Node can decide whether it can be deleted

egui_node_graph/src/editor_ui.rs

@@ -771,9 +771,16 @@ where
         // --- Interaction ---
 
         // Titlebar buttons
+        let can_delete = self.graph.nodes[self.node_id].user_data.can_delete(
+            self.node_id,
+            self.graph,
+            user_state,
+        );
+        if can_delete {
             if Self::close_button(ui, outer_rect).clicked() {
                 responses.push(NodeResponse::DeleteNodeUi(self.node_id));
             };
+        }
 
         let window_response = ui.interact(
             outer_rect,

egui_node_graph/src/traits.rs

@@ -102,6 +102,15 @@ where
     ) -> Option<egui::Color32> {
         None
     }
+
+    fn can_delete(
+        &self,
+        _node_id: NodeId,
+        _graph: &Graph<Self, Self::DataType, Self::ValueType>,
+        _user_state: &mut Self::UserState,
+    ) -> bool {
+        true
+    }
 }
 
 /// This trait can be implemented by any user type. The trait tells the library