Drag all the selected models (#357)

The motion of the selected group has been broken in v3.
The original behavior was to employ the default implementation of
QGraphicsItem::mouseMoveEvent that moves all the selected objects
together.

Now the motion is wrapped into a MoveNodeCommand, we need to shift
the selected group manually, one-by-one, by providing new positions to
the Graph Model

Author: zmoth

src/NodeGraphicsObject.cpp

@@ -337,7 +337,6 @@ mouseMoveEvent(QGraphicsSceneMouseEvent* event)
     auto diff = event->pos() - event->lastPos();
 
     nodeScene()->undoStack().push(new MoveNodeCommand(nodeScene(),
-                                                      _nodeId,
                                                       diff));
 
     event->accept();

src/UndoCommands.cpp

@@ -445,39 +445,51 @@ redo()
 
 MoveNodeCommand::
 MoveNodeCommand(BasicGraphicsScene* scene,
-                NodeId const nodeId,
                 QPointF const &diff)
   : _scene(scene)
-  , _nodeId(nodeId)
   , _diff(diff)
 {
+  _selectedNodes.clear();
+  for (QGraphicsItem * item : _scene->selectedItems())
+  {
+    if (auto n = qgraphicsitem_cast<NodeGraphicsObject*>(item))
+    {
+      _selectedNodes.insert(n->nodeId());
+    }
+  }
 }
 
 void
 MoveNodeCommand::
 undo()
 {
-  auto oldPos = 
-    _scene->graphModel().nodeData(_nodeId,
-                                  NodeRole::Position).value<QPointF>();
+  for (auto nodeId : _selectedNodes)
+  {
+    auto oldPos = 
+      _scene->graphModel().nodeData(nodeId,
+                                    NodeRole::Position).value<QPointF>();
 
-  oldPos -= _diff;
+    oldPos -= _diff;
 
-  _scene->graphModel().setNodeData(_nodeId, NodeRole::Position, oldPos);
+    _scene->graphModel().setNodeData(nodeId, NodeRole::Position, oldPos);
+  }
 }
 
 
 void
 MoveNodeCommand::
 redo()
 {
-  auto oldPos = 
-    _scene->graphModel().nodeData(_nodeId,
-                                  NodeRole::Position).value<QPointF>();
+  for (auto nodeId : _selectedNodes)
+  {
+    auto oldPos = 
+      _scene->graphModel().nodeData(nodeId,
+                                    NodeRole::Position).value<QPointF>();
 
-  oldPos += _diff;
+    oldPos += _diff;
 
-  _scene->graphModel().setNodeData(_nodeId, NodeRole::Position, oldPos);
+    _scene->graphModel().setNodeData(nodeId, NodeRole::Position, oldPos);
+  }
 }
 
 
@@ -495,10 +507,12 @@ mergeWith(QUndoCommand const *c)
 {
   auto mc = static_cast<MoveNodeCommand const*>(c);
 
-  _diff += mc->_diff;
-
-  return true;
+  if (_selectedNodes == mc->_selectedNodes)
+  {
+    _diff += mc->_diff;
+    return true;
+  }
+  return false;
 }
 
-//
-}
+} // namespace QtNodes

src/UndoCommands.hpp

@@ -6,6 +6,8 @@
 #include <QtCore/QPointF>
 #include <QtCore/QJsonObject>
 
+#include <unordered_set>
+
 namespace QtNodes
 {
 
@@ -92,7 +94,6 @@ class MoveNodeCommand : public QUndoCommand
 {
 public:
   MoveNodeCommand(BasicGraphicsScene* scene,
-                  NodeId const nodeId,
                   QPointF const &diff);
 
   void undo() override;
@@ -111,9 +112,9 @@ class MoveNodeCommand : public QUndoCommand
 
 private:
   BasicGraphicsScene* _scene;
-  NodeId _nodeId;
+  std::unordered_set<NodeId> _selectedNodes;
   QPointF _diff;
 };
 
 
-}
+} // namespace QtNodes