gltfpack: Refactor .obj parsing a little bit

This change splits nodes and materials parsing and keeps mesh group
parsing loop so that the code looks more similar to what we used to have
when we just had one group. That will also make it easier to ensure the
relationships between objects and nodes stay 1-1.

gltf/parseobj.cpp

@@ -21,11 +21,8 @@ static int textureIndex(const std::vector<std::string>& textures, const char* na
 	return -1;
 }
 
-static cgltf_data* parseSceneObj(fastObjMesh* obj)
+static void parseMaterialsObj(fastObjMesh* obj, cgltf_data* data)
 {
-	cgltf_data* data = (cgltf_data*)calloc(1, sizeof(cgltf_data));
-	data->memory.free_func = defaultFree;
-
 	std::vector<std::string> textures;
 
 	for (unsigned int mi = 0; mi < obj->material_count; ++mi)
@@ -97,7 +94,10 @@ static cgltf_data* parseSceneObj(fastObjMesh* obj)
 			gm.alpha_mode = cgltf_alpha_mode_blend;
 		}
 	}
+}
 
+static void parseNodesObj(fastObjMesh* obj, cgltf_data* data)
+{
 	data->nodes = (cgltf_node*)calloc(obj->object_count, sizeof(cgltf_node));
 	data->nodes_count = obj->object_count;
 
@@ -122,8 +122,6 @@ static cgltf_data* parseSceneObj(fastObjMesh* obj)
 
 		data->scenes->nodes[oi] = node;
 	}
-
-	return data;
 }
 
 static void parseMeshObj(fastObjMesh* obj, unsigned int face_offset, unsigned int face_vertex_offset, unsigned int face_count, unsigned int face_vertex_count, unsigned int index_count, Mesh& mesh)
@@ -214,49 +212,44 @@ static void parseMeshObj(fastObjMesh* obj, unsigned int face_offset, unsigned in
 	assert(index_offset == index_count);
 }
 
-static void parseMeshesObj(fastObjMesh* obj, cgltf_data* data, std::vector<Mesh>& meshes)
+static void parseMeshGroupObj(fastObjMesh* obj, const fastObjGroup& og, cgltf_data* data, cgltf_node* node, std::vector<Mesh>& meshes)
 {
-	for (unsigned int oi = 0; oi < obj->object_count; ++oi)
+	unsigned int face_vertex_offset = og.index_offset;
+	unsigned int face_end_offset = og.face_offset + og.face_count;
+
+	for (unsigned int face_offset = og.face_offset; face_offset < face_end_offset; )
 	{
-		const fastObjGroup& og = obj->objects[oi];
+		unsigned int mi = obj->face_materials[face_offset];
 
-		unsigned int face_vertex_offset = og.index_offset;
-		unsigned int face_end_offset = og.face_offset + og.face_count;
+		unsigned int face_count = 0;
+		unsigned int face_vertex_count = 0;
+		unsigned int index_count = 0;
 
-		for (unsigned int face_offset = og.face_offset; face_offset < face_end_offset; )
+		for (unsigned int fj = face_offset; fj < face_end_offset && obj->face_materials[fj] == mi; ++fj)
 		{
-			unsigned int mi = obj->face_materials[face_offset];
-
-			unsigned int face_count = 0;
-			unsigned int face_vertex_count = 0;
-			unsigned int index_count = 0;
-
-			for (unsigned int fj = face_offset; fj < face_end_offset && obj->face_materials[fj] == mi; ++fj)
-			{
-				face_count += 1;
-				face_vertex_count += obj->face_vertices[fj];
-				index_count += (obj->face_vertices[fj] - 2) * 3;
-			}
+			face_count += 1;
+			face_vertex_count += obj->face_vertices[fj];
+			index_count += (obj->face_vertices[fj] - 2) * 3;
+		}
 
-			meshes.push_back(Mesh());
-			Mesh& mesh = meshes.back();
+		meshes.push_back(Mesh());
+		Mesh& mesh = meshes.back();
 
-			if (data->materials_count)
-			{
-				assert(mi < data->materials_count);
-				mesh.material = &data->materials[mi];
-			}
+		if (data->materials_count)
+		{
+			assert(mi < data->materials_count);
+			mesh.material = &data->materials[mi];
+		}
 
-			mesh.type = cgltf_primitive_type_triangles;
-			mesh.targets = 0;
+		mesh.type = cgltf_primitive_type_triangles;
+		mesh.targets = 0;
 
-			mesh.nodes.push_back(&data->nodes[oi]);
+		mesh.nodes.push_back(node);
 
-			parseMeshObj(obj, face_offset, face_vertex_offset, face_count, face_vertex_count, index_count, mesh);
+		parseMeshObj(obj, face_offset, face_vertex_offset, face_count, face_vertex_count, index_count, mesh);
 
-			face_offset += face_count;
-			face_vertex_offset += face_vertex_count;
-		}
+		face_offset += face_count;
+		face_vertex_offset += face_vertex_count;
 	}
 }
 
@@ -270,9 +263,16 @@ cgltf_data* parseObj(const char* path, std::vector<Mesh>& meshes, const char** e
 		return 0;
 	}
 
-	cgltf_data* data = parseSceneObj(obj);
+	cgltf_data* data = (cgltf_data*)calloc(1, sizeof(cgltf_data));
+	data->memory.free_func = defaultFree;
+
+	parseMaterialsObj(obj, data);
 
-	parseMeshesObj(obj, data, meshes);
+	parseNodesObj(obj, data);
+	assert(data->nodes_count == obj->object_count);
+
+	for (unsigned int oi = 0; oi < obj->object_count; ++oi)
+		parseMeshGroupObj(obj, obj->objects[oi], data, &data->nodes[oi], meshes);
 
 	fast_obj_destroy(obj);