Enhance overworld editor with music editing features and custom overworld support

- Added a new Music tab in the Map Properties panel for editing music tracks associated with different game states.
- Implemented functionality to save music data for both Light and Dark World maps.
- Updated feature flags to enable custom overworld features based on ASM version, improving flexibility for ROM modifications.
- Enhanced UI elements with tooltips and popups for better user guidance on custom overworld settings.

src/app/core/features.h

@@ -65,7 +65,8 @@ class FeatureFlags {
       // Save overworld properties to the Rom.
       bool kSaveOverworldProperties = true;
 
-      // Load custom overworld data from the ROM and enable UI.
+      // Enable custom overworld features for vanilla ROMs or override detection.
+      // If ZSCustomOverworld ASM is already applied, features are auto-enabled.
       bool kLoadCustomOverworld = false;
       
       // Apply ZSCustomOverworld ASM patches when upgrading ROM versions.
@@ -134,8 +135,19 @@ struct FlagsMenu {
              &FeatureFlags::get().overworld.kSaveOverworldItems);
     Checkbox("Save Overworld Properties",
              &FeatureFlags::get().overworld.kSaveOverworldProperties);
-    Checkbox("Load Custom Overworld",
+    Checkbox("Enable Custom Overworld Features",
              &FeatureFlags::get().overworld.kLoadCustomOverworld);
+    ImGui::SameLine();
+    if (ImGui::Button("?")) {
+      ImGui::OpenPopup("CustomOverworldHelp");
+    }
+    if (ImGui::BeginPopup("CustomOverworldHelp")) {
+      ImGui::Text("This flag enables ZSCustomOverworld features.");
+      ImGui::Text("If ZSCustomOverworld ASM is already applied to the ROM,");
+      ImGui::Text("features are auto-enabled regardless of this flag.");
+      ImGui::Text("For vanilla ROMs, enable this to use custom features.");
+      ImGui::EndPopup();
+    }
     Checkbox("Apply ZSCustomOverworld ASM",
              &FeatureFlags::get().overworld.kApplyZSCustomOverworldASM);
   }

src/app/editor/overworld/map_properties.cc

@@ -155,6 +155,12 @@ void MapPropertiesSystem::DrawMapPropertiesPanel(int current_map, bool& show_map
       ImGui::EndTabItem();
     }
     
+    // Music Tab
+    if (ImGui::BeginTabItem("Music")) {
+      DrawMusicTab(current_map);
+      ImGui::EndTabItem();
+    }
+    
     ImGui::EndTabBar();
   }
 }
@@ -521,6 +527,43 @@ void MapPropertiesSystem::DrawBasicPropertiesTab(int current_map) {
     }
     HOVER_HINT("Enable Mosaic effect for the current map");
     
+    // Add music editing controls
+    TableNextColumn(); ImGui::Text("Music (Beginning)");
+    TableNextColumn();
+    if (gui::InputHexByte("##Music0", 
+                          overworld_->mutable_overworld_map(current_map)->mutable_area_music(0),
+                          kInputFieldSize)) {
+      RefreshMapProperties();
+    }
+    HOVER_HINT("Music track for game beginning state");
+    
+    TableNextColumn(); ImGui::Text("Music (Zelda)");
+    TableNextColumn();
+    if (gui::InputHexByte("##Music1", 
+                          overworld_->mutable_overworld_map(current_map)->mutable_area_music(1),
+                          kInputFieldSize)) {
+      RefreshMapProperties();
+    }
+    HOVER_HINT("Music track for Zelda rescued state");
+    
+    TableNextColumn(); ImGui::Text("Music (Master Sword)");
+    TableNextColumn();
+    if (gui::InputHexByte("##Music2", 
+                          overworld_->mutable_overworld_map(current_map)->mutable_area_music(2),
+                          kInputFieldSize)) {
+      RefreshMapProperties();
+    }
+    HOVER_HINT("Music track for Master Sword obtained state");
+    
+    TableNextColumn(); ImGui::Text("Music (Agahnim)");
+    TableNextColumn();
+    if (gui::InputHexByte("##Music3", 
+                          overworld_->mutable_overworld_map(current_map)->mutable_area_music(3),
+                          kInputFieldSize)) {
+      RefreshMapProperties();
+    }
+    HOVER_HINT("Music track for Agahnim defeated state");
+    
     ImGui::EndTable();
   }
 }
@@ -667,6 +710,74 @@ void MapPropertiesSystem::DrawTileGraphicsTab(int current_map) {
   }
 }
 
+void MapPropertiesSystem::DrawMusicTab(int current_map) {
+  ImGui::Text("Music Settings for Different Game States:");
+  Separator();
+  
+  if (BeginTable("MusicSettings", 2, ImGuiTableFlags_Borders | ImGuiTableFlags_SizingFixedFit)) {
+    ImGui::TableSetupColumn("Game State", ImGuiTableColumnFlags_WidthFixed, 150);
+    ImGui::TableSetupColumn("Music Track ID", ImGuiTableColumnFlags_WidthStretch);
+    
+    const char* music_state_names[] = {
+      "Beginning (Pre-Zelda)",
+      "Zelda Rescued", 
+      "Master Sword Obtained",
+      "Agahnim Defeated"
+    };
+    
+    const char* music_descriptions[] = {
+      "Music before rescuing Zelda",
+      "Music after rescuing Zelda from Hyrule Castle",
+      "Music after obtaining the Master Sword",
+      "Music after defeating Agahnim (Dark World)"
+    };
+    
+    for (int i = 0; i < 4; i++) {
+      TableNextColumn();
+      ImGui::Text("%s", music_state_names[i]);
+      
+      TableNextColumn();
+      if (gui::InputHexByte(absl::StrFormat("##Music%d", i).c_str(),
+                            overworld_->mutable_overworld_map(current_map)->mutable_area_music(i),
+                            kInputFieldSize)) {
+        RefreshMapProperties();
+        
+        // Update the ROM directly since music is not automatically saved
+        int music_address = 0;
+        switch (i) {
+          case 0: music_address = zelda3::kOverworldMusicBeginning + current_map; break;
+          case 1: music_address = zelda3::kOverworldMusicZelda + current_map; break;
+          case 2: music_address = zelda3::kOverworldMusicMasterSword + current_map; break;
+          case 3: music_address = zelda3::kOverworldMusicAgahnim + current_map; break;
+        }
+        
+        if (music_address > 0) {
+          (*rom_)[music_address] = *overworld_->mutable_overworld_map(current_map)->mutable_area_music(i);
+        }
+      }
+      if (ImGui::IsItemHovered()) {
+        ImGui::SetTooltip("%s", music_descriptions[i]);
+      }
+    }
+    
+    ImGui::EndTable();
+  }
+  
+  Separator();
+  ImGui::Text("Music tracks control the background music for different");
+  ImGui::Text("game progression states on this overworld map.");
+  
+  // Show common music track IDs for reference
+  Separator();
+  ImGui::Text("Common Music Track IDs:");
+  ImGui::BulletText("0x02 - Overworld Theme");
+  ImGui::BulletText("0x05 - Kakariko Village");
+  ImGui::BulletText("0x07 - Lost Woods");
+  ImGui::BulletText("0x09 - Dark World Theme");
+  ImGui::BulletText("0x0F - Ganon's Tower");
+  ImGui::BulletText("0x11 - Death Mountain");
+}
+
 void MapPropertiesSystem::RefreshMapProperties() {
   // Implementation would refresh map properties
 }

src/app/editor/overworld/map_properties.h

@@ -64,6 +64,7 @@ class MapPropertiesSystem {
   void DrawSpritePropertiesTab(int current_map);
   void DrawCustomFeaturesTab(int current_map);
   void DrawTileGraphicsTab(int current_map);
+  void DrawMusicTab(int current_map);
   
   // Utility methods
   void RefreshMapProperties();

src/app/editor/overworld/overworld_editor.cc

@@ -802,6 +802,8 @@ void OverworldEditor::CheckForOverworldEdits() {
           // Calculate the index within the overall map structure
           int index_x = local_map_x * tiles_per_local_map + tile16_x;
           int index_y = local_map_y * tiles_per_local_map + tile16_y;
+          overworld_.set_current_world(current_world_);
+          overworld_.set_current_map(current_map_);
           int tile16_id = overworld_.GetTileFromPosition(
               ow_map_canvas_.selected_tiles()[i]);
           selected_world[index_x][index_y] = tile16_id;
@@ -818,6 +820,8 @@ void OverworldEditor::CheckForSelectRectangle() {
 
   // Single tile case
   if (ow_map_canvas_.selected_tile_pos().x != -1) {
+    overworld_.set_current_world(current_world_);
+    overworld_.set_current_map(current_map_);
     current_tile16_ =
         overworld_.GetTileFromPosition(ow_map_canvas_.selected_tile_pos());
     ow_map_canvas_.set_selected_tile_pos(ImVec2(-1, -1));
@@ -831,13 +835,18 @@ void OverworldEditor::CheckForSelectRectangle() {
     }
 
     if (ow_map_canvas_.selected_tiles().size() > 0) {
+      // Set the current world and map in overworld for proper tile lookup
+      overworld_.set_current_world(current_world_);
+      overworld_.set_current_map(current_map_);
       for (auto &each : ow_map_canvas_.selected_tiles()) {
         tile16_ids.push_back(overworld_.GetTileFromPosition(each));
       }
     }
   }
   // Create a composite image of all the tile16s selected
-  ow_map_canvas_.DrawBitmapGroup(tile16_ids, tile16_blockset_, 0x10);
+  if (!tile16_ids.empty()) {
+    ow_map_canvas_.DrawBitmapGroup(tile16_ids, tile16_blockset_, 0x10, ow_map_canvas_.global_scale());
+  }
 }
 
 absl::Status OverworldEditor::Copy() {
@@ -847,6 +856,8 @@ absl::Status OverworldEditor::Copy() {
       !ow_map_canvas_.selected_tiles().empty()) {
     std::vector<int> ids;
     ids.reserve(ow_map_canvas_.selected_tiles().size());
+    overworld_.set_current_world(current_world_);
+    overworld_.set_current_map(current_map_);
     for (const auto &pos : ow_map_canvas_.selected_tiles()) {
       ids.push_back(overworld_.GetTileFromPosition(pos));
     }
@@ -972,8 +983,22 @@ absl::Status OverworldEditor::CheckForCurrentMap() {
                                parent_map_y * kOverworldMapSize, large_map_size,
                                large_map_size);
   } else {
-    const int current_map_x = current_highlighted_map % 8;
-    const int current_map_y = current_highlighted_map / 8;
+    // Calculate map coordinates accounting for world offset
+    int current_map_x, current_map_y;
+    if (current_world_ == 0) {
+      // Light World (0x00-0x3F)
+      current_map_x = current_highlighted_map % 8;
+      current_map_y = current_highlighted_map / 8;
+    } else if (current_world_ == 1) {
+      // Dark World (0x40-0x7F)
+      current_map_x = (current_highlighted_map - 0x40) % 8;
+      current_map_y = (current_highlighted_map - 0x40) / 8;
+    } else {
+      // Special World (0x80-0x9F) - use display coordinates based on current_world_
+      // The special world maps are displayed in the same 8x8 grid as LW/DW
+      current_map_x = (current_highlighted_map - 0x80) % 8;
+      current_map_y = (current_highlighted_map - 0x80) / 8;
+    }
     ow_map_canvas_.DrawOutline(current_map_x * kOverworldMapSize,
                                current_map_y * kOverworldMapSize,
                                kOverworldMapSize, kOverworldMapSize);
@@ -1012,7 +1037,12 @@ void OverworldEditor::CheckForMousePan() {
 
 void OverworldEditor::DrawOverworldCanvas() {
   if (all_gfx_loaded_) {
-    if (core::FeatureFlags::get().overworld.kLoadCustomOverworld) {
+    // Use ASM version with flag as override to determine UI
+    uint8_t asm_version = (*rom_)[zelda3::OverworldCustomASMHasBeenApplied];
+    bool use_custom_overworld = (asm_version != 0xFF) || 
+                                core::FeatureFlags::get().overworld.kLoadCustomOverworld;
+    
+    if (use_custom_overworld) {
       map_properties_system_->DrawSimplifiedMapSettings(
           current_world_, current_map_, current_map_lock_,
           show_map_properties_panel_, show_custom_bg_color_editor_,
@@ -1434,6 +1464,7 @@ absl::Status OverworldEditor::Save() {
   }
   if (core::FeatureFlags::get().overworld.kSaveOverworldProperties) {
     RETURN_IF_ERROR(overworld_.SaveMapProperties());
+    RETURN_IF_ERROR(overworld_.SaveMusic());
   }
   return absl::OkStatus();
 }

src/app/gui/canvas.cc

@@ -559,8 +559,22 @@ void Canvas::DrawSelectRect(int current_map, int tile_size, float scale) {
   const float scaled_size = tile_size * scale;
   static bool dragging = false;
   constexpr int small_map_size = 0x200;
-  int superY = current_map / 8;
-  int superX = current_map % 8;
+  
+  // Calculate superX and superY accounting for world offset
+  int superY, superX;
+  if (current_map < 0x40) {
+    // Light World
+    superY = current_map / 8;
+    superX = current_map % 8;
+  } else if (current_map < 0x80) {
+    // Dark World
+    superY = (current_map - 0x40) / 8;
+    superX = (current_map - 0x40) % 8;
+  } else {
+    // Special World
+    superY = (current_map - 0x80) / 8;
+    superX = (current_map - 0x80) % 8;
+  }
 
   // Handle right click for single tile selection
   if (IsMouseClicked(ImGuiMouseButton_Right)) {
@@ -758,6 +772,11 @@ void Canvas::DrawBitmapGroup(std::vector<int> &group, gfx::Tilemap &tilemap,
   int i = 0;
   for (int y = 0; y < tiles_per_col + 1; ++y) {
     for (int x = 0; x < tiles_per_row + 1; ++x) {
+      // Check bounds to prevent access violations
+      if (i >= static_cast<int>(group.size())) {
+        break;
+      }
+      
       int tile_id = group[i];
 
       // Check if tile_id is within the range of tile16_individual_
@@ -770,10 +789,15 @@ void Canvas::DrawBitmapGroup(std::vector<int> &group, gfx::Tilemap &tilemap,
 
         // Draw the tile bitmap at the calculated position
         gfx::RenderTile(tilemap, tile_id);
-        DrawBitmap(tilemap.tile_bitmaps[tile_id], tile_pos_x, tile_pos_y, scale,
-                   150.0f);
-        i++;
+        if (tilemap.tile_bitmaps.find(tile_id) != tilemap.tile_bitmaps.end()) {
+          DrawBitmap(tilemap.tile_bitmaps[tile_id], tile_pos_x, tile_pos_y, scale, 150);
+        }
       }
+      i++;
+    }
+    // Break outer loop if we've run out of tiles
+    if (i >= static_cast<int>(group.size())) {
+      break;
     }
   }
 

src/app/zelda3/overworld/overworld.cc

@@ -120,8 +120,12 @@ absl::Status Overworld::AssembleMap32Tiles() {
                               rom()->version_constants().kMap32TileTR,
                               rom()->version_constants().kMap32TileBL,
                               rom()->version_constants().kMap32TileBR};
-  if (rom()->data()[kMap32ExpandedFlagPos] != 0x04 &&
-      core::FeatureFlags::get().overworld.kLoadCustomOverworld) {
+  
+  // Use ASM version to determine expanded tile32 support, with flag as override
+  uint8_t asm_version = (*rom_)[zelda3::OverworldCustomASMHasBeenApplied];
+  bool use_custom_overworld = (asm_version != 0xFF) || 
+                              core::FeatureFlags::get().overworld.kLoadCustomOverworld;
+  if (rom()->data()[kMap32ExpandedFlagPos] != 0x04 && use_custom_overworld) {
     map32address[0] = rom()->version_constants().kMap32TileTL;
     map32address[1] = kMap32TileTRExpanded;
     map32address[2] = kMap32TileBLExpanded;
@@ -169,8 +173,12 @@ absl::Status Overworld::AssembleMap32Tiles() {
 absl::Status Overworld::AssembleMap16Tiles() {
   int tpos = kMap16Tiles;
   int num_tile16 = kNumTile16Individual;
-  if (rom()->data()[kMap16ExpandedFlagPos] != 0x0F &&
-      core::FeatureFlags::get().overworld.kLoadCustomOverworld) {
+  
+  // Use ASM version to determine expanded tile16 support, with flag as override
+  uint8_t asm_version = (*rom_)[zelda3::OverworldCustomASMHasBeenApplied];
+  bool use_custom_overworld = (asm_version != 0xFF) || 
+                              core::FeatureFlags::get().overworld.kLoadCustomOverworld;
+  if (rom()->data()[kMap16ExpandedFlagPos] != 0x0F && use_custom_overworld) {
     tpos = kMap16TilesExpanded;
     num_tile16 = NumberOfMap16Ex;
     expanded_tile16_ = true;
@@ -313,12 +321,17 @@ absl::Status Overworld::LoadEntrances() {
   int ow_entrance_pos_ptr = kOverworldEntrancePos;
   int ow_entrance_id_ptr = kOverworldEntranceEntranceId;
   int num_entrances = 129;
-  if (rom()->data()[kOverworldEntranceExpandedFlagPos] != 0xB8 &&
-      core::FeatureFlags::get().overworld.kLoadCustomOverworld) {
+  
+  // Use ASM version to determine expanded entrance support, with flag as override
+  uint8_t asm_version = (*rom_)[zelda3::OverworldCustomASMHasBeenApplied];
+  bool use_custom_overworld = (asm_version != 0xFF) || 
+                              core::FeatureFlags::get().overworld.kLoadCustomOverworld;
+  if (rom()->data()[kOverworldEntranceExpandedFlagPos] != 0xB8 && use_custom_overworld) {
     ow_entrance_map_ptr = kOverworldEntranceMapExpanded;
     ow_entrance_pos_ptr = kOverworldEntrancePosExpanded;
     ow_entrance_id_ptr = kOverworldEntranceEntranceIdExpanded;
     expanded_entrances_ = true;
+    num_entrances = 256;  // Expanded entrance count
   }
 
   for (int i = 0; i < num_entrances; i++) {
@@ -416,16 +429,38 @@ absl::Status Overworld::LoadExits() {
 }
 
 absl::Status Overworld::LoadItems() {
-  ASSIGN_OR_RETURN(uint32_t pointer,
-                   rom()->ReadLong(zelda3::kOverworldItemsAddress));
-  uint32_t pointer_pc = SnesToPc(pointer);  // 1BC2F9 -> 0DC2F9
-  for (int i = 0; i < 128; i++) {
-    ASSIGN_OR_RETURN(uint16_t word_address,
-                     rom()->ReadWord(pointer_pc + i * 2));
-    uint32_t addr = (pointer & 0xFF0000) | word_address;  // 1B F9  3C
+  // byte asmVersion = ROM.DATA[Constants.OverworldCustomASMHasBeenApplied];
+
+  //           // Version 0x03 of the OW ASM added item support for the SW.
+  //           int maxOW = asmVersion >= 0x03 && asmVersion != 0xFF ? Constants.NumberOfOWMaps : 0x80;
+
+  //           int pointerSNES = ROM.ReadLong(Constants.overworldItemsAddress);
+  //           this.ItemPointerAddress = Utils.SnesToPc(pointerSNES); // 0x1BC2F9 -> 0x0DC2F9
+
+  // Version 0x03 of the OW ASM added item support for the SW.
+  uint8_t asm_version = (*rom_)[zelda3::OverworldCustomASMHasBeenApplied];
+  
+  // Determine max number of overworld maps based on ASM version
+  int max_ow = (asm_version >= 0x03 && asm_version != 0xFF) ? kNumOverworldMaps : 0x80;
+  
+  ASSIGN_OR_RETURN(uint32_t pointer_snes, 
+                   rom()->ReadLong(zelda3::overworldItemsAddress));
+  uint32_t item_pointer_address = SnesToPc(pointer_snes);  // 0x1BC2F9 -> 0x0DC2F9
+  
+  for (int i = 0; i < max_ow; i++) {
+    ASSIGN_OR_RETURN(uint8_t bank_byte, rom()->ReadByte(zelda3::overworldItemsAddressBank));
+    int bank = bank_byte & 0x7F;
+    
+    ASSIGN_OR_RETURN(uint8_t addr_low, rom()->ReadByte(item_pointer_address + (i * 2)));
+    ASSIGN_OR_RETURN(uint8_t addr_high, rom()->ReadByte(item_pointer_address + (i * 2) + 1));
+    
+    uint32_t addr = (bank << 16) +     // 1B
+                    (addr_high << 8) + // F9  
+                    addr_low;          // 3C
     addr = SnesToPc(addr);
 
-    if (overworld_maps_[i].is_large_map()) {
+    // Check if this is a large map and skip if not the parent
+    if (overworld_maps_[i].area_size() != zelda3::AreaSizeEnum::SmallArea) {
       if (overworld_maps_[i].parent() != (uint8_t)i) {
         continue;
       }
@@ -442,13 +477,10 @@ absl::Status Overworld::LoadItems() {
 
       int p = (((b2 & 0x1F) << 8) + b1) >> 1;
 
-      int x = p % 64;
+      int x = p % 0x40;  // Use 0x40 instead of 64 to match ZS
       int y = p >> 6;
 
-      int fakeID = i;
-      if (fakeID >= 64) {
-        fakeID -= 64;
-      }
+      int fakeID = i % 0x40;  // Use modulo 0x40 to match ZS
 
       int sy = fakeID / 8;
       int sx = fakeID - (sy * 8);
@@ -467,15 +499,35 @@ absl::Status Overworld::LoadItems() {
 
 absl::Status Overworld::LoadSprites() {
   std::vector<std::future<absl::Status>> futures;
-  futures.emplace_back(std::async(std::launch::async, [this]() {
-    return LoadSpritesFromMap(kOverworldSpritesBeginning, 64, 0);
-  }));
-  futures.emplace_back(std::async(std::launch::async, [this]() {
-    return LoadSpritesFromMap(kOverworldSpritesZelda, 144, 1);
-  }));
-  futures.emplace_back(std::async(std::launch::async, [this]() {
-    return LoadSpritesFromMap(kOverworldSpritesAgahnim, 144, 2);
-  }));
+  
+  // Use ASM version to determine sprite table locations, with flag as override
+  uint8_t asm_version = (*rom_)[zelda3::OverworldCustomASMHasBeenApplied];
+  bool use_custom_overworld = (asm_version != 0xFF) || 
+                              core::FeatureFlags::get().overworld.kLoadCustomOverworld;
+  
+  if (use_custom_overworld && asm_version >= 3 && asm_version != 0xFF) {
+    // v3: Use expanded sprite tables
+    futures.emplace_back(std::async(std::launch::async, [this]() {
+      return LoadSpritesFromMap(overworldSpritesBeginingExpanded, 64, 0);
+    }));
+    futures.emplace_back(std::async(std::launch::async, [this]() {
+      return LoadSpritesFromMap(overworldSpritesZeldaExpanded, 144, 1);
+    }));
+    futures.emplace_back(std::async(std::launch::async, [this]() {
+      return LoadSpritesFromMap(overworldSpritesAgahnimExpanded, 144, 2);
+    }));
+  } else {
+    // Vanilla/v2: Use original sprite tables
+    futures.emplace_back(std::async(std::launch::async, [this]() {
+      return LoadSpritesFromMap(kOverworldSpritesBeginning, 64, 0);
+    }));
+    futures.emplace_back(std::async(std::launch::async, [this]() {
+      return LoadSpritesFromMap(kOverworldSpritesZelda, 144, 1);
+    }));
+    futures.emplace_back(std::async(std::launch::async, [this]() {
+      return LoadSpritesFromMap(kOverworldSpritesAgahnim, 144, 2);
+    }));
+  }
 
   for (auto &future : futures) {
     future.wait();
@@ -532,6 +584,7 @@ absl::Status Overworld::Save(Rom *rom) {
   RETURN_IF_ERROR(SaveOverworldMaps())
   RETURN_IF_ERROR(SaveEntrances())
   RETURN_IF_ERROR(SaveExits())
+  RETURN_IF_ERROR(SaveMusic())
   RETURN_IF_ERROR(SaveAreaSizes())
   return absl::OkStatus();
 }
@@ -1602,6 +1655,30 @@ absl::Status Overworld::SaveMapProperties() {
   return absl::OkStatus();
 }
 
+absl::Status Overworld::SaveMusic() {
+  util::logf("Saving Music Data");
+  
+  // Save music data for Light World maps
+  for (int i = 0; i < kDarkWorldMapIdStart; i++) {
+    RETURN_IF_ERROR(rom()->WriteByte(kOverworldMusicBeginning + i,
+                                     overworld_maps_[i].area_music(0)));
+    RETURN_IF_ERROR(rom()->WriteByte(kOverworldMusicZelda + i,
+                                     overworld_maps_[i].area_music(1)));
+    RETURN_IF_ERROR(rom()->WriteByte(kOverworldMusicMasterSword + i,
+                                     overworld_maps_[i].area_music(2)));
+    RETURN_IF_ERROR(rom()->WriteByte(kOverworldMusicAgahnim + i,
+                                     overworld_maps_[i].area_music(3)));
+  }
+
+  // Save music data for Dark World maps
+  for (int i = kDarkWorldMapIdStart; i < kSpecialWorldMapIdStart; i++) {
+    RETURN_IF_ERROR(rom()->WriteByte(kOverworldMusicDarkWorld + (i - kDarkWorldMapIdStart),
+                                     overworld_maps_[i].area_music(0)));
+  }
+
+  return absl::OkStatus();
+}
+
 absl::Status Overworld::SaveAreaSizes() {
   util::logf("Saving V3 Area Sizes");
   

src/app/zelda3/overworld/overworld.h

@@ -87,6 +87,29 @@ constexpr int kMap32ExpandedFlagPos = 0x01772E;              // 0x04
 constexpr int kMap16ExpandedFlagPos = 0x02FD28;              // 0x0F
 constexpr int kOverworldEntranceExpandedFlagPos = 0x0DB895;  // 0xB8
 
+constexpr int overworldSpritesBeginingExpanded = 0x141438;
+constexpr int overworldSpritesZeldaExpanded = 0x141578;
+constexpr int overworldSpritesAgahnimExpanded = 0x1416B8;
+constexpr int overworldSpritesDataStartExpanded = 0x04C881;
+
+constexpr int overworldSpecialSpriteGFXGroupExpandedTemp = 0x0166E1;
+constexpr int overworldSpecialSpritePaletteExpandedTemp = 0x016701;
+
+constexpr int ExpandedOverlaySpace = 0x120000;
+
+constexpr int overworldTilesType = 0x071459;
+constexpr int overworldMessages = 0x03F51D;
+constexpr int overworldMessagesExpanded = 0x1417F8;
+
+constexpr int overworldItemsPointers = 0x0DC2F9;
+constexpr int overworldItemsAddress = 0x0DC8B9; // 1BC2F9
+constexpr int overworldItemsAddressBank = 0x0DC8BF;
+constexpr int overworldItemsEndData = 0x0DC89C; // 0DC89E
+
+constexpr int overworldBombDoorItemLocationsNew = 0x012644;
+constexpr int overworldItemsPointersNew = 0x012784;
+constexpr int overworldItemsStartDataNew = 0x0DC2F9;
+
 constexpr int kOverworldCompressedMapPos = 0x058000;
 constexpr int kOverworldCompressedOverflowPos = 0x137FFF;
 
@@ -138,6 +161,7 @@ class Overworld {
   absl::Status SaveMap32Tiles();
 
   absl::Status SaveMapProperties();
+  absl::Status SaveMusic();
   absl::Status SaveAreaSizes();
 
   auto rom() const { return rom_; }
@@ -212,6 +236,7 @@ class Overworld {
   }
   auto is_loaded() const { return is_loaded_; }
   void set_current_map(int i) { current_map_ = i; }
+  void set_current_world(int world) { current_world_ = world; }
   auto map_tiles() const { return map_tiles_; }
   auto mutable_map_tiles() { return &map_tiles_; }
   auto all_items() const { return all_items_; }

src/app/zelda3/overworld/overworld_item.h

@@ -19,6 +19,10 @@ constexpr int kOverworldItemsAddress = 0xDC8B9;  // 1BC2F9
 constexpr int kOverworldItemsBank = 0xDC8BF;
 constexpr int kOverworldItemsEndData = 0xDC89C;  // 0DC89E
 
+constexpr int kOverworldBombDoorItemLocationsNew = 0x012644;
+constexpr int kOverworldItemsPointersNew = 0x012784;
+constexpr int kOverworldItemsStartDataNew = 0x0DC2F9;
+
 class OverworldItem : public GameEntity {
  public:
   OverworldItem() = default;

src/app/zelda3/overworld/overworld_map.cc

@@ -18,16 +18,21 @@ OverworldMap::OverworldMap(int index, Rom *rom)
     : index_(index), parent_(index), rom_(rom) {
   LoadAreaInfo();
 
-  if (core::FeatureFlags::get().overworld.kLoadCustomOverworld) {
-    // If the custom overworld ASM has NOT already been applied, manually set
-    // the vanilla values.
-    uint8_t asm_version = (*rom_)[OverworldCustomASMHasBeenApplied];
-    if (asm_version == 0x00) {
+  // Use ASM version byte as source of truth, with flag as override
+  uint8_t asm_version = (*rom_)[OverworldCustomASMHasBeenApplied];
+  bool use_custom_overworld = (asm_version != 0xFF) || 
+                              core::FeatureFlags::get().overworld.kLoadCustomOverworld;
+  
+  if (use_custom_overworld) {
+    if (asm_version == 0x00 || asm_version == 0xFF) {
+      // No custom ASM applied but flag enabled - set up vanilla values manually
       LoadCustomOverworldData();
     } else {
+      // Custom overworld ASM applied - set up custom tileset
       SetupCustomTileset(asm_version);
     }
   }
+  // For vanilla ROMs without flag, LoadAreaInfo already handles everything
 }
 
 absl::Status OverworldMap::BuildMap(int count, int game_state, int world,

src/app/zelda3/overworld/overworld_map.h

@@ -67,6 +67,9 @@ constexpr int kOverworldPalettesScreenToSetNew = 0x4C635;
 constexpr int kOverworldSpecialSpriteGfxGroupExpandedTemp = 0x0166E1;
 constexpr int kOverworldSpecialSpritePaletteExpandedTemp = 0x016701;
 
+constexpr int transition_target_northExpanded = 0x1411B8;
+constexpr int transition_target_westExpanded = 0x1412F8;
+
 constexpr int kDarkWorldMapIdStart = 0x40;
 constexpr int kSpecialWorldMapIdStart = 0x80;