This sample intends to demonstrate how to share (vertex) buffers between OpenCL and OpenGL. How Does OpenCL-OpenGL Interop? chapter of the OpenCL-Guide lays out the fundamentals of OpenCL-OpenGL interoperability.

Key APIs and Concepts

The most important aspect of this sample is to understand how OpenCL-OpenGL interop contexts and shared resources are setup. The cl::util::get_interop_context function takes much of the tedium out of setting up such a context while the cl::util::InteropWindow adds "GLUT-like" features, dealing with typical windowed interop app control flow, making sure that API objects are created in the correct order.

Application flow

Application flow is primarily dictated by cl::sdk::InteropWindow, more specifically by cl::ask::InteropWindow::run(). For a detailed overview of what the InteropWindow utility does, please refer to the SDK library documentation.

Double buffering

The kernel used to implement the gravitational interaction and time-stepping in a fused manner uses double-buffering of some of the data. It is not possible to calculate forces between the particles and carry out the forward-Euler in the same kernel without global syncing. (Some praticles may have already updated their position while others are still summing up forces, using the now out-of-sync positions.)

Implicit interop context synchronization

This sample uses basic and implicit interop context synchronization. For a detailed overview on the various ways OpenCL and OpenGL can be synchronized, refer to Synchronizing the two APIs section of the OpenCL-OpenGL interop guide.

Used API surface

cl::sdk::InteropWindow
cl::Context::getInfo<CL_CONTEXT_DEVICES>()
cl::CommandQueue(cl::Context, cl::Device)
cl::util::get_program(cl::Context, cl::string)
cl::Program::build(cl::Device)
cl::KernelFunctor<...>(cl::Program, const char*)
cl::Buffer(cl::CommandQueue, Iter, Iter, bool)
cl::BufferGL::BufferGL(cl::Context, cl_mem_flags, cl_GLuint)
cl::copy(cl::CommandQueue, cl::Buffer, Iter, Iter)
cl::CommandQueue::enqueueAcquireGLObjects(const cl::vector<cl::Memory>*, const cl::vector<cl::Event>*, cl::Event*)
cl::CommandQueue::enqueueReleaseGLObjects(const cl::vector<cl::Memory>*, const cl::vector<cl::Event>*, cl::Event*)
cl::finish()
cl::Event::wait()