How to draw OpenCL calculated pixels to the screen with OpenGL?

Question

I wan't to do some calculated pixelart with OpenCL and display this directly on the display without CPU roundtripping. I could use interoperability of OpenCL with OpenGL and write to the texture-banks of the GPU and display the texture with OpenGL. I was wondering what would be the best way to do this, since I do not need any 3d stuff, just 2d pixelart.

Answer 1

The best way would be to use OpenCL/OpenGL interop, if your OpenCL implementation supports it. This allows OpenCL to access certain OpenGL objects (buffer objects and textures/renderbuffers). You won't be able to directly access the default OpenGL framebuffer (ie: the display), but you will be able to access an image bound to a framebuffer object. From there, you can, in OpenGL, do a framebuffer blit to the default framebuffer. Nothing will touch CPU memory.

You'll have to look up the specifics on CL/GL interop to learn the details however. The basic idea is that you create a renderbuffer in OpenGL (which you bind to an FBO). Then you hand that renderbuffer off to OpenCL, and do your computations into the renderbuffer. Once that's complete, you perform a glBlitFramebuffer to copy the data from the renderbuffer to the default framebuffer, then swap buffers to display it.