<!-- 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>