generateParticles method
Generates an amount of particles and initializes them.
This can be used to generate the initial particles or new particles when the options change
Implementation
@protected
List<Particle> generateParticles(int numParticles) {
return List.generate(numParticles, (i) => i).map((i) {
Particle p = Particle();
initParticle(p);
return p;
}).toList();
}