Add a WebGL layer clipping example
This commit is contained in:
Éric Lemoine
Tom Payne
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examples/layer-clipping-webgl.html
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51
examples/layer-clipping-webgl.html
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<!doctype html>
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<html lang="en">
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<head>
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<meta charset="utf-8">
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<meta http-equiv="X-UA-Compatible" content="chrome=1">
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<meta name="viewport" content="initial-scale=1.0, user-scalable=no, width=device-width">
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<link rel="stylesheet" href="../css/ol.css" type="text/css">
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<link rel="stylesheet" href="../resources/bootstrap/css/bootstrap.min.css" type="text/css">
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<link rel="stylesheet" href="../resources/layout.css" type="text/css">
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<link rel="stylesheet" href="../resources/bootstrap/css/bootstrap-responsive.min.css" type="text/css">
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<title>Layer WebGL clipping example</title>
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</head>
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<body>
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<div class="navbar navbar-inverse navbar-fixed-top">
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<div class="navbar-inner">
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<div class="container">
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<a class="brand" href="./"><img src="../resources/logo.png"> OpenLayers 3 Examples</a>
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</div>
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</div>
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</div>
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<div class="container-fluid">
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<div class="row-fluid">
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<div class="span12">
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<div id="map" class="map"></div>
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</div>
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</div>
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<div class="row-fluid">
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<div class="span12">
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<h4 id="title">Layer WebGL clipping example</h4>
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<p id="shortdesc">Layer WebGL clipping example.</p>
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<div id="docs">
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<p>This example shows how to use the <code>precompose</code> and <code>postcompose</code> rendering hooks to clip layers using WebGL.</p>
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<p>See the <a href="layer-clipping-webgl.js" target="_blank">layer-clipping-webgl.js source</a> to see how this is done.</p>
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</div>
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<div id="tags">clipping, webgl, openstreetmap</div>
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</div>
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</div>
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</div>
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<script src="loader.js?id=layer-clipping-webgl" type="text/javascript"></script>
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<script src="../resources/example-behaviour.js" type="text/javascript"></script>
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</body>
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</html>
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93
examples/layer-clipping-webgl.js
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93
examples/layer-clipping-webgl.js
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goog.require('ol.Map');
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goog.require('ol.RendererHint');
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goog.require('ol.View2D');
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goog.require('ol.layer.Tile');
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goog.require('ol.source.OSM');
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var osm = new ol.layer.Tile({
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source: new ol.source.OSM()
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});
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var map = new ol.Map({
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layers: [osm],
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renderer: ol.RendererHint.WEBGL,
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target: 'map',
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view: new ol.View2D({
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center: [0, 0],
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zoom: 2
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})
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});
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var fragmentShaderSource = [
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'precision mediump float;',
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'void main() {',
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'}'
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].join('');
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var vertexShaderSource = [
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'attribute vec2 a_position;',
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'void main() {',
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'gl_Position = vec4(a_position, 0, 1);',
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'}'
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].join('');
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osm.on('precompose', function(event) {
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var context = event.getGlContext();
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var gl = context.getGL();
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var program = gl.createProgram();
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var vertexShader = gl.createShader(gl.VERTEX_SHADER);
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gl.shaderSource(vertexShader, vertexShaderSource);
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gl.compileShader(vertexShader);
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gl.attachShader(program, vertexShader);
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var fragmentShader = gl.createShader(gl.FRAGMENT_SHADER);
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gl.shaderSource(fragmentShader, fragmentShaderSource);
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gl.compileShader(fragmentShader);
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gl.attachShader(program, fragmentShader);
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gl.linkProgram(program);
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context.useProgram(program);
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var positionLocation = gl.getAttribLocation(program, 'a_position');
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gl.enable(gl.STENCIL_TEST);
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gl.colorMask(false, false, false, false);
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gl.stencilOp(gl.KEEP, gl.KEEP, gl.REPLACE);
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gl.stencilFunc(gl.ALWAYS, 1, 0xff);
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var buffer = gl.createBuffer();
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gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
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gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
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// first band
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-1.0, -1.0, -0.75, -1.0, -1.0, 1.0,
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-1.0, 1.0, -0.75, -1.0, -0.75, 1.0,
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// second band
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-0.5, -1.0, -0.25, -1.0, -0.5, 1.0,
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-0.5, 1.0, -0.25, -1.0, -0.25, 1.0,
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// third band
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0.0, -1.0, 0.25, -1.0, 0.0, 1.0,
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0.0, 1.0, 0.25, -1.0, 0.25, 1.0,
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// forth band
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0.5, -1.0, 0.75, -1.0, 0.5, 1.0,
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0.5, 1.0, 0.75, -1.0, 0.75, 1.0
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]), gl.STATIC_DRAW);
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gl.enableVertexAttribArray(positionLocation);
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gl.vertexAttribPointer(positionLocation, 2, gl.FLOAT, false, 0, 0);
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gl.drawArrays(gl.TRIANGLES, 0, 24);
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gl.bindBuffer(gl.ARRAY_BUFFER, null);
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gl.deleteBuffer(buffer);
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gl.colorMask(true, true, true, true);
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gl.stencilFunc(gl.NOTEQUAL, 0, 0xff);
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gl.stencilOp(gl.KEEP, gl.KEEP, gl.KEEP);
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});
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osm.on('postcompose', function(event) {
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var context = event.getGlContext();
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var gl = context.getGL();
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gl.disable(gl.STENCIL_TEST);
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});
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