fix the getWindowToGraphPosition function (#41)

Author: ellthompson

src/graph-view-node.js

@@ -455,7 +455,7 @@ class GraphViewNode {
         switch (event) {
             case 'updatePosition': {
                 nodeView.on('element:pointerup', () => {
-                    var newPos = this._graphView.getWindowToGraphPosition(nodeView.getBBox());
+                    var newPos = this._graphView.getWindowToGraphPosition(nodeView.getBBox(), false);
                     callback(this.nodeData.id, newPos);
                 });
                 break;

src/graph-view.js

@@ -157,13 +157,17 @@ class GraphView extends JointGraph {
         }
     }
 
-    getWindowToGraphPosition(pos) {
+    getWindowToGraphPosition(pos, usePaperPosition = true) {
         const scale = this._paper.scale().sx;
         const translate = this._paper.translate();
-        const boundingClientRect = this._paper.el.getBoundingClientRect();
+        if (usePaperPosition) {
+            const paperPosition = this._paper.el.getBoundingClientRect();
+            pos.x -= paperPosition.x;
+            pos.y -= paperPosition.y;
+        }
         return new Vec2(
-            (-translate.tx / scale) + ((pos.x - boundingClientRect.x) / scale),
-            (-translate.ty / scale) + ((pos.y - boundingClientRect.y) / scale)
+            (-translate.tx / scale) + (pos.x / scale),
+            (-translate.ty / scale) + (pos.y / scale)
         );
     }