Stripe[] stripes = new Stripe[40];

void setup() {
  size(640,480);
    for (int i =0; i<stripes.length; i++){
      stripes[i] = new Stripe();
    }
}
  
  
void draw(){
  background(100);
  for (int i = 0; i<stripes.length; i++) {
    stripes[i].rollover(mouseX,mouseY);
    stripes[i].move();
    stripes[i].display();
  }
}

class Stripe { 
  float x;
  float speed;
  float w;
  boolean mouse;
  
  Stripe() {
    x=0;
    speed=random(1);
    w=random(10,30);
    mouse=false;
  }
  
  void display(){
    if (mouse){
      fill(255);
    }else{
      fill(255,50);
    }
    noStroke();
    rect(x,0,w,height);
  }
  
  void move(){
    x+= speed;
    if(x>width+20) x =-20;
  }
  
  void rollover(int mx, int my){
    if (mx > x && mx < x + w){
      mouse = true;
    }else{
      mouse = false;
    }
  }
}