[NV305.67] compute shader texture sampling reads zero

[Ambator]

Hi there,

I stumbled upon this bug(?) a couple of times by now:
1. create a texture, make it immutable
2. upload data from cpu to the texture
3. bind texture to some texture unit (not image unit - actually, I haven't tested that)
4. run compute shader
-> read some data from that texture
Result: read is always 0.
If I use the same texture in some program in an old compute shader fashion (quad; vertex/fragment shader), it works.
If - between step 2 and 4 - the texture is read by some fragment shader, the compute program IS able to read data from the texture.

Some more hints about my application (although it shouldn't matter)
- I have a small OpenGL library, which wraps most of the OpenGL "objects"... so no code here.
- I use DSA (I just like OOP thinking)
- Am I correct that the 305.67 is still the only driver supporting OpenGL 4.3? I tried the others and (although the nvidia page partially says differently) they do not give me an 4.3 context (card: 560ti).

Best

Update:
I just tried the new driver 306.63 and it behaves the same .
Furthermore I ran into an example, where even the trick with first using the texture in a fragment shader does not help, the compute shader always reads 0. I tried the "same" shader as a fragment shader with framebuffers etc. and it there it works as expected.

[randall]

I have also noticed this issue. I am sure that this is a driver bug.

[Piers Daniell]

I was not able to reproduce a problem with the code pasted below. Could you provide some code that reproduces the issue. Are you sampling the texture with texture() or texelFetch()?

int main(int argc, char const * argv[])
{
    GLuint cs = glCreateShader(GL_COMPUTE_SHADER);
    GLchar const * css[] = {
        "#version 430 core\n"
        "\n"
        "layout(local_size_x=16, local_size_y=16) in;\n"
        "\n"
        "uniform usampler2D tex;\n"
        "layout(binding = 0) buffer Output {\n"
        "    uint output[16][16];\n"
        "};\n"
        "\n"
        "void main()\n"
        "{\n"
        "    uint x = gl_LocalInvocationID.x;\n"
        "    uint y = gl_LocalInvocationID.y;\n"
        "    output[y][x] = texelFetch(tex, ivec2(x, y), 0).x;\n"
        "}\n"
    };
    glShaderSource(cs, PDK_ARRAY_SIZE(css), css, 0);
    glCompileShader(cs);
 
 
    GLuint pgm = glCreateProgram();
    glAttachShader(pgm, cs);
    glLinkProgram(pgm);
    glUseProgram(pgm);
 
 
    GLuint tex;
    glGenTextures(1, &tex);
    glBindTexture(GL_TEXTURE_2D, tex);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexStorage2D(GL_TEXTURE_2D, 1, GL_R32UI, 16, 16);
    GLuint texels[16][16] = { 0 };
    for (int height = 0; height < 16; ++height) {
        for (int width = 0; width < 16; ++width) {
            texels[height][width] = width + height * 16;
        }
    }
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
    glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 16, 16, GL_RED_INTEGER, GL_UNSIGNED_INT, texels);
 
 
    GLuint ssbo;
    glGenBuffers(1, &ssbo);
    glBindBuffer(GL_SHADER_STORAGE_BUFFER, ssbo);
    GLuint output[16][16] = { 0 };
    glBufferData(GL_SHADER_STORAGE_BUFFER, sizeof output, output, GL_STREAM_DRAW);
    glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, ssbo);
 
 
    glDispatchCompute(1, 1, 1);
    glGetBufferSubData(GL_SHADER_STORAGE_BUFFER, 0, sizeof output, output);
 
 
    if (memcmp(output, texels, sizeof output)) {
        printf("ERROR: texture read failed\n");
        return EXIT_FAILURE;
    }
 
 
    return EXIT_SUCCESS;
}

[randall]

I have tried various sampling functions (texture, texelFetch and others). My code is similar but:
- uses glTexImage2D instead of glTexStorage2D
- uses GL_RGBA32F as an internalformat

[Piers Daniell]

I modified my repro app as pasted below, using GL_RGBA32F and glTexImage2D, but I was still unable to reproduce a problem. Does my app work for you? What GPU are you using?

typedef GLfloat vec4[4];
 
 
int main(int argc, char const * argv[])
{
    GLuint cs = glCreateShader(GL_COMPUTE_SHADER);
    GLchar const * css[] = {
        "#version 430 core\n"
        "\n"
        "layout(local_size_x=16, local_size_y=16) in;\n"
        "\n"
        "uniform sampler2D tex;\n"
        "layout(binding = 0) buffer Output {\n"
        "    vec4 output[16][16];\n"
        "};\n"
        "\n"
        "void main()\n"
        "{\n"
        "    uint x = gl_LocalInvocationID.x;\n"
        "    uint y = gl_LocalInvocationID.y;\n"
        "    output[y][x] = texelFetch(tex, ivec2(x, y), 0);\n"
        "}\n"
    };
    glShaderSource(cs, PDK_ARRAY_SIZE(css), css, 0);
    glCompileShader(cs);
 
 
    GLuint pgm = glCreateProgram();
    glAttachShader(pgm, cs);
    glLinkProgram(pgm);
    glUseProgram(pgm);
 
 
    GLuint tex;
    glGenTextures(1, &tex);
    glBindTexture(GL_TEXTURE_2D, tex);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    vec4 texels[16][16] = { 0 };
    for (int height = 0; height < 16; ++height) {
        for (int width = 0; width < 16; ++width) {
            texels[height][width][0] = float(width + height * 16) / 256.0f;
            texels[height][width][1] = float(width + height * 16) / 256.0f;
            texels[height][width][2] = float(width + height * 16) / 256.0f;
            texels[height][width][3] = float(width + height * 16) / 256.0f;
        }
    }
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA32F, 16, 16, 0, GL_RGBA, GL_FLOAT, texels);
 
 
    GLuint ssbo;
    glGenBuffers(1, &ssbo);
    glBindBuffer(GL_SHADER_STORAGE_BUFFER, ssbo);
    vec4 output[16][16] = { 0 };
    glBufferData(GL_SHADER_STORAGE_BUFFER, sizeof output, output, GL_STREAM_DRAW);
    glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, ssbo);
 
 
    glDispatchCompute(1, 1, 1);
    glGetBufferSubData(GL_SHADER_STORAGE_BUFFER, 0, sizeof output, output);
 
 
    if (memcmp(output, texels, sizeof output)) {
        printf("ERROR: texture read failed\n");
        return EXIT_FAILURE;
    }
 
 
    return EXIT_SUCCESS;
}

[randall]

Your code reproduces the problem on my machine.

Driver: 306.63
OS: Windows 7 x64
GPU: GeForce GTS 450

[Johnny Tremain]

Hey Ambator. If you have a different gpu, you should try that.

The reason is I had a similar issue, but it was dealing with glBindSampler. One time it was nVidia driver issue.

The other is was because I forgot to set one setting resulting in texture sampling returns 0 and textureSize returns 0 even though i uploaded and pulled down the texture to verify it is valid.

You may be facing a similar issue.

[Piers Daniell]

Thanks for the information. I failed to reproduce this with my GF108, but I am able to reproduce with a GF104, which matches your GPU. I will investigate the issue.

[Piers Daniell]

We have found the bug in our driver that's causing textures to not work properly with compute shaders. This issue is fixed and will be released soon with a new driver update.

In the mean time you can work around the issue by referencing the texture(s) you intend to use with compute from a non-compute shader (or fixed-function) before dispatching the compute.

For example, with my sample application above you could add the following:

    ...
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA32F, 16, 16, 0, GL_RGBA, GL_FLOAT, texels);
    // Work around starts here
    glUseProgram(0); // use fixed-function
    glEnable(GL_TEXTURE_2D); // enable texture sampling
    glDrawArrays(GL_TRIANGLES, 0, 0); // draw nothing
    glDisable(GL_TEXTURE_2D);
    glUseProgram(pgm); // restore the compute program
    // Work around ends here
 
    GLuint ssbo;
    ...

[randall]

Thanks for the info. I am glad that you have fixed that. I am waiting for the next driver release.