Can't speak for WebGL APIs, but in OpenGL (and other C++ graphics/GPGPU platforms), it is certainly possible (and necessary) to write fully interactive real-tim

Can't speak for WebGL APIs, but in OpenGL (and other C++ graphics/GPGPU platforms), it is certainly possible (and necessary) to write fully interactive real-time apps that rely on a few rounds of communication between GPU and CPU code every frame. At 60 fps, you have 16 ms per frame. As long as you aren't copying huge arrays back and forth, I'd say you can budget in the 1 ms order-of-magnitude per data transfer. I don't know much of that would be avoidable if you were actually closer to the metal than the raw OpenGL C++ API call