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

canvas { border: 1px solid black; }


</style>
</head>
<body>

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


</body>
<script>

const vs = `
attribute vec4 position;
attribute vec4 position1;  // second vertex for triangle
attribute vec4 position2;  // third vertex for triangle
uniform mat4 matrix;

bool vertexClippe