patch for #452 - Adding events to Layer class to signal the start, end, and cancelling of a layer load. Thanks to Bart for the idea and followthrough with this patch.

git-svn-id: http://svn.openlayers.org/trunk/openlayers@2200 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer/WMS/Untiled.js

@@ -30,7 +30,10 @@ OpenLayers.Layer.WMS.Untiled.prototype =
 
     /** @type OpenLayers.Tile.Image */
     tile: null,
-    
+
+    /** did the image finish loading before a new draw was initiated?
+     * @type Boolean */
+    doneLoading: false,
 
     /**
     * @constructor
@@ -108,6 +111,10 @@ OpenLayers.Layer.WMS.Untiled.prototype =
      * @param {Boolean} dragging
      */
     moveTo:function(bounds, zoomChanged, dragging) {
+        if (!this.doneLoading) {
+            this.events.triggerEvent("loadcancel"); 
+            this.doneLoading = true; 
+        }
         OpenLayers.Layer.HTTPRequest.prototype.moveTo.apply(this,arguments);
         
         if (bounds == null) {
@@ -155,10 +162,18 @@ OpenLayers.Layer.WMS.Untiled.prototype =
                 this.tile = null;
             }
 
+            this.events.triggerEvent("loadstart");
+            this.doneLoading = false;
             if (!this.tile) {
                 this.tile = new OpenLayers.Tile.Image(this, pos, tileBounds, 
                                                      url, tileSize);
                 this.tile.draw();
+                var onload = function() { 
+                    this.doneLoading = true; 
+                    this.events.triggerEvent("loadend"); 
+                }
+                OpenLayers.Event.observe(this.tile.imgDiv, 'load',
+                                         onload.bindAsEventListener(this));
             } else {
                 this.tile.moveTo(tileBounds, pos);
             }