make drag handler work with touch events, p=lotsofpeople, r=tschaub (closes #2995)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@11189 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Events.js

@@ -90,6 +90,20 @@ OpenLayers.Event = {
         return event.target || event.srcElement;
     },
 
+    /**
+     * Method: isSingleTouch
+     * Determine whether event was caused by a single touch
+     *
+     * Parameters:
+     * event - {Event}
+     *
+     * Returns:
+     * {Boolean}
+     */
+    isSingleTouch: function(event) {
+        return event.touches && event.touches.length == 1;
+    },
+
     /**
      * Method: isLeftClick
      * Determine whether event was caused by a left click. 
@@ -369,7 +383,8 @@ OpenLayers.Events = OpenLayers.Class({
         "mouseover", "mouseout",
         "mousedown", "mouseup", "mousemove", 
         "click", "dblclick", "rightclick", "dblrightclick",
-        "resize", "focus", "blur"
+        "resize", "focus", "blur",
+        "touchstart", "touchmove", "touchend"
     ],
 
     /** 
@@ -846,10 +861,16 @@ OpenLayers.Events = OpenLayers.Class({
         if (!this.element.offsets) {
             this.element.offsets = OpenLayers.Util.pagePosition(this.element);
         }
+        var clientX = evt.clientX;
+        var clientY = evt.clientY;
+        if (evt.touches && evt.touches.length > 0) {
+            clientX = evt.touches[0].clientX;
+            clientY = evt.touches[0].clientY;
+        }
         return new OpenLayers.Pixel(
-            (evt.clientX + this.element.scrolls[0]) - this.element.offsets[0]
+            (clientX + this.element.scrolls[0]) - this.element.offsets[0]
                          - this.element.lefttop[0], 
-            (evt.clientY + this.element.scrolls[1]) - this.element.offsets[1]
+            (clientY + this.element.scrolls[1]) - this.element.offsets[1]
                          - this.element.lefttop[1]
         ); 
     },