Port "Improve touchscreen dragging"

From https://github.com/open-craft/jsinput-vectordraw/pull/32

vectordraw/public/js/vectordraw.js

@@ -409,12 +409,15 @@ function VectorDrawXBlock(runtime, element, init_args) {
         return true;
     };
 
-    VectorDraw.prototype.objectsUnderMouse = function(coords) {
-        var filter = function(el) {
-            return !(el instanceof JXG.Image) && el.hasPoint(coords.scrCoords[1], coords.scrCoords[2]);
-        };
-        return _.filter(_.values(this.board.objects), filter);
-    };
+    VectorDraw.prototype.objectsUnderMouse = function(){
+        var targetObjects = [];
+        var highlightedObjects = this.board.highlightedObjects
+        var keys = Object.keys(highlightedObjects);
+        for (var i = 0; i < keys.length; i++) {
+            targetObjects.push( highlightedObjects[keys[i]] );
+        }
+        return targetObjects
+    }
 
     VectorDraw.prototype.onBoardDown = function(evt) {
         this.pushHistory();