From 0f5cadfb56100a02c45637fc2db436d3c0ffcd74 Mon Sep 17 00:00:00 2001
From: lawnjelly <lawnjelly@gmail.com>
Date: Mon, 20 May 2024 08:56:04 +0100
Subject: [PATCH] Fix Viewport interpolation mode

Viewport interpolation mode is a special case, which should be set to ON instead of INHERIT.
---
 doc/classes/Viewport.xml | 1 +
 scene/main/viewport.cpp  | 7 +++++++
 2 files changed, 8 insertions(+)

diff --git a/doc/classes/Viewport.xml b/doc/classes/Viewport.xml
index 1adde175aa4..c1018551871 100644
--- a/doc/classes/Viewport.xml
+++ b/doc/classes/Viewport.xml
@@ -246,6 +246,7 @@
 		<member name="own_world" type="bool" setter="set_use_own_world" getter="is_using_own_world" default="false">
 			If [code]true[/code], the viewport will use a unique copy of the [World] defined in [member world].
 		</member>
+		<member name="physics_interpolation_mode" type="int" setter="set_physics_interpolation_mode" getter="get_physics_interpolation_mode" overrides="Node" enum="Node.PhysicsInterpolationMode" default="2" />
 		<member name="physics_object_picking" type="bool" setter="set_physics_object_picking" getter="get_physics_object_picking" default="false">
 			If [code]true[/code], the objects rendered by viewport become subjects of mouse picking process.
 		</member>
diff --git a/scene/main/viewport.cpp b/scene/main/viewport.cpp
index ef92a88fadd..74680b195d0 100644
--- a/scene/main/viewport.cpp
+++ b/scene/main/viewport.cpp
@@ -3681,6 +3681,13 @@ Viewport::Viewport() {
 	local_input_handled = false;
 	handle_input_locally = true;
 	physics_last_id = 0; //ensures first time there will be a check
+
+	// Physics interpolation mode for viewports is a special case.
+	// Typically viewports will be housed within Controls,
+	// and Controls default to PHYSICS_INTERPOLATION_MODE_OFF.
+	// Viewports can thus inherit physics interpolation OFF, which is unexpected.
+	// Setting to ON allows each viewport to have a fresh interpolation state.
+	set_physics_interpolation_mode(Node::PHYSICS_INTERPOLATION_MODE_ON);
 }
 
 Viewport::~Viewport() {