Expose FileDialog callbacks for getting custom icons

doc/classes/FileDialog.xml

@@ -131,6 +131,34 @@
 				[b]Note:[/b] [FileDialog] will update its internal [ItemList] of favorites when its visibility changes. Be sure to call this method earlier if you want your changes to have effect.
 			</description>
 		</method>
+		<method name="set_get_icon_callback" qualifiers="static">
+			<return type="void" />
+			<param index="0" name="callback" type="Callable" />
+			<description>
+				Sets the callback used by the [FileDialog] nodes to get a file icon, when [constant DISPLAY_LIST] mode is used. The callback should take a single [String] argument (file path), and return a [Texture2D]. If an invalid texture is returned, the [theme_item file] icon will be used instead.
+			</description>
+		</method>
+		<method name="set_get_thumbnail_callback" qualifiers="static">
+			<return type="void" />
+			<param index="0" name="callback" type="Callable" />
+			<description>
+				Sets the callback used by the [FileDialog] nodes to get a file icon, when [constant DISPLAY_THUMBNAILS] mode is used. The callback should take a single [String] argument (file path), and return a [Texture2D]. If an invalid texture is returned, the [theme_item file_thumbnail] icon will be used instead.
+				Thumbnails are usually more complex and may take a while to load. To avoid stalling the application, you can use [ImageTexture] to asynchronously create the thumbnail.
+				[codeblock]
+				func _ready():
+					FileDialog.set_get_thumbnail_callback(thumbnail_method)
+
+				func thumbnail_method(path):
+					var image_texture = ImageTexture.new()
+					make_thumbnail_async(path, image_texture)
+					return image_texture
+
+				func make_thumbnail_async(path, image_texture):
+					var thumbnail_texture = await generate_thumbnail(path) # Some method that generates a thumbnail.
+					image_texture.set_image(thumbnail_texture.get_image())
+				[/codeblock]
+			</description>
+		</method>
 		<method name="set_option_default">
 			<return type="void" />
 			<param index="0" name="option" type="int" />

editor/editor_node.cpp

@@ -687,6 +687,10 @@ void EditorNode::_update_theme(bool p_skip_creation) {
 		_update_renderer_color();
 	}
 
+	Ref<Texture2D> thumbnail_icon = gui_base->get_theme_icon(SNAME("file_thumbnail"), SNAME("FileDialog"));
+	default_thumbnail.instantiate();
+	default_thumbnail->set_image(thumbnail_icon->get_image());
+
 	editor_dock_manager->update_tab_styles();
 	editor_dock_manager->update_docks_menu();
 	editor_dock_manager->set_tab_icon_max_width(theme->get_constant(SNAME("class_icon_size"), EditorStringName(Editor)));
@@ -5625,6 +5629,19 @@ Ref<Texture2D> EditorNode::_file_dialog_get_icon(const String &p_path) {
 	return singleton->icon_type_cache["Object"];
 }
 
+Ref<Texture2D> EditorNode::_file_dialog_get_thumbnail(const String &p_path) {
+	Ref<ImageTexture> texture = singleton->default_thumbnail->duplicate();
+	EditorResourcePreview::get_singleton()->queue_resource_preview(p_path, callable_mp_static(EditorNode::_file_dialog_thumbnail_callback).bind(texture));
+	return texture;
+}
+
+void EditorNode::_file_dialog_thumbnail_callback(const String &p_path, const Ref<Texture2D> &p_preview, const Ref<Texture2D> &p_small_preview, Ref<ImageTexture> p_texture) {
+	ERR_FAIL_COND(p_texture.is_null());
+	if (p_preview.is_valid()) {
+		p_texture->set_image(p_preview->get_image());
+	}
+}
+
 void EditorNode::_build_icon_type_cache() {
 	List<StringName> tl;
 	theme->get_icon_list(EditorStringName(EditorIcons), &tl);
@@ -7817,7 +7834,8 @@ EditorNode::EditorNode() {
 	EditorContextMenuPluginManager::create();
 
 	// Used for previews.
-	FileDialog::get_icon_func = _file_dialog_get_icon;
+	FileDialog::set_get_icon_callback(callable_mp_static(_file_dialog_get_icon));
+	FileDialog::set_get_thumbnail_callback(callable_mp_static(_file_dialog_get_thumbnail));
 	FileDialog::register_func = _file_dialog_register;
 	FileDialog::unregister_func = _file_dialog_unregister;
 
@@ -8919,7 +8937,6 @@ EditorNode::~EditorNode() {
 	GDExtensionEditorPlugins::editor_node_add_plugin = nullptr;
 	GDExtensionEditorPlugins::editor_node_remove_plugin = nullptr;
 
-	FileDialog::get_icon_func = nullptr;
 	FileDialog::register_func = nullptr;
 	FileDialog::unregister_func = nullptr;
 

editor/editor_node.h

@@ -46,6 +46,7 @@ class ConfirmationDialog;
 class Control;
 class FileDialog;
 class HBoxContainer;
+class ImageTexture;
 class MenuBar;
 class MenuButton;
 class OptionButton;
@@ -512,6 +513,10 @@ private:
 	}
 
 	static Ref<Texture2D> _file_dialog_get_icon(const String &p_path);
+	static Ref<Texture2D> _file_dialog_get_thumbnail(const String &p_path);
+	static void _file_dialog_thumbnail_callback(const String &p_path, const Ref<Texture2D> &p_preview, const Ref<Texture2D> &p_small_preview, Ref<ImageTexture> p_texture);
+	Ref<ImageTexture> default_thumbnail;
+
 	static void _file_dialog_register(FileDialog *p_dialog);
 	static void _file_dialog_unregister(FileDialog *p_dialog);
 	static void _editor_file_dialog_register(EditorFileDialog *p_dialog);

scene/gui/file_dialog.cpp

@@ -577,6 +577,24 @@ bool FileDialog::_is_open_should_be_disabled() {
 	return false;
 }
 
+void FileDialog::_thumbnail_callback(const Ref<Texture2D> &p_texture, const String &p_path) {
+	if (display_mode == DISPLAY_LIST || p_texture.is_null()) {
+		return;
+	}
+
+	if (!p_path.begins_with(full_dir)) {
+		return;
+	}
+
+	const String file_name = p_path.get_file();
+	for (int i = 0; i < file_list->get_item_count(); i++) {
+		if (file_list->get_item_text(i) == file_name) {
+			file_list->set_item_icon(i, p_texture);
+			break;
+		}
+	}
+}
+
 void FileDialog::_go_up() {
 	_change_dir("..");
 	_push_history();
@@ -778,7 +796,7 @@ void FileDialog::update_file_list() {
 		file_list->set_max_columns(1);
 		file_list->set_max_text_lines(1);
 		file_list->set_fixed_column_width(0);
-		file_list->set_fixed_icon_size(Size2());
+		file_list->set_fixed_icon_size(theme_cache.file->get_size());
 	}
 
 	dir_access->list_dir_begin();
@@ -948,13 +966,44 @@ void FileDialog::update_file_list() {
 
 	for (const FileInfo &info : filtered_files) {
 		file_list->add_item(info.name);
-		if (get_icon_func) {
-			Ref<Texture2D> icon = get_icon_func(base_dir.path_join(info.name));
+		const String path = base_dir.path_join(info.name);
+
+		if (display_mode == DISPLAY_LIST) {
+			Ref<Texture2D> icon;
+			if (get_icon_callback.is_valid()) {
+				const Variant &v = path;
+				const Variant *argptrs[1] = { &v };
+				Variant vicon;
+
+				Callable::CallError ce;
+				get_icon_callback.callp(argptrs, 1, vicon, ce);
+				if (unlikely(ce.error != Callable::CallError::CALL_OK)) {
+					ERR_PRINT(vformat("Error calling FileDialog's icon callback: %s.", Variant::get_callable_error_text(get_icon_callback, argptrs, 1, ce)));
+				}
+				icon = vicon;
+			}
+			if (icon.is_null()) {
+				icon = theme_cache.file;
+			}
+			file_list->set_item_icon(-1, icon);
+		} else { // DISPLAY_THUMBNAILS
+			Ref<Texture2D> icon;
+			if (get_thumbnail_callback.is_valid()) {
+				const Variant &v = path;
+				const Variant *argptrs[1] = { &v };
+				Variant vicon;
+
+				Callable::CallError ce;
+				get_thumbnail_callback.callp(argptrs, 1, vicon, ce);
+				if (unlikely(ce.error != Callable::CallError::CALL_OK)) {
+					ERR_PRINT(vformat("Error calling FileDialog's thumbnail callback: %s.", Variant::get_callable_error_text(get_thumbnail_callback, argptrs, 1, ce)));
+				}
+				icon = vicon;
+			}
+			if (icon.is_null()) {
+				icon = theme_cache.file;
+			}
 			file_list->set_item_icon(-1, icon);
-		} else if (display_mode == DISPLAY_THUMBNAILS) {
-			file_list->set_item_icon(-1, theme_cache.file_thumbnail);
-		} else {
-			file_list->set_item_icon(-1, theme_cache.file);
 		}
 		file_list->set_item_icon_modulate(-1, theme_cache.file_icon_color);
 
@@ -1983,6 +2032,8 @@ void FileDialog::_bind_methods() {
 	ClassDB::bind_static_method("FileDialog", D_METHOD("get_favorite_list"), &FileDialog::get_favorite_list);
 	ClassDB::bind_static_method("FileDialog", D_METHOD("set_recent_list", "recents"), &FileDialog::set_recent_list);
 	ClassDB::bind_static_method("FileDialog", D_METHOD("get_recent_list"), &FileDialog::get_recent_list);
+	ClassDB::bind_static_method("FileDialog", D_METHOD("set_get_icon_callback", "callback"), &FileDialog::set_get_icon_callback);
+	ClassDB::bind_static_method("FileDialog", D_METHOD("set_get_thumbnail_callback", "callback"), &FileDialog::set_get_thumbnail_callback);
 
 	ClassDB::bind_method(D_METHOD("invalidate"), &FileDialog::invalidate);
 
@@ -2118,6 +2169,14 @@ void FileDialog::set_default_show_hidden_files(bool p_show) {
 	default_show_hidden_files = p_show;
 }
 
+void FileDialog::set_get_icon_callback(const Callable &p_callback) {
+	get_icon_callback = p_callback;
+}
+
+void FileDialog::set_get_thumbnail_callback(const Callable &p_callback) {
+	get_thumbnail_callback = p_callback;
+}
+
 void FileDialog::set_use_native_dialog(bool p_native) {
 	use_native_dialog = p_native;
 
@@ -2143,6 +2202,7 @@ FileDialog::FileDialog() {
 	set_hide_on_ok(false);
 	set_size(Size2(640, 360));
 	set_default_ok_text(ETR("Save")); // Default mode text.
+	thumbnail_callback = callable_mp(this, &FileDialog::_thumbnail_callback);
 
 	for (int i = 0; i < CUSTOMIZATION_MAX; i++) {
 		customization_flags[i] = true;

scene/gui/file_dialog.h

@@ -146,10 +146,11 @@ public:
 		CUSTOMIZATION_MAX
 	};
 
-	typedef Ref<Texture2D> (*GetIconFunc)(const String &);
 	typedef void (*RegisterFunc)(FileDialog *);
 
-	inline static GetIconFunc get_icon_func = nullptr;
+	inline static Callable get_icon_callback;
+	inline static Callable get_thumbnail_callback;
+
 	inline static RegisterFunc register_func = nullptr;
 	inline static RegisterFunc unregister_func = nullptr;
 
@@ -189,6 +190,7 @@ private:
 	String root_prefix;
 	String full_dir;
 
+	Callable thumbnail_callback;
 	bool is_invalidating = false;
 
 	VBoxContainer *main_vbox = nullptr;
@@ -338,6 +340,7 @@ private:
 	void _native_dialog_cb_with_options(bool p_ok, const Vector<String> &p_files, int p_filter, const Dictionary &p_selected_options);
 
 	bool _is_open_should_be_disabled();
+	void _thumbnail_callback(const Ref<Texture2D> &p_texture, const String &p_path);
 
 	TypedArray<Dictionary> _get_options() const;
 	void _update_option_controls();
@@ -430,6 +433,9 @@ public:
 
 	static void set_default_show_hidden_files(bool p_show);
 
+	static void set_get_icon_callback(const Callable &p_callback);
+	static void set_get_thumbnail_callback(const Callable &p_callback);
+
 	void invalidate();
 
 	void deselect_all();

scene/gui/item_list.cpp

@@ -208,11 +208,20 @@ void ItemList::set_item_icon(int p_idx, const Ref<Texture2D> &p_icon) {
 	}
 	ERR_FAIL_INDEX(p_idx, items.size());
 
-	if (items[p_idx].icon == p_icon) {
+	Item &item = items.write[p_idx];
+	if (item.icon == p_icon) {
 		return;
 	}
 
-	items.write[p_idx].icon = p_icon;
+	const Callable redraw = callable_mp((CanvasItem *)this, &CanvasItem::queue_redraw);
+	if (item.icon.is_valid()) {
+		item.icon->disconnect_changed(redraw);
+	}
+	item.icon = p_icon;
+	if (p_icon.is_valid()) {
+		p_icon->connect_changed(redraw);
+	}
+
 	queue_redraw();
 	shape_changed = true;
 }