env/opencv-4.8.0/samples/cpp/tutorial_code/gpu/gpu-thrust-interop/main.cu

#include "Thrust_interop.hpp"
#include <opencv2/core/cuda_stream_accessor.hpp>

#include <thrust/transform.h>
#include <thrust/random.h>
#include <thrust/sort.h>
#include <thrust/system/cuda/execution_policy.h>
//! [prg]
struct prg
{
  float a, b;

  __host__ __device__
    prg(float _a = 0.f, float _b = 1.f) : a(_a), b(_b) {};

  __host__ __device__
    float operator()(const unsigned int n) const
  {
    thrust::default_random_engine rng;
    thrust::uniform_real_distribution<float> dist(a, b);
    rng.discard(n);
    return dist(rng);
  }
};
//! [prg]


//! [pred_greater]
template<typename T> struct pred_greater
{
  T value;
  __host__ __device__ pred_greater(T value_) : value(value_){}
  __host__ __device__ bool operator()(const T& val) const
  {
    return val > value;
  }
};
//! [pred_greater]


int main(void)
{
  // Generate a 2 channel row matrix with 100 elements.  Set the first channel to be the element index, and the second to be a randomly
  // generated value.  Sort by the randomly generated value while maintaining index association.
  //! [sort]
  {
    cv::cuda::GpuMat d_data(1, 100, CV_32SC2);
    // Thrust compatible begin and end iterators to channel 1 of this matrix
    auto keyBegin = GpuMatBeginItr<int>(d_data, 1);
    auto keyEnd = GpuMatEndItr<int>(d_data, 1);
    // Thrust compatible begin and end iterators to channel 0 of this matrix
    auto idxBegin = GpuMatBeginItr<int>(d_data, 0);
    auto idxEnd = GpuMatEndItr<int>(d_data, 0);
    // Fill the index channel with a sequence of numbers from 0 to 100
    thrust::sequence(idxBegin, idxEnd);
    // Fill the key channel with random numbers between 0 and 10.  A counting iterator is used here to give an integer value for each location as an input to prg::operator()
    thrust::transform(thrust::make_counting_iterator(0), thrust::make_counting_iterator(d_data.cols), keyBegin, prg(0, 10));
    // Sort the key channel and index channel such that the keys and indecies stay together
    thrust::sort_by_key(keyBegin, keyEnd, idxBegin);

    cv::Mat h_idx(d_data);
  }
  //! [sort]

  // Randomly fill a row matrix with 100 elements between -1 and 1
  //! [random]
  {
    cv::cuda::GpuMat d_value(1, 100, CV_32F);
    auto valueBegin = GpuMatBeginItr<float>(d_value);
    auto valueEnd = GpuMatEndItr<float>(d_value);
    thrust::transform(thrust::make_counting_iterator(0), thrust::make_counting_iterator(d_value.cols), valueBegin, prg(-1, 1));

    cv::Mat h_value(d_value);
  }
  //! [random]

  // OpenCV has count non zero, but what if you want to count a specific value?
  //! [count_value]
  {
    cv::cuda::GpuMat d_value(1, 100, CV_32S);
    d_value.setTo(cv::Scalar(0));
    d_value.colRange(10, 50).setTo(cv::Scalar(15));
    auto count = thrust::count(GpuMatBeginItr<int>(d_value), GpuMatEndItr<int>(d_value), 15);
    std::cout << count << std::endl;
  }
  //! [count_value]

  // Randomly fill an array then copy only values greater than 0.  Perform these tasks on a stream.
  //! [copy_greater]
  {
    cv::cuda::GpuMat d_value(1, 100, CV_32F);
    auto valueBegin = GpuMatBeginItr<float>(d_value);
    auto valueEnd = GpuMatEndItr<float>(d_value);
    cv::cuda::Stream stream;
    //! [random_gen_stream]
    // Same as the random generation code from before except now the transformation is being performed on a stream
    thrust::transform(thrust::system::cuda::par.on(cv::cuda::StreamAccessor::getStream(stream)), thrust::make_counting_iterator(0), thrust::make_counting_iterator(d_value.cols), valueBegin, prg(-1, 1));
    //! [random_gen_stream]
    // Count the number of values we are going to copy
    int count = thrust::count_if(thrust::system::cuda::par.on(cv::cuda::StreamAccessor::getStream(stream)), valueBegin, valueEnd, pred_greater<float>(0.0));
    // Allocate a destination for copied values
    cv::cuda::GpuMat d_valueGreater(1, count, CV_32F);
    // Copy values that satisfy the predicate.
    thrust::copy_if(thrust::system::cuda::par.on(cv::cuda::StreamAccessor::getStream(stream)), valueBegin, valueEnd, GpuMatBeginItr<float>(d_valueGreater), pred_greater<float>(0.0));
    cv::Mat h_greater(d_valueGreater);
  }
  //! [copy_greater]

  return 0;
}