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Add a WebGL layer clipping example

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Éric Lemoine
2013-11-18 16:14:39 +01:00
committed by Tom Payne
parent 215344af71
commit c217c95e6d
2 changed files with 144 additions and 0 deletions
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examples/layer-clipping-webgl.html Normal file
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<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="chrome=1">
<meta name="viewport" content="initial-scale=1.0, user-scalable=no, width=device-width">
<link rel="stylesheet" href="../css/ol.css" type="text/css">
<link rel="stylesheet" href="../resources/bootstrap/css/bootstrap.min.css" type="text/css">
<link rel="stylesheet" href="../resources/layout.css" type="text/css">
<link rel="stylesheet" href="../resources/bootstrap/css/bootstrap-responsive.min.css" type="text/css">
<title>Layer WebGL clipping example</title>
</head>
<body>
<div class="navbar navbar-inverse navbar-fixed-top">
<div class="navbar-inner">
<div class="container">
<a class="brand" href="./"><img src="../resources/logo.png"> OpenLayers 3 Examples</a>
</div>
</div>
</div>
<div class="container-fluid">
<div class="row-fluid">
<div class="span12">
<div id="map" class="map"></div>
</div>
</div>
<div class="row-fluid">
<div class="span12">
<h4 id="title">Layer WebGL clipping example</h4>
<p id="shortdesc">Layer WebGL clipping example.</p>
<div id="docs">
<p>This example shows how to use the <code>precompose</code> and <code>postcompose</code> rendering hooks to clip layers using WebGL.</p>
<p>See the <a href="layer-clipping-webgl.js" target="_blank">layer-clipping-webgl.js source</a> to see how this is done.</p>
</div>
<div id="tags">clipping, webgl, openstreetmap</div>
</div>
</div>
</div>
<script src="loader.js?id=layer-clipping-webgl" type="text/javascript"></script>
<script src="../resources/example-behaviour.js" type="text/javascript"></script>
</body>
</html>

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examples/layer-clipping-webgl.js Normal file
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goog.require('ol.Map');
goog.require('ol.RendererHint');
goog.require('ol.View2D');
goog.require('ol.layer.Tile');
goog.require('ol.source.OSM');
var osm = new ol.layer.Tile({
source: new ol.source.OSM()
});
var map = new ol.Map({
layers: [osm],
renderer: ol.RendererHint.WEBGL,
target: 'map',
view: new ol.View2D({
center: [0, 0],
zoom: 2
})
});
var fragmentShaderSource = [
'precision mediump float;',
'void main() {',
'}'
].join('');
var vertexShaderSource = [
'attribute vec2 a_position;',
'void main() {',
'gl_Position = vec4(a_position, 0, 1);',
'}'
].join('');
osm.on('precompose', function(event) {
var context = event.getGlContext();
var gl = context.getGL();
var program = gl.createProgram();
var vertexShader = gl.createShader(gl.VERTEX_SHADER);
gl.shaderSource(vertexShader, vertexShaderSource);
gl.compileShader(vertexShader);
gl.attachShader(program, vertexShader);
var fragmentShader = gl.createShader(gl.FRAGMENT_SHADER);
gl.shaderSource(fragmentShader, fragmentShaderSource);
gl.compileShader(fragmentShader);
gl.attachShader(program, fragmentShader);
gl.linkProgram(program);
context.useProgram(program);
var positionLocation = gl.getAttribLocation(program, 'a_position');
gl.enable(gl.STENCIL_TEST);
gl.colorMask(false, false, false, false);
gl.stencilOp(gl.KEEP, gl.KEEP, gl.REPLACE);
gl.stencilFunc(gl.ALWAYS, 1, 0xff);
var buffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
// first band
-1.0, -1.0, -0.75, -1.0, -1.0, 1.0,
-1.0, 1.0, -0.75, -1.0, -0.75, 1.0,
// second band
-0.5, -1.0, -0.25, -1.0, -0.5, 1.0,
-0.5, 1.0, -0.25, -1.0, -0.25, 1.0,
// third band
0.0, -1.0, 0.25, -1.0, 0.0, 1.0,
0.0, 1.0, 0.25, -1.0, 0.25, 1.0,
// forth band
0.5, -1.0, 0.75, -1.0, 0.5, 1.0,
0.5, 1.0, 0.75, -1.0, 0.75, 1.0
]), gl.STATIC_DRAW);
gl.enableVertexAttribArray(positionLocation);
gl.vertexAttribPointer(positionLocation, 2, gl.FLOAT, false, 0, 0);
gl.drawArrays(gl.TRIANGLES, 0, 24);
gl.bindBuffer(gl.ARRAY_BUFFER, null);
gl.deleteBuffer(buffer);
gl.colorMask(true, true, true, true);
gl.stencilFunc(gl.NOTEQUAL, 0, 0xff);
gl.stencilOp(gl.KEEP, gl.KEEP, gl.KEEP);
});
osm.on('postcompose', function(event) {
var context = event.getGlContext();
var gl = context.getGL();
gl.disable(gl.STENCIL_TEST);
});