Spatial Hashing and Blobbiness(!)

So though I have not yet gotten to add any real user interaction to the program, I'm pretty pleased with my progress for the week.

It turns out the Heckbert particle data structure was doing too much to be worth using for this part of the project since I only need a simple spatial data structure with a constant radius of interaction. I coded up a very basic spatial hash grid. Right now, the domain is finite for simplicity but I think if I choose a good hash function I should be able to essentially only create buckets where there are particles in the bucket. For now though, the grid is large enough to address any animations I would want to simulate and fine enough to get save on search time. The data structure is able to find all particles within the radius of interaction (which is also the grid size) by only searching within its own bucket and the neighboring 26 buckets instead of searching the entire space. I wrote a test program to make sure the spatial hashing grid is able to correctly find its neighbors. Every time step, the grid is regridded by looping through the particles and updating their buckets in O(n). Here is a video of the test program running:



The selected particle is in blue (I am using the arrow keys to toggle the selection) and its neighbors are colored red. I added some random particle movement to test that the regridding is working correctly. The boundaries of the grid are also shown.

I have implemented Lagrangian viscoelastic fluid dynamics in a method very similar to the Clavet et al. paper. The springs were tricky to get stable, and required some tweaking. Here is an entertaining video of the entire thing blowing up while debugging the springs.



Even with the speedup from the spatial data structure, I am still having difficulty getting it to run at real time for 1000 particles. Running at 100 particles though, I am still able to get enough resolution to see droplets forming. And best of all, I was able to get some blobby surface tension effects by tweaking the rest pressure parameter. The parameters could still use some more tweaking, e.g. probably way too much elasticity and viscosity right now, but I'm pretty happy with my progress. Anyway, here are some videos of my blobby particles:



For next week, I am planning on trying to speedup the framerate, starting to add in user interaction and working on getting the implicit formulation working. It might be worth trying a simple marching cubes method just to see how fast it is, vis a vis this openSource implementation Joe sent me: http://paulbourke.net/geometry/polygonise/

Alpha reviews coming up... hope it goes okay