From d2350d494a022006393cfe7388566686eafe78cf Mon Sep 17 00:00:00 2001
From: huisedenanhai <winser@pku.edu.cn>
Date: Sat, 19 Nov 2022 22:16:48 +0800
Subject: [PATCH 1/2] Node can decide whether it can be deleted

---
 egui_node_graph/src/editor_ui.rs | 13 ++++++++++---
 egui_node_graph/src/traits.rs    |  9 +++++++++
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/egui_node_graph/src/editor_ui.rs b/egui_node_graph/src/editor_ui.rs
index 8af69f2..874868e 100644
--- a/egui_node_graph/src/editor_ui.rs
+++ b/egui_node_graph/src/editor_ui.rs
@@ -771,9 +771,16 @@ where
         // --- Interaction ---
 
         // Titlebar buttons
-        if Self::close_button(ui, outer_rect).clicked() {
-            responses.push(NodeResponse::DeleteNodeUi(self.node_id));
-        };
+        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,
diff --git a/egui_node_graph/src/traits.rs b/egui_node_graph/src/traits.rs
index 6f02320..a9cf2ef 100644
--- a/egui_node_graph/src/traits.rs
+++ b/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

From 76ab0bd9e11be0205de38a617e77741c5c039da2 Mon Sep 17 00:00:00 2001
From: huisedenanhai <winser@pku.edu.cn>
Date: Mon, 21 Nov 2022 22:32:32 +0800
Subject: [PATCH 2/2] Collapse if statement

---
 egui_node_graph/src/editor_ui.rs | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/egui_node_graph/src/editor_ui.rs b/egui_node_graph/src/editor_ui.rs
index 874868e..d3e9369 100644
--- a/egui_node_graph/src/editor_ui.rs
+++ b/egui_node_graph/src/editor_ui.rs
@@ -776,11 +776,10 @@ where
             self.graph,
             user_state,
         );
-        if can_delete {
-            if Self::close_button(ui, outer_rect).clicked() {
-                responses.push(NodeResponse::DeleteNodeUi(self.node_id));
-            };
-        }
+
+        if can_delete && Self::close_button(ui, outer_rect).clicked() {
+            responses.push(NodeResponse::DeleteNodeUi(self.node_id));
+        };
 
         let window_response = ui.interact(
             outer_rect,