模型加载重要代码

这点需结合代码全部才好理解，可以跳过此点直接看程序代码

读取3D模型

Assimp::Importer importer;
const aiScene *scene = importer.ReadFile(path, aiProcess_Triangulate | aiProcess_FlipUVs);

ReadFile的第二个参数是一些后期处理(Post-processing)的选项

aiProcess_Triangulate:如果模型不是（全部）由三角形组成，它需要将模型所有的图元形状变换为三角形
aiProcess_FlipUVs:在处理的时候翻转y轴的纹理坐标
aiProcess_GenNormals：如果模型不包含法向量的话，就为每个顶点创建法线。
aiProcess_SplitLargeMeshes：将比较大的网格分割成更小的子网格，如果你的渲染有最大顶点数限制，只能渲染较小的网格，那么它会非常有用。
aiProcess_OptimizeMeshes：和上个选项相反，它会将多个小网格拼接为一个大的网格，减少绘制调用从而进行优化。

递归处理结点的网格

代码

void processNode(aiNode *node, const aiScene *scene)
{// 处理节点所有的网格（如果有的话）for(unsigned int i = 0; i < node->mNumMeshes; i++){aiMesh *mesh = scene->mMeshes[node->mMeshes[i]]; meshes.push_back(processMesh(mesh, scene));         }// 递归接下来对它的子节点重复这一过程for(unsigned int i = 0; i < node->mNumChildren; i++){processNode(node->mChildren[i], scene);}
}

说明

本可以不用递归处理任何节点，渲染时只需要遍历场景对象的所有网格即可
- 为什么要递归处理网格
  
  使用节点的最初想法是将网格之间定义一个父子关系。通过这样递归地遍历这层关系，我们就能将某个网格定义为另一个网格的父网格了。
- 例子
  
  位移一个汽车的网格时，你可以保证它的所有子网格（比如引擎网格、方向盘网格、轮胎网格）都会随着一起位移。这样的系统能够用父子关系很容易地实现。

加载纹理优化

大多数场景都会在多个网格中重用部分纹理，所以不需要每次加载网格用的纹理，应该存储到vector中判断是否加载过，是加载过就只需将加载过的纹理放到vector的后面就行

vector loadMaterialTextures(aiMaterial *mat, aiTextureType type, string typeName)
{vector textures;for(unsigned int i = 0; i < mat->GetTextureCount(type); i++){aiString str;mat->GetTexture(type, i, &str);bool 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; break;}}if(!skip){   // 如果纹理还没有被加载，则加载它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); // 添加到已加载的纹理中}}return textures;
}

程序代码

Model类加载模型流程

例子1：渲染模型

代码

model.h

#pragma once
#include  #include 
#include 
#include 
#include 
#include 
#include //#include 
//#include 
#include "Mesh.h"
#include "Core/Shader/Shader.h"#include 
#include 
#include 
#include 
#include 
#include 
using namespace std;// 辅助方法：从路径中加载材质
//unsigned int TextureFromFile(const char* path, const string& directory, bool gamma = false);
unsigned int TextureFromFile(const char* path, const string& directory, bool gamma = false) {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;
}
class Model
{
public:vector textures_loaded;vector meshes;string directory;bool gammaCorrection;// 构造函数Model(string const& path, bool gamma = false) : gammaCorrection(gamma) {loadModel(path);}// 绘画void Draw(Shader& shader) {for (unsigned int i = 0; i < meshes.size(); i++) {meshes[i].Draw(shader);}}
private:// 加载模型void loadModel(string const &path) {Assimp::Importer importer;const aiScene* scene = importer.ReadFile(path, aiProcess_Triangulate | aiProcess_GenSmoothNormals | aiProcess_FlipUVs | aiProcess_CalcTangentSpace);if (!scene || scene->mFlags & AI_SCENE_FLAGS_INCOMPLETE || !scene->mRootNode) {cout << "ERROR::ASSIMP:: " << importer.GetErrorString() << endl;return;}directory = path.substr(0, path.find_last_of("/"));// 保存目录// 处理结点processNode(scene->mRootNode, scene);}/// /// 递归处理结点下的网格，处理完网格就新建一个自定义的mesh类并添加到vector中存储所有网格/// 
/// 根结点，递归过程中变成子结点/// 场景void processNode(aiNode* node, const aiScene* scene) {// 处理当前结点下的每一个网格for (unsigned int i = 0; i < node->mNumMeshes; i++) {aiMesh* mesh = scene->mMeshes[node->mMeshes[i]];// 在scene哪个网格meshes.push_back(processMesh(mesh, scene));// 处理网格后，保存为我们自己的类}// 递归处理子节点for (unsigned int i = 0; i < node->mNumChildren; i++) {processNode(node->mChildren[i], scene);}}/// /// 处理结点下的网格，读取绘制网格所需的顶点、法线、贴图/// 
/// 具体的网格数据/// 哪个场景下/// 返回自定义mesh类Mesh processMesh(aiMesh* mesh, const aiScene* scene) {vector vertices;vector indices;vector textures;for (unsigned int i = 0; i < mesh->mNumVertices; i++) {Vertex vertex;glm::vec3 vector;vector.x = mesh->mVertices[i].x;vector.y = mesh->mVertices[i].y;vector.z = mesh->mVertices[i].z;vertex.Position = vector;if (mesh->HasNormals()) {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]) {glm::vec2 vec;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;}else {vertex.TexCoords = glm::vec2(0.0f, 0.0f);}vertices.push_back(vertex);}// 网格下有众多面，面的绘制索引存储起来for (unsigned int i = 0; i < mesh->mNumFaces; i++) {aiFace face = mesh->mFaces[i];for (unsigned int j = 0; j < face.mNumIndices; j++) {indices.push_back(face.mIndices[j]);}}aiMaterial* material = scene->mMaterials[mesh->mMaterialIndex];// 1.漫反射贴图vector diffuseMaps = loadMaterialTextures(material, aiTextureType_DIFFUSE, "texture_diffuse");textures.insert(textures.end(), diffuseMaps.begin(), diffuseMaps.end());// 2.镜面光贴图vector specularMaps = loadMaterialTextures(material, aiTextureType_SPECULAR, "texture_specular");textures.insert(textures.end(), specularMaps.begin(), specularMaps.end());// 3.法线贴图vector normalMaps = loadMaterialTextures(material, aiTextureType_HEIGHT, "texture_normal");textures.insert(textures.end(), normalMaps.begin(), normalMaps.end());// 4.高度图vector heightMaps = loadMaterialTextures(material, aiTextureType_AMBIENT, "texture_height");textures.insert(textures.end(), heightMaps.begin(), heightMaps.end());return Mesh(vertices, indices, textures);}/// /// 处理网格的辅助方法：加载一个网格下对应的类型贴图/// 
/// 场景下网格对应的材质/// 材质类型/// 自定义格式名/// 返回这个网格下，对应材质类型的材质vector loadMaterialTextures(aiMaterial* mat, aiTextureType type, string typeName) {vector textures;for (unsigned int i = 0; i < mat->GetTextureCount(type); i++) {aiString str;mat->GetTexture(type, i, &str);bool skip = false;for (unsigned int j = 0; j < textures_loaded.size(); j++) {// 加载过if (std::strcmp(textures_loaded[j].path.data(), str.C_Str()) == 0) {textures.push_back(textures_loaded[i]);// 放在后面skip = true;break;}}if (!skip) {Texture texture;texture.id = TextureFromFile(str.C_Str(), this->directory);texture.type = typeName;texture.path = str.C_Str();textures.push_back(texture);        // 未知也要增加textures_loaded.push_back(texture);// 添加到已知}}return textures;}
};

cpp

#include 
#include 
#include #include 
#include 
#include #include "Core/Shader/Shader.h"
#include "Core/Camera/Camera.h"
#include "Core/LoadModel/Model.h"#include 
#include "MyFileSystem.h"void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void mouse_callback(GLFWwindow* window, double xpos, double ypos);
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset);
void processInput(GLFWwindow* window);
unsigned int loadTexture(const char* path);// settings
const unsigned int SCR_WIDTH = 1920;
const unsigned int SCR_HEIGHT = 1080;// camera
Camera camera(glm::vec3(0.0f, 0.0f, 3.0f));
float lastX = SCR_WIDTH / 2.0f;
float lastY = SCR_HEIGHT / 2.0f;
bool firstMouse = true;// timing
float deltaTime = 0.0f;
float lastFrame = 0.0f;
// lighting
glm::vec3 lightPos(1.2f, 1.0f, 2.0f);int main()
{// glfw: initialize and configure// ------------------------------glfwInit();glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);#ifdef __APPLE__glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif// glfw window creation// --------------------GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);if (window == NULL){std::cout << "Failed to create GLFW window" << std::endl;glfwTerminate();return -1;}glfwMakeContextCurrent(window);glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);glfwSetCursorPosCallback(window, mouse_callback);glfwSetScrollCallback(window, scroll_callback);// tell GLFW to capture our mouseglfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);// glad: load all OpenGL function pointers// ---------------------------------------if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)){std::cout << "Failed to initialize GLAD" << std::endl;return -1;}// configure global opengl state// -----------------------------glEnable(GL_DEPTH_TEST);// build and compile our shader zprogram// ------------------------------------//Shader lightingShader("1.colors.vs", "1.colors.fs");// 物体的光照shaderShader ourShader("assest/shader/3模型/3.1.模型加载.vs", "assest/shader/3模型/3.1.模型加载.fs");// 加载模型Model ourModel(FileSystem::getPath("assest/model/nanosuit/nanosuit.obj"));// render loop// -----------while (!glfwWindowShouldClose(window)){// per-frame time logic// --------------------float currentFrame = static_cast(glfwGetTime());deltaTime = currentFrame - lastFrame;lastFrame = currentFrame;// input// -----processInput(window);// render// ------glClearColor(0.1f, 0.1f, 0.1f, 1.0f);glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);// be sure to activate shader when setting uniforms/drawing objectsourShader.use();// view/projection transformationsglm::mat4 projection = glm::perspective(glm::radians(camera.Zoom), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f);glm::mat4 view = camera.GetViewMatrix();ourShader.setMat4("projection", projection);ourShader.setMat4("view", view);// 渲染这个模型glm::mat4 model = glm::mat4(1.0f);model = glm::translate(model, glm::vec3(0.0f, 0.0f, 0.0f));model = glm::scale(model, glm::vec3(1.0f, 1.0f, 1.0f));ourShader.setMat4("model", model);ourModel.Draw(ourShader);// glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)// -------------------------------------------------------------------------------glfwSwapBuffers(window);glfwPollEvents();}// glfw: terminate, clearing all previously allocated GLFW resources.// ------------------------------------------------------------------glfwTerminate();return 0;
}
....

glsl

#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec3 aNormal;
layout (location = 2) in vec2 aTexCoords;out vec2 TexCoords;  uniform mat4 model;
uniform mat4 view;
uniform mat4 projection;void main()
{TexCoords = aTexCoords;gl_Position = projection * view * model * vec4(aPos, 1.0);
}

#version 330 core
out vec4 FragColor;in vec2 TexCoords;uniform sampler2D texture_diffuse1;void main(){FragColor = texture(texture_diffuse1, TexCoords);
}

效果

例子2：添加点光源

代码

#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec3 aNormal;
layout (location = 2) in vec2 aTexCoords;out vec3 FragPos;  
out vec3 Normal;
out vec2 TexCoords;uniform mat4 model;
uniform mat4 view;
uniform mat4 projection;void main()
{gl_Position = projection * view * model * vec4(aPos, 1.0);FragPos = vec3(model * vec4(aPos, 1.0));Normal = mat3(transpose(inverse(model))) * aNormal;TexCoords = aTexCoords;
}

#version 330 core
out vec4 FragColor;in vec3 FragPos;
in vec3 Normal;
in vec2 TexCoords;// 纹理坐标uniform vec3 viewPos;uniform sampler2D texture_diffuse1;// 纹理单元
uniform sampler2D texture_specular1;// 纹理单元// 点光源
struct PointLight  {vec3 position;  vec3 ambient;vec3 diffuse;vec3 specular;float constant; // 常数float linear;   // 一次项float quadratic;// 二次项
};#define NR_POINT_LIGHTS 2
uniform PointLight pointLights[NR_POINT_LIGHTS];// 计算点光源影响当前片段的颜色
vec3 CalcPointLight(PointLight light, vec3 normal, vec3 fragPos, vec3 viewDir){vec3 lightDir = normalize(light.position - fragPos);// 漫反射光照分量float diff = max(dot(normal, lightDir), 0.0);// 镜面光光照分量vec3 reflectDir = reflect(-lightDir, normal);float spec = pow(max(dot(viewDir, reflectDir), 0.0), 32);// 衰减float distance = length(light.position - fragPos);float attenuation = 1.0 / (light.constant + light.linear * distance +light.quadratic * distance * distance);// 合并结果vec3 ambient = light.ambient * vec3(texture(texture_diffuse1, TexCoords));vec3 diffuse = light.diffuse * diff * vec3(texture(texture_diffuse1, TexCoords));vec3 specular = light.specular * spec * vec3(texture(texture_specular1, TexCoords));ambient *= attenuation;diffuse *= attenuation;specular *= attenuation;return (ambient + diffuse + specular);
}void main(){ // 属性vec3 norm = normalize(Normal);vec3 viewDir = normalize(viewPos - FragPos);vec3 result;// 点光源for(int i = 0; i < NR_POINT_LIGHTS; i++){result += CalcPointLight(pointLights[i], norm, FragPos, viewDir);}//vec4 diffuse = texture(texture_diffuse1, TexCoords);//vec4 specular = texture(texture_specular1, TexCoords);FragColor = vec4(result, 1.0);
}

// 点光源
ourShader.use();
ourShader.setVec3("pointLights[0].position", pointLightPositions[0]);
ourShader.setVec3("pointLights[0].ambient", 0.4f, 0.4f, 0.4f);
ourShader.setVec3("pointLights[0].diffuse", 0.8f, 0.8f, 0.8f);
ourShader.setVec3("pointLights[0].specular", 1.0f, 1.0f, 1.0f);
ourShader.setFloat("pointLights[0].constant", 1.0f);
ourShader.setFloat("pointLights[0].linear", 0.09f);
ourShader.setFloat("pointLights[0].quadratic", 0.032f);ourShader.setVec3("pointLights[1].position", pointLightPositions[1]);
ourShader.setVec3("pointLights[1].ambient", 0.4f, 0.4f, 0.4f);
ourShader.setVec3("pointLights[1].diffuse", 0.8f, 0.8f, 0.8f);
ourShader.setVec3("pointLights[1].specular", 1.0f, 1.0f, 1.0f);
ourShader.setFloat("pointLights[1].constant", 1.0f);
ourShader.setFloat("pointLights[1].linear", 0.09f);
ourShader.setFloat("pointLights[1].quadratic", 0.032f);
while (!glfwWindowShouldClose(window))
{        ourShader.use();ourShader.setVec3("viewPos", camera.Position);// view/projection transformationsglm::mat4 projection = glm::perspective(glm::radians(camera.Zoom), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f);glm::mat4 view = camera.GetViewMatrix();ourShader.setMat4("projection", projection);ourShader.setMat4("view", view);// 渲染这个模型glm::mat4 model = glm::mat4(1.0f);model = glm::translate(model, glm::vec3(0.0f, 0.0f, 0.0f));model = glm::scale(model, glm::vec3(0.1f, 0.1f, 0.1f));ourShader.setMat4("model", model);ourModel.Draw(ourShader);
......
// 上一节自定义mesh写的函数
void Draw(Shader& shader) {// 绑定适合的纹理unsigned int diffuseNr = 1;unsigned int specularNr = 1;unsigned int normalNr = 1;unsigned int heightNr = 1;for (unsigned int i = 0; i < textures.size(); i++) {glActiveTexture(GL_TEXTURE0 + i);string number;string name = textures[i].type;if (name == "texture_diffuse") {number = std::to_string(diffuseNr++);}else if (name == "texture_specular") {number = std::to_string(specularNr++);}else if (name == "texture_normal") {number = std::to_string(normalNr++);}else if (name == "texture_height") {number = std::to_string(heightNr++);}// 给shader的采样器设置纹理单元glUniform1i(glGetUniformLocation(shader.ID, (name + number).c_str()), i);glBindTexture(GL_TEXTURE_2D, textures[i].id);}// 绘画glBindVertexArray(VAO);glDrawElements(GL_TRIANGLES, static_cast(indices.size()), GL_UNSIGNED_INT, 0);// 绘画完设为默认值glActiveTexture(GL_TEXTURE0);
}