2

I've been having trouble sending data to an SSBO for use by a compute shader. Unfortunately, the khronos docs say "TODO" and I cant make their sample code work, and people seem to do very slightly different things Example 1 Example 2 Example 3 - can anyone help?

(I've snipped out other parts of code I've written that I don't think are relevant - but the entire codebase is here . Here's what I've got so far:

SSBO Initialization with some data

std::vector<glm::vec4> data = { glm::vec4(1.0, 0.0, 0.0, 1.0), glm::vec4(1.0, 0.0, 0.0, 1.0) };

GLuint SSBO;
glGenBuffers(1, &SSBO);
glBindBuffer(GL_SHADER_STORAGE_BUFFER, SSBO);
glBufferData(GL_SHADER_STORAGE_BUFFER, data.size() * sizeof(glm::vec4), &data[0], GL_DYNAMIC_DRAW);

//the khronos docs put this line in
//glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 1, SSBO);

glBindBuffer(GL_SHADER_STORAGE_BUFFER, 0);

Update loop

s_Data.compute_shader.use();

-- snip: bind a texture --

int ssbo_binding = 1;
int block_index = glGetProgramResourceIndex(s_Data.compute_shader.ID, GL_SHADER_STORAGE_BLOCK, "bufferData");
glShaderStorageBlockBinding(s_Data.compute_shader.ID, block_index, ssbo_binding );
glBindBufferBase(GL_SHADER_STORAGE_BUFFER, ssbo_binding, SSBO);

glDispatchCompute( X workers, Y workers, 1);

//Synchronize all writes to the framebuffer image
glMemoryBarrier(GL_SHADER_IMAGE_ACCESS_BARRIER_BIT);

// Reset bindings
glBindBufferBase(GL_SHADER_STORAGE_BUFFER, ssbo_binding, 0);
glBindImageTexture(0, 0, 0, false, 0, GL_READ_WRITE, GL_RGBA32F);
glUseProgram(0);

-- snip: render output texture to screen --

Compute Shader

#version 430 core

layout(binding = 0, rgba16f) uniform image2D outTexture;

layout(std430, binding = 1 ) readonly buffer bufferData
{
    vec4 data[];
};

layout (local_size_x = 16, local_size_y = 8) in;
void main(void) {
    ivec2 px = ivec2(gl_GlobalInvocationID.xy);
    ivec2 size = imageSize(outTexture);

    vec3 color;
    if(data.length() > 0)
    {
        //green = data
        color = vec3(0.2, 0.6, 0.2);
    } else
    {
        //red = bad
        color = vec3(0.6, 0.2, 0.2);
    }

    imageStore(outTexture, px, vec4(color, 1.0));
}

Currently my screen displays red indicating no data is being sent via the SSBO.

Edit:

Found the issue. The .length() method in the compute shader does not work.

Turtwiggy
  • 21
  • 3

1 Answers1

0

I found the issue in the compute shader.

The .length() was returning the wrong value. I queried data[0] and data[1] and they returned the correctly set values in the compute shader - so this was the problem (but I don't necessarily have the solution)

Turtwiggy
  • 21
  • 3