gltfpack: Implement support for KHR_materials_transmission

This change simply propagates KHR_materials_transmission parameters
through, supporting material merging as well.

It also fixes a problem with texture set filtering, where we ignored
texture sets that might have only been used in clearcoat layer.

gltf/material.cpp

@@ -109,6 +109,17 @@ static bool areMaterialComponentsEqual(const cgltf_clearcoat& lhs, const cgltf_c
 	return true;
 }
 
+static bool areMaterialComponentsEqual(const cgltf_transmission& lhs, const cgltf_transmission& rhs)
+{
+	if (!areTextureViewsEqual(lhs.transmission_texture, rhs.transmission_texture))
+		return false;
+
+	if (lhs.transmission_factor != rhs.transmission_factor)
+		return false;
+
+	return true;
+}
+
 static bool areMaterialsEqual(cgltf_data* data, const cgltf_material& lhs, const cgltf_material& rhs, const Settings& settings)
 {
 	if (lhs.has_pbr_metallic_roughness != rhs.has_pbr_metallic_roughness)
@@ -129,6 +140,12 @@ static bool areMaterialsEqual(cgltf_data* data, const cgltf_material& lhs, const
 	if (lhs.has_clearcoat && !areMaterialComponentsEqual(lhs.clearcoat, rhs.clearcoat))
 		return false;
 
+	if (lhs.has_transmission != rhs.has_transmission)
+		return false;
+
+	if (lhs.has_transmission && !areMaterialComponentsEqual(lhs.transmission, rhs.transmission))
+		return false;
+
 	if (!areTextureViewsEqual(lhs.normal_texture, rhs.normal_texture))
 		return false;
 
@@ -239,6 +256,22 @@ bool usesTextureSet(const cgltf_material& material, int set)
 			return true;
 	}
 
+	if (material.has_clearcoat)
+	{
+		const cgltf_clearcoat& clearcoat = material.clearcoat;
+
+		if (clearcoat.clearcoat_texture.texture && clearcoat.clearcoat_texture.texcoord == set)
+			return true;
+	}
+
+	if (material.has_transmission)
+	{
+		const cgltf_transmission& transmission = material.transmission;
+
+		if (transmission.transmission_texture.texture && transmission.transmission_texture.texcoord == set)
+			return true;
+	}
+
 	if (material.normal_texture.texture && material.normal_texture.texcoord == set)
 		return true;
 

gltf/write.cpp

@@ -343,6 +343,25 @@ static void writeMaterialComponent(std::string& json, const cgltf_data* data, co
 	append(json, "}");
 }
 
+static void writeMaterialComponent(std::string& json, const cgltf_data* data, const cgltf_transmission& tm, const QuantizationTexture* qt)
+{
+	comma(json);
+	append(json, "\"KHR_materials_transmission\":{");
+	if (tm.transmission_texture.texture)
+	{
+		comma(json);
+		append(json, "\"transmissionTexture\":");
+		writeTextureInfo(json, data, tm.transmission_texture, qt);
+	}
+	if (tm.transmission_factor != 0)
+	{
+		comma(json);
+		append(json, "\"transmissionFactor\":");
+		append(json, tm.transmission_factor);
+	}
+	append(json, "}");
+}
+
 void writeMaterial(std::string& json, const cgltf_data* data, const cgltf_material& material, const QuantizationTexture* qt)
 {
 	if (material.name && *material.name)
@@ -412,7 +431,7 @@ void writeMaterial(std::string& json, const cgltf_data* data, const cgltf_materi
 		append(json, "\"doubleSided\":true");
 	}
 
-	if (material.has_pbr_specular_glossiness || material.has_clearcoat || material.unlit)
+	if (material.has_pbr_specular_glossiness || material.has_clearcoat || material.has_transmission || material.unlit)
 	{
 		comma(json);
 		append(json, "\"extensions\":{");
@@ -427,6 +446,11 @@ void writeMaterial(std::string& json, const cgltf_data* data, const cgltf_materi
 			writeMaterialComponent(json, data, material.clearcoat, qt);
 		}
 
+		if (material.has_transmission)
+		{
+			writeMaterialComponent(json, data, material.transmission, qt);
+		}
+
 		if (material.unlit)
 		{
 			comma(json);