var sSize = 10;

var curSecond = 0;

var prevSecond = 0;

var fps = 0;

var curFps = 0;

​

function setup() {

  createCanvas(600, 400);

}

​

function draw() {

  background(0);

  strokeWeight(0);

  stroke(255);

  rectMode(CENTER);

​

  for (var x = sSize; x <= width; x += sSize) {

    for (var y = sSize; y <= height; y += sSize) {

      var r = map(x, 0, width, 0, 255);

      var g = map(mouseX, 0, 600, 0, 255);

      var b = map(y, 0, height, 0, 255);

      fill(r, g, b);

      square(x, y, sSize);

    }

  }

  curSecond = (Date.now() / 1000) | 0;

  if (curSecond == prevSecond) {

    curFps++;

  } else {

    prevSecond = curSecond;

    fps = curFps;

    curFps = 0;

    console.log("FPS: " + fps);

  }

}

​