ParticleSystem.pde

//Particles
class ParticleSystem{
  ArrayList<Particle> particles;
 
  PVector origin;
   
  boolean paused;
   
  ParticleSystem(){
    particles = new ArrayList<Particle>(); 
    origin = new PVector();
  }
 
  void addParticle(){
    particles.add(new Particle(origin));
  }
 
  void run(){
    Iterator<Particle> it = particles.iterator();
  
    while(it.hasNext()){
      Particle p = it.next();
      
      if(paused){
        p.display();
        
        continue;
      }
    
    p.run();
    
    if(p.isDead())
      it.remove();
      
    }
  }
 
  boolean isEmpty(){
    if(particles.size() == 0)
      return true;
      
    return false;
 }
 
  void applyForce(PVector force){
    
    if(!paused)
      for(Particle p : particles){
        p.applyForce(force);
      }
  }

}

class Particle{
  PVector location;
  PVector velocity;
  PVector acceleration;
  
  float mass = 1;
  float lifespan;
  
  Particle(PVector l){
    location = new PVector(l.x,l.y);
    acceleration = new PVector();
    velocity = new PVector(random(-1,1),random(-1,1));
    lifespan = 255;
  }
  
  void update(){
    velocity.add(acceleration);
    location.add(velocity);
    
    acceleration.mult(0);
    
    lifespan -= 8.0f;
  }
  
  void display(){
    
    pushMatrix();
    
    translate(location.x,location.y);
    
    stroke(255,lifespan);
    fill(255, lifespan);
    
    ellipse(0,0,0.5,0.5);
    
    popMatrix();
  }
  
  void run(){
    update();
    display();
  }
  
  void applyForce(PVector force){
    PVector f = force.get();
    f.div(mass);
    acceleration.add(f);
  }
  
  boolean isDead(){
    if(lifespan < 0.0)
      return true;
    else
      return false;
  }
}