Introduce the concept of global theme contexts

This commit adds the default theme context, which replaces
the need to manually check the project and the default theme
all the time; simplifies related code.

It also adds framework for custom theme contexts, to be used
by the editor. Custom contexts can be attached to any node,
and not necessarily a GUI/Window node. Contexts do no break
theme inheritance and only define which global themes a node
uses as a fallback.

Contexts propagate NOTIFICATION_THEME_CHANGED when one of their
global themes changes. This ensures that global themes act just
like themes assigned to individual nodes and can be previewed
live in the editor.

scene/3d/label_3d.cpp

@@ -780,42 +780,31 @@ Ref<Font> Label3D::_get_font_or_default() const {
 		return font_override;
 	}
 
-	// Check the project-defined Theme resource.
-	if (ThemeDB::get_singleton()->get_project_theme().is_valid()) {
-		List<StringName> theme_types;
-		ThemeDB::get_singleton()->get_project_theme()->get_type_dependencies(get_class_name(), StringName(), &theme_types);
+	StringName theme_name = "font";
+	List<StringName> theme_types;
+	ThemeDB::get_singleton()->get_native_type_dependencies(get_class_name(), &theme_types);
+
+	ThemeContext *global_context = ThemeDB::get_singleton()->get_default_theme_context();
+	for (const Ref<Theme> &theme : global_context->get_themes()) {
+		if (theme.is_null()) {
+			continue;
+		}
 
 		for (const StringName &E : theme_types) {
-			if (ThemeDB::get_singleton()->get_project_theme()->has_theme_item(Theme::DATA_TYPE_FONT, "font", E)) {
-				Ref<Font> f = ThemeDB::get_singleton()->get_project_theme()->get_theme_item(Theme::DATA_TYPE_FONT, "font", E);
-				if (f.is_valid()) {
-					theme_font = f;
-					theme_font->connect_changed(callable_mp(const_cast<Label3D *>(this), &Label3D::_font_changed));
-				}
-				return f;
+			if (!theme->has_font(theme_name, E)) {
+				continue;
 			}
-		}
-	}
 
-	// Lastly, fall back on the items defined in the default Theme, if they exist.
-	{
-		List<StringName> theme_types;
-		ThemeDB::get_singleton()->get_default_theme()->get_type_dependencies(get_class_name(), StringName(), &theme_types);
-
-		for (const StringName &E : theme_types) {
-			if (ThemeDB::get_singleton()->get_default_theme()->has_theme_item(Theme::DATA_TYPE_FONT, "font", E)) {
-				Ref<Font> f = ThemeDB::get_singleton()->get_default_theme()->get_theme_item(Theme::DATA_TYPE_FONT, "font", E);
-				if (f.is_valid()) {
-					theme_font = f;
-					theme_font->connect_changed(callable_mp(const_cast<Label3D *>(this), &Label3D::_font_changed));
-				}
-				return f;
+			Ref<Font> f = theme->get_font(theme_name, E);
+			if (f.is_valid()) {
+				theme_font = f;
+				theme_font->connect_changed(callable_mp(const_cast<Label3D *>(this), &Label3D::_font_changed));
 			}
+			return f;
 		}
 	}
 
-	// If they don't exist, use any type to return the default/empty value.
-	Ref<Font> f = ThemeDB::get_singleton()->get_default_theme()->get_theme_item(Theme::DATA_TYPE_FONT, "font", StringName());
+	Ref<Font> f = global_context->get_fallback_theme()->get_font(theme_name, StringName());
 	if (f.is_valid()) {
 		theme_font = f;
 		theme_font->connect_changed(callable_mp(const_cast<Label3D *>(this), &Label3D::_font_changed));

scene/gui/control.cpp

@@ -2465,6 +2465,11 @@ bool Control::has_theme_owner_node() const {
 	return data.theme_owner->has_owner_node();
 }
 
+void Control::set_theme_context(ThemeContext *p_context, bool p_propagate) {
+	ERR_MAIN_THREAD_GUARD;
+	data.theme_owner->set_owner_context(p_context, p_propagate);
+}
+
 void Control::set_theme(const Ref<Theme> &p_theme) {
 	ERR_MAIN_THREAD_GUARD;
 	if (data.theme == p_theme) {
@@ -3124,7 +3129,9 @@ void Control::_notification(int p_notification) {
 				notification(NOTIFICATION_TRANSLATION_CHANGED);
 			}
 #endif
-			notification(NOTIFICATION_THEME_CHANGED);
+
+			// Emits NOTIFICATION_THEME_CHANGED internally.
+			set_theme_context(ThemeDB::get_singleton()->get_nearest_theme_context(this));
 		} break;
 
 		case NOTIFICATION_POST_ENTER_TREE: {
@@ -3134,6 +3141,7 @@ void Control::_notification(int p_notification) {
 		} break;
 
 		case NOTIFICATION_EXIT_TREE: {
+			set_theme_context(nullptr, false);
 			release_focus();
 			get_viewport()->_gui_remove_control(this);
 		} break;
@@ -3632,7 +3640,7 @@ void Control::_bind_methods() {
 }
 
 Control::Control() {
-	data.theme_owner = memnew(ThemeOwner);
+	data.theme_owner = memnew(ThemeOwner(this));
 }
 
 Control::~Control() {

scene/gui/control.h

@@ -42,6 +42,7 @@ class Viewport;
 class Label;
 class Panel;
 class ThemeOwner;
+class ThemeContext;
 
 class Control : public CanvasItem {
 	GDCLASS(Control, CanvasItem);
@@ -553,6 +554,8 @@ public:
 	Node *get_theme_owner_node() const;
 	bool has_theme_owner_node() const;
 
+	void set_theme_context(ThemeContext *p_context, bool p_propagate = true);
+
 	void set_theme(const Ref<Theme> &p_theme);
 	Ref<Theme> get_theme() const;
 

scene/main/window.cpp

@@ -1269,7 +1269,9 @@ void Window::_notification(int p_what) {
 				notification(NOTIFICATION_TRANSLATION_CHANGED);
 			}
 #endif
-			notification(NOTIFICATION_THEME_CHANGED);
+
+			// Emits NOTIFICATION_THEME_CHANGED internally.
+			set_theme_context(ThemeDB::get_singleton()->get_nearest_theme_context(this));
 		} break;
 
 		case NOTIFICATION_READY: {
@@ -1313,6 +1315,8 @@ void Window::_notification(int p_what) {
 		} break;
 
 		case NOTIFICATION_EXIT_TREE: {
+			set_theme_context(nullptr, false);
+
 			if (transient) {
 				_clear_transient();
 			}
@@ -1889,6 +1893,11 @@ bool Window::has_theme_owner_node() const {
 	return theme_owner->has_owner_node();
 }
 
+void Window::set_theme_context(ThemeContext *p_context, bool p_propagate) {
+	ERR_MAIN_THREAD_GUARD;
+	theme_owner->set_owner_context(p_context, p_propagate);
+}
+
 void Window::set_theme(const Ref<Theme> &p_theme) {
 	ERR_MAIN_THREAD_GUARD;
 	if (theme == p_theme) {
@@ -2887,7 +2896,7 @@ Window::Window() {
 		max_size_used = max_size; // Update max_size_used.
 	}
 
-	theme_owner = memnew(ThemeOwner);
+	theme_owner = memnew(ThemeOwner(this));
 	RS::get_singleton()->viewport_set_update_mode(get_viewport_rid(), RS::VIEWPORT_UPDATE_DISABLED);
 }
 

scene/main/window.h

@@ -39,6 +39,7 @@ class Font;
 class Shortcut;
 class StyleBox;
 class ThemeOwner;
+class ThemeContext;
 
 class Window : public Viewport {
 	GDCLASS(Window, Viewport)
@@ -365,6 +366,8 @@ public:
 	Node *get_theme_owner_node() const;
 	bool has_theme_owner_node() const;
 
+	void set_theme_context(ThemeContext *p_context, bool p_propagate = true);
+
 	void set_theme(const Ref<Theme> &p_theme);
 	Ref<Theme> get_theme() const;
 

scene/resources/font.cpp

@@ -2779,48 +2779,25 @@ Ref<Font> FontVariation::_get_base_font_or_default() const {
 		return base_font;
 	}
 
-	// Check the project-defined Theme resource.
-	if (ThemeDB::get_singleton()->get_project_theme().is_valid()) {
-		List<StringName> theme_types;
-		ThemeDB::get_singleton()->get_project_theme()->get_type_dependencies(get_class_name(), StringName(), &theme_types);
+	StringName theme_name = "font";
+	List<StringName> theme_types;
+	ThemeDB::get_singleton()->get_native_type_dependencies(get_class_name(), &theme_types);
 
-		for (const StringName &E : theme_types) {
-			if (ThemeDB::get_singleton()->get_project_theme()->has_theme_item(Theme::DATA_TYPE_FONT, "font", E)) {
-				Ref<Font> f = ThemeDB::get_singleton()->get_project_theme()->get_theme_item(Theme::DATA_TYPE_FONT, "font", E);
-				if (f == this) {
-					continue;
-				}
-				if (f.is_valid()) {
-					theme_font = f;
-					theme_font->connect_changed(callable_mp(reinterpret_cast<Font *>(const_cast<FontVariation *>(this)), &Font::_invalidate_rids), CONNECT_REFERENCE_COUNTED);
-				}
-				return f;
-			}
+	ThemeContext *global_context = ThemeDB::get_singleton()->get_default_theme_context();
+	for (const Ref<Theme> &theme : global_context->get_themes()) {
+		if (theme.is_null()) {
+			continue;
 		}
-	}
-
-	// Lastly, fall back on the items defined in the default Theme, if they exist.
-	if (ThemeDB::get_singleton()->get_default_theme().is_valid()) {
-		List<StringName> theme_types;
-		ThemeDB::get_singleton()->get_default_theme()->get_type_dependencies(get_class_name(), StringName(), &theme_types);
 
 		for (const StringName &E : theme_types) {
-			if (ThemeDB::get_singleton()->get_default_theme()->has_theme_item(Theme::DATA_TYPE_FONT, "font", E)) {
-				Ref<Font> f = ThemeDB::get_singleton()->get_default_theme()->get_theme_item(Theme::DATA_TYPE_FONT, "font", E);
-				if (f == this) {
-					continue;
-				}
-				if (f.is_valid()) {
-					theme_font = f;
-					theme_font->connect_changed(callable_mp(reinterpret_cast<Font *>(const_cast<FontVariation *>(this)), &Font::_invalidate_rids), CONNECT_REFERENCE_COUNTED);
-				}
-				return f;
+			if (!theme->has_font(theme_name, E)) {
+				continue;
 			}
-		}
 
-		// If they don't exist, use any type to return the default/empty value.
-		Ref<Font> f = ThemeDB::get_singleton()->get_default_theme()->get_theme_item(Theme::DATA_TYPE_FONT, "font", StringName());
-		if (f != this) {
+			Ref<Font> f = theme->get_font(theme_name, E);
+			if (f == this) {
+				continue;
+			}
 			if (f.is_valid()) {
 				theme_font = f;
 				theme_font->connect_changed(callable_mp(reinterpret_cast<Font *>(const_cast<FontVariation *>(this)), &Font::_invalidate_rids), CONNECT_REFERENCE_COUNTED);
@@ -2829,6 +2806,15 @@ Ref<Font> FontVariation::_get_base_font_or_default() const {
 		}
 	}
 
+	Ref<Font> f = global_context->get_fallback_theme()->get_font(theme_name, StringName());
+	if (f != this) {
+		if (f.is_valid()) {
+			theme_font = f;
+			theme_font->connect_changed(callable_mp(reinterpret_cast<Font *>(const_cast<FontVariation *>(this)), &Font::_invalidate_rids), CONNECT_REFERENCE_COUNTED);
+		}
+		return f;
+	}
+
 	return Ref<Font>();
 }
 
@@ -3131,48 +3117,25 @@ Ref<Font> SystemFont::_get_base_font_or_default() const {
 		return base_font;
 	}
 
-	// Check the project-defined Theme resource.
-	if (ThemeDB::get_singleton()->get_project_theme().is_valid()) {
-		List<StringName> theme_types;
-		ThemeDB::get_singleton()->get_project_theme()->get_type_dependencies(get_class_name(), StringName(), &theme_types);
+	StringName theme_name = "font";
+	List<StringName> theme_types;
+	ThemeDB::get_singleton()->get_native_type_dependencies(get_class_name(), &theme_types);
 
-		for (const StringName &E : theme_types) {
-			if (ThemeDB::get_singleton()->get_project_theme()->has_theme_item(Theme::DATA_TYPE_FONT, "font", E)) {
-				Ref<Font> f = ThemeDB::get_singleton()->get_project_theme()->get_theme_item(Theme::DATA_TYPE_FONT, "font", E);
-				if (f == this) {
-					continue;
-				}
-				if (f.is_valid()) {
-					theme_font = f;
-					theme_font->connect_changed(callable_mp(reinterpret_cast<Font *>(const_cast<SystemFont *>(this)), &Font::_invalidate_rids), CONNECT_REFERENCE_COUNTED);
-				}
-				return f;
-			}
+	ThemeContext *global_context = ThemeDB::get_singleton()->get_default_theme_context();
+	for (const Ref<Theme> &theme : global_context->get_themes()) {
+		if (theme.is_null()) {
+			continue;
 		}
-	}
-
-	// Lastly, fall back on the items defined in the default Theme, if they exist.
-	if (ThemeDB::get_singleton()->get_default_theme().is_valid()) {
-		List<StringName> theme_types;
-		ThemeDB::get_singleton()->get_default_theme()->get_type_dependencies(get_class_name(), StringName(), &theme_types);
 
 		for (const StringName &E : theme_types) {
-			if (ThemeDB::get_singleton()->get_default_theme()->has_theme_item(Theme::DATA_TYPE_FONT, "font", E)) {
-				Ref<Font> f = ThemeDB::get_singleton()->get_default_theme()->get_theme_item(Theme::DATA_TYPE_FONT, "font", E);
-				if (f == this) {
-					continue;
-				}
-				if (f.is_valid()) {
-					theme_font = f;
-					theme_font->connect_changed(callable_mp(reinterpret_cast<Font *>(const_cast<SystemFont *>(this)), &Font::_invalidate_rids), CONNECT_REFERENCE_COUNTED);
-				}
-				return f;
+			if (!theme->has_font(theme_name, E)) {
+				continue;
 			}
-		}
 
-		// If they don't exist, use any type to return the default/empty value.
-		Ref<Font> f = ThemeDB::get_singleton()->get_default_theme()->get_theme_item(Theme::DATA_TYPE_FONT, "font", StringName());
-		if (f != this) {
+			Ref<Font> f = theme->get_font(theme_name, E);
+			if (f == this) {
+				continue;
+			}
 			if (f.is_valid()) {
 				theme_font = f;
 				theme_font->connect_changed(callable_mp(reinterpret_cast<Font *>(const_cast<SystemFont *>(this)), &Font::_invalidate_rids), CONNECT_REFERENCE_COUNTED);
@@ -3181,6 +3144,15 @@ Ref<Font> SystemFont::_get_base_font_or_default() const {
 		}
 	}
 
+	Ref<Font> f = global_context->get_fallback_theme()->get_font(theme_name, StringName());
+	if (f != this) {
+		if (f.is_valid()) {
+			theme_font = f;
+			theme_font->connect_changed(callable_mp(reinterpret_cast<Font *>(const_cast<SystemFont *>(this)), &Font::_invalidate_rids), CONNECT_REFERENCE_COUNTED);
+		}
+		return f;
+	}
+
 	return Ref<Font>();
 }
 

scene/resources/primitive_meshes.cpp

@@ -3466,32 +3466,24 @@ Ref<Font> TextMesh::_get_font_or_default() const {
 		return font_override;
 	}
 
-	// Check the project-defined Theme resource.
-	if (ThemeDB::get_singleton()->get_project_theme().is_valid()) {
-		List<StringName> theme_types;
-		ThemeDB::get_singleton()->get_project_theme()->get_type_dependencies(get_class_name(), StringName(), &theme_types);
-
-		for (const StringName &E : theme_types) {
-			if (ThemeDB::get_singleton()->get_project_theme()->has_theme_item(Theme::DATA_TYPE_FONT, "font", E)) {
-				return ThemeDB::get_singleton()->get_project_theme()->get_theme_item(Theme::DATA_TYPE_FONT, "font", E);
-			}
+	StringName theme_name = "font";
+	List<StringName> theme_types;
+	ThemeDB::get_singleton()->get_native_type_dependencies(get_class_name(), &theme_types);
+
+	ThemeContext *global_context = ThemeDB::get_singleton()->get_default_theme_context();
+	for (const Ref<Theme> &theme : global_context->get_themes()) {
+		if (theme.is_null()) {
+			continue;
 		}
-	}
-
-	// Lastly, fall back on the items defined in the default Theme, if they exist.
-	{
-		List<StringName> theme_types;
-		ThemeDB::get_singleton()->get_default_theme()->get_type_dependencies(get_class_name(), StringName(), &theme_types);
 
 		for (const StringName &E : theme_types) {
-			if (ThemeDB::get_singleton()->get_default_theme()->has_theme_item(Theme::DATA_TYPE_FONT, "font", E)) {
-				return ThemeDB::get_singleton()->get_default_theme()->get_theme_item(Theme::DATA_TYPE_FONT, "font", E);
+			if (theme->has_font(theme_name, E)) {
+				return theme->get_font(theme_name, E);
 			}
 		}
 	}
 
-	// If they don't exist, use any type to return the default/empty value.
-	return ThemeDB::get_singleton()->get_default_theme()->get_theme_item(Theme::DATA_TYPE_FONT, "font", StringName());
+	return global_context->get_fallback_theme()->get_font(theme_name, StringName());
 }
 
 void TextMesh::set_font_size(int p_size) {

scene/resources/theme.cpp

@@ -1263,11 +1263,7 @@ void Theme::get_type_dependencies(const StringName &p_base_type, const StringNam
 	}
 
 	// Continue building the chain using native class hierarchy.
-	StringName class_name = p_base_type;
-	while (class_name != StringName()) {
-		p_list->push_back(class_name);
-		class_name = ClassDB::get_parent_class_nocheck(class_name);
-	}
+	ThemeDB::get_singleton()->get_native_type_dependencies(p_base_type, p_list);
 }
 
 // Internal methods for getting lists as a Vector of String (compatible with public API).

scene/theme/theme_db.cpp

@@ -32,6 +32,9 @@
 
 #include "core/config/project_settings.h"
 #include "core/io/resource_loader.h"
+#include "scene/gui/control.h"
+#include "scene/main/node.h"
+#include "scene/main/window.h"
 #include "scene/resources/font.h"
 #include "scene/resources/style_box.h"
 #include "scene/resources/texture.h"
@@ -40,18 +43,18 @@
 #include "servers/text_server.h"
 
 // Default engine theme creation and configuration.
+
 void ThemeDB::initialize_theme() {
+	// Default theme-related project settings.
+
 	// Allow creating the default theme at a different scale to suit higher/lower base resolutions.
 	float default_theme_scale = GLOBAL_DEF(PropertyInfo(Variant::FLOAT, "gui/theme/default_theme_scale", PROPERTY_HINT_RANGE, "0.5,8,0.01", PROPERTY_USAGE_DEFAULT | PROPERTY_USAGE_RESTART_IF_CHANGED), 1.0);
 
-	String theme_path = GLOBAL_DEF_RST(PropertyInfo(Variant::STRING, "gui/theme/custom", PROPERTY_HINT_FILE, "*.tres,*.res,*.theme", PROPERTY_USAGE_DEFAULT | PROPERTY_USAGE_RESTART_IF_CHANGED), "");
-
-	String font_path = GLOBAL_DEF_RST(PropertyInfo(Variant::STRING, "gui/theme/custom_font", PROPERTY_HINT_FILE, "*.tres,*.res,*.otf,*.ttf,*.woff,*.woff2,*.fnt,*.font,*.pfb,*.pfm", PROPERTY_USAGE_DEFAULT | PROPERTY_USAGE_RESTART_IF_CHANGED), "");
+	String project_theme_path = GLOBAL_DEF_RST(PropertyInfo(Variant::STRING, "gui/theme/custom", PROPERTY_HINT_FILE, "*.tres,*.res,*.theme", PROPERTY_USAGE_DEFAULT | PROPERTY_USAGE_RESTART_IF_CHANGED), "");
+	String project_font_path = GLOBAL_DEF_RST(PropertyInfo(Variant::STRING, "gui/theme/custom_font", PROPERTY_HINT_FILE, "*.tres,*.res,*.otf,*.ttf,*.woff,*.woff2,*.fnt,*.font,*.pfb,*.pfm", PROPERTY_USAGE_DEFAULT | PROPERTY_USAGE_RESTART_IF_CHANGED), "");
 
 	TextServer::FontAntialiasing font_antialiasing = (TextServer::FontAntialiasing)(int)GLOBAL_DEF_RST(PropertyInfo(Variant::INT, "gui/theme/default_font_antialiasing", PROPERTY_HINT_ENUM, "None,Grayscale,LCD Subpixel", PROPERTY_USAGE_DEFAULT | PROPERTY_USAGE_RESTART_IF_CHANGED), 1);
-
 	TextServer::Hinting font_hinting = (TextServer::Hinting)(int)GLOBAL_DEF_RST(PropertyInfo(Variant::INT, "gui/theme/default_font_hinting", PROPERTY_HINT_ENUM, "None,Light,Normal", PROPERTY_USAGE_DEFAULT | PROPERTY_USAGE_RESTART_IF_CHANGED), TextServer::HINTING_LIGHT);
-
 	TextServer::SubpixelPositioning font_subpixel_positioning = (TextServer::SubpixelPositioning)(int)GLOBAL_DEF_RST(PropertyInfo(Variant::INT, "gui/theme/default_font_subpixel_positioning", PROPERTY_HINT_ENUM, "Disabled,Auto,One Half of a Pixel,One Quarter of a Pixel", PROPERTY_USAGE_DEFAULT | PROPERTY_USAGE_RESTART_IF_CHANGED), TextServer::SUBPIXEL_POSITIONING_AUTO);
 
 	const bool font_msdf = GLOBAL_DEF_RST("gui/theme/default_font_multichannel_signed_distance_field", false);
@@ -60,35 +63,42 @@ void ThemeDB::initialize_theme() {
 	GLOBAL_DEF_RST(PropertyInfo(Variant::INT, "gui/theme/lcd_subpixel_layout", PROPERTY_HINT_ENUM, "Disabled,Horizontal RGB,Horizontal BGR,Vertical RGB,Vertical BGR"), 1);
 	ProjectSettings::get_singleton()->set_restart_if_changed("gui/theme/lcd_subpixel_layout", false);
 
-	Ref<Font> font;
-	if (!font_path.is_empty()) {
-		font = ResourceLoader::load(font_path);
-		if (font.is_valid()) {
-			set_fallback_font(font);
+	// Attempt to load custom project theme and font.
+
+	if (!project_theme_path.is_empty()) {
+		Ref<Theme> theme = ResourceLoader::load(project_theme_path);
+		if (theme.is_valid()) {
+			set_project_theme(theme);
 		} else {
-			ERR_PRINT("Error loading custom font '" + font_path + "'");
+			ERR_PRINT("Error loading custom project theme '" + project_theme_path + "'");
 		}
 	}
 
-	// Always make the default theme to avoid invalid default font/icon/style in the given theme.
-	if (RenderingServer::get_singleton()) {
-		make_default_theme(default_theme_scale, font, font_subpixel_positioning, font_hinting, font_antialiasing, font_msdf, font_generate_mipmaps);
-	}
-
-	if (!theme_path.is_empty()) {
-		Ref<Theme> theme = ResourceLoader::load(theme_path);
-		if (theme.is_valid()) {
-			set_project_theme(theme);
+	Ref<Font> project_font;
+	if (!project_font_path.is_empty()) {
+		project_font = ResourceLoader::load(project_font_path);
+		if (project_font.is_valid()) {
+			set_fallback_font(project_font);
 		} else {
-			ERR_PRINT("Error loading custom theme '" + theme_path + "'");
+			ERR_PRINT("Error loading custom project font '" + project_font_path + "'");
 		}
 	}
+
+	// Always generate the default theme to serve as a fallback for all required theme definitions.
+
+	if (RenderingServer::get_singleton()) {
+		make_default_theme(default_theme_scale, project_font, font_subpixel_positioning, font_hinting, font_antialiasing, font_msdf, font_generate_mipmaps);
+	}
+
+	_init_default_theme_context();
 }
 
 void ThemeDB::initialize_theme_noproject() {
 	if (RenderingServer::get_singleton()) {
 		make_default_theme(1.0, Ref<Font>());
 	}
+
+	_init_default_theme_context();
 }
 
 void ThemeDB::finalize_theme() {
@@ -96,6 +106,7 @@ void ThemeDB::finalize_theme() {
 		WARN_PRINT("Finalizing theme when there is no RenderingServer is an error; check the order of operations.");
 	}
 
+	_finalize_theme_contexts();
 	default_theme.unref();
 
 	fallback_font.unref();
@@ -103,7 +114,7 @@ void ThemeDB::finalize_theme() {
 	fallback_stylebox.unref();
 }
 
-// Universal fallback Theme resources.
+// Global Theme resources.
 
 void ThemeDB::set_default_theme(const Ref<Theme> &p_default) {
 	default_theme = p_default;
@@ -188,7 +199,117 @@ Ref<StyleBox> ThemeDB::get_fallback_stylebox() {
 	return fallback_stylebox;
 }
 
+void ThemeDB::get_native_type_dependencies(const StringName &p_base_type, List<StringName> *p_list) {
+	ERR_FAIL_NULL(p_list);
+
+	// TODO: It may make sense to stop at Control/Window, because their parent classes cannot be used in
+	// a meaningful way.
+	StringName class_name = p_base_type;
+	while (class_name != StringName()) {
+		p_list->push_back(class_name);
+		class_name = ClassDB::get_parent_class_nocheck(class_name);
+	}
+}
+
+// Global theme contexts.
+
+ThemeContext *ThemeDB::create_theme_context(Node *p_node, List<Ref<Theme>> &p_themes) {
+	ERR_FAIL_COND_V(!p_node->is_inside_tree(), nullptr);
+	ERR_FAIL_COND_V(theme_contexts.has(p_node), nullptr);
+	ERR_FAIL_COND_V(p_themes.is_empty(), nullptr);
+
+	ThemeContext *context = memnew(ThemeContext);
+	context->node = p_node;
+	context->parent = get_nearest_theme_context(p_node);
+	context->set_themes(p_themes);
+
+	theme_contexts[p_node] = context;
+	_propagate_theme_context(p_node, context);
+
+	p_node->connect("tree_exited", callable_mp(this, &ThemeDB::destroy_theme_context).bind(p_node));
+
+	return context;
+}
+
+void ThemeDB::destroy_theme_context(Node *p_node) {
+	ERR_FAIL_COND(!theme_contexts.has(p_node));
+
+	p_node->disconnect("tree_exited", callable_mp(this, &ThemeDB::destroy_theme_context));
+
+	ThemeContext *context = theme_contexts[p_node];
+
+	theme_contexts.erase(p_node);
+	_propagate_theme_context(p_node, context->parent);
+
+	memdelete(context);
+}
+
+void ThemeDB::_propagate_theme_context(Node *p_from_node, ThemeContext *p_context) {
+	Control *from_control = Object::cast_to<Control>(p_from_node);
+	Window *from_window = from_control ? nullptr : Object::cast_to<Window>(p_from_node);
+
+	if (from_control) {
+		from_control->set_theme_context(p_context);
+	} else if (from_window) {
+		from_window->set_theme_context(p_context);
+	}
+
+	for (int i = 0; i < p_from_node->get_child_count(); i++) {
+		Node *child_node = p_from_node->get_child(i);
+
+		// If the child is the root of another global context, stop the propagation
+		// in this branch.
+		if (theme_contexts.has(child_node)) {
+			theme_contexts[child_node]->parent = p_context;
+			continue;
+		}
+
+		_propagate_theme_context(child_node, p_context);
+	}
+}
+
+void ThemeDB::_init_default_theme_context() {
+	default_theme_context = memnew(ThemeContext);
+
+	List<Ref<Theme>> themes;
+	themes.push_back(project_theme);
+	themes.push_back(default_theme);
+	default_theme_context->set_themes(themes);
+}
+
+void ThemeDB::_finalize_theme_contexts() {
+	if (default_theme_context) {
+		memdelete(default_theme_context);
+		default_theme_context = nullptr;
+	}
+	while (theme_contexts.size()) {
+		HashMap<Node *, ThemeContext *>::Iterator E = theme_contexts.begin();
+		memdelete(E->value);
+		theme_contexts.remove(E);
+	}
+}
+
+ThemeContext *ThemeDB::get_default_theme_context() const {
+	return default_theme_context;
+}
+
+ThemeContext *ThemeDB::get_nearest_theme_context(Node *p_for_node) const {
+	ERR_FAIL_COND_V(!p_for_node->is_inside_tree(), nullptr);
+
+	Node *parent_node = p_for_node->get_parent();
+	while (parent_node) {
+		if (theme_contexts.has(parent_node)) {
+			return theme_contexts[parent_node];
+		}
+
+		parent_node = parent_node->get_parent();
+	}
+
+	return nullptr;
+}
+
 // Object methods.
+
 void ThemeDB::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("get_default_theme"), &ThemeDB::get_default_theme);
 	ClassDB::bind_method(D_METHOD("get_project_theme"), &ThemeDB::get_project_theme);
@@ -214,7 +335,8 @@ void ThemeDB::_bind_methods() {
 	ADD_SIGNAL(MethodInfo("fallback_changed"));
 }
 
-// Memory management, reference, and initialization
+// Memory management, reference, and initialization.
+
 ThemeDB *ThemeDB::singleton = nullptr;
 
 ThemeDB *ThemeDB::get_singleton() {
@@ -223,13 +345,15 @@ ThemeDB *ThemeDB::get_singleton() {
 
 ThemeDB::ThemeDB() {
 	singleton = this;
-
-	// Universal default values, final fallback for every theme.
-	fallback_base_scale = 1.0;
-	fallback_font_size = 16;
 }
 
 ThemeDB::~ThemeDB() {
+	// For technical reasons unit tests recreate and destroy the default
+	// theme over and over again. Make sure that finalize_theme() also
+	// frees any objects that can be recreated by initialize_theme*().
+
+	_finalize_theme_contexts();
+
 	default_theme.unref();
 	project_theme.unref();
 
@@ -239,3 +363,43 @@ ThemeDB::~ThemeDB() {
 
 	singleton = nullptr;
 }
+
+void ThemeContext::_emit_changed() {
+	emit_signal(SNAME("changed"));
+}
+
+void ThemeContext::set_themes(List<Ref<Theme>> &p_themes) {
+	for (const Ref<Theme> &theme : themes) {
+		theme->disconnect_changed(callable_mp(this, &ThemeContext::_emit_changed));
+	}
+
+	themes.clear();
+
+	for (const Ref<Theme> &theme : p_themes) {
+		if (theme.is_null()) {
+			continue;
+		}
+
+		themes.push_back(theme);
+		theme->connect_changed(callable_mp(this, &ThemeContext::_emit_changed));
+	}
+
+	_emit_changed();
+}
+
+List<Ref<Theme>> ThemeContext::get_themes() const {
+	return themes;
+}
+
+Ref<Theme> ThemeContext::get_fallback_theme() const {
+	// We expect all contexts to be valid and non-empty, but just in case...
+	if (themes.size() == 0) {
+		return ThemeDB::get_singleton()->get_default_theme();
+	}
+
+	return themes.back()->get();
+}
+
+void ThemeContext::_bind_methods() {
+	ADD_SIGNAL(MethodInfo("changed"));
+}

scene/theme/theme_db.h

@@ -35,26 +35,39 @@
 #include "core/object/ref_counted.h"
 
 class Font;
+class Node;
 class StyleBox;
 class Texture2D;
 class Theme;
+class ThemeContext;
 
 class ThemeDB : public Object {
 	GDCLASS(ThemeDB, Object);
 
 	static ThemeDB *singleton;
 
-	// Universal Theme resources used when no other theme has the item.
+	// Global Theme resources used by the default theme context.
+
 	Ref<Theme> default_theme;
 	Ref<Theme> project_theme;
 
 	// Universal default values, final fallback for every theme.
-	float fallback_base_scale;
+
+	float fallback_base_scale = 1.0;
 	Ref<Font> fallback_font;
-	int fallback_font_size;
+	int fallback_font_size = 16;
 	Ref<Texture2D> fallback_icon;
 	Ref<StyleBox> fallback_stylebox;
 
+	// Global theme contexts used to scope global Theme resources.
+
+	ThemeContext *default_theme_context = nullptr;
+	HashMap<Node *, ThemeContext *> theme_contexts;
+
+	void _propagate_theme_context(Node *p_from_node, ThemeContext *p_context);
+	void _init_default_theme_context();
+	void _finalize_theme_contexts();
+
 protected:
 	static void _bind_methods();
 
@@ -63,7 +76,7 @@ public:
 	void initialize_theme_noproject();
 	void finalize_theme();
 
-	// Universal Theme resources
+	// Global Theme resources.
 
 	void set_default_theme(const Ref<Theme> &p_default);
 	Ref<Theme> get_default_theme();
@@ -71,7 +84,7 @@ public:
 	void set_project_theme(const Ref<Theme> &p_project_default);
 	Ref<Theme> get_project_theme();
 
-	// Universal default values.
+	// Universal fallback values.
 
 	void set_fallback_base_scale(float p_base_scale);
 	float get_fallback_base_scale();
@@ -88,9 +101,45 @@ public:
 	void set_fallback_stylebox(const Ref<StyleBox> &p_stylebox);
 	Ref<StyleBox> get_fallback_stylebox();
 
+	void get_native_type_dependencies(const StringName &p_base_type, List<StringName> *p_list);
+
+	// Global theme contexts.
+
+	ThemeContext *create_theme_context(Node *p_node, List<Ref<Theme>> &p_themes);
+	void destroy_theme_context(Node *p_node);
+
+	ThemeContext *get_default_theme_context() const;
+	ThemeContext *get_nearest_theme_context(Node *p_for_node) const;
+
+	// Memory management, reference, and initialization.
+
 	static ThemeDB *get_singleton();
 	ThemeDB();
 	~ThemeDB();
 };
 
+class ThemeContext : public Object {
+	GDCLASS(ThemeContext, Object);
+
+	friend class ThemeDB;
+
+	Node *node = nullptr;
+	ThemeContext *parent = nullptr;
+
+	// Themes are stacked in the order of relevance, for easy iteration.
+	// This means that the first theme is the one you should check first,
+	// and the last theme is the fallback theme where every lookup ends.
+	List<Ref<Theme>> themes;
+
+	void _emit_changed();
+
+protected:
+	static void _bind_methods();
+
+public:
+	void set_themes(List<Ref<Theme>> &p_themes);
+	List<Ref<Theme>> get_themes() const;
+	Ref<Theme> get_fallback_theme() const;
+};
+
 #endif // THEME_DB_H

scene/theme/theme_owner.cpp

@@ -66,6 +66,52 @@ bool ThemeOwner::has_owner_node() const {
 	return bool(owner_control || owner_window);
 }
 
+void ThemeOwner::set_owner_context(ThemeContext *p_context, bool p_propagate) {
+	ThemeContext *default_context = ThemeDB::get_singleton()->get_default_theme_context();
+
+	if (owner_context && owner_context->is_connected("changed", callable_mp(this, &ThemeOwner::_owner_context_changed))) {
+		owner_context->disconnect("changed", callable_mp(this, &ThemeOwner::_owner_context_changed));
+	} else if (default_context->is_connected("changed", callable_mp(this, &ThemeOwner::_owner_context_changed))) {
+		default_context->disconnect("changed", callable_mp(this, &ThemeOwner::_owner_context_changed));
+	}
+
+	owner_context = p_context;
+
+	if (owner_context) {
+		owner_context->connect("changed", callable_mp(this, &ThemeOwner::_owner_context_changed));
+	} else {
+		default_context->connect("changed", callable_mp(this, &ThemeOwner::_owner_context_changed));
+	}
+
+	if (p_propagate) {
+		_owner_context_changed();
+	}
+}
+
+void ThemeOwner::_owner_context_changed() {
+	if (!holder->is_inside_tree()) {
+		// We ignore theme changes outside of tree, because NOTIFICATION_ENTER_TREE covers everything.
+		return;
+	}
+
+	Control *c = Object::cast_to<Control>(holder);
+	Window *w = c == nullptr ? Object::cast_to<Window>(holder) : nullptr;
+
+	if (c) {
+		c->notification(Control::NOTIFICATION_THEME_CHANGED);
+	} else if (w) {
+		w->notification(Window::NOTIFICATION_THEME_CHANGED);
+	}
+}
+
+ThemeContext *ThemeOwner::_get_active_owner_context() const {
+	if (owner_context) {
+		return owner_context;
+	}
+
+	return ThemeDB::get_singleton()->get_default_theme_context();
+}
+
 // Theme propagation.
 
 void ThemeOwner::assign_theme_on_parented(Node *p_for_node) {
@@ -158,9 +204,7 @@ void ThemeOwner::get_theme_type_dependencies(const Node *p_for_node, const Strin
 	const Window *for_w = Object::cast_to<Window>(p_for_node);
 	ERR_FAIL_COND_MSG(!for_c && !for_w, "Only Control and Window nodes and derivatives can be polled for theming.");
 
-	Ref<Theme> default_theme = ThemeDB::get_singleton()->get_default_theme();
-	Ref<Theme> project_theme = ThemeDB::get_singleton()->get_project_theme();
-
+	StringName type_name = p_for_node->get_class_name();
 	StringName type_variation;
 	if (for_c) {
 		type_variation = for_c->get_theme_type_variation();
@@ -168,31 +212,23 @@ void ThemeOwner::get_theme_type_dependencies(const Node *p_for_node, const Strin
 		type_variation = for_w->get_theme_type_variation();
 	}
 
-	if (p_theme_type == StringName() || p_theme_type == p_for_node->get_class_name() || p_theme_type == type_variation) {
-		if (project_theme.is_valid() && project_theme->get_type_variation_base(type_variation) != StringName()) {
-			project_theme->get_type_dependencies(p_for_node->get_class_name(), type_variation, r_list);
-		} else {
-			default_theme->get_type_dependencies(p_for_node->get_class_name(), type_variation, r_list);
+	// If we are looking for dependencies of the current class (or a variantion of it), check themes from the context.
+	if (p_theme_type == StringName() || p_theme_type == type_name || p_theme_type == type_variation) {
+		ThemeContext *global_context = _get_active_owner_context();
+		for (const Ref<Theme> &theme : global_context->get_themes()) {
+			if (theme.is_valid() && theme->get_type_variation_base(type_variation) != StringName()) {
+				theme->get_type_dependencies(type_name, type_variation, r_list);
+				return;
+			}
 		}
-	} else {
-		default_theme->get_type_dependencies(p_theme_type, StringName(), r_list);
-	}
-}
 
-Node *ThemeOwner::_get_next_owner_node(Node *p_from_node) const {
-	Node *parent = p_from_node->get_parent();
-
-	Control *parent_c = Object::cast_to<Control>(parent);
-	if (parent_c) {
-		return parent_c->get_theme_owner_node();
-	} else {
-		Window *parent_w = Object::cast_to<Window>(parent);
-		if (parent_w) {
-			return parent_w->get_theme_owner_node();
-		}
+		// If nothing was found, get the native dependencies for the current class.
+		ThemeDB::get_singleton()->get_native_type_dependencies(type_name, r_list);
+		return;
 	}
 
-	return nullptr;
+	// Otherwise, get the native dependencies for the provided theme type.
+	ThemeDB::get_singleton()->get_native_type_dependencies(p_theme_type, r_list);
 }
 
 Variant ThemeOwner::get_theme_item_in_types(Theme::DataType p_data_type, const StringName &p_name, List<StringName> p_theme_types) {
@@ -215,24 +251,20 @@ Variant ThemeOwner::get_theme_item_in_types(Theme::DataType p_data_type, const S
 		owner_node = _get_next_owner_node(owner_node);
 	}
 
-	// Secondly, check the project-defined Theme resource.
-	if (ThemeDB::get_singleton()->get_project_theme().is_valid()) {
-		for (const StringName &E : p_theme_types) {
-			if (ThemeDB::get_singleton()->get_project_theme()->has_theme_item(p_data_type, p_name, E)) {
-				return ThemeDB::get_singleton()->get_project_theme()->get_theme_item(p_data_type, p_name, E);
+	// Second, check global themes from the appropriate context.
+	ThemeContext *global_context = _get_active_owner_context();
+	for (const Ref<Theme> &theme : global_context->get_themes()) {
+		if (theme.is_valid()) {
+			for (const StringName &E : p_theme_types) {
+				if (theme->has_theme_item(p_data_type, p_name, E)) {
+					return theme->get_theme_item(p_data_type, p_name, E);
+				}
 			}
 		}
 	}
 
-	// Lastly, fall back on the items defined in the default Theme, if they exist.
-	for (const StringName &E : p_theme_types) {
-		if (ThemeDB::get_singleton()->get_default_theme()->has_theme_item(p_data_type, p_name, E)) {
-			return ThemeDB::get_singleton()->get_default_theme()->get_theme_item(p_data_type, p_name, E);
-		}
-	}
-
-	// If they don't exist, use any type to return the default/empty value.
-	return ThemeDB::get_singleton()->get_default_theme()->get_theme_item(p_data_type, p_name, p_theme_types[0]);
+	// Finally, if no match exists, use any type to return the default/empty value.
+	return global_context->get_fallback_theme()->get_theme_item(p_data_type, p_name, StringName());
 }
 
 bool ThemeOwner::has_theme_item_in_types(Theme::DataType p_data_type, const StringName &p_name, List<StringName> p_theme_types) {
@@ -255,22 +287,19 @@ bool ThemeOwner::has_theme_item_in_types(Theme::DataType p_data_type, const Stri
 		owner_node = _get_next_owner_node(owner_node);
 	}
 
-	// Secondly, check the project-defined Theme resource.
-	if (ThemeDB::get_singleton()->get_project_theme().is_valid()) {
-		for (const StringName &E : p_theme_types) {
-			if (ThemeDB::get_singleton()->get_project_theme()->has_theme_item(p_data_type, p_name, E)) {
-				return true;
+	// Second, check global themes from the appropriate context.
+	ThemeContext *global_context = _get_active_owner_context();
+	for (const Ref<Theme> &theme : global_context->get_themes()) {
+		if (theme.is_valid()) {
+			for (const StringName &E : p_theme_types) {
+				if (theme->has_theme_item(p_data_type, p_name, E)) {
+					return true;
+				}
 			}
 		}
 	}
 
-	// Lastly, fall back on the items defined in the default Theme, if they exist.
-	for (const StringName &E : p_theme_types) {
-		if (ThemeDB::get_singleton()->get_default_theme()->has_theme_item(p_data_type, p_name, E)) {
-			return true;
-		}
-	}
-
+	// Finally, if no match exists, return false.
 	return false;
 }
 
@@ -290,17 +319,17 @@ float ThemeOwner::get_theme_default_base_scale() {
 		owner_node = _get_next_owner_node(owner_node);
 	}
 
-	// Secondly, check the project-defined Theme resource.
-	if (ThemeDB::get_singleton()->get_project_theme().is_valid()) {
-		if (ThemeDB::get_singleton()->get_project_theme()->has_default_base_scale()) {
-			return ThemeDB::get_singleton()->get_project_theme()->get_default_base_scale();
+	// Second, check global themes from the appropriate context.
+	ThemeContext *global_context = _get_active_owner_context();
+	for (const Ref<Theme> &theme : global_context->get_themes()) {
+		if (theme.is_valid()) {
+			if (theme->has_default_base_scale()) {
+				return theme->get_default_base_scale();
+			}
 		}
 	}
 
-	// Lastly, fall back on the default Theme.
-	if (ThemeDB::get_singleton()->get_default_theme()->has_default_base_scale()) {
-		return ThemeDB::get_singleton()->get_default_theme()->get_default_base_scale();
-	}
+	// Finally, if no match exists, return the universal default.
 	return ThemeDB::get_singleton()->get_fallback_base_scale();
 }
 
@@ -320,17 +349,17 @@ Ref<Font> ThemeOwner::get_theme_default_font() {
 		owner_node = _get_next_owner_node(owner_node);
 	}
 
-	// Secondly, check the project-defined Theme resource.
-	if (ThemeDB::get_singleton()->get_project_theme().is_valid()) {
-		if (ThemeDB::get_singleton()->get_project_theme()->has_default_font()) {
-			return ThemeDB::get_singleton()->get_project_theme()->get_default_font();
+	// Second, check global themes from the appropriate context.
+	ThemeContext *global_context = _get_active_owner_context();
+	for (const Ref<Theme> &theme : global_context->get_themes()) {
+		if (theme.is_valid()) {
+			if (theme->has_default_font()) {
+				return theme->get_default_font();
+			}
 		}
 	}
 
-	// Lastly, fall back on the default Theme.
-	if (ThemeDB::get_singleton()->get_default_theme()->has_default_font()) {
-		return ThemeDB::get_singleton()->get_default_theme()->get_default_font();
-	}
+	// Finally, if no match exists, return the universal default.
 	return ThemeDB::get_singleton()->get_fallback_font();
 }
 
@@ -350,17 +379,17 @@ int ThemeOwner::get_theme_default_font_size() {
 		owner_node = _get_next_owner_node(owner_node);
 	}
 
-	// Secondly, check the project-defined Theme resource.
-	if (ThemeDB::get_singleton()->get_project_theme().is_valid()) {
-		if (ThemeDB::get_singleton()->get_project_theme()->has_default_font_size()) {
-			return ThemeDB::get_singleton()->get_project_theme()->get_default_font_size();
+	// Second, check global themes from the appropriate context.
+	ThemeContext *global_context = _get_active_owner_context();
+	for (const Ref<Theme> &theme : global_context->get_themes()) {
+		if (theme.is_valid()) {
+			if (theme->has_default_font_size()) {
+				return theme->get_default_font_size();
+			}
 		}
 	}
 
-	// Lastly, fall back on the default Theme.
-	if (ThemeDB::get_singleton()->get_default_theme()->has_default_font_size()) {
-		return ThemeDB::get_singleton()->get_default_theme()->get_default_font_size();
-	}
+	// Finally, if no match exists, return the universal default.
 	return ThemeDB::get_singleton()->get_fallback_font_size();
 }
 
@@ -377,3 +406,19 @@ Ref<Theme> ThemeOwner::_get_owner_node_theme(Node *p_owner_node) const {
 
 	return Ref<Theme>();
 }
+
+Node *ThemeOwner::_get_next_owner_node(Node *p_from_node) const {
+	Node *parent = p_from_node->get_parent();
+
+	Control *parent_c = Object::cast_to<Control>(parent);
+	if (parent_c) {
+		return parent_c->get_theme_owner_node();
+	} else {
+		Window *parent_w = Object::cast_to<Window>(parent);
+		if (parent_w) {
+			return parent_w->get_theme_owner_node();
+		}
+	}
+
+	return nullptr;
+}

scene/theme/theme_owner.h

@@ -36,11 +36,18 @@
 
 class Control;
 class Node;
+class ThemeContext;
 class Window;
 
 class ThemeOwner : public Object {
+	Node *holder = nullptr;
+
 	Control *owner_control = nullptr;
 	Window *owner_window = nullptr;
+	ThemeContext *owner_context = nullptr;
+
+	void _owner_context_changed();
+	ThemeContext *_get_active_owner_context() const;
 
 	Node *_get_next_owner_node(Node *p_from_node) const;
 	Ref<Theme> _get_owner_node_theme(Node *p_owner_node) const;
@@ -52,6 +59,8 @@ public:
 	Node *get_owner_node() const;
 	bool has_owner_node() const;
 
+	void set_owner_context(ThemeContext *p_context, bool p_propagate = true);
+
 	// Theme propagation.
 
 	void assign_theme_on_parented(Node *p_for_node);
@@ -69,7 +78,7 @@ public:
 	Ref<Font> get_theme_default_font();
 	int get_theme_default_font_size();
 
-	ThemeOwner() {}
+	ThemeOwner(Node *p_holder) { holder = p_holder; }
 	~ThemeOwner() {}
 };
 

tests/test_main.cpp

@@ -238,7 +238,9 @@ struct GodotTestCaseListener : public doctest::IReporter {
 			RenderingServerDefault::get_singleton()->set_render_loop_enabled(false);
 
 			// ThemeDB requires RenderingServer to initialize the default theme.
-			// So we have to do this for each test case.
+			// So we have to do this for each test case. Also make sure there is
+			// no residual theme from something else.
+			ThemeDB::get_singleton()->finalize_theme();
 			ThemeDB::get_singleton()->initialize_theme_noproject();
 
 			physics_server_3d = PhysicsServer3DManager::get_singleton()->new_default_server();