Particle-based physics (III)

The particle-based physics engine included in APOCALYX is useful not only to simulate flags and cloths, but also other kind of objects with different physical properties.
In fact, the rigid constaints that link particles are resolved spreading the calculations over several frames (the method, known as relaxation, guarantees convergenge, but not immediately). If the satisfaction of the constraints is further relaxed, the body built of that particles and sticks looks like a soft body rather a rigid body, as the jelly cube that you can see in the screenshot.

Other links may be designed to achieve perticular effects and behave like ropes, bumpers, springs or dampers, instead of rigid sticks. To simulate those different links, there is no need to modify the core of the constraint solver, but only the required stick lenghts. For example, a rope is a stick that can be shorter than a given length, but not longer; a bumper is just the opposite of a rope; a spring restore its lenght at a rate proportional to that length itself; a damper restores its length at a rate proportional to the length restoring rate itself; and so on.
Even if the algorithm it quite simple, the range of effects that one can achieve is remarkable.