createCanvas(400, 400);

  colorMode(HSB);

  noStroke();

}

​

function draw() {

  let leftHue = map(mouseX, 0, width, 0, 90);

  fill(leftHue, 100, 100);

  rect(0, 0, width/4, height);

  fill(360 - leftHue, 100, 100);

  rect(width/4, 0, width/4, height);

  fill(180 + leftHue, 100, 100);

  rect(2*width/4, 0, width/4, height);

  fill(180 - leftHue , 100, 100);

  rect(3*width/4, 0, width/4, height);

  // for (let i = 0; i < width; i +=1) {

  //   let hueColor = map(i, 0, width, 0, 360);

  //   stroke(hueColor, 100, 100);

  //   line(i, 0, i, height);

  // }

}