Add follow system theme settings

doc/classes/EditorSettings.xml

@@ -703,6 +703,9 @@
 		<member name="interface/theme/draw_extra_borders" type="bool" setter="" getter="">
 			If [code]true[/code], draws additional borders around interactive UI elements in the editor. This is automatically enabled when using the [b]Black (OLED)[/b] theme preset, as this theme preset uses a fully black background.
 		</member>
+		<member name="interface/theme/follow_system_theme" type="bool" setter="" getter="">
+			If [code]true[/code], the editor theme preset will attempt to automatically match the system theme.
+		</member>
 		<member name="interface/theme/icon_and_font_color" type="int" setter="" getter="">
 			The icon and font color scheme to use in the editor.
 			- [b]Auto[/b] determines the color scheme to use automatically based on [member interface/theme/base_color].
@@ -722,6 +725,10 @@
 		<member name="interface/theme/spacing_preset" type="String" setter="" getter="">
 			The editor theme spacing preset to use. See also [member interface/theme/base_spacing] and [member interface/theme/additional_spacing].
 		</member>
+		<member name="interface/theme/use_system_accent_color" type="bool" setter="" getter="">
+			If [code]true[/code], set accent color based on system settings.
+			[b]Note:[/b] This setting is only effective on Windows and MacOS.
+		</member>
 		<member name="interface/touchscreen/enable_long_press_as_right_click" type="bool" setter="" getter="">
 			If [code]true[/code], long press on touchscreen is treated as right click.
 			[b]Note:[/b] Defaults to [code]true[/code] on touchscreen devices.

editor/editor_node.cpp

@@ -665,6 +665,8 @@ void EditorNode::_notification(int p_what) {
 
 			callable_mp(this, &EditorNode::_begin_first_scan).call_deferred();
 
+			DisplayServer::get_singleton()->set_system_theme_change_callback(callable_mp(this, &EditorNode::_update_theme));
+
 			/* DO NOT LOAD SCENES HERE, WAIT FOR FILE SCANNING AND REIMPORT TO COMPLETE */
 		} break;
 
@@ -768,6 +770,9 @@ void EditorNode::_notification(int p_what) {
 			EditorFileDialog::set_default_show_hidden_files(EDITOR_GET("filesystem/file_dialog/show_hidden_files"));
 			EditorFileDialog::set_default_display_mode((EditorFileDialog::DisplayMode)EDITOR_GET("filesystem/file_dialog/display_mode").operator int());
 
+			follow_system_theme = EDITOR_GET("interface/theme/follow_system_theme");
+			use_system_accent_color = EDITOR_GET("interface/theme/use_system_accent_color");
+
 			if (EditorThemeManager::is_generated_theme_outdated()) {
 				_update_theme();
 			}
@@ -3071,6 +3076,35 @@ void EditorNode::_save_screenshot(NodePath p_path) {
 	ERR_FAIL_COND_MSG(error != OK, "Cannot save screenshot to file '" + p_path + "'.");
 }
 
+void EditorNode::_check_system_theme_changed() {
+	DisplayServer *display_server = DisplayServer::get_singleton();
+
+	bool system_theme_changed = false;
+
+	if (follow_system_theme) {
+		if (display_server->get_base_color() != last_system_base_color) {
+			system_theme_changed = true;
+			last_system_base_color = display_server->get_base_color();
+		}
+
+		if (display_server->is_dark_mode_supported() && display_server->is_dark_mode() != last_dark_mode_state) {
+			system_theme_changed = true;
+			last_dark_mode_state = display_server->is_dark_mode();
+		}
+	}
+
+	if (use_system_accent_color) {
+		if (display_server->get_accent_color() != last_system_accent_color) {
+			system_theme_changed = true;
+			last_system_accent_color = display_server->get_accent_color();
+		}
+	}
+
+	if (system_theme_changed) {
+		_update_theme();
+	}
+}
+
 void EditorNode::_tool_menu_option(int p_idx) {
 	switch (tool_menu->get_item_id(p_idx)) {
 		case TOOLS_ORPHAN_RESOURCES: {
@@ -7527,6 +7561,15 @@ EditorNode::EditorNode() {
 	String exec = OS::get_singleton()->get_executable_path();
 	// Save editor executable path for third-party tools.
 	EditorSettings::get_singleton()->set_project_metadata("editor_metadata", "executable_path", exec);
+
+	follow_system_theme = EDITOR_GET("interface/theme/follow_system_theme");
+	use_system_accent_color = EDITOR_GET("interface/theme/use_system_accent_color");
+	system_theme_timer = memnew(Timer);
+	system_theme_timer->set_wait_time(1.0);
+	system_theme_timer->connect("timeout", callable_mp(this, &EditorNode::_check_system_theme_changed));
+	add_child(system_theme_timer);
+	system_theme_timer->set_owner(get_owner());
+	system_theme_timer->set_autostart(true);
 }
 
 EditorNode::~EditorNode() {

editor/editor_node.h

@@ -357,6 +357,13 @@ private:
 
 	Ref<Theme> theme;
 
+	Timer *system_theme_timer = nullptr;
+	bool follow_system_theme = false;
+	bool use_system_accent_color = false;
+	bool last_dark_mode_state = false;
+	Color last_system_base_color = Color(0, 0, 0, 0);
+	Color last_system_accent_color = Color(0, 0, 0, 0);
+
 	PopupMenu *recent_scenes = nullptr;
 	String _recent_scene;
 	List<String> previous_scenes;
@@ -533,6 +540,8 @@ private:
 	void _screenshot(bool p_use_utc = false);
 	void _save_screenshot(NodePath p_path);
 
+	void _check_system_theme_changed();
+
 	void _tool_menu_option(int p_idx);
 	void _export_as_menu_option(int p_idx);
 	void _update_file_menu_opened();

editor/editor_settings.cpp

@@ -464,11 +464,13 @@ void EditorSettings::_load_defaults(Ref<ConfigFile> p_extra_config) {
 	EDITOR_SETTING(Variant::FLOAT, PROPERTY_HINT_RANGE, "interface/inspector/float_drag_speed", 5.0, "0.1,100,0.01")
 
 	// Theme
+	EDITOR_SETTING(Variant::BOOL, PROPERTY_HINT_ENUM, "interface/theme/follow_system_theme", false, "")
 	EDITOR_SETTING(Variant::STRING, PROPERTY_HINT_ENUM, "interface/theme/preset", "Default", "Default,Breeze Dark,Godot 2,Gray,Light,Solarized (Dark),Solarized (Light),Black (OLED),Custom")
 	EDITOR_SETTING(Variant::STRING, PROPERTY_HINT_ENUM, "interface/theme/spacing_preset", "Default", "Compact,Default,Spacious,Custom")
 	EDITOR_SETTING(Variant::INT, PROPERTY_HINT_ENUM, "interface/theme/icon_and_font_color", 0, "Auto,Dark,Light")
 	EDITOR_SETTING(Variant::COLOR, PROPERTY_HINT_NONE, "interface/theme/base_color", Color(0.2, 0.23, 0.31), "")
 	EDITOR_SETTING(Variant::COLOR, PROPERTY_HINT_NONE, "interface/theme/accent_color", Color(0.41, 0.61, 0.91), "")
+	EDITOR_SETTING(Variant::BOOL, PROPERTY_HINT_NONE, "interface/theme/use_system_accent_color", false, "")
 	EDITOR_SETTING(Variant::FLOAT, PROPERTY_HINT_RANGE, "interface/theme/contrast", 0.3, "-1,1,0.01")
 	EDITOR_SETTING(Variant::BOOL, PROPERTY_HINT_NONE, "interface/theme/draw_extra_borders", false, "")
 	EDITOR_SETTING(Variant::FLOAT, PROPERTY_HINT_RANGE, "interface/theme/icon_saturation", 1.0, "0,2,0.01")

editor/themes/editor_theme_manager.cpp

@@ -252,6 +252,29 @@ EditorThemeManager::ThemeConfiguration EditorThemeManager::_create_theme_config(
 
 	// Handle main theme preset.
 	{
+		const bool follow_system_theme = EDITOR_GET("interface/theme/follow_system_theme");
+		const bool use_system_accent_color = EDITOR_GET("interface/theme/use_system_accent_color");
+		DisplayServer *display_server = DisplayServer::get_singleton();
+		Color system_base_color = display_server->get_base_color();
+		Color system_accent_color = display_server->get_accent_color();
+
+		if (follow_system_theme) {
+			String dark_theme = "Default";
+			String light_theme = "Light";
+
+			config.preset = light_theme; // Assume light theme if we can't detect system theme attributes.
+
+			if (system_base_color == Color(0, 0, 0, 0)) {
+				if (display_server->is_dark_mode_supported() && display_server->is_dark_mode()) {
+					config.preset = dark_theme;
+				}
+			} else {
+				if (system_base_color.get_luminance() < 0.5) {
+					config.preset = dark_theme;
+				}
+			}
+		}
+
 		if (config.preset != "Custom") {
 			Color preset_accent_color;
 			Color preset_base_color;
@@ -308,6 +331,16 @@ EditorThemeManager::ThemeConfiguration EditorThemeManager::_create_theme_config(
 			EditorSettings::get_singleton()->set_initial_value("interface/theme/draw_extra_borders", config.draw_extra_borders);
 		}
 
+		if (follow_system_theme && system_base_color != Color(0, 0, 0, 0)) {
+			config.base_color = system_base_color;
+			config.preset = "Custom";
+		}
+
+		if (use_system_accent_color && system_accent_color != Color(0, 0, 0, 0)) {
+			config.accent_color = system_accent_color;
+			config.preset = "Custom";
+		}
+
 		// Enforce values in case they were adjusted or overridden.
 		EditorSettings::get_singleton()->set_manually("interface/theme/preset", config.preset);
 		EditorSettings::get_singleton()->set_manually("interface/theme/accent_color", config.accent_color);