From da628411d25b42767a79f14ef5c6a14c7ea8340c Mon Sep 17 00:00:00 2001
From: lawnjelly <lawnjelly@gmail.com>
Date: Wed, 4 May 2022 19:56:06 +0100
Subject: [PATCH] Physics Interpolation - Flush transforms after physics tick

Leftover transforms from the physics tick were being flushed during idle, which was causing problems for physics interpolation.

This PR flushes the transforms at the end of the physics tick when physics interpolation is active.
---
 core/os/main_loop.h       | 1 +
 main/main.cpp             | 2 ++
 scene/main/scene_tree.cpp | 8 ++++++++
 scene/main/scene_tree.h   | 1 +
 4 files changed, 12 insertions(+)

diff --git a/core/os/main_loop.h b/core/os/main_loop.h
index b9b2b688a..5685bbdaf 100644
--- a/core/os/main_loop.h
+++ b/core/os/main_loop.h
@@ -67,6 +67,7 @@ public:
 
 	virtual void init();
 	virtual bool iteration(float p_time);
+	virtual void iteration_end() {}
 	virtual bool idle(float p_time);
 	virtual void finish();
 
diff --git a/main/main.cpp b/main/main.cpp
index 7927bf46a..c36ccfc8f 100644
--- a/main/main.cpp
+++ b/main/main.cpp
@@ -2215,6 +2215,8 @@ bool Main::iteration() {
 
 		message_queue->flush();
 
+		OS::get_singleton()->get_main_loop()->iteration_end();
+
 		physics_process_ticks = MAX(physics_process_ticks, OS::get_singleton()->get_ticks_usec() - physics_begin); // keep the largest one for reference
 		physics_process_max = MAX(OS::get_singleton()->get_ticks_usec() - physics_begin, physics_process_max);
 		Engine::get_singleton()->_physics_frames++;
diff --git a/scene/main/scene_tree.cpp b/scene/main/scene_tree.cpp
index 62008ca25..c2268828c 100644
--- a/scene/main/scene_tree.cpp
+++ b/scene/main/scene_tree.cpp
@@ -535,6 +535,14 @@ void SceneTree::client_physics_interpolation_remove_spatial(SelfList<Spatial> *p
 	_client_physics_interpolation._spatials_list.remove(p_elem);
 }
 
+void SceneTree::iteration_end() {
+	// When physics interpolation is active, we want all pending transforms
+	// to be flushed to the VisualServer before finishing a physics tick.
+	if (_physics_interpolation_enabled) {
+		flush_transform_notifications();
+	}
+}
+
 bool SceneTree::iteration(float p_time) {
 	root_lock++;
 
diff --git a/scene/main/scene_tree.h b/scene/main/scene_tree.h
index bfe44e670..fda8c88f3 100644
--- a/scene/main/scene_tree.h
+++ b/scene/main/scene_tree.h
@@ -305,6 +305,7 @@ public:
 	virtual void init();
 
 	virtual bool iteration(float p_time);
+	virtual void iteration_end();
 	virtual bool idle(float p_time);
 
 	virtual void finish();