Example demonstrating a spyglass effect
Riffing off of the layer swipe example, this one demonstrates viewing one layer over another though a lens.
This commit is contained in:
Tim Schaub
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examples/layer-spy.html
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examples/layer-spy.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 Spy 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 spy example</h4>
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<p id="shortdesc">View a portion of one layer over another</p>
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<div id="docs">
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<p>
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Layer rendering can be manipulated in <code>precompose</code> and <code>postcompose</code> event listeners.
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These listeners get an event with a reference to the Canvas rendering context.
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In this example, the <code>precompose</code> listener sets a clipping mask around the most
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recent mouse position, giving you a spyglass effect for viewing one layer over another.
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</p>
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<p>
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Move around the map to see the effect. Use the ↑ up and ↓ down arrow keys to adjust the spyglass size.
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</p>
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<p>See the <a href="layer-spy.js" target="_blank">layer-spy.js source</a> to see how this is done.</p>
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</div>
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<div id="tags">spy, image manipulation</div>
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</div>
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</div>
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</div>
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<script src="jquery.min.js" type="text/javascript"></script>
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<script src="loader.js?id=layer-spy" 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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68
examples/layer-spy.js
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examples/layer-spy.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.proj');
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goog.require('ol.source.BingMaps');
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var key = 'Ak-dzM4wZjSqTlzveKz5u0d4IQ4bRzVI309GxmkgSVr1ewS6iPSrOvOKhA-CJlm3';
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var roads = new ol.layer.Tile({
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source: new ol.source.BingMaps({key: key, imagerySet: 'Road'})
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});
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var imagery = new ol.layer.Tile({
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source: new ol.source.BingMaps({key: key, imagerySet: 'Aerial'})
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});
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var map = new ol.Map({
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layers: [roads, imagery],
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renderer: ol.RendererHint.CANVAS,
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target: 'map',
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view: new ol.View2D({
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center: ol.proj.transform([-109, 46.5], 'EPSG:4326', 'EPSG:3857'),
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zoom: 6
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})
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});
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var radius = 75;
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$(document).keydown(function(evt) {
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if (evt.which === 38) {
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radius = Math.min(radius + 5, 150);
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map.requestRenderFrame();
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} else if (evt.which === 40) {
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radius = Math.max(radius - 5, 25);
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map.requestRenderFrame();
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}
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});
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// get the pixel position with every move
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var mousePosition = null;
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$(map.getViewport()).on('mousemove', function(evt) {
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mousePosition = map.getEventPixel(evt.originalEvent);
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map.requestRenderFrame();
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}).on('mouseout', function() {
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mousePosition = null;
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map.requestRenderFrame();
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});
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// before rendering the layer, do some clipping
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imagery.on('precompose', function(event) {
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var ctx = event.getContext();
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ctx.save();
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ctx.beginPath();
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if (mousePosition) {
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// only show a circle around the mouse
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ctx.arc(mousePosition[0], mousePosition[1], radius, 0, 2 * Math.PI);
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ctx.lineWidth = 5;
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ctx.strokeStyle = 'rgba(0,0,0,0.5)';
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ctx.stroke();
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}
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ctx.clip();
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});
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// after rendering the layer, restore the canvas context
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imagery.on('postcompose', function(event) {
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var ctx = event.getContext();
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ctx.restore();
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});
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