Drop mouse focus and over when gui input is globally disabled

Since some porjects may be relying on the former behavior, this is opt-in via a new project setting, disabled by default, but enabled for new projects, since it's the new standard behavior (and the only one in 4.0).

doc/classes/ProjectSettings.xml

@@ -538,6 +538,12 @@
 		<member name="gui/common/default_scroll_deadzone" type="int" setter="" getter="" default="0">
 			Default value for [member ScrollContainer.scroll_deadzone], which will be used for all [ScrollContainer]s unless overridden.
 		</member>
+		<member name="gui/common/drop_mouse_on_gui_input_disabled" type="bool" setter="" getter="" default="false">
+			If enabled, the moment [member Viewport.gui_disable_input] is set to [code]false[/code] to disable GUI input in a viewport, current mouse over and mouse focus will be dropped.
+			That behavior helps to keep a robust GUI state, with no surprises when input is resumed regardless what has happened in the meantime.
+			If disabled, the legacy behavior is used, which consists in just not doing anything besides the GUI input disable itself.
+			[b]Note:[/b] This is set to [code]true[/code] by default for new projects and is the recommended setting.
+		</member>
 		<member name="gui/common/swap_ok_cancel" type="bool" setter="" getter="">
 			If [code]true[/code], swaps OK and Cancel buttons in dialogs on Windows and UWP to follow interface conventions.
 		</member>

editor/project_manager.cpp

@@ -470,6 +470,7 @@ private:
 					initial_settings["application/config/icon"] = "res://icon.png";
 					initial_settings["rendering/environment/default_environment"] = "res://default_env.tres";
 					initial_settings["physics/common/enable_pause_aware_picking"] = true;
+					initial_settings["gui/common/drop_mouse_on_gui_input_disabled"] = true;
 
 					if (ProjectSettings::get_singleton()->save_custom(dir.plus_file("project.godot"), initial_settings, Vector<String>(), false) != OK) {
 						set_message(TTR("Couldn't create project.godot in project path."), MESSAGE_ERROR);

main/main.cpp

@@ -1219,6 +1219,7 @@ Error Main::setup(const char *execpath, int argc, char *argv[], bool p_second_ph
 	Engine::get_singleton()->set_target_fps(GLOBAL_DEF("debug/settings/fps/force_fps", 0));
 	ProjectSettings::get_singleton()->set_custom_property_info("debug/settings/fps/force_fps", PropertyInfo(Variant::INT, "debug/settings/fps/force_fps", PROPERTY_HINT_RANGE, "0,1000,1"));
 	GLOBAL_DEF("physics/common/enable_pause_aware_picking", false);
+	GLOBAL_DEF("gui/common/drop_mouse_on_gui_input_disabled", false);
 
 	GLOBAL_DEF("debug/settings/stdout/print_fps", false);
 	GLOBAL_DEF("debug/settings/stdout/verbose_stdout", false);

scene/main/viewport.cpp

@@ -2058,9 +2058,7 @@ void Viewport::_gui_input_event(Ref<InputEvent> p_event) {
 			}
 
 			if (gui.mouse_focus_mask == 0 && over != gui.mouse_over) {
-				if (gui.mouse_over) {
+				_drop_mouse_over();
-					_gui_call_notification(gui.mouse_over, Control::NOTIFICATION_MOUSE_EXIT);
-				}
 
 				_gui_cancel_tooltip();
 
@@ -2177,9 +2175,7 @@ void Viewport::_gui_input_event(Ref<InputEvent> p_event) {
 		}
 
 		if (over != gui.mouse_over) {
-			if (gui.mouse_over) {
+			_drop_mouse_over();
-				_gui_call_notification(gui.mouse_over, Control::NOTIFICATION_MOUSE_EXIT);
-			}
 
 			_gui_cancel_tooltip();
 
@@ -2715,6 +2711,13 @@ void Viewport::_drop_mouse_focus() {
 	}
 }
 
+void Viewport::_drop_mouse_over() {
+	if (gui.mouse_over) {
+		_gui_call_notification(gui.mouse_over, Control::NOTIFICATION_MOUSE_EXIT);
+		gui.mouse_over = nullptr;
+	}
+}
+
 void Viewport::_drop_physics_mouseover(bool p_paused_only) {
 	physics_has_last_mousepos = false;
 
@@ -2958,6 +2961,14 @@ bool Viewport::gui_has_modal_stack() const {
 }
 
 void Viewport::set_disable_input(bool p_disable) {
+	if (p_disable == disable_input) {
+		return;
+	}
+	if (p_disable && GLOBAL_GET("gui/common/drop_mouse_on_gui_input_disabled")) {
+		_drop_mouse_focus();
+		_drop_mouse_over();
+		_gui_cancel_tooltip();
+	}
 	disable_input = p_disable;
 }
 

scene/main/viewport.h

@@ -413,6 +413,7 @@ private:
 	void _canvas_layer_remove(CanvasLayer *p_canvas_layer);
 
 	void _drop_mouse_focus();
+	void _drop_mouse_over();
 	void _drop_physics_mouseover(bool p_paused_only = false);
 
 	void _update_canvas_items(Node *p_node);