Index: trunk/FACT++/www/viewer/index.js
===================================================================
--- trunk/FACT++/www/viewer/index.js	(revision 17718)
+++ trunk/FACT++/www/viewer/index.js	(revision 17719)
@@ -766,7 +766,14 @@
         return;
 
-    var mouse = getClickPosition();
+    // get click position relative to canvas
+    var rect = event.target.getBoundingClientRect();
+
+    var x =  event.clientX - rect.left;
+    var y =  event.clientY - rect.top;
+
+    var mouse = { x: x, y: y };
+
+    // convert click position to pixel index
     var index = getIndex(event.target.id, mouse);
-
     if (index<0)
         return;
@@ -779,10 +786,10 @@
 function getClickPosition(event)
 {
-    var event = window.event;
-
-    if (event.offsetX !== undefined && event.offsetY !== undefined)
-        return { x: event.offsetX, y: event.offsetY };
-
-    return { x: event.layerX, y: event.layerY };
+    var rect = event.target.getBoundingClientRect();
+
+    var x =  event.clientX - rect.left;
+    var y =  event.clientY - rect.top;
+
+    return { x: x, y: y };
 }