OpenGL Compute Shader Invocations
c++, compute-shader, gpgpu, opengl
Solution
I resolved the problem. The problem was just the number of work-groups I dispatched. numParticles/WORK_GROUP_SIZE will be round off because both variables are integers. That caused too little dispatched work-groups with different numbers of particles.
When I got 1000 particles, then only 1000/128 = 7 work-groups are dispatched. Every work-group has the size of 128. That means I get 7*128 = 896 threads and thus 104 particles won't move at all. Since numParticles%128 may range from 0...128 I just dispatched one more work-group:
glDispatchCompute((_numParticles/WORK_GROUP_SIZE)+1, 1, 1);
And every particle moves from now on. :)
Problem
I got a question related to the new compute shaders. I am currently working on a particle system. I store all my particles in shader-storage-buffer to access them in the compute shader. Then I dispatch an one dimensional work group. ``` #define WORK_GROUP_SIZE 128 _shaderManager->useProgram("computeProg"); glDispatchCompute((_numParticles/WORK_GROUP_SIZE), 1, 1); glMemoryBarrier(GL_SHADER_STORAGE_BARRIER_BIT); ``` My compute shader: ``` #version 430 struct particle{ vec4 currentPos; vec4 oldPos; }; layout(std430, binding=0) buffer particles{ struct particle p[]; }; layout (local_size_x = 128, local_size_y = 1, local_size_z = 1) in; void main(){ uint gid = gl_GlobalInvocationID.x; p[gid].currentPos.x += 100; } ``` But somehow not all particles are affected. I am doing it the same way it was done in this example, but it doesn't work. http://education.siggraph.org/media/conference/S2012_Materials/ComputeShader_6pp.pdf Edit: After I called glMemoryBarrier(GL_SHADER_STORAGE_BARRIER_BIT) I go on like this: ``` _shaderManager->useProgram("shaderProg"); glBindBuffer(GL_ARRAY_BUFFER, shaderStorageBufferID); glVertexPointer(4,GL_FLOAT,sizeof(glm::vec4), (void*)0); glEnableClientState(GL_VERTEX_ARRAY); glDrawArrays(GL_POINTS, 0, _numParticles); glDisableClientState(GL_VERTEX_ARRAY); ``` So which bit would be appropriate to use in this case?