OpenGL model 模型

9.9.2 model 模型

一个模型拥有多个网格组成，并配有相应的处理函数，如节点处理、网格处理、加载模型、加载纹理、渲染等

模型类：

class Model{
public:Model(char* path) {loadModel(path);}void Draw(Shader shader);private:std::vector<Mesh> meshes;std::string directory;void loadModel(std::string path);void processNode(aiNode* node, const aiScene* scene);Mesh processMesh(aiMesh* mesh, const aiScene* scene);std::vector<Texture> loadMaterialtextures(aiMaterial* mat, aiTextureType type, std::string typeName);
};

下面介绍相关函数：

（1）draw 函数

这函数只需要遍历成员变量meshes，调用每个mesh的Draw函数就可以了。

//渲染
void Model::Draw(Shader shader) {for (int i = 0; i < meshes.size(); ++i)meshes[i].Draw(shader);
}

（2）loadModel

在这函数中，我们会把模型用Assimp加载进来，保存成一个scene对象。这是Assimp的一个根对象。模型加载成scene对象之后，我们就可以从里面读取数据进行转换纹理。

//加载模型
void Model::loadModel(std::string path) {//导入成scene对象Assimp::Importer importer;const aiScene* scene = importer.ReadFile(path, aiProcess_Triangulate | aiProcess_FlipUVs);//检测是否成功if (!scene || scene->mFlags & AI_SCENE_FLAGS_INCOMPLETE || !scene->mRootNode) {std::cout << "Assimp加载模型失败，错误信息: " << importer.GetErrorString() << std::endl;return;}directory = path.substr(0, path.find_last_of('/'));processNode(scene->mRootNode, scene);
}

（3）processNode

processNode来处理节点数据，每一个节点都可能包含子节点，所以这个函数会在其内部进行递归调用。Assimp的节点类中包含一些网格索引信息，检索和处理每个网格是我们的函数要做的主要事情。

//处理节点
void Model::processNode(aiNode* node, const aiScene* scene) {//处理节点的所有网格信息for (int i = 0; i < node->mNumMeshes; ++i) {aiMesh* mesh = scene->mMeshes[node->mMeshes[i]];meshes.push_back(processMesh(mesh, scene));}//对所有的子节点做相同处理for (int i = 0; i < node->mNumChildren; ++i) {processNode(node->mChildren[i], scene);}
}

（4）processMesh

将一个aiMesh对象转换成我们的mesh对象并不难，我们所要做的就是获取aiMesh中网格的所有属性，然后将其保存到mesh对象中。

//处理网格
Mesh Model::processMesh(aiMesh* mesh, const aiScene* scene) {std::vector<Vertex> vertices;std::vector<unsigned int> indices;std::vector<Texture> textures;for (int i = 0; i < mesh->mNumVertices; ++i) {Vertex vertex;//处理顶点，法线和纹理坐标...vertices.push_back(vertex);}//处理索引...//处理材质if (mesh->mMaterialIndex >= 0) {...}return Mesh(vertices, indices, textures);
}

processMesh中网格处理

收拾一个网格基本上有三个步骤要做：检索所有的顶点数据、检索所有的网格索引、检索相关的材质数据。将处理完成的数据保存到3个向量中，传递给Mesh的构造函数，生成一个新的Mesh对象返回。

检索顶点数据：在mVertices（位置），mNormals（法线），mTextureCoords（纹理坐标）

//处理顶点，法线和纹理坐标
glm::vec3 vector;
vector.x = mesh->mVertices[i].x;
vector.y = mesh->mVertices[i].y;
vector.z = mesh->mVertices[i].z;
vertex.Position = vector;vector.x = mesh->mNormals[i].x;
vector.y = mesh->mNormals[i].y;
vector.z = mesh->mNormals[i].z;
vertex.Normal = vector;if (mesh->mTextureCoords[0]) {  //看看是否有纹理信息glm::vec2 vec;vec.x = mesh->mTextureCoords[0][i].x;vec.y = mesh->mTextureCoords[0][i].y;vertex.TexCoords = vec;
}
elsevertex.TexCoords = glm::vec2(0.0f, 0.0f);

检索索引：

//处理索引
for (int i = 0; i < mesh->mNumFaces; ++i) {aiFace face = mesh->mFaces[i];for (int j = 0; j < face.mNumIndices; ++j)indices.push_back(face.mIndices[j]);
}

相关材质：

//处理材质
if (mesh->mMaterialIndex >= 0) {aiMaterial* material = scene->mMaterials[mesh->mMaterialIndex];std::vector<Texture> diffuseMaps = loadMaterialtextures(material,aiTextureType_DIFFUSE, "texture_diffuse");textures.insert(textures.end(), diffuseMaps.begin(), diffuseMaps.end());std::vector<Texture> specularMaps = loadMaterialtextures(material,aiTextureType_SPECULAR, "texture_specular");textures.insert(textures.end(), specularMaps.begin(), specularMaps.end());
}std::vector<Texture> Model::loadMaterialtextures(aiMaterial* mat, aiTextureType type, std::string typeName) {std::vector<Texture> textures;for (int i = 0; i < mat->GetTextureCount(type); ++i) {aiString str;mat->GetTexture(type, i, &str);Texture texture;texture.id = TextureFromFile(str.C_Str(), directory);texture.type = typeName;texture.path = str.C_Str();textures.push_back(texture);}return textures;
}

纹理复用：加载纹理前先搜索已经加载的纹理，如果没加载过就加载，加载过了直接保存。

std::vector<Texture> Model::loadMaterialtextures(aiMaterial* mat, aiTextureType type, std::string typeName) {std::vector<Texture> textures;for (int i = 0; i < mat->GetTextureCount(type); ++i) {aiString str;mat->GetTexture(type, i, &str);bool skip = false;for (int j = 0; j < textures_loaded.size(); ++j) {if (std::strcmp(textures_loaded[j].path.c_str(), str.C_Str()) == 0) {textures.push_back(textures_loaded[j]);skip = true;break;}}if (!skip) {Texture texture;texture.id = TextureFromFile(str.C_Str(), directory);texture.type = typeName;texture.path = str.C_Str();textures.push_back(texture);textures_loaded.push_back(texture);}}return textures;
}

完整代码：

#ifndef MODEL_H
#define MODEL_H#include <glad/glad.h> #include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <stb_image.h>
#include <assimp/Importer.hpp>
#include <assimp/scene.h>
#include <assimp/postprocess.h>#include <learnopengl/mesh.h>
#include <learnopengl/shader.h>#include <string>
#include <fstream>
#include <sstream>
#include <iostream>
#include <map>
#include <vector>
using namespace std;unsigned int TextureFromFile(const char *path, const string &directory, bool gamma = false);class Model 
{
public:// model data vector<Texture> textures_loaded;	// stores all the textures loaded so far, optimization to make sure textures aren't loaded more than once.vector<Mesh>    meshes;string directory;bool gammaCorrection;// constructor, expects a filepath to a 3D model.Model(string const &path, bool gamma = false) : gammaCorrection(gamma){loadModel(path);}// draws the model, and thus all its meshesvoid Draw(Shader &shader){for(unsigned int i = 0; i < meshes.size(); i++)meshes[i].Draw(shader);}private:// loads a model with supported ASSIMP extensions from file and stores the resulting meshes in the meshes vector.void loadModel(string const &path){// read file via ASSIMPAssimp::Importer importer;const aiScene* scene = importer.ReadFile(path, aiProcess_Triangulate | aiProcess_GenSmoothNormals | aiProcess_FlipUVs | aiProcess_CalcTangentSpace);// check for errorsif(!scene || scene->mFlags & AI_SCENE_FLAGS_INCOMPLETE || !scene->mRootNode) // if is Not Zero{cout << "ERROR::ASSIMP:: " << importer.GetErrorString() << endl;return;}// retrieve the directory path of the filepathdirectory = path.substr(0, path.find_last_of('/'));// process ASSIMP's root node recursivelyprocessNode(scene->mRootNode, scene);}// processes a node in a recursive fashion. Processes each individual mesh located at the node and repeats this process on its children nodes (if any).void processNode(aiNode *node, const aiScene *scene){// process each mesh located at the current nodefor(unsigned int i = 0; i < node->mNumMeshes; i++){// the node object only contains indices to index the actual objects in the scene. // the scene contains all the data, node is just to keep stuff organized (like relations between nodes).aiMesh* mesh = scene->mMeshes[node->mMeshes[i]];meshes.push_back(processMesh(mesh, scene));}// after we've processed all of the meshes (if any) we then recursively process each of the children nodesfor(unsigned int i = 0; i < node->mNumChildren; i++){processNode(node->mChildren[i], scene);}}Mesh processMesh(aiMesh *mesh, const aiScene *scene){// data to fillvector<Vertex> vertices;vector<unsigned int> indices;vector<Texture> textures;// walk through each of the mesh's verticesfor(unsigned int i = 0; i < mesh->mNumVertices; i++){Vertex vertex;glm::vec3 vector; // we declare a placeholder vector since assimp uses its own vector class that doesn't directly convert to glm's vec3 class so we transfer the data to this placeholder glm::vec3 first.// positionsvector.x = mesh->mVertices[i].x;vector.y = mesh->mVertices[i].y;vector.z = mesh->mVertices[i].z;vertex.Position = vector;// normalsif (mesh->HasNormals()){vector.x = mesh->mNormals[i].x;vector.y = mesh->mNormals[i].y;vector.z = mesh->mNormals[i].z;vertex.Normal = vector;}// texture coordinatesif(mesh->mTextureCoords[0]) // does the mesh contain texture coordinates?{glm::vec2 vec;// a vertex can contain up to 8 different texture coordinates. We thus make the assumption that we won't // use models where a vertex can have multiple texture coordinates so we always take the first set (0).vec.x = mesh->mTextureCoords[0][i].x; vec.y = mesh->mTextureCoords[0][i].y;vertex.TexCoords = vec;// tangentvector.x = mesh->mTangents[i].x;vector.y = mesh->mTangents[i].y;vector.z = mesh->mTangents[i].z;vertex.Tangent = vector;// bitangentvector.x = mesh->mBitangents[i].x;vector.y = mesh->mBitangents[i].y;vector.z = mesh->mBitangents[i].z;vertex.Bitangent = vector;}elsevertex.TexCoords = glm::vec2(0.0f, 0.0f);vertices.push_back(vertex);}// now wak through each of the mesh's faces (a face is a mesh its triangle) and retrieve the corresponding vertex indices.for(unsigned int i = 0; i < mesh->mNumFaces; i++){aiFace face = mesh->mFaces[i];// retrieve all indices of the face and store them in the indices vectorfor(unsigned int j = 0; j < face.mNumIndices; j++)indices.push_back(face.mIndices[j]);        }// process materialsaiMaterial* material = scene->mMaterials[mesh->mMaterialIndex];    // we assume a convention for sampler names in the shaders. Each diffuse texture should be named// as 'texture_diffuseN' where N is a sequential number ranging from 1 to MAX_SAMPLER_NUMBER. // Same applies to other texture as the following list summarizes:// diffuse: texture_diffuseN// specular: texture_specularN// normal: texture_normalN// 1. diffuse mapsvector<Texture> diffuseMaps = loadMaterialTextures(material, aiTextureType_DIFFUSE, "texture_diffuse");textures.insert(textures.end(), diffuseMaps.begin(), diffuseMaps.end());// 2. specular mapsvector<Texture> specularMaps = loadMaterialTextures(material, aiTextureType_SPECULAR, "texture_specular");textures.insert(textures.end(), specularMaps.begin(), specularMaps.end());// 3. normal mapsstd::vector<Texture> normalMaps = loadMaterialTextures(material, aiTextureType_HEIGHT, "texture_normal");textures.insert(textures.end(), normalMaps.begin(), normalMaps.end());// 4. height mapsstd::vector<Texture> heightMaps = loadMaterialTextures(material, aiTextureType_AMBIENT, "texture_height");textures.insert(textures.end(), heightMaps.begin(), heightMaps.end());// return a mesh object created from the extracted mesh datareturn Mesh(vertices, indices, textures);}// checks all material textures of a given type and loads the textures if they're not loaded yet.// the required info is returned as a Texture struct.vector<Texture> loadMaterialTextures(aiMaterial *mat, aiTextureType type, string typeName){vector<Texture> textures;for(unsigned int i = 0; i < mat->GetTextureCount(type); i++){aiString str;mat->GetTexture(type, i, &str);// check if texture was loaded before and if so, continue to next iteration: skip loading a new texturebool skip = false;for(unsigned int j = 0; j < textures_loaded.size(); j++){if(std::strcmp(textures_loaded[j].path.data(), str.C_Str()) == 0){textures.push_back(textures_loaded[j]);skip = true; // a texture with the same filepath has already been loaded, continue to next one. (optimization)break;}}if(!skip){   // if texture hasn't been loaded already, load itTexture texture;texture.id = TextureFromFile(str.C_Str(), this->directory);texture.type = typeName;texture.path = str.C_Str();textures.push_back(texture);textures_loaded.push_back(texture);  // store it as texture loaded for entire model, to ensure we won't unnecessary load duplicate textures.}}return textures;}
};unsigned int TextureFromFile(const char *path, const string &directory, bool gamma)
{string filename = string(path);filename = directory + '/' + filename;unsigned int textureID;glGenTextures(1, &textureID);int width, height, nrComponents;unsigned char *data = stbi_load(filename.c_str(), &width, &height, &nrComponents, 0);if (data){GLenum format;if (nrComponents == 1)format = GL_RED;else if (nrComponents == 3)format = GL_RGB;else if (nrComponents == 4)format = GL_RGBA;glBindTexture(GL_TEXTURE_2D, textureID);glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, GL_UNSIGNED_BYTE, data);glGenerateMipmap(GL_TEXTURE_2D);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);stbi_image_free(data);}else{std::cout << "Texture failed to load at path: " << path << std::endl;stbi_image_free(data);}return textureID;
}
#endif

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