<!-- 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; uniform float uDepth; void main(void) { gl_Position = vec4(aVertexPosition, uDepth); } </script> <script id="shader-fs-0" type="x-shader/x-fragment"> precision lowp float; void main(void) { gl_FragColor = vec4(0.5, 0.5, 0.5, 1.0); } </script> <script id="shader-fs-1" type="x-shader/x-fragment"> precision lowp float; void main(void) { gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0); } </script> </head> <body> <canvas id="canvas" width="128" height="128"></canvas> <script type="text/javascript;version=1.8"> "use strict"; let canvas, gl; let program = []; let squareVerticesPositionBuffer; let vertexPositionAttribute = []; let depthUniform = []; window.onload = function() { canvas = document.querySelector("canvas"); gl = canvas.getContext("webgl", { preserveDrawingBuffer: true }); gl.clearColor(0.0, 0.0, 0.0, 1.0); initProgram(0); initProgram(1); initBuffers(); drawScene(); } function initProgram(i) { let vertexShader = getShader("shader-vs"); let fragmentShader = getShader("shader-fs-" + i); program[i] = gl.createProgram(); gl.attachShader(program[i], vertexShader); gl.attachShader(program[i], fragmentShader); gl.linkProgram(program[i]); vertexPositionAttribute[i] = gl.getAttribLocation(program[i], "aVertexPosition"); gl.enableVertexAttribArray(vertexPositionAttribute[i]); depthUniform[i] = gl.getUniformLocation(program[i], "uDepth"); } function getShader(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() { squareVerticesPositionBuffer = gl.createBuffer(); gl.bindBuffer(gl.ARRAY_BUFFER, squareVerticesPositionBuffer); gl.bufferData(gl.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.STATIC_DRAW); } function drawScene() { gl.clear(gl.COLOR_BUFFER_BIT); for (let i = 0; i < 2; i++) { gl.bindBuffer(gl.ARRAY_BUFFER, squareVerticesPositionBuffer); gl.vertexAttribPointer(vertexPositionAttribute[i], 3, gl.FLOAT, false, 0, 0); gl.useProgram(program[i]); gl.uniform1f(depthUniform[i], i + 1); blend(i); gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4); } window.requestAnimationFrame(drawScene); } function blend(i) { if (i == 0) { gl.disable(gl.BLEND); } else if (i == 1) { gl.enable(gl.BLEND); gl.blendColor(0.5, 0, 0, 0.25); gl.blendEquationSeparate( gl.FUNC_REVERSE_SUBTRACT, gl.FUNC_SUBTRACT); gl.blendFuncSeparate( gl.CONSTANT_COLOR, gl.ONE_MINUS_CONSTANT_COLOR, gl.ONE_MINUS_CONSTANT_COLOR, gl.CONSTANT_COLOR); } } </script> </body> </html>