From a98200bb4c1edb2c982577fb01b30075665ab488 Mon Sep 17 00:00:00 2001
From: lhofhansl <larsh@apache.org>
Date: Sun, 10 Dec 2023 10:12:37 -0800
Subject: [PATCH] Avoid movement jitter (#13093)

This allows the client and server to agree on the position of objects and attached players even when there is lag.
---
 src/client/client.cpp | 4 ++--
 src/collision.cpp     | 6 +++---
 src/constants.h       | 7 +++++++
 src/server.cpp        | 4 ++--
 4 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/src/client/client.cpp b/src/client/client.cpp
index c17fa2ab9..a49578ae0 100644
--- a/src/client/client.cpp
+++ b/src/client/client.cpp
@@ -393,8 +393,8 @@ void Client::connect(Address address, bool is_local_server)
 void Client::step(float dtime)
 {
 	// Limit a bit
-	if (dtime > 2.0)
-		dtime = 2.0;
+	if (dtime > DTIME_LIMIT)
+		dtime = DTIME_LIMIT;
 
 	m_animation_time += dtime;
 	if(m_animation_time > 60.0)
diff --git a/src/collision.cpp b/src/collision.cpp
index 0649b5ced..0814791ed 100644
--- a/src/collision.cpp
+++ b/src/collision.cpp
@@ -241,13 +241,13 @@ collisionMoveResult collisionMoveSimple(Environment *env, IGameDef *gamedef,
 	/*
 		Calculate new velocity
 	*/
-	if (dtime > 0.5f) {
+	if (dtime > DTIME_LIMIT) {
 		if (!time_notification_done) {
 			time_notification_done = true;
-			infostream << "collisionMoveSimple: maximum step interval exceeded,"
+			warningstream << "collisionMoveSimple: maximum step interval exceeded,"
 					" lost movement details!"<<std::endl;
 		}
-		dtime = 0.5f;
+		dtime = DTIME_LIMIT;
 	} else {
 		time_notification_done = false;
 	}
diff --git a/src/constants.h b/src/constants.h
index b9d4f8d70..1ebfc7503 100644
--- a/src/constants.h
+++ b/src/constants.h
@@ -56,6 +56,13 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 // Override for the previous one when distance of block is very low
 #define BLOCK_SEND_DISABLE_LIMITS_MAX_D 1
 
+/*
+    Client/Server
+*/
+
+// Limit maximum dtime in client/server step(...) and for collision detection
+#define DTIME_LIMIT 2.5f
+
 /*
     Map-related things
 */
diff --git a/src/server.cpp b/src/server.cpp
index 78b706336..67c3a8592 100644
--- a/src/server.cpp
+++ b/src/server.cpp
@@ -577,8 +577,8 @@ void Server::stop()
 void Server::step(float dtime)
 {
 	// Limit a bit
-	if (dtime > 2.0)
-		dtime = 2.0;
+	if (dtime > DTIME_LIMIT)
+		dtime = DTIME_LIMIT;
 	{
 		MutexAutoLock lock(m_step_dtime_mutex);
 		m_step_dtime += dtime;