​

function setup() {

  createCanvas(400, 400);

  print("use: mouse x,y for center\nmouseWheel zoom");

}

​

function draw() {

  translate(mouseX, mouseY);

  scale(zoom);

  background(200, 200, 0);

  noFill();

  stroke(0, 0, 200);

  strokeWeight(5);

  for (let i = 0; i < 10; i++) circle(0, 0, (i + 1) * 100);

}

​

function mouseWheel(event) {

  zoom += event.delta * 0.1; // rollover at 0 ( mirroring )

  print("zoom " + nf(zoom,1,1));

}