From 62ad2c3bc1dd3a1a70d9eefbe2fac8fcbe426a1b Mon Sep 17 00:00:00 2001
From: pecksin <78765996+pecksin@users.noreply.github.com>
Date: Wed, 16 Feb 2022 17:06:00 -0500
Subject: [PATCH] Use absolute value for bouncy in collision (#11969)

[backport: removed devtest change and protocol_version comparison]
---
 src/collision.cpp | 3 ++-
 src/nodedef.cpp   | 7 ++++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/collision.cpp b/src/collision.cpp
index d85a56884..ccc3a058d 100644
--- a/src/collision.cpp
+++ b/src/collision.cpp
@@ -303,7 +303,8 @@ collisionMoveResult collisionMoveSimple(Environment *env, IGameDef *gamedef,
 			if (!f.walkable)
 				continue;
 
-			int n_bouncy_value = itemgroup_get(f.groups, "bouncy");
+			// Negative bouncy may have a meaning, but we need +value here.
+			int n_bouncy_value = abs(itemgroup_get(f.groups, "bouncy"));
 
 			int neighbors = 0;
 			if (f.drawtype == NDT_NODEBOX &&
diff --git a/src/nodedef.cpp b/src/nodedef.cpp
index 8a5542837..1dd130ece 100644
--- a/src/nodedef.cpp
+++ b/src/nodedef.cpp
@@ -452,7 +452,12 @@ void ContentFeatures::serialize(std::ostream &os, u16 protocol_version) const
 	writeU16(os, groups.size());
 	for (const auto &group : groups) {
 		os << serializeString16(group.first);
-		writeS16(os, group.second);
+		if (group.first.compare("bouncy") == 0) {
+			// Clients may choke on negative bouncy value
+			writeS16(os, abs(group.second));
+		} else {
+			writeS16(os, group.second);
+		}
 	}
 	writeU8(os, param_type);
 	writeU8(os, param_type_2);