trigger an event when the layer's opacity change. r=elemoine (closes #2112)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@9616 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer.js

@@ -1109,6 +1109,12 @@ OpenLayers.Layer = OpenLayers.Class({
                 OpenLayers.Util.modifyDOMElement(element, null, null, null, 
                                                  null, null, null, opacity);
             }
+            if (this.map != null) {
+                this.map.events.triggerEvent("changelayer", {
+                    layer: this,
+                    property: "opacity"
+                });
+            }
         }
     },
 

lib/OpenLayers/Map.js

@@ -61,12 +61,12 @@ OpenLayers.Map = OpenLayers.Class({
      *  - *removelayer* triggered after a layer has been removed.  The event
      *      object will include a *layer* property that references the removed
      *      layer.
-     *  - *changelayer* triggered after a layer name change, order change, or
+     *  - *changelayer* triggered after a layer name change, order change,
-     *      visibility change (due to resolution thresholds).  Listeners will
+     *      opacity change or visibility change (due to resolution thresholds).
-     *      receive an event object with *layer* and *property* properties.  The
+     *      Listeners will receive an event object with *layer* and *property*
-     *      *layer* property will be a reference to the changed layer.  The
+     *      properties.  The *layer* property will be a reference to the
-     *      *property* property will be a key to the changed property (name,
+     *      changed layer.  The *property* property will be a key to the
-     *      visibility, or order).
+     *      changed property (name, order, opacity or visibility).
      *  - *movestart* triggered after the start of a drag, pan, or zoom
      *  - *move* triggered after each drag, pan, or zoom
      *  - *moveend* triggered after a drag, pan, or zoom completes

tests/Layer.html

@@ -469,7 +469,36 @@
         t.eq(hasBase, true, "when afterAdd is called, map has a base layer");
         
     }
+    
+    function test_setOpacity(t) {
+        t.plan(5);
 
+        var map, layer, log;
+        
+        map = new OpenLayers.Map("map");
+        layer = new OpenLayers.Layer("");
+        map.addLayer(layer);
+
+        log = [];
+        map.events.register('changelayer', t, function(event) {
+            log.push({layer: event.layer, property: event.property});
+        });
+        layer.setOpacity(0.42);
+        t.eq(layer.opacity, 0.42,
+             "setOpacity() set layer.opacity to correct value");
+        t.eq(log.length, 1,
+             "setOpacity() triggers changelayer once");
+        t.ok(log[0].layer == layer,
+             "changelayer listener called with expected layer");
+        t.eq(log[0].property, "opacity",
+             "changelayer listener called with expected property");
+
+        // This call must not trig the event because the opacity value is the same.
+        log = [];
+        layer.setOpacity(0.42);
+        t.eq(log.length, 0,
+             "setOpacity() does not trigger changelayer if the opacity value is the same");
+    }
 
 
 /******