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<!-- Any copyright is dedicated to the Public Domain.
http://creativecommons.org/publicdomain/zero/1.0/ -->
<!doctype html>
<html>
<head>
<meta charset="utf-8"/>
<title>WebGL editor test page</title>
<script id="shader-vs" type="x-shader/x-vertex">
precision lowp float;
attribute vec3 aVertexPosition;
void main(void) {
gl_Position = vec4(aVertexPosition, 1);
}
</script>
<script id="shader-fs" type="x-shader/x-fragment">
precision lowp float;
uniform vec3 uColor;
void main(void) {
gl_FragColor = vec4(uColor, 1);
}
</script>
</head>
<body>
<canvas id="canvas1" width="128" height="128"></canvas>
<canvas id="canvas2" width="128" height="128"></canvas>
<script type="text/javascript;version=1.8">
"use strict";
let canvas = [], gl = [];
let program = [];
let squareVerticesPositionBuffer = [];
let vertexPositionAttribute = [];
let colorUniform = [];
window.onload = function() {
for (let i = 0; i < 2; i++) {
canvas[i] = document.querySelector("#canvas" + (i + 1));
gl[i] = canvas[i].getContext("webgl", { preserveDrawingBuffer: true });
gl[i].clearColor(0.0, 0.0, 0.0, 1.0);
initProgram(i);
initBuffers(i);
drawScene(i);
}
}
function initProgram(i) {
let vertexShader = getShader(gl[i], "shader-vs");
let fragmentShader = getShader(gl[i], "shader-fs");
program[i] = gl[i].createProgram();
gl[i].attachShader(program[i], vertexShader);
gl[i].attachShader(program[i], fragmentShader);
gl[i].linkProgram(program[i]);
vertexPositionAttribute[i] = gl[i].getAttribLocation(program[i], "aVertexPosition");
gl[i].enableVertexAttribArray(vertexPositionAttribute[i]);
colorUniform[i] = gl[i].getUniformLocation(program[i], "uColor");
}
function getShader(gl, id) {
let script = document.getElementById(id);
let source = script.textContent;
let shader;
if (script.type == "x-shader/x-fragment") {
shader = gl.createShader(gl.FRAGMENT_SHADER);
} else if (script.type == "x-shader/x-vertex") {
shader = gl.createShader(gl.VERTEX_SHADER);
}
gl.shaderSource(shader, source);
gl.compileShader(shader);
return shader;
}
function initBuffers(i) {
squareVerticesPositionBuffer[i] = gl[i].createBuffer();
gl[i].bindBuffer(gl[i].ARRAY_BUFFER, squareVerticesPositionBuffer[i]);
gl[i].bufferData(gl[i].ARRAY_BUFFER, new Float32Array([
1.0, 1.0, 0.0,
-1.0, 1.0, 0.0,
1.0, -1.0, 0.0,
-1.0, -1.0, 0.0
]), gl[i].STATIC_DRAW);
}
function drawScene(i) {
gl[i].clear(gl[i].COLOR_BUFFER_BIT);
gl[i].bindBuffer(gl[i].ARRAY_BUFFER, squareVerticesPositionBuffer[i]);
gl[i].vertexAttribPointer(vertexPositionAttribute[i], 3, gl[i].FLOAT, false, 0, 0);
gl[i].useProgram(program[i]);
gl[i].uniform3fv(colorUniform[i], i == 0 ? [1, 1, 0] : [0, 1, 1]);
gl[i].drawArrays(gl[i].TRIANGLE_STRIP, 0, 4);
window.requestAnimationFrame(() => drawScene(i));
}
</script>
</body>
</html>
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