openlayers/examples/styles-context.html

   1 <html xmlns="http://www.w3.org/1999/xhtml">
   2   <head>
   3     <title>OpenLayers Vector Styles</title>
   4     <link rel="stylesheet" href="../theme/default/style.css" type="text/css" />
   5     <link rel="stylesheet" href="style.css" type="text/css" />
   6     <script src="../lib/OpenLayers.js"></script>
   7     <script type="text/javascript">
   8         var map;
   9
  10         function init(){
  11             map = new OpenLayers.Map('map', {maxResolution:'auto'});
  12             var wms = new OpenLayers.Layer.WMS( "OpenLayers WMS",
  13                 "http://labs.metacarta.com/wms/vmap0", {layers: 'basic'} );
  14             map.addLayer(wms);
  15             map.setCenter(new OpenLayers.LonLat(0, 0), 0);
  16
  17             // Strategy 1:  Style features based on some attribute.
  18
  19             // create 50 random features in the northern hemisphere
  20             // give them a "type" attribute that will be used to style
  21             // them by size
  22             var features = new Array(50);
  23             for (var i=0; i<features.length; i++) {
  24                 features[i] = new OpenLayers.Feature.Vector(
  25                     new OpenLayers.Geometry.Point(
  26                         (360 * Math.random()) - 180, 90 * Math.random()
  27                     ), {
  28                         type: 5 + parseInt(5 * Math.random())
  29                     }
  30                 );
  31             }
  32
  33             // create the layer styleMap with a simple symbolizer template
  34             var layer1 = new OpenLayers.Layer.Vector('Points', {
  35                 styleMap: new OpenLayers.StyleMap({
  36                     pointRadius: "${type}", // based on feature.attributes.type
  37                     fillColor: "#666666"
  38                 })
  39             });
  40             layer1.addFeatures(features);
  41
  42             // Strategy 2:  Style features based on something besides attributes.
  43
  44             // create 50 random features in the southern hemisphere
  45             var features = new Array(50);
  46             for (var i=0; i<features.length; i++) {
  47                 features[i] = new OpenLayers.Feature.Vector(
  48                     new OpenLayers.Geometry.Point(
  49                         (360 * Math.random()) - 180, -90 * Math.random()
  50                     ), {
  51                         type: 5 + parseInt(5 * Math.random())
  52                     }
  53                 );
  54             }
  55             // create the layer styleMap by giving the default style a context
  56             var colors = ["red", "green", "blue"];
  57             var context = {
  58                 getColor: function(feature) {
  59                     var region = parseInt((feature.geometry.x + 180) / 120);
  60                     return colors[region];
  61                 },
  62                 getType: function(feature) {
  63                     return feature.attributes["type"];
  64                 }
  65             };
  66             var template = {
  67                 pointRadius: "${getType}", // using context.getType(feature)
  68                 fillColor: "${getColor}" // using context.getColor(feature)
  69             };
  70             var style = new OpenLayers.Style(template, {context: context});
  71             var layer2 = new OpenLayers.Layer.Vector('Points', {
  72                 styleMap: new OpenLayers.StyleMap(style)
  73             });
  74             layer2.addFeatures(features);
  75
  76
  77             map.addLayers([layer1, layer2]);
  78         }
  79     </script>
  80   </head>
  81   <body onload="init()">
  82     <h1 id="title">Feature Styles Example</h1>
  83
  84     <div id="tags"></div>
  85
  86     <p id="shortdesc">
  87         To style features with a custom function that evaluates each feature, use
  88         the context option of an OpenLayers.Style object.  If the context object
  89         contains a function and this function is referenced in a symbolizer, the
  90         function will be called with the feature as an argument..
  91     </p>
  92
  93     <div id="map" class="smallmap"></div>
  94
  95     <div id="docs">
  96         <p>Features in the northern hemisphere are styled according to their
  97         "type" attribute.  This is accomplished with a simple template that
  98         is evaluated with the feature attributes as context.</p>
  99         <p>Features in the sourthern hemisphere are styled according to a
 100         combination of their attributes and non-attribute properties.  This
 101         is accomplished using an advanced template that calls functions
 102         on the context object passed to the Style constructor.</p>
 103     </div>
 104   </body>
 105 </html>