From 3c5e0d10fc169ecdd062f7afa20a2b0faeaf3a7f Mon Sep 17 00:00:00 2001
From: Lars Mueller <appgurulars@gmx.de>
Date: Mon, 9 Dec 2024 00:45:37 +0100
Subject: [PATCH] Rotate meshnode normals correctly instead of recalculating

---
 src/client/content_mapblock.cpp |  2 --
 src/client/mesh.cpp             | 12 ++++++++----
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/src/client/content_mapblock.cpp b/src/client/content_mapblock.cpp
index 25d303156..49abbd4fa 100644
--- a/src/client/content_mapblock.cpp
+++ b/src/client/content_mapblock.cpp
@@ -1673,8 +1673,6 @@ void MapblockMeshGenerator::drawMeshNode()
 			modified = false;
 		if (modified) {
 			recalculateBoundingBox(mesh);
-			// FIXME: we should rotate the normals too, instead of recalculating
-			meshmanip->recalculateNormals(mesh, true, false);
 		}
 	} else {
 		warningstream << "drawMeshNode(): missing mesh" << std::endl;
diff --git a/src/client/mesh.cpp b/src/client/mesh.cpp
index 012b9a45a..eb56d3580 100644
--- a/src/client/mesh.cpp
+++ b/src/client/mesh.cpp
@@ -249,10 +249,14 @@ static void rotateMesh(scene::IMesh *mesh, float degrees)
 	float c = std::cos(degrees);
 	float s = std::sin(degrees);
 	auto rotator = [c, s] (video::S3DVertex *vertex) {
-		float u = vertex->Pos.*U;
-		float v = vertex->Pos.*V;
-		vertex->Pos.*U = c * u - s * v;
-		vertex->Pos.*V = s * u + c * v;
+		auto rotate_vec = [c, s] (v3f &vec) {
+			float u = vec.*U;
+			float v = vec.*V;
+			vec.*U = c * u - s * v;
+			vec.*V = s * u + c * v;
+		};
+		rotate_vec(vertex->Pos);
+		rotate_vec(vertex->Normal);
 	};
 	applyToMesh(mesh, rotator);
 }