Don't delete tiles that have been added using the stack mode

src/Classes/Cels/CelTileMap.gd

@@ -20,6 +20,9 @@ func update_tileset() -> void:
 	if TileSetPanel.tile_editing_mode == TileSetPanel.TileEditingMode.AUTO:
 		for j in range(tileset.tiles.size() - 1, 0, -1):
 			var tile := tileset.tiles[j]
+			if tile.mode_added == TileSetPanel.TileEditingMode.STACK:
+				# Don't delete tiles that have been added using the stack mode.
+				continue
 			var tile_used := false
 			for i in indices.size():
 				var x_coord := float(tileset.tile_size.x) * (i % indices_x)
@@ -28,7 +31,7 @@ func update_tileset() -> void:
 				var image_portion := image.get_region(rect)
 				if image_portion.is_invisible():
 					continue
-				if image_portion.get_data() == tile.get_data():
+				if image_portion.get_data() == tile.image.get_data():
 					tile_used = true
 					break
 			if not tile_used:
@@ -45,27 +48,29 @@ func update_tileset() -> void:
 		if TileSetPanel.tile_editing_mode == TileSetPanel.TileEditingMode.MANUAL:
 			if index == 0 or tileset.tiles.size() <= index:
 				if tileset.tiles.size() <= 1:
-					tileset.add_tile(image_portion)
+					tileset.add_tile(image_portion, TileSetPanel.tile_editing_mode)
 					indices[i] = tileset.tiles.size() - 1
 				continue
-			if image_portion.get_data() != tileset.tiles[index].get_data():
+			if image_portion.get_data() != tileset.tiles[index].image.get_data():
 				tileset.replace_tile_at(image_portion, index)
 				# TODO: Update the rest of the tilemap
-		else:
+		else:  # Auto or stack
 			var found_tile := false
 			for j in range(1, tileset.tiles.size()):
 				var tile := tileset.tiles[j]
-				if image_portion.get_data() == tile.get_data():
+				if image_portion.get_data() == tile.image.get_data():
 					indices[i] = j
 					found_tile = true
 					break
 			if not found_tile:
 				if removed_tile_indices.is_empty():
-					tileset.add_tile(image_portion)
+					tileset.add_tile(image_portion, TileSetPanel.tile_editing_mode)
 					indices[i] = tileset.tiles.size() - 1
 				else:
 					var index_position := removed_tile_indices.pop_back() as int
-					tileset.insert_tile(image_portion, index_position)
+					tileset.insert_tile(
+						image_portion, index_position, TileSetPanel.tile_editing_mode
+					)
 					indices[i] = index_position
 
 

src/Classes/TileSetCustom.gd

@@ -5,7 +5,16 @@ signal updated
 
 var name := ""
 var tile_size: Vector2i
-var tiles: Array[Image] = []
+var tiles: Array[Tile] = []
+
+
+class Tile:
+	var image: Image
+	var mode_added: TileSetPanel.TileEditingMode
+
+	func _init(_image: Image, _mode_added: TileSetPanel.TileEditingMode) -> void:
+		image = _image
+		mode_added = _mode_added
 
 
 func _init(_tile_size: Vector2i, _name := "") -> void:
@@ -15,15 +24,17 @@ func _init(_tile_size: Vector2i, _name := "") -> void:
 	#var indices_y := ceili(float(_project_size.y) / tile_size.y)
 	#tiles.resize(indices_x * indices_y + 1)
 	var empty_image := Image.create_empty(tile_size.x, tile_size.y, false, Image.FORMAT_RGBA8)
-	tiles.append(empty_image)
+	tiles.append(Tile.new(empty_image, TileSetPanel.tile_editing_mode))
 
 
-func add_tile(tile: Image) -> void:
+func add_tile(image: Image, edit_mode: TileSetPanel.TileEditingMode) -> void:
+	var tile := Tile.new(image, edit_mode)
 	tiles.append(tile)
 	updated.emit()
 
 
-func insert_tile(tile: Image, position: int) -> void:
+func insert_tile(image: Image, position: int, edit_mode: TileSetPanel.TileEditingMode) -> void:
+	var tile := Tile.new(image, edit_mode)
 	tiles.insert(position, tile)
 	updated.emit()
 
@@ -34,5 +45,5 @@ func remove_tile_at_index(index: int) -> void:
 
 
 func replace_tile_at(new_tile: Image, index: int) -> void:
-	tiles[index].copy_from(new_tile)
+	tiles[index].image.copy_from(new_tile)
 	updated.emit()

src/UI/TilesPanel.gd

@@ -38,7 +38,7 @@ func _update_tileset() -> void:
 	for tile in tileset.tiles:
 		var texture_rect := TextureButton.new()
 		texture_rect.custom_minimum_size = Vector2i(32, 32)
-		texture_rect.texture_normal = ImageTexture.create_from_image(tile)
+		texture_rect.texture_normal = ImageTexture.create_from_image(tile.image)
 		h_flow_container.add_child(texture_rect)