cuda-samples/Samples/3_CUDA_Features/cdpBezierTessellation/BezierLineCDP.cu

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#include <stdio.h>
#include <cuda_runtime_api.h>
#include <helper_cuda.h>
#include <string.h>

__forceinline__ __device__ float2 operator+(float2 a, float2 b) {
  float2 c;
  c.x = a.x + b.x;
  c.y = a.y + b.y;
  return c;
}

__forceinline__ __device__ float2 operator-(float2 a, float2 b) {
  float2 c;
  c.x = a.x - b.x;
  c.y = a.y - b.y;
  return c;
}

__forceinline__ __device__ float2 operator*(float a, float2 b) {
  float2 c;
  c.x = a * b.x;
  c.y = a * b.y;
  return c;
}

__forceinline__ __device__ float length(float2 a) {
  return sqrtf(a.x * a.x + a.y * a.y);
}

#define MAX_TESSELLATION 32
struct BezierLine {
  float2 CP[3];
  float2 *vertexPos;
  int nVertices;
};

__global__ void computeBezierLinePositions(int lidx, BezierLine *bLines,
                                           int nTessPoints) {
  int idx = threadIdx.x + blockDim.x * blockIdx.x;

  if (idx < nTessPoints) {
    float u = (float)idx / (float)(nTessPoints - 1);
    float omu = 1.0f - u;

    float B3u[3];

    B3u[0] = omu * omu;
    B3u[1] = 2.0f * u * omu;
    B3u[2] = u * u;

    float2 position = {0, 0};

    for (int i = 0; i < 3; i++) {
      position = position + B3u[i] * bLines[lidx].CP[i];
    }

    bLines[lidx].vertexPos[idx] = position;
  }
}

__global__ void computeBezierLinesCDP(BezierLine *bLines, int nLines) {
  int lidx = threadIdx.x + blockDim.x * blockIdx.x;

  if (lidx < nLines) {
    float curvature = length(bLines[lidx].CP[1] -
                             0.5f * (bLines[lidx].CP[0] + bLines[lidx].CP[2])) /
                      length(bLines[lidx].CP[2] - bLines[lidx].CP[0]);
    int nTessPoints = min(max((int)(curvature * 16.0f), 4), MAX_TESSELLATION);

    if (bLines[lidx].vertexPos == NULL) {
      bLines[lidx].nVertices = nTessPoints;
      cudaMalloc((void **)&bLines[lidx].vertexPos,
                 nTessPoints * sizeof(float2));
    }

    computeBezierLinePositions<<<ceilf((float)bLines[lidx].nVertices / 32.0f),
                                 32>>>(lidx, bLines, bLines[lidx].nVertices);
  }
}

__global__ void freeVertexMem(BezierLine *bLines, int nLines) {
  int lidx = threadIdx.x + blockDim.x * blockIdx.x;

  if (lidx < nLines) cudaFree(bLines[lidx].vertexPos);
}

unsigned int checkCapableSM35Device(int argc, char **argv) {
  // Get device properties
  cudaDeviceProp properties;
  int device_count = 0, device = -1;

  if (checkCmdLineFlag(argc, (const char **)argv, "device")) {
    device = getCmdLineArgumentInt(argc, (const char **)argv, "device");

    cudaDeviceProp properties;
    checkCudaErrors(cudaGetDeviceProperties(&properties, device));

    if (properties.major > 3 ||
        (properties.major == 3 && properties.minor >= 5)) {
      printf("Running on GPU  %d (%s)\n", device, properties.name);
    } else {
      printf(
          "cdpBezierTessellation requires GPU devices with compute SM 3.5 or "
          "higher.");
      printf("Current GPU device has compute SM %d.%d. Exiting...\n",
             properties.major, properties.minor);
      return EXIT_FAILURE;
    }

  } else {
    checkCudaErrors(cudaGetDeviceCount(&device_count));

    for (int i = 0; i < device_count; ++i) {
      checkCudaErrors(cudaGetDeviceProperties(&properties, i));

      if (properties.major > 3 ||
          (properties.major == 3 && properties.minor >= 5)) {
        device = i;
        printf("Running on GPU %d (%s)\n", i, properties.name);
        break;
      }

      printf("GPU %d %s does not support CUDA Dynamic Parallelism\n", i,
             properties.name);
    }
  }
  if (device == -1) {
    fprintf(stderr,
            "cdpBezierTessellation requires GPU devices with compute SM 3.5 or "
            "higher.  Exiting...\n");
    return EXIT_WAIVED;
  }

  return EXIT_SUCCESS;
}

#define N_LINES 256
#define BLOCK_DIM 64
int main(int argc, char **argv) {
  BezierLine *bLines_h = new BezierLine[N_LINES];

  float2 last = {0, 0};

  for (int i = 0; i < N_LINES; i++) {
    bLines_h[i].CP[0] = last;

    for (int j = 1; j < 3; j++) {
      bLines_h[i].CP[j].x = (float)rand() / (float)RAND_MAX;
      bLines_h[i].CP[j].y = (float)rand() / (float)RAND_MAX;
    }

    last = bLines_h[i].CP[2];
    bLines_h[i].vertexPos = NULL;
    bLines_h[i].nVertices = 0;
  }

  unsigned int sm35Ret = checkCapableSM35Device(argc, argv);
  if (sm35Ret != EXIT_SUCCESS) {
    exit(sm35Ret);
  }

  BezierLine *bLines_d;
  checkCudaErrors(cudaMalloc((void **)&bLines_d, N_LINES * sizeof(BezierLine)));
  checkCudaErrors(cudaMemcpy(bLines_d, bLines_h, N_LINES * sizeof(BezierLine),
                             cudaMemcpyHostToDevice));
  printf("Computing Bezier Lines (CUDA Dynamic Parallelism Version) ... ");
  computeBezierLinesCDP<<<(unsigned int)ceil((float)N_LINES / (float)BLOCK_DIM),
                          BLOCK_DIM>>>(bLines_d, N_LINES);
  printf("Done!\n");

  // Do something to draw the lines here

  freeVertexMem<<<(unsigned int)ceil((float)N_LINES / (float)BLOCK_DIM),
                  BLOCK_DIM>>>(bLines_d, N_LINES);
  checkCudaErrors(cudaFree(bLines_d));
  delete[] bLines_h;

  exit(EXIT_SUCCESS);
}