Example demonstrating a spyglass effect

Riffing off of the layer swipe example, this one demonstrates viewing one layer over another though a lens.
2014-01-10 13:32:54 -07:00
parent ab0268a8f1
commit 29e3794845
2 changed files with 128 additions and 0 deletions
--- a/examples/layer-spy.html
+++ b/examples/layer-spy.html
@@ -0,0 +1,60 @@
+<!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 Spy 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 spy example</h4>
+          <p id="shortdesc">View a portion of one layer over another</p>
+          <div id="docs">
+            <p>
+              Layer rendering can be manipulated in <code>precompose</code> and <code>postcompose</code> event listeners.
+              These listeners get an event with a reference to the Canvas rendering context.
+              In this example, the <code>precompose</code> listener sets a clipping mask around the most
+              recent mouse position, giving you a spyglass effect for viewing one layer over another.
+            </p>
+            <p>
+              Move around the map to see the effect.  Use the ↑ up and ↓ down arrow keys to adjust the spyglass size.
+            </p>
+            <p>See the <a href="layer-spy.js" target="_blank">layer-spy.js source</a> to see how this is done.</p>
+          </div>
+          <div id="tags">spy, image manipulation</div>
+        </div>
+
+      </div>
+
+    </div>
+
+    <script src="jquery.min.js" type="text/javascript"></script>
+    <script src="loader.js?id=layer-spy" type="text/javascript"></script>
+    <script src="../resources/example-behaviour.js" type="text/javascript"></script>
+
+  </body>
+</html>
--- a/examples/layer-spy.js
+++ b/examples/layer-spy.js
@@ -0,0 +1,68 @@
+goog.require('ol.Map');
+goog.require('ol.RendererHint');
+goog.require('ol.View2D');
+goog.require('ol.layer.Tile');
+goog.require('ol.proj');
+goog.require('ol.source.BingMaps');
+
+var key = 'Ak-dzM4wZjSqTlzveKz5u0d4IQ4bRzVI309GxmkgSVr1ewS6iPSrOvOKhA-CJlm3';
+
+var roads = new ol.layer.Tile({
+  source: new ol.source.BingMaps({key: key, imagerySet: 'Road'})
+});
+
+var imagery = new ol.layer.Tile({
+  source: new ol.source.BingMaps({key: key, imagerySet: 'Aerial'})
+});
+
+var map = new ol.Map({
+  layers: [roads, imagery],
+  renderer: ol.RendererHint.CANVAS,
+  target: 'map',
+  view: new ol.View2D({
+    center: ol.proj.transform([-109, 46.5], 'EPSG:4326', 'EPSG:3857'),
+    zoom: 6
+  })
+});
+
+var radius = 75;
+$(document).keydown(function(evt) {
+  if (evt.which === 38) {
+    radius = Math.min(radius + 5, 150);
+    map.requestRenderFrame();
+  } else if (evt.which === 40) {
+    radius = Math.max(radius - 5, 25);
+    map.requestRenderFrame();
+  }
+});
+
+// get the pixel position with every move
+var mousePosition = null;
+$(map.getViewport()).on('mousemove', function(evt) {
+  mousePosition = map.getEventPixel(evt.originalEvent);
+  map.requestRenderFrame();
+}).on('mouseout', function() {
+  mousePosition = null;
+  map.requestRenderFrame();
+});
+
+// before rendering the layer, do some clipping
+imagery.on('precompose', function(event) {
+  var ctx = event.getContext();
+  ctx.save();
+  ctx.beginPath();
+  if (mousePosition) {
+    // only show a circle around the mouse
+    ctx.arc(mousePosition[0], mousePosition[1], radius, 0, 2 * Math.PI);
+    ctx.lineWidth = 5;
+    ctx.strokeStyle = 'rgba(0,0,0,0.5)';
+    ctx.stroke();
+  }
+  ctx.clip();
+});
+
+// after rendering the layer, restore the canvas context
+imagery.on('postcompose', function(event) {
+  var ctx = event.getContext();
+  ctx.restore();
+});