let aspeed=1;

function setup() {

  createCanvas(windowWidth, windowHeight);

  colorMode(HSB,360,100,100);

  noStroke();

  speed=1;

}

​

function draw() {

  background(220);

  a+=aspeed;

  aspeed=bounce(a,0,360,aspeed);

  for(let i=0;i<2;i++){

    let h=i*a;

    h%=360;

    fill(h,100,100);

    let x=i*width/2;

    rect(x,0,width/2,height)

  }

}

​

function bounce(pos,low,high,speed){

    if(pos<low||pos>high) return speed*=-1;

     else return speed;

}