Particle-based physics

The engine includes several open source libraries and a lot are written by other programmers, but I also wrote myself some of them. An example is the particle-based physics engine, that I called SimulAxion.
You may ask what a particle-based physics engine is. I first read about it in an old paper by Thomas Jakobsen, who designed the dead-body simulator of the first chapter of the Hitman series: “Hitman: Codename 47”. In that paper Thomas described a simple way to simulate rigid-bodies, soft-bodies and cloths, through the use of particles linked by sticks. In practice, the particles follow the usual laws of dynamics, but also they are constrained in their motion by rigid connections with nearby particles. At the time it was designed, that was the fastest way to create a believable physics behavior with little computational effort. In fact, the satisfaction of constraints is performed through a mathematical method known as relaxation: the particles move back and forth for a while, thus solving in a few steps a problem difficult to fix all at once.
Thanks to this idea, you can see APOCALYX performing nice looking flags and cloths. Now, because of faster hardware, other more accurate methods are available, but there is no reason to apply more complex algorithms, when simpler ones still work quite well.