How to read back a CUDA Texture for testing?

Question

Ok, so far, I can create an array on the host computer (of type float), and copy it to the gpu, then bring it back to the host as another array (to test if the copy was succ

Answer 1

readTexels() is a kernel (__global__) function, i.e. it runs on the GPU. Therefore you need to use the correct syntax to launch a kernel.

Take a look through the CUDA Programming Guide and some of the SDK samples, both available via the NVIDIA CUDA site to see how to launch a kernel.

Hint: It'll end up something like readTexels<<<grid,block>>>(...)

Answer 2

Briefly:

------------- in your main.cu ---------------------------------------------------------------------------------------

-1. Define the texture as a globlal variable

       texture refTexture; // global variable !
       // meaning: address the texture with (x,y) (2D) and get an unsinged int

In the main function:

-2. Use arrays combined with texture

    cudaArray* myArray; // declar.
    // ask for memory
    cudaMallocArray (   &myArray,

                        &refTex.channelDesc, /* with this you don't need to fill a channel descriptor */
                        width,

                        height); 

-3. copy data from CPU to GPU (to the array)

 cudaMemcpyToArray ( arrayCudaEntrada, // destination: the array

                        0, 0, // offsets 
                        sourceData, // pointer uint*
                        widthheightsizeof(uint), // total amount of bytes to be copied 
                        cudaMemcpyHostToDevice);

-4. bind texture and array

    cudaBindTextureToArray( refTex,arrayCudaEntrada)

-5. change some parameters in the texture

   refTextura_In.normalized = false; // don't automatically convert fetched data to [0,1[
      refTextura_In.addressMode[0] = cudaAddressModeClamp;  // if my indexing is out of bounds: automatically use a valid indexing (0 if negative index, last if too great index)
      refTextura_In.addressMode[1] = cudaAddressModeClamp;

---------- in the kernel --------------------------------------------------------

    // find out indexes (f,c) to process by this thread
     uint f = (blockIdx.x * blockDim.x) + threadIdx.x;
     uint c = (blockIdx.y * blockDim.y) + threadIdx.y;


  // this is curious and necessary: indexes for reading from a texture
  // are floats !. Even if you are certain to access (4,5) you have
  // match the "center" this is (4.5, 5.5)
  uint read = tex2D( refTex, c+0.5f, f+0.5f); // texRef is a global variable

Now You process read and write the results to other zone of the device global memory, not to the texture itself !