Realtime 2D Gravity Simulation

This has been a fun side project I've wanted to work on for a while. I had originally just planned on doing a GPU based particle fluid, but I got sidetracked by the nice looking results of the gravity simulation. (Sorry about all the compression artifacts, kind of impossible to avoid when uploading something like this to youtube) It is still very much a work in progress. This uses a grid based approach to simulating gravity for extremly high particle counts. All calculations are performed exclusively on the GPU. Multiple levels of detail are used (I settled on 4), to get fairly accurate approximations for nearby particles, and rough approximations for distant particles. There are quite a few known issues. Most notable would be a pretty significant dampening effect, since intra-pixel particle forces are very underestimated. Additionally, sometimes large collections of particles moving in unison seem to hit invisible walls. I suspect this might have to do with down-sampling always usin