C++解析obj模型文件方法介绍
作者:略游
一、前言
tinyobjloader地址:
而tinyobjloader库只有一个头文件,可以很方便的读取obj文件。支持材质,不过不支持骨骼动画,vulkan官方教程便是使用的它。不过没有骨骼动画还是有很大的局限性,这里只是分享一下怎么读取材质和拆分网格。
二、中间文件
我抽象了一个ModelObject类表示模型数据,而一个ModelObject包含多个Sub模型,每个Sub模型使用同一材质(有的人称为图元Primitive或DrawCall)。最后我将其保存为文件,这样我的引擎便可直接解析ModelObject文件,而不是再去读obj、fbx等其他文件了。
这一节可以跳过,下一节是真正使用tinyobjloader库。
//一个文件会有多个ModelObject,一个ModelObject根据材质分为多个ModelSub //注意ModelSub为一个材质,需要读取时合并网格 class ModelObject { friend class VK; public: //从源文件加载模型 static vector<ModelObject*> Create(string_view path_name); void Load(string_view path_name); //保存到文件 void SaveToFile(string_view path_name); private: vector<ModelObjectSub> _allSub; //下标减1 为材质,0为没有材质 vector<Vertex> _allVertex;//顶点缓存 vector<uint32_t> _allIndex;//索引缓存 vector<ModelObjectMaterial> _allMaterial;//所有材质 //------------------不同格式加载实现-------------------------------- //obj static vector<ModelObject*> _load_obj(string_view path_name); static vector<ModelObject*> _load_obj_2(string_view path_name); };
ModelObjectSub只是表示在索引缓存的一段范围:
//模型三角形范围 struct ModelTriangleRange { ModelTriangleRange() : _countTriangle{ 0 }, _offsetIndex{ 0 } {} size_t _countTriangle; size_t _offsetIndex; }; //子模型对象 范围 struct ModelObjectSub { ModelTriangleRange _range; };
而ModelObjectMaterial表示模型材质:
//! 材质 struct Material { glm::vec4 _diffuseAlbedo;//漫反射率 glm::vec3 _fresnelR0; //菲涅耳系数 float _roughness; //粗糙度 }; //模型对象 材质 struct ModelObjectMaterial { //最后转为Model时,变为可以用的着色器资源 Material _material; string _materialName; //路径为空,则表示没有(VK加载时会返回0) string _pathTexDiffuse; string _pathTexNormal; };
三、使用
首先引入头文件:
#define TINYOBJLOADER_IMPLEMENTATION #include <tiny_obj_loader.h>
接口原型,将obj文件变为多个ModelObject:
vector<ModelObject*> ModelObject::_load_obj_2(string_view path_name);
取得文件名,和文件所在路径(会自动加载路径下的同名mtl文件,里面包含了材质):
string str_path = string{ path_name }; string str_base = String::EraseFilename(path_name); const char* filename = str_path.c_str(); const char* basepath = str_base.c_str();
基本数据:
debug(format("开始加载obj文件:{},{}", filename, basepath)); bool triangulate = true;//三角化 tinyobj::attrib_t attrib; // 所有的数据放在这里 std::vector<tinyobj::shape_t> shapes;//子模型 std::vector<tinyobj::material_t> materials;//材质 std::string warn; std::string err;
加载并打印一些信息:
bool b_read = tinyobj::LoadObj(&attrib, &shapes, &materials, &warn, &err, filename, basepath, triangulate); //打印错误 if (!warn.empty()) debug_warn(warn); if (!err.empty()) debug_err(err); if (!b_read) { debug_err(format("读取obj文件失败:{}", path_name)); return {}; } debug(format("顶点数:{}", attrib.vertices.size() / 3)); debug(format("法线数:{}", attrib.normals.size() / 3)); debug(format("UV数:{}", attrib.texcoords.size() / 2)); debug(format("子模型数:{}", shapes.size())); debug(format("材质数:{}", materials.size()));
这将打印以下数据:
由于obj文件只产生一个ModelObject,我们如下添加一个,并返回顶点、索引、材质等引用,用于后面填充:
//obj只有一个ModelObject vector<ModelObject*> ret; ModelObject* model_object = new ModelObject; std::vector<Vertex>& mo_vertices = model_object->_allVertex; std::vector<uint32_t>& mo_indices = model_object->_allIndex; vector<ModelObjectMaterial>& mo_material = model_object->_allMaterial; ret.push_back(model_object);
首先记录材质信息:
//------------------获取材质------------------- mo_material.resize(materials.size()); for (size_t i = 0; i < materials.size(); ++i) { tinyobj::material_t m = materials[i]; debug(format("材质:{},{}", i, m.name)); ModelObjectMaterial& material = model_object->_allMaterial[i]; material._materialName = m.name; material._material._diffuseAlbedo = { m.diffuse[0], m.diffuse[1], m.diffuse[2], 1.0f }; material._material._fresnelR0 = { m.specular[0], m.specular[1], m.specular[2] }; material._material._roughness = ShininessToRoughness(m.shininess); if(!m.diffuse_texname.empty()) material._pathTexDiffuse = str_base + m.diffuse_texname; if (!m.normal_texname.empty()) material._pathTexNormal = str_base + m.normal_texname; }
这将产生以下输出:
然后遍历shape,按材质记录顶点。这里需要注意的是,一个obj文件有多个shape,每个shape由n个三角面组成。而每个三角形拥有独立的材质编号,所以这里按材质分别记录,而不是一般的合并为整体:
//------------------获取模型------------------- //按 材质 放入面的顶点 vector<vector<tinyobj::index_t>> all_sub; all_sub.resize(1 + materials.size());//0为默认 for (size_t i = 0; i < shapes.size(); i++) {//每一个子shape tinyobj::shape_t& shape = shapes[i]; size_t num_index = shape.mesh.indices.size(); size_t num_face = shape.mesh.num_face_vertices.size(); debug(format("读取子模型:{},{}", i, shape.name)); debug(format("索引数:{};面数:{}", num_index, num_face)); //当前mesh下标(每个面递增3) size_t index_offset = 0; //每一个面 for (size_t j = 0; j < num_face; ++j) { int index_mat = shape.mesh.material_ids[j];//每个面的材质 vector<tinyobj::index_t>& sub_idx = all_sub[1 + index_mat]; sub_idx.push_back(shape.mesh.indices[index_offset++]); sub_idx.push_back(shape.mesh.indices[index_offset++]); sub_idx.push_back(shape.mesh.indices[index_offset++]); } }
按材质记录顶点的索引(tinyobj::index_t)后,接下来就是读取顶点的实际数据,并防止重复读取:
//生成子模型,并填入顶点 std::unordered_map<tinyobj::index_t, size_t, hash_idx, equal_idx> uniqueVertices;//避免重复插入顶点 size_t i = 0; for (vector<tinyobj::index_t>& sub_idx : all_sub) { ModelObjectSub sub; sub._range._offsetIndex = i; sub._range._countTriangle = sub_idx.size() / 3; model_object->_allSub.push_back(sub); for (tinyobj::index_t& idx : sub_idx) { auto iter = uniqueVertices.find(idx); if (iter == uniqueVertices.end()) { Vertex v; //v v._pos[0] = attrib.vertices[idx.vertex_index * 3 + 0]; v._pos[1] = attrib.vertices[idx.vertex_index * 3 + 1]; v._pos[2] = attrib.vertices[idx.vertex_index * 3 + 2]; // vt v._texCoord[0] = attrib.texcoords[idx.texcoord_index * 2 + 0]; v._texCoord[1] = attrib.texcoords[idx.texcoord_index * 2 + 1]; v._texCoord[1] = 1.0f - v._texCoord[1]; uniqueVertices[idx] = mo_vertices.size(); mo_indices.push_back((uint32_t)mo_vertices.size()); mo_vertices.push_back(v); } else { mo_indices.push_back((uint32_t)iter->second); } ++i; } } debug(format("解析obj模型完成:v{},i{}", mo_vertices.size(), mo_indices.size())); return ret;
上面用到的哈希函数:
struct equal_idx { bool operator()(const tinyobj::index_t& a, const tinyobj::index_t& b) const { return a.vertex_index == b.vertex_index && a.texcoord_index == b.texcoord_index && a.normal_index == b.normal_index; } }; struct hash_idx { size_t operator()(const tinyobj::index_t& a) const { return ((a.vertex_index ^ a.texcoord_index << 1) >> 1) ^ (a.normal_index << 1); } };
最后打印出来的数据如下:
对于材质的处理,漫反射贴图即是基本贴图,而法线(凹凸)贴图、漫反射率、菲涅耳系数、光滑度等需要渲染管线支持并与光照计算产生效果。
四、完整代码
可以此处获取最新的源码(我会改用Assimp,并添加骨骼动画、Blinn-Phong光照模型),也可以用后面的:传送门
如果有用,欢迎点赞、收藏、关注,我将更新更多C++相关的文章。
#define TINYOBJLOADER_IMPLEMENTATION #include <tiny_obj_loader.h> struct equal_idx { bool operator()(const tinyobj::index_t& a, const tinyobj::index_t& b) const { return a.vertex_index == b.vertex_index && a.texcoord_index == b.texcoord_index && a.normal_index == b.normal_index; } }; struct hash_idx { size_t operator()(const tinyobj::index_t& a) const { return ((a.vertex_index ^ a.texcoord_index << 1) >> 1) ^ (a.normal_index << 1); } }; float ShininessToRoughness(float Ypoint) { float a = -1; float b = 2; float c; c = (Ypoint / 100) - 1; float D; D = b * b - (4 * a * c); float x1; x1 = (-b + sqrt(D)) / (2 * a); return x1; } vector<ModelObject*> ModelObject::_load_obj_2(string_view path_name) { string str_path = string{ path_name }; string str_base = String::EraseFilename(path_name); const char* filename = str_path.c_str(); const char* basepath = str_base.c_str(); bool triangulate = true; debug(format("开始加载obj文件:{},{}", filename, basepath)); tinyobj::attrib_t attrib; // 所有的数据放在这里 std::vector<tinyobj::shape_t> shapes;//子模型 std::vector<tinyobj::material_t> materials; std::string warn; std::string err; bool b_read = tinyobj::LoadObj(&attrib, &shapes, &materials, &warn, &err, filename, basepath, triangulate); //打印错误 if (!warn.empty()) debug_warn(warn); if (!err.empty()) debug_err(err); if (!b_read) { debug_err(format("读取obj文件失败:{}", path_name)); return {}; } debug(format("顶点数:{}", attrib.vertices.size() / 3)); debug(format("法线数:{}", attrib.normals.size() / 3)); debug(format("UV数:{}", attrib.texcoords.size() / 2)); debug(format("子模型数:{}", shapes.size())); debug(format("材质数:{}", materials.size())); //obj只有一个ModelObject vector<ModelObject*> ret; ModelObject* model_object = new ModelObject; std::vector<Vertex>& mo_vertices = model_object->_allVertex; std::vector<uint32_t>& mo_indices = model_object->_allIndex; vector<ModelObjectMaterial>& mo_material = model_object->_allMaterial; ret.push_back(model_object); //------------------获取材质------------------- mo_material.resize(materials.size()); for (size_t i = 0; i < materials.size(); ++i) { tinyobj::material_t m = materials[i]; debug(format("材质:{},{}", i, m.name)); ModelObjectMaterial& material = model_object->_allMaterial[i]; material._materialName = m.name; material._material._diffuseAlbedo = { m.diffuse[0], m.diffuse[1], m.diffuse[2], 1.0f }; material._material._fresnelR0 = { m.specular[0], m.specular[1], m.specular[2] }; material._material._roughness = ShininessToRoughness(m.shininess); if(!m.diffuse_texname.empty()) material._pathTexDiffuse = str_base + m.diffuse_texname; if (!m.normal_texname.empty())//注意这里凹凸贴图(bump_texname)更常见 material._pathTexNormal = str_base + m.normal_texname; } //------------------获取模型------------------- //按 材质 放入面的顶点 vector<vector<tinyobj::index_t>> all_sub; all_sub.resize(1 + materials.size());//0为默认 for (size_t i = 0; i < shapes.size(); i++) {//每一个子shape tinyobj::shape_t& shape = shapes[i]; size_t num_index = shape.mesh.indices.size(); size_t num_face = shape.mesh.num_face_vertices.size(); debug(format("读取子模型:{},{}", i, shape.name)); debug(format("索引数:{};面数:{}", num_index, num_face)); //当前mesh下标(每个面递增3) size_t index_offset = 0; //每一个面 for (size_t j = 0; j < num_face; ++j) { int index_mat = shape.mesh.material_ids[j];//每个面的材质 vector<tinyobj::index_t>& sub_idx = all_sub[1 + index_mat]; sub_idx.push_back(shape.mesh.indices[index_offset++]); sub_idx.push_back(shape.mesh.indices[index_offset++]); sub_idx.push_back(shape.mesh.indices[index_offset++]); } } //生成子模型,并填入顶点 std::unordered_map<tinyobj::index_t, size_t, hash_idx, equal_idx> uniqueVertices;//避免重复插入顶点 size_t i = 0; for (vector<tinyobj::index_t>& sub_idx : all_sub) { ModelObjectSub sub; sub._range._offsetIndex = i; sub._range._countTriangle = sub_idx.size() / 3; model_object->_allSub.push_back(sub); for (tinyobj::index_t& idx : sub_idx) { auto iter = uniqueVertices.find(idx); if (iter == uniqueVertices.end()) { Vertex v; //v v._pos[0] = attrib.vertices[idx.vertex_index * 3 + 0]; v._pos[1] = attrib.vertices[idx.vertex_index * 3 + 1]; v._pos[2] = attrib.vertices[idx.vertex_index * 3 + 2]; // vt v._texCoord[0] = attrib.texcoords[idx.texcoord_index * 2 + 0]; v._texCoord[1] = attrib.texcoords[idx.texcoord_index * 2 + 1]; v._texCoord[1] = 1.0f - v._texCoord[1]; uniqueVertices[idx] = mo_vertices.size(); mo_indices.push_back((uint32_t)mo_vertices.size()); mo_vertices.push_back(v); } else { mo_indices.push_back((uint32_t)iter->second); } ++i; } } debug(format("解析obj模型完成:v{},i{}", mo_vertices.size(), mo_indices.size())); return ret; }
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