First example of using OpenCL in OpenCV 3.x

opencl-opencv-first-example.cpp

// This example shows how to create
// a context from a specified device type
// using OpenCL wrappers provided by OpenCV 3.x
//
// The default platform is the zero-th platform
// returned by clGetPlatformIDs.
//
// To compile it on Mac OS X, add `-framework opencl`
// to CXX_FLAGS

#include <iostream>
#include <opencv2/core/ocl.hpp>

int main()
{
  cv::ocl::Context ctx;
  ctx.create(cv::ocl::Device::TYPE_CPU);
  std::cout << ctx.ndevices() << std::endl;

  std::cout << (ctx.create() ? "true":"false") << std::endl;

  return 0;
}
// output:
//1
//false