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

<script src="https://twgljs.org/dist/4.x/twgl.min.js"></script>


</body>
<script>

const vs = `#version 300 es
void main() {
  gl_Position = vec4(0, 0, 0, 1);
  gl_PointSize = 1.0;
}
`;

const fs = `#version 300 es
precision highp float;
uniform sampler2D tex;
out vec4 outColor;
void main() {
  int level = 0;
  ivec2 size = textureSi