[Bug 109057] texelFetch from GL_TEXTURE_2D_MULTISAMPLE with integer format fails

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=109057

            Bug ID: 109057
           Summary: texelFetch from GL_TEXTURE_2D_MULTISAMPLE with integer
                    format fails
           Product: Mesa
           Version: git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: minor
          Priority: medium
         Component: Drivers/DRI/i965
          Assignee: intel-3d-bugs at lists.freedesktop.org
          Reporter: max.schwarz at online.de
        QA Contact: intel-3d-bugs at lists.freedesktop.org

Created attachment 142804
  --> https://bugs.freedesktop.org/attachment.cgi?id=142804&action=edit
example (needs GLFW and GLEW)

Hi,

I noticed that it seems impossible to read from multisampled textures using
texelFetch() if the texture uses an integral format (like GL_R8UI).

I attached a small test for this, where a GL_TEXTURE_2D_MULTISAMPLE is written
to by a fragment shader, and then read from in another fragment shader.

I'm using a "uint" output in the writing shader, and "usampler2DMS" in the
reading shader - so in my opinion, everything is set up correctly. I haven't
got a lot of experience in the OpenGL world, so there might be something I'm
missing.
The code works on NVidia drivers, though.

Using Mesa (tested on i965 and nouveau), the test fails - we always obtain
zeros from texelFetch().

Most interestingly, it works if I (incorrectly) use GL_R32F as the texture
type, even though the shaders both expect integers.

To compile the sample, use:
g++ -std=c++11 -o intel_multisample intel_multisample.cpp -lglfw -lGL -lGLEW

Then run it:
./intel_multisample GL_R8UI # fails
./intel_multisample GL_R32F # works

My hardware:
00:02.0 VGA compatible controller: Intel Corporation HD Graphics 530 (rev 06)
02:00.0 3D controller: NVIDIA Corporation GM108M [GeForce 940MX] (rev a2)

I'd be glad to help with further debugging if it turns out to be a real bug.

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