[Mesa-dev] [Bug 107295] Access violation on glDrawArrays with count >= 2048

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=107295

            Bug ID: 107295
           Summary: Access violation on glDrawArrays with count >= 2048
           Product: Mesa
           Version: 18.0
          Hardware: x86 (IA32)
                OS: Windows (All)
            Status: NEW
          Severity: major
          Priority: medium
         Component: Drivers/Gallium/llvmpipe
          Assignee: mesa-dev at lists.freedesktop.org
          Reporter: paul at binksoftware.nl
        QA Contact: mesa-dev at lists.freedesktop.org

I found this issue first on a 10.x version. The issue still remains in version
18.0.

I use an OpenGL 3.3 Core context and a set of shaders that converts points to
simple flat shaded cones using a geometry shader given the following:

* Position, normal and color as vertex attributes
* Base radius and length as uniforms

The cones are made out of 8 sides (16 triangles total including the base).

Calling glDrawArrays(GL_POINTS, 0, 3000) will cause an access violation in the
DLL (opengl32). All points are stored into a single buffer object described by
a VAO. Further testing shows that the maximum count that will not crash is
2047. Splitting the call works fine, i.e.:

glDrawArrays(GL_POINTS, 0, 1500)
glDrawArrays(GL_POINTS, 1500, 1500)

According to llvmpipe, the maximum recommended vertex count for draw range
elements is 3000 (there's no specific value for just glDrawArrays). This is
just a recommended value, where larger values may only decrease performance,
but it's already crashing way before 3000 is reached.

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