let y = 0;

let w = 40;

let h = 40;

let xjump = 2;

let yjump = 3;

​

function setup() {

  createCanvas(400,400);

  background(100);

}

​

function draw() {

  colorMode(HSB);

  fill(

    map(x,0,width,0,360),

    map(mouseX,0,width,0,100),

    map(y,0,height,0,100)

  );

  rect(x,y,w,h);

  x = x + xjump;

  y = y + yjump;

if(x >= width || x <= 0){

  xjump = xjump * -1;

  }

if(y >= height || y <= 0){

    yjump = yjump * -1;

    }

​

}