Merge branch '26-get-object-id-from-graph' into 'master'

Resolve "Get object ID from graph"

Closes #26

See merge request totem/ind!16

grapheditorxblock/src/js/grapheditorxblock.js

@@ -67,6 +67,43 @@ function GraphEditorXBlock(runtime, element, data) {
     });
 }
 
+/**
+ * Function: pickCell
+ *
+ * Enter a mode in which the user can pick a cell, without changing the
+ * selection. When the user has picked the cell, a callback function is run
+ * with the cell as argument.
+ *
+ * Parameters:
+ *
+ * graph - graph object to operate on
+ * callback - callback function to run after picking cell
+ */
+function pickCell(graph, callback) {
+    var listener = {
+        mouseDown: function(sender, evt) {},
+        mouseMove: function(sender, evt) {},
+        mouseUp: function(sender, evt) {
+            // Only perform the callback if we clicked on a cell, not elsewhere
+            // on the canvas.
+            if (typeof evt.state !== 'undefined') {
+                callback(evt.state.cell);
+            }
+            // Consuime the event, so it will not also trigger a change of
+            // selection.
+            evt.consume();
+            // Remove the new listener.
+            graph.removeMouseListener(listener);
+            // Make the graph writable again.
+            graph.setEnabled(true);
+        }
+    };
+    // Add our new listener.
+    graph.mouseListeners.unshift(listener);
+    // Make the graph read-only while the user is picking their cell.
+    graph.setEnabled(false);
+}
+
 /**
  * Save to the XBlock data.
  *