texture_volume.cu

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#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/*
 * Paint a 3D texture with a gradient in X (blue) and Z (green), and have every
 * other Z slice have full red.
 */
__global__ void cuda_kernel_texture_volume(unsigned char *surface, int width,
                                           int height, int depth, size_t pitch,
                                           size_t pitchSlice) {
  int x = blockIdx.x * blockDim.x + threadIdx.x;
  int y = blockIdx.y * blockDim.y + threadIdx.y;

  // in the case where, due to quantization into grids, we have
  // more threads than pixels, skip the threads which don't
  // correspond to valid pixels
  if (x >= width || y >= height) return;

  // walk across the Z slices of this texture.  it should be noted that
  // this is far from optimal data access.
  for (int z = 0; z < depth; ++z) {
    // get a pointer to this pixel
    unsigned char *pixel = surface + z * pitchSlice + y * pitch + 4 * x;
    pixel[0] = 255 * x / (width - 1);  // blue
    pixel[1] = 255 * z / (depth - 1);  // green
    pixel[2] = 255 * (z % 2);          // red
    pixel[3] = 255;                    // alpha
  }
}

extern "C" void cuda_texture_volume(void *surface, int width, int height,
                                    int depth, size_t pitch, size_t pitchSlice,
                                    float t) {
  cudaError_t error = cudaSuccess;

  dim3 Db = dim3(16, 16);  // block dimensions are fixed to be 256 threads
  dim3 Dg = dim3((width + Db.x - 1) / Db.x, (height + Db.y - 1) / Db.y);

  cuda_kernel_texture_volume<<<Dg, Db>>>((unsigned char *)surface, width,
                                         height, depth, pitch, pitchSlice);

  error = cudaGetLastError();

  if (error != cudaSuccess) {
    printf("cuda_kernel_texture_volume() failed to launch error = %d\n", error);
  }
}