Groundbreaking!! Godot resources can now be flagged to be local to the scene being edited!

This means that each time this scene is instanced, the resource will be unique!
As such, thanks to this, the following features were implemented:
-ButtonGroup is no longer a control, it's now a resource local to the scene
-ViewportTexture can be created from the editor and set to any object, making ViewportSprite and other kind of nodes obsolete!

scene/gui/base_button.cpp

@@ -29,10 +29,23 @@
 #include "base_button.h"
 #include "os/keyboard.h"
 #include "print_string.h"
-#include "button_group.h"
 #include "scene/scene_string_names.h"
 #include "scene/main/viewport.h"
 
+
+void BaseButton::_unpress_group() {
+
+	if (!button_group.is_valid())
+		return;
+
+	for (Set<BaseButton*>::Element *E=button_group->buttons.front();E;E=E->next()) {
+		if (E->get()==this)
+			continue;
+
+		E->get()->set_pressed(false);
+	}
+}
+
 void BaseButton::_gui_input(InputEvent p_event) {
 
 
@@ -69,6 +82,8 @@ void BaseButton::_gui_input(InputEvent p_event) {
 						}
 
 						emit_signal("pressed");
+						_unpress_group();
+
 
 					} else {
 
@@ -79,6 +94,8 @@ void BaseButton::_gui_input(InputEvent p_event) {
 							get_script_instance()->call(SceneStringNames::get_singleton()->_pressed,NULL,0,ce);
 						}
 						emit_signal("pressed");
+						_unpress_group();
+
 
 						toggled(status.pressed);
 						emit_signal("toggled",status.pressed);
@@ -139,6 +156,9 @@ void BaseButton::_gui_input(InputEvent p_event) {
 
 					}
 
+					_unpress_group();
+
+
 				}
 
 				status.press_attempt=false;
@@ -212,6 +232,9 @@ void BaseButton::_gui_input(InputEvent p_event) {
 						}
 						emit_signal("toggled",status.pressed);
 					}
+
+					_unpress_group();
+
 				}
 
 				accept_event();
@@ -266,24 +289,12 @@ void BaseButton::_notification(int p_what) {
 
 	if (p_what==NOTIFICATION_ENTER_TREE) {
 
-		CanvasItem *ci=this;
-		while(ci) {
 
-			ButtonGroup *bg = ci->cast_to<ButtonGroup>();
-			if (bg) {
-
-				group=bg;
-				group->_add_button(this);
-			}
-
-			ci=ci->get_parent_item();
-		}
 	}
 
 	if (p_what==NOTIFICATION_EXIT_TREE) {
 
-		if (group)
-			group->_remove_button(this);
+
 	}
 
 	if (p_what==NOTIFICATION_VISIBILITY_CHANGED && !is_visible()) {
@@ -306,8 +317,9 @@ void BaseButton::pressed() {
 
 void BaseButton::toggled(bool p_pressed) {
 
-	if (get_script_instance())
+	if (get_script_instance()) {
 		get_script_instance()->call("toggled",p_pressed);
+	}
 
 }
 
@@ -336,6 +348,11 @@ void BaseButton::set_pressed(bool p_pressed) {
 		return;
 	_change_notify("pressed");
 	status.pressed=p_pressed;
+
+	if (p_pressed) {
+		_unpress_group();
+
+	}
 	update();
 }
 
@@ -463,6 +480,29 @@ String BaseButton::get_tooltip(const Point2& p_pos) const {
 	return tooltip;
 }
 
+
+void BaseButton::set_button_group(const Ref<ButtonGroup>& p_group) {
+
+	if (button_group.is_valid()) {
+		button_group->buttons.erase(this);
+	}
+
+	button_group=p_group;
+
+	if (button_group.is_valid()) {
+		button_group->buttons.insert(this);
+	}
+
+	update(); //checkbox changes to radio if set a buttongroup
+
+}
+
+Ref<ButtonGroup> BaseButton::get_button_group() const {
+
+	return button_group;
+}
+
+
 void BaseButton::_bind_methods() {
 
 	ClassDB::bind_method(_MD("_gui_input"),&BaseButton::_gui_input);
@@ -479,9 +519,13 @@ void BaseButton::_bind_methods() {
 	ClassDB::bind_method(_MD("get_draw_mode"),&BaseButton::get_draw_mode);
 	ClassDB::bind_method(_MD("set_enabled_focus_mode","mode"),&BaseButton::set_enabled_focus_mode);
 	ClassDB::bind_method(_MD("get_enabled_focus_mode"),&BaseButton::get_enabled_focus_mode);
+
 	ClassDB::bind_method(_MD("set_shortcut","shortcut"),&BaseButton::set_shortcut);
 	ClassDB::bind_method(_MD("get_shortcut"),&BaseButton::get_shortcut);
 
+	ClassDB::bind_method(_MD("set_button_group","button_group"),&BaseButton::set_button_group);
+	ClassDB::bind_method(_MD("get_button_group"),&BaseButton::get_button_group);
+
 	BIND_VMETHOD(MethodInfo("_pressed"));
 	BIND_VMETHOD(MethodInfo("_toggled",PropertyInfo(Variant::BOOL,"pressed")));
 
@@ -495,6 +539,7 @@ void BaseButton::_bind_methods() {
 	ADD_PROPERTYNZ( PropertyInfo( Variant::BOOL, "click_on_press"), _SCS("set_click_on_press"), _SCS("get_click_on_press"));
 	ADD_PROPERTY( PropertyInfo( Variant::INT,"enabled_focus_mode", PROPERTY_HINT_ENUM, "None,Click,All" ), _SCS("set_enabled_focus_mode"), _SCS("get_enabled_focus_mode") );
 	ADD_PROPERTY( PropertyInfo( Variant::OBJECT, "shortcut",PROPERTY_HINT_RESOURCE_TYPE,"ShortCut"), _SCS("set_shortcut"), _SCS("get_shortcut"));
+	ADD_PROPERTY( PropertyInfo( Variant::OBJECT, "group",PROPERTY_HINT_RESOURCE_TYPE,"ButtonGroup"), _SCS("set_button_group"), _SCS("get_button_group"));
 
 
 	BIND_CONSTANT( DRAW_NORMAL );
@@ -516,7 +561,11 @@ BaseButton::BaseButton() {
 	status.pressing_button=0;
 	set_focus_mode( FOCUS_ALL );
 	enabled_focus_mode = FOCUS_ALL;
-	group=NULL;
+
+
+	if (button_group.is_valid()) {
+		button_group->buttons.erase(this);
+	}
 
 
 }
@@ -525,4 +574,30 @@ BaseButton::~BaseButton()
 {
 }
 
+void ButtonGroup::get_buttons(List<BaseButton*> *r_buttons) {
 
+	for (Set<BaseButton*>::Element *E=buttons.front();E;E=E->next()) {
+		r_buttons->push_back(E->get());
+	}
+}
+
+BaseButton* ButtonGroup::get_pressed_button() {
+
+	for (Set<BaseButton*>::Element *E=buttons.front();E;E=E->next()) {
+		if (E->get()->is_pressed())
+			return E->get();
+	}
+
+	return NULL;
+
+}
+
+void ButtonGroup::_bind_methods() {
+
+	ClassDB::bind_method(_MD("get_pressed_button:BaseButton"),&ButtonGroup::get_pressed_button);
+}
+
+ButtonGroup::ButtonGroup() {
+
+	set_local_to_scene(true);
+}