Pass array into shader

OpenGL
1

hi,

what are the good ways to pass a large array (obtained by cuda code) to fragment/vertex shader?

thanks

2

If I understand correctly, you want to pass the data generated to a buffer using cuda code to the fragment/vertex shader.

I would recommend using uniform buffers or texture buffers. The former provides usually faster access, the later provides much larger storage.

3

so uniform data are allocated to shared memory from cuda point of view?

I have tried set a large uniform array and copy to it, but it does not work.

So binding texture is the only way? I prefer something like “cudaMemcpy” to pass the data to the shader…

4

so uniform data are allocated to shared memory from cuda point of view?

No, he said uniform [b]buffers[/b].

I prefer something like “cudaMemcpy” to pass the data to the shader…

But using the buffer as a buffer texture or a uniform buffer doesn’t involve a memory copy. You just use CUDA to write directly to the buffer, then use the buffer as a uniform buffer or a buffer texture and read from your shader.

5

One thing worth thinking about: since you are using CUDA, it means you are using NVIDIA hardware… so I strongly suggest you look into GL_NV_shader_buffer_load. The basic setup you would have is the following:

Create buffer object so that CUDA and GL can share it.
Let CUDA do it’s thing
API calls to let GL use the buffer object
Use GL_NV_shader_buffer_load to access buffer object contents from shader…

Looking at http://developer.download.nvidia.com/compute/cuda/2_3/toolkit/docs/online/group__CUDART__OPENGL.html it looks like one does this:



initBO(void)
{
  /*-- create GL buffer object -- */
  glGenBuffers();
  glBindBuffer();
  glBufferData();

  /** --register to CUDA --*/  
  cudaGLRegisterBufferObject();
}

void
computeToBO(void)
{
   /* -- map  buffer object to CUDA */
   cudaGLMapBufferObject();

   /* CUDA call to compute */
   CUDAComputeBaby();

   /* unmap buffer object from CUDA*/
   cudaGLUnmapBufferObject();
}

void
useBO(void)
{
   //use buffer object freely in GL... the best one if by far to 
   //fetch the Buffer objects GPU address and use that value as a uniform,
   //see GL_NV_shader_buffer_load.
   
}

void
whatever(void)
{
  init_CUDA();
  
  initBO();
  while(keep_render_bender)
  {
     computeToBO();
     useBO();
  }
}

naturally, likely you will want to have 2 buffer objects flying around, one where you compute to, and the other that you use to render from and swapping between the two.

Since you are using CUDA, I strongly recommend that you also use GL_NV_shader_buffer_load, as it allows much more flexible and natural access to the buffer object data… binding the buffer object to a uniform (known as uniform buffer objects and bindable uniforms) has size limitations and texture buffer objects (i.e. a buffer object becomes the data source for a large array) forces one to have that the data is just an array of simple data types: AvecN where A=float, int8, int16, int32, uint8, uint16 or uint32 and N=1,2 or 4 (GeForce 4xx cards support N=3 though).

6

hey, guys, got plenty stuff here! many thanks for these information!

7

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