Mass-Aggregate, or also known as Particle or Verlet Physics are systems that govern a set of point particles, each with a specific mass. The particles then interact with each other through force generators.
Please see physics systems for a general overview of physics systems in Trial.
A particle is a physics-entity and a located-entity. As discussed, it has no "size", so there's no associated shape or primitive at all. By default, a Verlet integration scheme is used to update the particle state, which should be stable enough for most game uses.
Particles also implement resolve-hit and the associated resolve-velocity and resolve-intersection functions, responsible for resolving a contact between two particles. However, since particles have no size of their own, they cannot by themselves generate contacts.
Instead, the responsibility of contact generation falls onto the hit-generator which must simply implement the generate-hits function as described for the physics systems. The following set of contact generators is provided out of the box:
particle-link
A mixin class for any contact generator between two particles a and b.
particle-cable
A particle cable is similar to a bungee-force wherein the two particles are prevented from separating farther than the max-length, invoking the restitution factor if exceeded.
particle-rod
And the rod is similar to a spring-force with a specific distance between the particles being enforced.
Finally, the mass-aggregate-system allows you to run a simulation with particles, using hit-generators for contact generation. Similar to forces and particles, you can add and remove generators with enter and leave.
Otherwise the mass aggregate system implements all the necessary functionality to generate and resolve contacts, and to integrate the simulation, so no special care has to be taken.
Note that this system uses an object per particle and per contact or force generator. This does not scale well to thousands let alone millions of objects. A special matrix-based solver would have to be written to handle such scales.