Adding interior ring digitizing for polygons. Thanks jachym for the initial work. r=ahocevar (closes #1894)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@10828 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

examples/donut.js

@@ -0,0 +1,38 @@
+var map = new OpenLayers.Map({
+    div: "map",
+    layers: [
+        new OpenLayers.Layer.OSM(),
+        new OpenLayers.Layer.Vector()
+    ],
+    center: new OpenLayers.LonLat(0, 0),
+    zoom: 1
+});
+
+var draw = new OpenLayers.Control.DrawFeature(
+    map.layers[1],
+    OpenLayers.Handler.Polygon,
+    {handlerOptions: {holeModifier: "altKey"}}
+);
+map.addControl(draw);
+
+// optionally listen for sketch events on the layer
+var output = document.getElementById("output");
+function updateOutput(event) {
+    window.setTimeout(function() {
+        output.innerHTML = event.type + " " + event.feature.id;
+    }, 100);
+}
+map.layers[1].events.on({
+    sketchmodified: updateOutput,
+    sketchcomplete: updateOutput
+})
+
+// add behavior to UI elements
+function toggleControl(element) {
+    if (element.value === "polygon" && element.checked) {
+        draw.activate();
+    } else {
+        draw.deactivate();
+    }
+}
+document.getElementById("noneToggle").checked = true;