[BUG] createGLBuffer and copyToGLBuffer do not point to the same device

Start with forge/examples/opencl and cl_helpers.h, especially get_devices and the two createCLGLContext overloads. Reproduce the failure on a system with multiple graphics cards, then trace which OpenCL device each OpenGL buffer operation uses. Done means the examples create and copy GL buffers through the same device without relying on selecting the last device.

If you have more than one display cards, all the examples in forge/examples/opencl will fail.

A temporary workaround is to modify createCLGLContext in cl_helpers.h so that cl::Context always use the last device instead of the first device. But it is not a solution at all.

void get_devices(const forge::Window &wnd,
                 std::vector<cl::Platform> &platforms_interop,
                 std::vector<Device> &devices_interop) {
  std::vector<cl::Platform> platforms;
  Platform::get(&platforms);

  for (auto platform : platforms) {
    std::vector<cl::Device> devices;
    try {
      platform.getDevices(CL_DEVICE_TYPE_GPU, &devices);
      for (auto device : devices) {
        if (checkGLInterop(platform, device, wnd)) {
          devices_interop.push_back(device);
          platforms_interop.push_back(platform);
        }
      }

    } catch (const cl::Error &err) {
      if (err.err() != CL_DEVICE_NOT_FOUND) {
        std::cout << "Platform: " << platform.getInfo<CL_PLATFORM_NAME>()
                  << " got error = " << err.err() << std::endl;
        throw std::runtime_error("Fatal Error!");
      }
    }
  }
  if (devices_interop.size() == 0)
    throw std::runtime_error("No CL-GL sharing contexts found");
}

cl::Context createCLGLContext(const forge::Window &wnd, cl::Platform platform,
                              cl::Device device) {
  // std::cout << "Platform: " << platform.getInfo<CL_PLATFORM_NAME>()
  //           << std::endl;
  // std::cout << "Device: " << device.getInfo<CL_DEVICE_NAME>() << std::endl;
#if defined(OS_MAC)
  CGLContextObj cgl_current_ctx = CGLGetCurrentContext();
  CGLShareGroupObj cgl_share_group = CGLGetShareGroup(cgl_current_ctx);

  cl_context_properties cps[] = {CL_CONTEXT_PROPERTY_USE_CGL_SHAREGROUP_APPLE,
                                 (cl_context_properties)cgl_share_group, 0};
#elif defined(OS_LNX)
  cl_context_properties cps[] = {CL_GL_CONTEXT_KHR,
                                 (cl_context_properties)wnd.context(),
                                 CL_GLX_DISPLAY_KHR,
                                 (cl_context_properties)wnd.display(),
                                 CL_CONTEXT_PLATFORM,
                                 (cl_context_properties)platform(),
                                 0};
#else /* OS_WIN */
  cl_context_properties cps[] = {CL_GL_CONTEXT_KHR,
                                 (cl_context_properties)wnd.context(),
                                 CL_WGL_HDC_KHR,
                                 (cl_context_properties)wnd.display(),
                                 CL_CONTEXT_PLATFORM,
                                 (cl_context_properties)platform(),
                                 0};
#endif
  return cl::Context(device, cps);
}

cl::Context createCLGLContext(const forge::Window &wnd) {
  std::vector<cl::Platform> platforms;
  std::vector<Device> devices;
  get_devices(wnd, platforms, devices);
  for (size_t i = devices.size() - 1; i >= 0; i--) {
    // for (size_t i = 0; i < devices.size(); i++) {
    try {
      return createCLGLContext(wnd, platforms[i], devices[i]);

    } catch (const cl::Error &err) {
      std::cout << "[createCLGLContext]Error:" << err.err() << std::endl;
    }
  }
  return cl::Context();
}