cuda-samples/Samples/lineOfSight/lineOfSight.cu

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// This sample is an implementation of a simple line-of-sight algorithm:
// Given a height map and a ray originating at some observation point,
// it computes all the points along the ray that are visible from the
// observation point.
// It is based on the description made in "Guy E. Blelloch.  Vector models
// for data-parallel computing. MIT Press, 1990" and uses open source CUDA
// Thrust Library

#ifdef _WIN32
#define NOMINMAX
#endif

// includes, system
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <float.h>

// includes, project
#include <helper_functions.h>
#include <helper_cuda.h>
#include <helper_math.h>

// includes, library
#include <thrust/device_vector.h>
#include <thrust/host_vector.h>
#include <thrust/scan.h>
#include <thrust/copy.h>

////////////////////////////////////////////////////////////////////////////////
// declaration, types

// Boolean
typedef unsigned char Bool;
enum { False = 0, True = 1 };

// 2D height field
struct HeightField {
  int width;
  float *height;
};

// Ray
struct Ray {
  float3 origin;
  float2 dir;
  int length;
  float oneOverLength;
};

////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////
// declaration, forward
int runTest(int argc, char **argv);
__global__ void computeAngles_kernel(const Ray, float *, cudaTextureObject_t);
__global__ void computeVisibilities_kernel(const float *, const float *, int,
                                           Bool *);
void lineOfSight_gold(const HeightField, const Ray, Bool *);
__device__ __host__ float2 getLocation(const Ray, int);
__device__ __host__ float getAngle(const Ray, float2, float);

////////////////////////////////////////////////////////////////////////////////
// Program main
////////////////////////////////////////////////////////////////////////////////
int main(int argc, char **argv) {
  int res = runTest(argc, argv);

  if (res != 1) {
    printf("Test failed!\n");
    exit(EXIT_FAILURE);
  }

  printf("Test passed\n");
  exit(EXIT_SUCCESS);
}

////////////////////////////////////////////////////////////////////////////////
//! Run a line-of-sight test for CUDA
////////////////////////////////////////////////////////////////////////////////
int runTest(int argc, char **argv) {
  ////////////////////////////////////////////////////////////////////////////
  // Device initialization

  printf("[%s] - Starting...\n", argv[0]);

  // use command-line specified CUDA device, otherwise use device with highest
  // Gflops/s
  findCudaDevice(argc, (const char **)argv);

  ////////////////////////////////////////////////////////////////////////////
  // Timer

  // Create
  StopWatchInterface *timer;
  sdkCreateTimer(&timer);

  // Number of iterations to get accurate timing
  uint numIterations = 100;

  ////////////////////////////////////////////////////////////////////////////
  // Height field

  HeightField heightField;

  // Allocate in host memory
  int2 dim = make_int2(10000, 100);
  heightField.width = dim.x;
  thrust::host_vector<float> height(dim.x * dim.y);
  heightField.height = (float *)&height[0];

  //
  // Fill in with an arbitrary sine surface
  for (int x = 0; x < dim.x; ++x)
    for (int y = 0; y < dim.y; ++y) {
      float amp = 0.1f * (x + y);
      float period = 2.0f + amp;
      *(heightField.height + dim.x * y + x) =
          amp * (sinf(sqrtf((float)(x * x + y * y)) * 2.0f * 3.1416f / period) +
                 1.0f);
    }

  // Allocate CUDA array in device memory
  cudaChannelFormatDesc channelDesc =
      cudaCreateChannelDesc(32, 0, 0, 0, cudaChannelFormatKindFloat);
  cudaArray *heightFieldArray;
  checkCudaErrors(
      cudaMallocArray(&heightFieldArray, &channelDesc, dim.x, dim.y));

  // Initialize device memory
  checkCudaErrors(cudaMemcpy2DToArray(
      heightFieldArray, 0, 0, heightField.height, dim.x * sizeof(float),
      dim.x * sizeof(float), dim.y, cudaMemcpyHostToDevice));

  cudaTextureObject_t heightFieldTex;
  cudaResourceDesc texRes;
  memset(&texRes, 0, sizeof(cudaResourceDesc));

  texRes.resType = cudaResourceTypeArray;
  texRes.res.array.array = heightFieldArray;

  cudaTextureDesc texDescr;
  memset(&texDescr, 0, sizeof(cudaTextureDesc));
  texDescr.normalizedCoords = false;
  texDescr.filterMode = cudaFilterModePoint;
  texDescr.addressMode[0] = cudaAddressModeClamp;
  texDescr.addressMode[1] = cudaAddressModeClamp;
  texDescr.readMode = cudaReadModeElementType;

  checkCudaErrors(
      cudaCreateTextureObject(&heightFieldTex, &texRes, &texDescr, NULL));

  //////////////////////////////////////////////////////////////////////////////
  // Ray (starts at origin and traverses the height field diagonally)

  Ray ray;
  ray.origin = make_float3(0, 0, 2.0f);
  int2 dir = make_int2(dim.x - 1, dim.y - 1);
  ray.dir = make_float2((float)dir.x, (float)dir.y);
  ray.length = max(abs(dir.x), abs(dir.y));
  ray.oneOverLength = 1.0f / ray.length;

  //////////////////////////////////////////////////////////////////////////////
  // View angles

  // Allocate view angles for each point along the ray
  thrust::device_vector<float> d_angles(ray.length);

  // Allocate result of max-scan operation on the array of view angles
  thrust::device_vector<float> d_scannedAngles(ray.length);

  //////////////////////////////////////////////////////////////////////////////
  // Visibility results

  // Allocate visibility results for each point along the ray
  thrust::device_vector<Bool> d_visibilities(ray.length);
  thrust::host_vector<Bool> h_visibilities(ray.length);
  thrust::host_vector<Bool> h_visibilitiesRef(ray.length);

  //////////////////////////////////////////////////////////////////////////////
  // Reference solution
  lineOfSight_gold(heightField, ray, (Bool *)&h_visibilitiesRef[0]);

  //////////////////////////////////////////////////////////////////////////////
  // Device solution

  // Execution configuration
  dim3 block(256);
  dim3 grid((uint)ceil(ray.length / (double)block.x));

  // Compute device solution
  printf("Line of sight\n");
  sdkStartTimer(&timer);

  for (uint i = 0; i < numIterations; ++i) {
    // Compute view angle for each point along the ray
    computeAngles_kernel<<<grid, block>>>(
        ray, thrust::raw_pointer_cast(&d_angles[0]), heightFieldTex);
    getLastCudaError("Kernel execution failed");

    // Perform a max-scan operation on the array of view angles
    thrust::inclusive_scan(d_angles.begin(), d_angles.end(),
                           d_scannedAngles.begin(), thrust::maximum<float>());
    getLastCudaError("Kernel execution failed");

    // Compute visibility results based on the array of view angles
    // and its scanned version
    computeVisibilities_kernel<<<grid, block>>>(
        thrust::raw_pointer_cast(&d_angles[0]),
        thrust::raw_pointer_cast(&d_scannedAngles[0]), ray.length,
        thrust::raw_pointer_cast(&d_visibilities[0]));
    getLastCudaError("Kernel execution failed");
  }

  cudaDeviceSynchronize();
  sdkStopTimer(&timer);
  getLastCudaError("Kernel execution failed");

  // Copy visibility results back to the host
  thrust::copy(d_visibilities.begin(), d_visibilities.end(),
               h_visibilities.begin());

  // Compare device visibility results against reference results
  bool res = compareData(thrust::raw_pointer_cast(&h_visibilitiesRef[0]),
                         thrust::raw_pointer_cast(&h_visibilities[0]),
                         ray.length, 0.0f, 0.0f);
  printf("Average time: %f ms\n\n", sdkGetTimerValue(&timer) / numIterations);
  sdkResetTimer(&timer);

  // Cleanup memory
  checkCudaErrors(cudaFreeArray(heightFieldArray));
  return res;
}

////////////////////////////////////////////////////////////////////////////////
//! Compute view angles for each point along the ray
//! @param ray         ray
//! @param angles      view angles
////////////////////////////////////////////////////////////////////////////////
__global__ void computeAngles_kernel(const Ray ray, float *angles,
                                     cudaTextureObject_t HeightFieldTex) {
  uint i = blockDim.x * blockIdx.x + threadIdx.x;

  if (i < ray.length) {
    float2 location = getLocation(ray, i + 1);
    float height = tex2D<float>(HeightFieldTex, location.x, location.y);
    float angle = getAngle(ray, location, height);
    angles[i] = angle;
  }
}

////////////////////////////////////////////////////////////////////////////////
//! Compute visibility for each point along the ray
//! @param angles          view angles
//! @param scannedAngles   max-scanned view angles
//! @param numAngles       number of view angles
//! @param visibilities    boolean array indicating the visibility of each point
//!                        along the ray
////////////////////////////////////////////////////////////////////////////////
__global__ void computeVisibilities_kernel(const float *angles,
                                           const float *scannedAngles,
                                           int numAngles, Bool *visibilities) {
  uint i = blockDim.x * blockIdx.x + threadIdx.x;

  if (i < numAngles) {
    visibilities[i] = scannedAngles[i] <= angles[i];
  }
}

////////////////////////////////////////////////////////////////////////////////
//! Compute reference data set
//! @param heightField     height field
//! @param ray             ray
//! @param visibilities    boolean array indicating the visibility of each point
//!                        along the ray
////////////////////////////////////////////////////////////////////////////////
void lineOfSight_gold(const HeightField heightField, const Ray ray,
                      Bool *visibilities) {
  float angleMax = asinf(-1.0f);

  for (int i = 0; i < ray.length; ++i) {
    float2 location = getLocation(ray, i + 1);
    float height =
        *(heightField.height + heightField.width * (int)floorf(location.y) +
          (int)floorf(location.x));
    float angle = getAngle(ray, location, height);

    if (angle > angleMax) {
      angleMax = angle;
      visibilities[i] = True;
    } else {
      visibilities[i] = False;
    }
  }
}

////////////////////////////////////////////////////////////////////////////////
//! Compute the 2D coordinates of the point located at i steps from the origin
//! of the ray
//! @param ray      ray
//! @param i        integer offset along the ray
////////////////////////////////////////////////////////////////////////////////
__device__ __host__ float2 getLocation(const Ray ray, int i) {
  float step = i * ray.oneOverLength;
  return make_float2(ray.origin.x, ray.origin.y) + ray.dir * step;
}

////////////////////////////////////////////////////////////////////////////////
//! Compute the angle of view between a 3D point and the origin of the ray
//! @param ray        ray
//! @param location   2D coordinates of the input point
//! @param height     height of the input point
////////////////////////////////////////////////////////////////////////////////
__device__ __host__ float getAngle(const Ray ray, float2 location,
                                   float height) {
  float2 dir = location - make_float2(ray.origin.x, ray.origin.y);
  return atanf((height - ray.origin.z) / length(dir));
}