New signal, in Scene_item, that will be emitted just before an item is

destroyed by the scene.

Polyhedron/demo/Polyhedron/Scene_item.cpp

@@ -4,6 +4,11 @@ const QColor Scene_item::defaultColor = QColor(100, 100, 255);
 
 Scene_item::~Scene_item() {}
 
+void Scene_item::itemAboutToBeDestroyed(Scene_item* item) {
+  if(this == item)
+    emit aboutToBeDestroyed();
+}
+
 // Rendering mode as a human readable string
 QString Scene_item::renderingModeName() const
 {

Polyhedron/demo/Polyhedron/Scene_item.h

@@ -76,6 +76,11 @@ public slots:
       rendering_mode = m; 
   }
 
+  virtual void itemAboutToBeDestroyed(Scene_item*);
+
+signals:
+  void aboutToBeDestroyed();
+
 protected:
   // The four basic properties
   QString name_;