From 524f0fc4894efab6e1276b2a7645ea1fbc08d65f Mon Sep 17 00:00:00 2001
From: Arseny Kapoulkine <arseny.kapoulkine@gmail.com>
Date: Thu, 16 Nov 2023 10:04:03 -0800
Subject: [PATCH] gltfpack: Remove normal streams from meshes with unlit
 materials

Unlit materials do not require normals or tangents; we already
automatically filter out tangents because of the lack of normal texture
or other material extensions, but normals were not removed until now.

This can reduce the amount of geometry we need to output; this also
mostly subsumes the redundant normal stream filtering for point clouds
as point clouds often have an unlit material, but for now we'll keep
that redundancy.

When material variants are used, we only do this when all material
variants for a given mesh are unlit. The use of the default material
also blocks this optimization as default material implies basic
lighting.
---
 gltf/gltfpack.cpp | 1 +
 gltf/gltfpack.h   | 2 ++
 gltf/material.cpp | 3 +++
 gltf/mesh.cpp     | 3 +++
 4 files changed, 9 insertions(+)

diff --git a/gltf/gltfpack.cpp b/gltf/gltfpack.cpp
index fabc586d..3e97d321 100644
--- a/gltf/gltfpack.cpp
+++ b/gltf/gltfpack.cpp
@@ -354,6 +354,7 @@ static void process(cgltf_data* data, const char* input_path, const char* output
 
 			mi.needsTangents |= vi.needsTangents;
 			mi.textureSetMask |= vi.textureSetMask;
+			mi.unlit &= vi.unlit;
 		}
 
 		filterStreams(mesh, mi);
diff --git a/gltf/gltfpack.h b/gltf/gltfpack.h
index c3257589..fed181ea 100644
--- a/gltf/gltfpack.h
+++ b/gltf/gltfpack.h
@@ -219,6 +219,8 @@ struct MaterialInfo
 
 	bool usesTextureTransform;
 	bool needsTangents;
+	bool unlit;
+
 	unsigned int textureSetMask;
 
 	int remap;
diff --git a/gltf/material.cpp b/gltf/material.cpp
index 59238ac1..9b1ad14a 100644
--- a/gltf/material.cpp
+++ b/gltf/material.cpp
@@ -500,6 +500,9 @@ static void analyzeMaterial(const cgltf_material& material, MaterialInfo& mi, cg
 	analyzeMaterialTexture(material.normal_texture, TextureKind_Normal, mi, data, textures, images);
 	analyzeMaterialTexture(material.occlusion_texture, TextureKind_Attrib, mi, data, textures, images);
 	analyzeMaterialTexture(material.emissive_texture, TextureKind_Color, mi, data, textures, images);
+
+	if (material.unlit)
+		mi.unlit = true;
 }
 
 void analyzeMaterials(cgltf_data* data, std::vector<MaterialInfo>& materials, std::vector<TextureInfo>& textures, std::vector<ImageInfo>& images)
diff --git a/gltf/mesh.cpp b/gltf/mesh.cpp
index 2f4b29fd..d99be38e 100644
--- a/gltf/mesh.cpp
+++ b/gltf/mesh.cpp
@@ -424,6 +424,9 @@ void filterStreams(Mesh& mesh, const MaterialInfo& mi)
 		if (stream.type == cgltf_attribute_type_texcoord && stream.index > keep_texture_set)
 			continue;
 
+		if (stream.type == cgltf_attribute_type_normal && mi.unlit)
+			continue;
+
 		if (stream.type == cgltf_attribute_type_tangent && !mi.needsTangents)
 			continue;