Queue redraw when MultiMesh instance transform changes

Fixes: #66849

This is a 4.0 version of #54899.

scene/2d/multimesh_instance_2d.cpp

@@ -30,6 +30,7 @@
 
 #include "multimesh_instance_2d.h"
 
+#include "core/core_string_names.h"
 #include "scene/scene_string_names.h"
 
 void MultiMeshInstance2D::_notification(int p_what) {
@@ -60,7 +61,16 @@ void MultiMeshInstance2D::_bind_methods() {
 }
 
 void MultiMeshInstance2D::set_multimesh(const Ref<MultiMesh> &p_multimesh) {
+	// Cleanup previous connection if any.
+	if (multimesh.is_valid()) {
+		multimesh->disconnect(CoreStringNames::get_singleton()->changed, callable_mp((CanvasItem *)this, &CanvasItem::queue_redraw));
+	}
 	multimesh = p_multimesh;
+
+	// Connect to the multimesh so the AABB can update when instance transforms are changed.
+	if (multimesh.is_valid()) {
+		multimesh->connect(CoreStringNames::get_singleton()->changed, callable_mp((CanvasItem *)this, &CanvasItem::queue_redraw));
+	}
 	queue_redraw();
 }
 

scene/resources/multimesh.cpp

@@ -242,6 +242,7 @@ void MultiMesh::set_instance_transform(int p_instance, const Transform3D &p_tran
 
 void MultiMesh::set_instance_transform_2d(int p_instance, const Transform2D &p_transform) {
 	RenderingServer::get_singleton()->multimesh_instance_set_transform_2d(multimesh, p_instance, p_transform);
+	emit_changed();
 }
 
 Transform3D MultiMesh::get_instance_transform(int p_instance) const {