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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;
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>
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