// Maximum lifetime
//   Particle system should be disabled while out of view. If they've been
//   out of view for more than the maximum particle lifetime, only
//   maximum particle lifetime is played back when the come into view again.
//
//   Optimally, they should be low-priority updateale (eg. per frame budget)
//   to prevent the hang that would occur when they come into view again


ParticleSystem:
  Just manages raw particles
  
ParticleRenderer:
  Converts particles to vertices (if neccessary) and draws them (usually
  through the PrimitiveBatch)

IEmitter:
  Emits particles

I { affector attractor influencer manipulator interferer }
  Influences particles (eg. wind, gravity)