<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">
<style>

body { margin: 0; }
canvas { width: 100vw; height: 100vh; display: block; }
.top { position: absolute; left: 5px; top: 5px; color: white; }


</style>
</head>
<body>

<script src="https://twgljs.org/dist/twgl.min.js"></script>
<canvas></canvas>
<div class="top">click to switch effects</div>


</body>
<script>

var vs = `
attribute vec4 position;

varying vec