float GRAVITY = .1;

class Particle{
   Invader i;
    float x,y,xs,ys;
    color c;
  Particle(Invader pi, boolean building){
      x = pi.x+(pi.w/2);
      y = pi.y + (pi.h/2);
      xs = random(-2,2);
      ys = random(-2,2   );
         c = color(255); 
      if(building && random(100) < 50){
         c = GREEN;
      }
  }

  Particle(Tank t){
      x = t.x+(t.w/2);
      y = t.y + (t.h/2);
      xs = random(-2,2);
      ys = random(-2,2   );
         c = GREEN;
      
  }


  Particle(float px, float py){
    x = random(px, px+INVADER_WIDTH);
    y = random(py, py+INVADER_HEIGHT);
    c= WHITE;
  }  
 
  
  void move(){
    ys += GRAVITY;
    x += xs;
    y += ys;
    if(y > height){
       particlesToKill.add(this); 
    }
  }
  
  void draw(){
     noStroke();
    fill(c);
   rect(x,y,3,3); 
  }
  
  
}