project_6/cccl_upstream/thrust/examples/discrete_voronoi.cu

#include <thrust/device_vector.h>
#include <thrust/extrema.h>
#include <thrust/host_vector.h>
#include <thrust/iterator/counting_iterator.h>
#include <thrust/random.h>

#include <cuda/std/tuple>

#include <cmath>
#include <fstream>
#include <iomanip>
#include <iostream>

#include "include/timer.h"

// Compute an approximate Voronoi Diagram with a Jump Flooding Algorithm (JFA)
//
// References
//   http://en.wikipedia.org/wiki/Voronoi_diagram
//   http://www.comp.nus.edu.sg/~tants/jfa.html
//   http://www.utdallas.edu/~guodongrong/Papers/Dissertation.pdf
//
// Thanks to David Coeurjolly for contributing this example

// minFunctor
// Tuple  = <seeds,seeds + k,seeds + m*k, seeds - k,
//           seeds - m*k, seeds+ k+m*k,seeds + k-m*k,
//           seeds- k+m*k,seeds - k+m*k, i>
struct voronoi_site_selector
{
  int m, n, k;

  __host__ __device__ voronoi_site_selector(int m, int n, int k)
      : m(m)
      , n(n)
      , k(k)
  {}

  // To decide I have to change my current Voronoi site
  __host__ __device__ int minVoro(int x_i, int y_i, int p, int q)
  {
    if (q == m * n)
    {
      return p;
    }

    // coordinates of points p and q
    int y_q = q / m;
    int x_q = q - y_q * m;
    int y_p = p / m;
    int x_p = p - y_p * m;

    // squared distances
    int d_iq = (x_i - x_q) * (x_i - x_q) + (y_i - y_q) * (y_i - y_q);
    int d_ip = (x_i - x_p) * (x_i - x_p) + (y_i - y_p) * (y_i - y_p);

    if (d_iq < d_ip)
    {
      return q; // q is closer
    }
    else
    {
      return p;
    }
  }

  // For each point p+{-k,0,k}, we keep the Site with minimum distance
  template <typename Tuple>
  __host__ __device__ int operator()(const Tuple& t)
  {
    // Current point and site
    int i = cuda::std::get<9>(t);
    int v = cuda::std::get<0>(t);

    // Current point coordinates
    int y = i / m;
    int x = i - y * m;

    if (x >= k)
    {
      v = minVoro(x, y, v, cuda::std::get<3>(t));

      if (y >= k)
      {
        v = minVoro(x, y, v, cuda::std::get<8>(t));
      }

      if (y + k < n)
      {
        v = minVoro(x, y, v, cuda::std::get<7>(t));
      }
    }

    if (x + k < m)
    {
      v = minVoro(x, y, v, cuda::std::get<1>(t));

      if (y >= k)
      {
        v = minVoro(x, y, v, cuda::std::get<6>(t));
      }
      if (y + k < n)
      {
        v = minVoro(x, y, v, cuda::std::get<5>(t));
      }
    }

    if (y >= k)
    {
      v = minVoro(x, y, v, cuda::std::get<4>(t));
    }
    if (y + k < n)
    {
      v = minVoro(x, y, v, cuda::std::get<2>(t));
    }

    // global return
    return v;
  }
};

// print an M-by-N array
template <typename T>
void print(int m, int n, const thrust::device_vector<T>& d_data)
{
  thrust::host_vector<T> h_data = d_data;

  for (int i = 0; i < m; i++)
  {
    for (int j = 0; j < n; j++)
    {
      std::cout << std::setw(4) << h_data[i * n + j] << " ";
    }
    std::cout << "\n";
  }
}

void generate_random_sites(thrust::host_vector<int>& t, int Nb, int m, int n)
{
  thrust::default_random_engine rng;
  thrust::uniform_int_distribution<int> dist(0, m * n - 1);

  for (int k = 0; k < Nb; k++)
  {
    int index = dist(rng);
    t[index]  = index + 1;
  }
}

// Export the tab to PGM image format
void vector_to_pgm(thrust::host_vector<int>& t, int m, int n, const char* out)
{
  assert(static_cast<int>(t.size()) == m * n && "Vector size does not match image dims.");

  std::fstream f(out, std::fstream::out);
  f << "P2\n";
  f << m << " " << n << "\n";
  f << "253\n";

  // Hash function to map values to [0,255]
  auto to_grey_level = [](int in_value) -> int {
    return (71 * in_value) % 253;
  };

  for (int value : t)
  {
    f << to_grey_level(value) << " ";
  }
  f << "\n";
  f.close();
}

/************Main Jfa loop********************/
// Perform a jump with step k
void jfa(thrust::device_vector<int>& in, thrust::device_vector<int>& out, unsigned int k, int m, int n)
{
  thrust::transform(
    thrust::make_zip_iterator(
      in.begin(),
      in.begin() + k,
      in.begin() + m * k, // NOLINT(bugprone-misplaced-widening-cast)
      in.begin() - k,
      in.begin() - m * k, // NOLINT(bugprone-misplaced-widening-cast)
      in.begin() + k + m * k, // NOLINT(bugprone-misplaced-widening-cast)
      in.begin() + k - m * k, // NOLINT(bugprone-misplaced-widening-cast)
      in.begin() - k + m * k, // NOLINT(bugprone-misplaced-widening-cast)
      in.begin() - k - m * k, // NOLINT(bugprone-misplaced-widening-cast)
      thrust::counting_iterator<int>(0)),
    thrust::make_zip_iterator(
      in.begin(),
      in.begin() + k,
      in.begin() + m * k, // NOLINT(bugprone-misplaced-widening-cast)
      in.begin() - k,
      in.begin() - m * k, // NOLINT(bugprone-misplaced-widening-cast)
      in.begin() + k + m * k, // NOLINT(bugprone-misplaced-widening-cast)
      in.begin() + k - m * k, // NOLINT(bugprone-misplaced-widening-cast)
      in.begin() - k + m * k, // NOLINT(bugprone-misplaced-widening-cast)
      in.begin() - k - m * k, // NOLINT(bugprone-misplaced-widening-cast)
      thrust::counting_iterator<int>(0))
      + n * m, // NOLINT(bugprone-misplaced-widening-cast)
    out.begin(),
    voronoi_site_selector(m, n, static_cast<int>(k)));
}
/********************************************/

void display_time(timer& t)
{
  std::cout << "  ( " << 1e3 * t.elapsed() << "ms )" << '\n';
}

int main()
{
  int m = 2048; // number of rows
  int n = 2048; // number of columns
  int s = 1000; // number of sites

  timer t;

  // Host vector to encode a 2D image
  std::cout << "[Initialize " << m << "x" << n << " Image]" << '\n';
  t.restart();
  thrust::host_vector<int> seeds_host(m * n, m * n);
  generate_random_sites(seeds_host, s, m, n);
  display_time(t);

  std::cout << "[Copy to Device]" << '\n';
  t.restart();
  thrust::device_vector<int> seeds = seeds_host;
  thrust::device_vector<int> temp(seeds);
  display_time(t);

  // JFA+1  : before entering the log(n) loop, we perform a jump with k=1
  std::cout << "[JFA stepping]" << '\n';
  t.restart();
  jfa(seeds, temp, 1, m, n);
  seeds.swap(temp);

  // JFA : main loop with k=n/2, n/4, ..., 1
  for (int k = thrust::max(m, n) / 2; k > 0; k /= 2)
  {
    jfa(seeds, temp, k, m, n);
    seeds.swap(temp);
  }

  display_time(t);
  std::cout << "  ( " << static_cast<double>(seeds.size()) / (1e6 * t.elapsed()) << " MPixel/s ) " << '\n';

  std::cout << "[Device to Host Copy]" << '\n';
  t.restart();
  seeds_host = seeds;
  display_time(t);

  std::cout << "[PGM Export]" << '\n';
  t.restart();
  vector_to_pgm(seeds_host, m, n, "discrete_voronoi.pgm");
  display_time(t);

  return 0;
}