新增 Prefab 系统：实体子树存取 + 编辑器 Save As Prefab/拖入实例化 + 脚本 Instantiate

App/editor/panels/HierarchyPanel.cpp

@@ -7,12 +7,16 @@
 //
 
 #include "HierarchyPanel.h"
+#include "AssetBrowserPanel.h"        // kPrefabDragPayload（Content Browser 源）
 #include "Engine/ECS/Components.h"
 #include "Engine/ECS/EntityHandle.h"   // CreateEntity 返回完整 EntityHandle
+#include "Engine/Serialization/SceneSerializer.h"
+#include "Engine/Core/Log.h"
 
 #include <imgui.h>
 
 #include <cstring>
+#include <filesystem>
 #include <string>
 #include <vector>
 
@@ -33,6 +37,34 @@ namespace {
         return "(unnamed)";
     }
 
+    // Prefab 拖入实例化（树节点/空白区落点共用）。根实体挂在场景根、
+    // 保留授权位姿；返回根实体（失败 entt::null）
+    entt::entity InstantiatePrefabDrop(const EditorContext& ctx,
+                                       const char* path)
+    {
+        if (!ctx.scene || !ctx.assets || !path) {
+            return entt::null;
+        }
+        return Engine::Serialization::SceneSerializer::InstantiatePrefab(
+            *ctx.scene, *ctx.assets, path);
+    }
+
+    // 实体名 → 合法文件名（路径分隔符/保留符净化；空名兜底）
+    std::string PrefabFileName(std::string name)
+    {
+        for (char& c : name) {
+            if (c == '/' || c == '\\' || c == ':' || c == '*' ||
+                c == '?' || c == '"' || c == '<' || c == '>' ||
+                c == '|') {
+                c = '_';
+            }
+        }
+        if (name.empty() || name == "(unnamed)") {
+            name = "prefab";
+        }
+        return name;
+    }
+
     // 递归绘制单节点（含子树）。返回值无意义，选中写 selected
     void DrawEntityNode(const EditorContext& ctx, entt::entity e,
                         entt::entity& selected)
@@ -78,7 +110,9 @@ namespace {
             ImGui::EndDragDropSource();
         }
 
-        // ---- 拖放目标：挂到本实体下（keepWorld，世界位姿不变）----
+        // ---- 拖放目标：挂到本实体下（keepWorld，世界位姿不变）；
+        //      Prefab 拖入 = 实例化子树后挂到本实体下（keepWorld 保持
+        //      授权世界位姿）----
         if (ImGui::BeginDragDropTarget()) {
             if (const ImGuiPayload* pl =
                     ImGui::AcceptDragDropPayload(kHierPayload)) {
@@ -91,6 +125,17 @@ namespace {
                     ctx.scene->SetParent(dragged, e);
                 }
             }
+            if (const ImGuiPayload* pl =
+                    ImGui::AcceptDragDropPayload(kPrefabDragPayload)) {
+                if (const entt::entity root =
+                        InstantiatePrefabDrop(ctx,
+                                              static_cast<const char*>(
+                                                  pl->Data));
+                    root != entt::null) {
+                    ctx.scene->SetParent(root, e);   // keepWorld 默认 true
+                    selected = root;
+                }
+            }
             ImGui::EndDragDropTarget();
         }
 
@@ -102,6 +147,19 @@ namespace {
                 ctx.scene->SetParent(child, e);
                 selected = child;
             }
+            if (ImGui::MenuItem("Save As Prefab")) {
+                // 固定目录 + 实体名派生文件名（无文件对话框库，与场景
+                // File 菜单同策略；重名覆盖，改名走文件系统）
+                const std::string path =
+                    "assets/prefabs/" +
+                    PrefabFileName(DisplayName(reg, e)) + ".prefab";
+                std::error_code ec;
+                std::filesystem::create_directories("assets/prefabs", ec);
+                if (Serialization::SceneSerializer::SerializePrefab(
+                        *ctx.scene, *ctx.assets, e, path)) {
+                    ENGINE_INFO("Hierarchy: prefab saved to '{}'", path);
+                }
+            }
             if (ctx.scene->GetParent(e) != entt::null &&
                 ImGui::MenuItem("Detach to Root")) {
                 ctx.scene->SetParent(e, entt::null);
@@ -194,7 +252,8 @@ void HierarchyPanel::Draw(const EditorContext& ctx, entt::entity& selected)
             DrawEntityNode(ctx, e, selected);
         });
 
-    // ---- 空白区 = 挂根落点（UE Outliner 拖到空白 = 顶层）----
+    // ---- 空白区 = 挂根落点（UE Outliner 拖到空白 = 顶层）；
+    //      Prefab 拖入 = 实例化到场景根（授权位姿）----
     ImVec2 rem = ImGui::GetContentRegionAvail();
     if (rem.y > 4.0f) {
         ImGui::InvisibleButton("##hier_drop_root", rem);
@@ -206,6 +265,14 @@ void HierarchyPanel::Draw(const EditorContext& ctx, entt::entity& selected)
                 ctx.scene->SetParent(static_cast<entt::entity>(bits),
                                      entt::null);
             }
+            if (const ImGuiPayload* pl =
+                    ImGui::AcceptDragDropPayload(kPrefabDragPayload)) {
+                if (const entt::entity root = InstantiatePrefabDrop(
+                        ctx, static_cast<const char*>(pl->Data));
+                    root != entt::null) {
+                    selected = root;
+                }
+            }
             ImGui::EndDragDropTarget();
         }
     }