From 4e347dcf45a538cac9c1d7e3c5a9859219ff4671 Mon Sep 17 00:00:00 2001
From: Tom Payne <twpayne@gmail.com>
Date: Thu, 19 Jul 2012 00:09:32 +0200
Subject: [PATCH] Don't drag on incompletely defined maps

---
 src/ol/control/drag.js | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/ol/control/drag.js b/src/ol/control/drag.js
index 8a8f0ebc01..3f54b46ea4 100644
--- a/src/ol/control/drag.js
+++ b/src/ol/control/drag.js
@@ -84,6 +84,11 @@ ol.control.Drag.prototype.handleDragEnd = goog.nullFunction;
  * @inheritDoc
  */
 ol.control.Drag.prototype.handleMapBrowserEvent = function(mapBrowserEvent) {
+  var center = mapBrowserEvent.map.getCenter();
+  var resolution = mapBrowserEvent.map.getResolution();
+  if (!goog.isDef(center) || !goog.isDef(resolution)) {
+    return;
+  }
   var browserEventObject;
   if (this.dragging_) {
     if (mapBrowserEvent.type == goog.events.EventType.MOUSEMOVE ||
@@ -107,7 +112,7 @@ ol.control.Drag.prototype.handleMapBrowserEvent = function(mapBrowserEvent) {
       this.startY = browserEventObject.offsetY;
       this.deltaX = 0;
       this.deltaY = 0;
-      this.startCenter = mapBrowserEvent.map.getCenter();
+      this.startCenter = center;
       this.startCoordinate = mapBrowserEvent.getCoordinate();
       if (this.handleDragStart(mapBrowserEvent)) {
         this.dragging_ = true;