index.html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>simultaneous contrast illusion</title>
<script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/0.4.13/p5.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/0.4.13/addons/p5.dom.min.js"></script>
<script>
function setup() {
var myCanvas = createCanvas(800, 400);
myCanvas.parent('p5js');
fondo = document.getElementById("fondo");
pos = document.getElementById("pos");
noStroke();
}
function draw() {
rectMode(CORNER);
fill( 1*fondo.value );
rect(0,0,400,400)
fill(255 - fondo.value);
rect(400,0,400,400)
rectMode(CENTER);
fill(128);
rect(pos.value,200,100,100);
rect(800-pos.value,200,100,100);
}
</script>
</head>
<body>
<input type="range" id="fondo" min="0" max="255" value="64">
<br>
<input type="range" id="pos" min="0" max="400" value="200">
<div id="p5js"></div>
</body>
</html>