texture_2d.cu

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

//
// Paint a 2D texture with a moving red/green hatch pattern on a
// strobing blue background.  Note that this kernel reads to and
// writes from the texture, hence why this texture was not mapped
// as WriteDiscard.
//
__global__ void cuda_kernel_texture_2d(unsigned char *surface, int width,
                                       int height, size_t pitch, float t) {
  int x = blockIdx.x * blockDim.x + threadIdx.x;
  int y = blockIdx.y * blockDim.y + threadIdx.y;
  float *pixel;

  // 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;

  // get a pointer to the pixel at (x,y)
  pixel = (float *)(surface + y * pitch) + 4 * x;

  // populate it
  float value_x = 0.5f + 0.5f * cos(t + 10.0f * ((2.0f * x) / width - 1.0f));
  float value_y = 0.5f + 0.5f * cos(t + 10.0f * ((2.0f * y) / height - 1.0f));
  pixel[0] = value_x > 0.5 ? 1 : 0;
  pixel[1] = value_y > 0.5 ? 1 : 0;
  pixel[2] = 0.5f + 0.5f * cos(t);
  pixel[3] = 1;  // alpha

  for (int i = 0; i < 6; ++i) {
    for (int j = 0; j < 4; ++j) {
      pixel[j] = sqrt(pixel[j]);
    }
  }

  for (int i = 0; i < 6; ++i) {
    for (int j = 0; j < 4; ++j) {
      pixel[j] *= pixel[j];
    }
  }
}

extern "C" void cuda_texture_2d(void *surface, int width, int height,
                                size_t pitch, 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_2d<<<Dg, Db>>>((unsigned char *)surface, width, height,
                                     pitch, t);

  error = cudaGetLastError();

  if (error != cudaSuccess) {
    printf("cuda_kernel_texture_2d() failed to launch error = %d\n", error);
  }
}