the point size set by glPointSize() is larger than 1,
gl_PrimitiveID constantly had a value of 0. As soon as the point size is
reduced to 1 or the type on primitive is changed to GL_TRIANGLES,
gl_PrimitiveID contains correct values. For rasterized points, the value of
gl_PrimitiveID in the fragment shader should equal the value of a
variable(declared using "flat") set to gl_VertexID in the vertex shader. Using
this workaround i was able to produce the desired values.

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