From fe1f72ab0ac8bcc233c91eb5b2d71bd2d2574cf8 Mon Sep 17 00:00:00 2001
From: Danila Shutov <dcbrwn2@gmail.com>
Date: Sun, 7 Jun 2020 19:14:00 +0300
Subject: [PATCH] Recalculate mesh normals for CAOs (#10000)

---
 src/client/content_cao.cpp |  8 ++++++++
 src/client/mesh.cpp        | 20 ++++++++++++++++++++
 src/client/mesh.h          |  6 ++++++
 3 files changed, 34 insertions(+)

diff --git a/src/client/content_cao.cpp b/src/client/content_cao.cpp
index 855729642..a6ce06d20 100644
--- a/src/client/content_cao.cpp
+++ b/src/client/content_cao.cpp
@@ -726,6 +726,14 @@ void GenericCAO::addToScene(ITextureSource *tsrc)
 				addAnimatedMeshSceneNode(mesh, m_matrixnode);
 			m_animated_meshnode->grab();
 			mesh->drop(); // The scene node took hold of it
+
+			if (!checkMeshNormals(mesh)) {
+				infostream << "GenericCAO: recalculating normals for mesh "
+					<< m_prop.mesh << std::endl;
+				m_smgr->getMeshManipulator()->
+						recalculateNormals(mesh, true, false);
+			}
+
 			m_animated_meshnode->animateJoints(); // Needed for some animations
 			m_animated_meshnode->setScale(m_prop.visual_size);
 
diff --git a/src/client/mesh.cpp b/src/client/mesh.cpp
index 4d73ead8a..91781373c 100644
--- a/src/client/mesh.cpp
+++ b/src/client/mesh.cpp
@@ -328,6 +328,26 @@ void recalculateBoundingBox(scene::IMesh *src_mesh)
 	src_mesh->setBoundingBox(bbox);
 }
 
+bool checkMeshNormals(scene::IMesh *mesh)
+{
+	u32 buffer_count = mesh->getMeshBufferCount();
+
+	for (u32 i = 0; i < buffer_count; i++) {
+		scene::IMeshBuffer *buffer = mesh->getMeshBuffer(i);
+
+		// Here we intentionally check only first normal, assuming that if buffer
+		// has it valid, then most likely all other ones are fine too. We can
+		// check all of the normals to have length, but it seems like an overkill
+		// hurting the performance and covering only really weird broken models.
+		f32 length = buffer->getNormal(0).getLength();
+
+		if (!isfinite(length) || fabs(length) < 1e-10)
+			return false;
+	}
+
+	return true;
+}
+
 scene::IMeshBuffer* cloneMeshBuffer(scene::IMeshBuffer *mesh_buffer)
 {
 	switch (mesh_buffer->getVertexType()) {
diff --git a/src/client/mesh.h b/src/client/mesh.h
index 0c4094de2..103c61e45 100644
--- a/src/client/mesh.h
+++ b/src/client/mesh.h
@@ -121,6 +121,12 @@ scene::IMesh* convertNodeboxesToMesh(const std::vector<aabb3f> &boxes,
 */
 void recalculateBoundingBox(scene::IMesh *src_mesh);
 
+/*
+	Check if mesh has valid normals and return true if it does.
+	We assume normal to be valid when it's 0 < length < Inf. and not NaN
+ */
+bool checkMeshNormals(scene::IMesh *mesh);
+
 /*
 	Vertex cache optimization according to the Forsyth paper:
 	http://home.comcast.net/~tom_forsyth/papers/fast_vert_cache_opt.html
-- 
2.25.1