Fix some ways to create inconsistent Viewport sizes

In the editor, it was possible to set the size of a `SubViewport` even
in cases where a parent `SubViewportContainer` had stretch enabled.

This PR disables editing a `SubViewport.size` while the parent disallows
it and it makes necessary adjustments during `NOTIFICATION_ENTER_TREE`.

(cherry picked from commit 34a7fc744762dcf66eff7e3b5e4d46e09e7c0bdc)

2 files changed, 9 insertions, 14 deletions

diff --git a/scene/gui/subviewport_container.cpp b/scene/gui/subviewport_container.cpp
index f10e1c2cd1..f9e96a44ed 100644
--- a/scene/gui/subviewport_container.cpp
+++ b/scene/gui/subviewport_container.cpp
@@ -58,6 +58,7 @@ void SubViewportContainer::set_stretch(bool p_enable) {
 	}
 
 	stretch = p_enable;
+	recalc_force_viewport_sizes();
 	update_minimum_size();
 	queue_sort();
 	queue_redraw();
@@ -75,10 +76,16 @@ void SubViewportContainer::set_stretch_shrink(int p_shrink) {
 
 	shrink = p_shrink;
 
+	recalc_force_viewport_sizes();
+	queue_redraw();
+}
+
+void SubViewportContainer::recalc_force_viewport_sizes() {
 	if (!stretch) {
 		return;
 	}
 
+	// If stretch is enabled, make sure that all child SubViwewports have the correct size.
 	for (int i = 0; i < get_child_count(); i++) {
 		SubViewport *c = Object::cast_to<SubViewport>(get_child(i));
 		if (!c) {
@@ -87,8 +94,6 @@ void SubViewportContainer::set_stretch_shrink(int p_shrink) {
 
 		c->set_size_force(get_size() / shrink);
 	}
-
-	queue_redraw();
 }
 
 int SubViewportContainer::get_stretch_shrink() const {
@@ -106,18 +111,7 @@ Vector<int> SubViewportContainer::get_allowed_size_flags_vertical() const {
 void SubViewportContainer::_notification(int p_what) {
 	switch (p_what) {
 		case NOTIFICATION_RESIZED: {
-			if (!stretch) {
-				return;
-			}
-
-			for (int i = 0; i < get_child_count(); i++) {
-				SubViewport *c = Object::cast_to<SubViewport>(get_child(i));
-				if (!c) {
-					continue;
-				}
-
-				c->set_size_force(get_size() / shrink);
-			}
+			recalc_force_viewport_sizes();
 		} break;
 
 		case NOTIFICATION_ENTER_TREE:
diff --git a/scene/gui/subviewport_container.h b/scene/gui/subviewport_container.h
index d3236b0c4e..c1a74e5b98 100644
--- a/scene/gui/subviewport_container.h
+++ b/scene/gui/subviewport_container.h
@@ -58,6 +58,7 @@ public:
 	virtual void unhandled_input(const Ref<InputEvent> &p_event) override;
 	void set_stretch_shrink(int p_shrink);
 	int get_stretch_shrink() const;
+	void recalc_force_viewport_sizes();
 
 	virtual Size2 get_minimum_size() const override;