Avoid color flash on window creation and resizing

doc/classes/RenderingServer.xml

@@ -1262,6 +1262,12 @@
 				Tries to free an object in the RenderingServer.
 			</description>
 		</method>
+		<method name="get_default_clear_color">
+			<return type="Color" />
+			<description>
+				Returns the default clear color which is used when a specific clear color has not been selected.
+			</description>
+		</method>
 		<method name="get_frame_setup_time_cpu" qualifiers="const">
 			<return type="float" />
 			<description>

editor/editor_node.cpp

@@ -688,6 +688,7 @@ void EditorNode::_notification(int p_what) {
 
 			if (theme_changed) {
 				theme = create_custom_theme(theme_base->get_theme());
+				DisplayServer::set_early_window_clear_color_override(true, theme->get_color(SNAME("background"), SNAME("Editor")));
 
 				theme_base->set_theme(theme);
 				gui_base->set_theme(theme);
@@ -6235,6 +6236,7 @@ EditorNode::EditorNode() {
 	// Exporters might need the theme.
 	EditorColorMap::create();
 	theme = create_custom_theme();
+	DisplayServer::set_early_window_clear_color_override(true, theme->get_color(SNAME("background"), SNAME("Editor")));
 
 	register_exporters();
 

editor/editor_themes.cpp

@@ -753,6 +753,7 @@ Ref<Theme> create_editor_theme(const Ref<Theme> p_theme) {
 	// Editor background
 	Color background_color_opaque = background_color;
 	background_color_opaque.a = 1.0;
+	theme->set_color("background", "Editor", background_color_opaque);
 	theme->set_stylebox("Background", "EditorStyles", make_flat_stylebox(background_color_opaque, default_margin_size, default_margin_size, default_margin_size, default_margin_size));
 
 	// Focus

editor/project_manager.cpp

@@ -2653,8 +2653,9 @@ ProjectManager::ProjectManager() {
 		AcceptDialog::set_swap_cancel_ok(swap_cancel_ok == 2);
 	}
 
-	set_anchors_and_offsets_preset(Control::PRESET_FULL_RECT);
-	set_theme(create_custom_theme());
+	Ref<Theme> theme = create_custom_theme();
+	set_theme(theme);
+	DisplayServer::set_early_window_clear_color_override(true, theme->get_color(SNAME("background"), SNAME("Editor")));
 
 	set_anchors_and_offsets_preset(Control::PRESET_FULL_RECT);
 

main/main.cpp

@@ -1920,6 +1920,9 @@ Error Main::setup2(Thread::ID p_main_tid_override) {
 			window_position = &position;
 		}
 
+		Color boot_bg_color = GLOBAL_DEF_BASIC("application/boot_splash/bg_color", boot_splash_bg_color);
+		DisplayServer::set_early_window_clear_color_override(true, boot_bg_color);
+
 		// rendering_driver now held in static global String in main and initialized in setup()
 		Error err;
 		display_server = DisplayServer::create(display_driver_idx, rendering_driver, window_mode, window_vsync_mode, window_flags, window_position, window_size, init_screen, err);
@@ -2085,7 +2088,7 @@ Error Main::setup2(Thread::ID p_main_tid_override) {
 			boot_logo->set_pixel(0, 0, Color(0, 0, 0, 0));
 		}
 
-		Color boot_bg_color = GLOBAL_DEF_BASIC("application/boot_splash/bg_color", boot_splash_bg_color);
+		Color boot_bg_color = GLOBAL_GET("application/boot_splash/bg_color");
 
 #if defined(TOOLS_ENABLED) && !defined(NO_EDITOR_SPLASH)
 		boot_bg_color =
@@ -2120,6 +2123,8 @@ Error Main::setup2(Thread::ID p_main_tid_override) {
 #endif
 	}
 
+	DisplayServer::set_early_window_clear_color_override(false);
+
 	MAIN_PRINT("Main: DCC");
 	RenderingServer::get_singleton()->set_default_clear_color(
 			GLOBAL_GET("rendering/environment/defaults/default_clear_color"));

platform/windows/display_server_windows.cpp

@@ -2543,6 +2543,25 @@ LRESULT DisplayServerWindows::WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARA
 				return 0;
 			}
 		} break;
+		case WM_ERASEBKGND: {
+			Color early_color;
+			if (!_get_window_early_clear_override(early_color)) {
+				break;
+			}
+			bool must_recreate_brush = !window_bkg_brush || window_bkg_brush_color != early_color.to_argb32();
+			if (must_recreate_brush) {
+				if (window_bkg_brush) {
+					DeleteObject(window_bkg_brush);
+				}
+				window_bkg_brush = CreateSolidBrush(RGB(early_color.get_r8(), early_color.get_g8(), early_color.get_b8()));
+			}
+			HDC hdc = (HDC)wParam;
+			RECT rect = {};
+			if (GetUpdateRect(hWnd, &rect, true)) {
+				FillRect(hdc, &rect, window_bkg_brush);
+			}
+			return 1;
+		} break;
 		case WM_PAINT: {
 			Main::force_redraw();
 		} break;
@@ -3982,7 +4001,7 @@ DisplayServerWindows::DisplayServerWindows(const String &p_rendering_driver, Win
 
 	memset(&wc, 0, sizeof(WNDCLASSEXW));
 	wc.cbSize = sizeof(WNDCLASSEXW);
-	wc.style = CS_HREDRAW | CS_VREDRAW | CS_OWNDC | CS_DBLCLKS;
+	wc.style = CS_OWNDC | CS_DBLCLKS;
 	wc.lpfnWndProc = (WNDPROC)::WndProc;
 	wc.cbClsExtra = 0;
 	wc.cbWndExtra = 0;

platform/windows/display_server_windows.h

@@ -452,6 +452,8 @@ class DisplayServerWindows : public DisplayServer {
 	bool in_dispatch_input_event = false;
 
 	WNDCLASSEXW wc;
+	HBRUSH window_bkg_brush = nullptr;
+	uint32_t window_bkg_brush_color = 0;
 
 	HCURSOR cursors[CURSOR_MAX] = { nullptr };
 	CursorShape cursor_shape = CursorShape::CURSOR_ARROW;

servers/display_server.cpp

@@ -38,6 +38,9 @@ DisplayServer *DisplayServer::singleton = nullptr;
 
 bool DisplayServer::hidpi_allowed = false;
 
+bool DisplayServer::window_early_clear_override_enabled = false;
+Color DisplayServer::window_early_clear_override_color = Color(0, 0, 0, 0);
+
 DisplayServer::DisplayServerCreate DisplayServer::server_create_functions[DisplayServer::MAX_SERVERS] = {
 	{ "headless", &DisplayServerHeadless::create_func, &DisplayServerHeadless::get_rendering_drivers_func }
 };
@@ -315,6 +318,23 @@ void DisplayServer::tts_post_utterance_event(TTSUtteranceEvent p_event, int p_id
 	}
 }
 
+bool DisplayServer::_get_window_early_clear_override(Color &r_color) {
+	if (window_early_clear_override_enabled) {
+		r_color = window_early_clear_override_color;
+		return true;
+	} else if (RenderingServer::get_singleton()) {
+		r_color = RenderingServer::get_singleton()->get_default_clear_color();
+		return true;
+	} else {
+		return false;
+	}
+}
+
+void DisplayServer::set_early_window_clear_color_override(bool p_enabled, Color p_color) {
+	window_early_clear_override_enabled = p_enabled;
+	window_early_clear_override_color = p_color;
+}
+
 void DisplayServer::mouse_set_mode(MouseMode p_mode) {
 	WARN_PRINT("Mouse is not supported by this display server.");
 }

servers/display_server.h

@@ -217,6 +217,16 @@ class DisplayServer : public Object {
 	virtual bool is_dark_mode() const { return false; };
 	virtual Color get_accent_color() const { return Color(0, 0, 0, 0); };
 
+private:
+	static bool window_early_clear_override_enabled;
+	static Color window_early_clear_override_color;
+
+protected:
+	static bool _get_window_early_clear_override(Color &r_color);
+
+public:
+	static void set_early_window_clear_color_override(bool p_enabled, Color p_color = Color(0, 0, 0, 0));
+
 	enum MouseMode {
 		MOUSE_MODE_VISIBLE,
 		MOUSE_MODE_HIDDEN,

servers/rendering/rendering_server_default.cpp

@@ -291,6 +291,10 @@ void RenderingServerDefault::set_boot_image(const Ref<Image> &p_image, const Col
 	RSG::rasterizer->set_boot_image(p_image, p_color, p_scale, p_use_filter);
 }
 
+Color RenderingServerDefault::get_default_clear_color() {
+	return RSG::texture_storage->get_default_clear_color();
+}
+
 void RenderingServerDefault::set_default_clear_color(const Color &p_color) {
 	RSG::viewport->set_default_clear_color(p_color);
 }

servers/rendering/rendering_server_default.h

@@ -986,6 +986,7 @@ class RenderingServerDefault : public RenderingServer {
 	virtual double get_frame_setup_time_cpu() const override;
 
 	virtual void set_boot_image(const Ref<Image> &p_image, const Color &p_color, bool p_scale, bool p_use_filter = true) override;
+	virtual Color get_default_clear_color() override;
 	virtual void set_default_clear_color(const Color &p_color) override;
 
 	virtual bool has_feature(Features p_feature) const override;

servers/rendering_server.cpp

@@ -2763,6 +2763,7 @@ void RenderingServer::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("get_white_texture"), &RenderingServer::get_white_texture);
 
 	ClassDB::bind_method(D_METHOD("set_boot_image", "image", "color", "scale", "use_filter"), &RenderingServer::set_boot_image, DEFVAL(true));
+	ClassDB::bind_method(D_METHOD("get_default_clear_color"), &RenderingServer::get_default_clear_color);
 	ClassDB::bind_method(D_METHOD("set_default_clear_color", "color"), &RenderingServer::set_default_clear_color);
 
 	ClassDB::bind_method(D_METHOD("has_feature", "feature"), &RenderingServer::has_feature);

servers/rendering_server.h

@@ -1560,6 +1560,7 @@ class RenderingServer : public Object {
 	virtual void mesh_add_surface_from_planes(RID p_mesh, const Vector<Plane> &p_planes);
 
 	virtual void set_boot_image(const Ref<Image> &p_image, const Color &p_color, bool p_scale, bool p_use_filter = true) = 0;
+	virtual Color get_default_clear_color() = 0;
 	virtual void set_default_clear_color(const Color &p_color) = 0;
 
 	enum Features {