Portfolio | Stefan Andersson

While a lot of the basics were already made for me, something that was completely missing, and surprisingly hard to find any info on, was temperature - which makes sense, I guess, but for my purposes it would be a lot neater to have temperature represented as values propagating through the fluid. Getting that to work was fairly straightforward once I understood how to work with multi-threading, then I simply adjusted the properties of the particles depending on their current temperature, so that the liquid could freeze and boil.

Something I learnt the (very) hard way is that particles in SPH will tend to get stuck in each other when they get too close, which means you have to tweak your settings to avoid pressure getting too high anywhere. I couldn’t find any information on how this is usually handled, so I just added an extra force field around particles to keep them apart. It works pretty well, but because I didn’t know what kind of pressures to expect in a game setting, I spent probably months tweaking the particles to survive as high pressures as possible. And that is another huge drawback to SPH - the algorithm is so sensitive to any changes in settings that it takes a long time to calibrate and if you then realize you want to change the scale of your simulation, you have to start over.

After making some serious optimizations, I was able to have huge amounts of particles. In this gif, I suspect I’ve simulated 131.072 particles at 100 fps, although it’s been a while since I last touched the project so take that with a grain of salt. It should also be noted that I’ve sped all the gifs up a fair bit. It turns out that even if I got the fps to a good place, having particles move faster meant less precision and so the whole thing would break down.

At most I managed to push it to 262.144 particles at 60 fps on PC but unfortunately Unity appeared to freeze if I increased the size of the grid any more, so the end result was kind of messy.

This is the final result and where I decided to stop. On the left is a block of ice and on the right is lukewarm water.
Now if you’re keen-eyed, you might’ve noticed there are a lot fewer particles than in the last gif. Well, no. And yes. What you’re actually seeing are the bins containing the particles and each bin can contain up to 16 particles. As you can see in the other gifs, the particles are quite far apart from each other (due to the aforementioned force field) and using the bins for visualization and the amount of particles in a bin as alpha turned out to give a much better-looking result with less performance overhead than something like metaballs would.