We're building a gravity simulation on a GPU using CUDA, and last time we actually got a working simulator running for a 2-body system. That was exciting, but there were some drawbacks, namely the printout-copy-paste-to-spreadsheet-and-graph way of visualizing the simulation. In this post we're going to remedy that issue with a simulation display that shows the position of the bodies graphically while the simulation is running and that also runs on the graphics card alongside the simulation. We'll even make the position buffer multipurpose so that we can calculate the positions directly into this buffer, and then turn around and draw those positions into a window from the same buffer. No copying required, not even automated copying.
Making this display for the gravity simulator turned out to be more difficult than I thought because I haven't programmed in OpenGL since the graphics course I took in college, and I've certainly never done any OpenGL-CUDA interop before. I managed to pull something together by leaning heavily on the N-Body sample project that's part of the nVidia CUDA sample projects. This sample project is also a gravity simulator, but the underlying simulation engine is substantially different than the one we've built so far. Even so, I was able to use the renderer without any modifications. Let's see how it works.
