LearnOpenGL-笔记-其二

鉴于之前学习的效率太低，我决定采用效率更高，见效更快的学习方法来学习我们的OpenGL章节。

着色器

这一节让我们对着色器做一个总结，我们不妨先看最后我们写好的着色器类：

#ifndef SHADER_H
#define SHADER_H

#include <glad/glad.h>
#include <glm/glm.hpp>

#include <string>
#include <fstream>
#include <sstream>
#include <iostream>

class Shader
{
public:
    unsigned int ID;
    // constructor generates the shader on the fly
    // ------------------------------------------------------------------------
    Shader(const char* vertexPath, const char* fragmentPath)
    {
        // 1. retrieve the vertex/fragment source code from filePath
        std::string vertexCode;
        std::string fragmentCode;
        std::ifstream vShaderFile;
        std::ifstream fShaderFile;
        // ensure ifstream objects can throw exceptions:
        vShaderFile.exceptions(std::ifstream::failbit | std::ifstream::badbit);
        fShaderFile.exceptions(std::ifstream::failbit | std::ifstream::badbit);//抛出异常
        try
        {
            // open files
            vShaderFile.open(vertexPath);
            fShaderFile.open(fragmentPath);
            std::stringstream vShaderStream, fShaderStream;
            // read file's buffer contents into streams
            vShaderStream << vShaderFile.rdbuf();//<<箭头的方向指向流的方向
            fShaderStream << fShaderFile.rdbuf();//直接获取ifstream的底层缓冲区//缓冲区（Buffer）
                                                 //在流对象（如文件流、网络流等）与硬件设备
                                                 //（如磁盘、网卡等）之间的交互中减少流对象访问
                                                 // 硬件设备的次数
            // close file handlers
            vShaderFile.close();
            fShaderFile.close();
            // convert stream into string
            vertexCode = vShaderStream.str();
            fragmentCode = fShaderStream.str();
        }
        catch (std::ifstream::failure& e)
        {
            std::cout << "ERROR::SHADER::FILE_NOT_SUCCESSFULLY_READ: " << e.what() << std::endl;
        }//e是我们的异常对象，.what()则返回描述错误原因的字符串如"failed to open file"
        const char* vShaderCode = vertexCode.c_str();//c_str()的作用将string类型字符串转换为c风格字符
                                                     //串，一般只有需要与C接口交互时才会使用
        const char* fShaderCode = fragmentCode.c_str();
        // 2. compile shaders
        unsigned int vertex, fragment;
        // vertex shader
        vertex = glCreateShader(GL_VERTEX_SHADER);
        glShaderSource(vertex, 1, &vShaderCode, NULL);
        glCompileShader(vertex);
        checkCompileErrors(vertex, "VERTEX");//着色器的流程：Create->Source->Compile，分别代表创建
                                             //着色器，着色器绑定源码，编译着色器，检查着色器状态
        // fragment Shader
        fragment = glCreateShader(GL_FRAGMENT_SHADER);
        glShaderSource(fragment, 1, &fShaderCode, NULL);
        glCompileShader(fragment);
        checkCompileErrors(fragment, "FRAGMENT");
        // shader Program
        ID = glCreateProgram();//ID是整个着色器程序的识别符
        glAttachShader(ID, vertex);
        glAttachShader(ID, fragment);
        glLinkProgram(ID);
        checkCompileErrors(ID, "PROGRAM");
        // delete the shaders as they're linked into our program now and no longer necessary
        glDeleteShader(vertex);
        glDeleteShader(fragment);//链接后就可以删除之前的顶点着色器和片元着色器了

    }
    // activate the shader
    // ------------------------------------------------------------------------
    void use() const
    {
        glUseProgram(ID);//激活着色器
    }
    // utility uniform functions//后续的函数统一设置着色器的uniform变量
    // ------------------------------------------------------------------------
    void setBool(const std::string& name, bool value) const
    {
        glUniform1i(glGetUniformLocation(ID, name.c_str()), (int)value);
    }
    // ------------------------------------------------------------------------
    void setInt(const std::string& name, int value) const
    {
        glUniform1i(glGetUniformLocation(ID, name.c_str()), value);
    }
    // ------------------------------------------------------------------------
    void setFloat(const std::string& name, float value) const
    {
        glUniform1f(glGetUniformLocation(ID, name.c_str()), value);
    }
    // ------------------------------------------------------------------------
    void setVec2(const std::string& name, const glm::vec2& value) const
    {
        glUniform2fv(glGetUniformLocation(ID, name.c_str()), 1, &value[0]);
    }
    void setVec2(const std::string& name, float x, float y) const
    {
        glUniform2f(glGetUniformLocation(ID, name.c_str()), x, y);
    }
    // ------------------------------------------------------------------------
    void setVec3(const std::string& name, const glm::vec3& value) const
    {
        glUniform3fv(glGetUniformLocation(ID, name.c_str()), 1, &value[0]);
    }
    void setVec3(const std::string& name, float x, float y, float z) const
    {
        glUniform3f(glGetUniformLocation(ID, name.c_str()), x, y, z);
    }
    // ------------------------------------------------------------------------
    void setVec4(const std::string& name, const glm::vec4& value) const
    {
        glUniform4fv(glGetUniformLocation(ID, name.c_str()), 1, &value[0]);
    }
    void setVec4(const std::string& name, float x, float y, float z, float w) const
    {
        glUniform4f(glGetUniformLocation(ID, name.c_str()), x, y, z, w);
    }
    // ------------------------------------------------------------------------
    void setMat2(const std::string& name, const glm::mat2& mat) const
    {
        glUniformMatrix2fv(glGetUniformLocation(ID, name.c_str()), 1, GL_FALSE, &mat[0][0]);
    }
    // ------------------------------------------------------------------------
    void setMat3(const std::string& name, const glm::mat3& mat) const
    {
        glUniformMatrix3fv(glGetUniformLocation(ID, name.c_str()), 1, GL_FALSE, &mat[0][0]);
    }
    // ------------------------------------------------------------------------
    void setMat4(const std::string& name, const glm::mat4& mat) const
    {
        glUniformMatrix4fv(glGetUniformLocation(ID, name.c_str()), 1, GL_FALSE, &mat[0][0]);
    }

private:
    // utility function for checking shader compilation/linking errors.
    // ------------------------------------------------------------------------
    void checkCompileErrors(GLuint shader, std::string type)
    {
        GLint success;
        GLchar infoLog[1024];
        if (type != "PROGRAM")
        {
            glGetShaderiv(shader, GL_COMPILE_STATUS, &success);//glGetShaderiv获取整个着色器状态
                                                               //检查编译阶段
            if (!success)
            {
                glGetShaderInfoLog(shader, 1024, NULL, infoLog);
                std::cout << "ERROR::SHADER_COMPILATION_ERROR of type: " << type << "\n" << infoLog << "\n -- --------------------------------------------------- -- " << std::endl;
            }
        }
        else
        {
            glGetProgramiv(shader, GL_LINK_STATUS, &success);//检查链接阶段
            if (!success)
            {
                glGetProgramInfoLog(shader, 1024, NULL, infoLog);
                std::cout << "ERROR::PROGRAM_LINKING_ERROR of type: " << type << "\n" << infoLog << "\n -- --------------------------------------------------- -- " << std::endl;
            }
        }
    }
};
#endif

这是作为我们的头文件存储的shader.h，我们在这里定义有关shader的方法，封装并简化OpenGL着色器（Shader）的创建、编译、链接和使用过程。我们来一段段分析这个着色器类：

unsigned int ID;
// constructor generates the shader on the fly
// ------------------------------------------------------------------------
Shader(const char* vertexPath, const char* fragmentPath)
{
    // 1. retrieve the vertex/fragment source code from filePath
    std::string vertexCode;
    std::string fragmentCode;
    std::ifstream vShaderFile;
    std::ifstream fShaderFile;
    // ensure ifstream objects can throw exceptions:
    vShaderFile.exceptions(std::ifstream::failbit | std::ifstream::badbit);
    fShaderFile.exceptions(std::ifstream::failbit | std::ifstream::badbit);//抛出异常
    try
    {
        // open files
        vShaderFile.open(vertexPath);
        fShaderFile.open(fragmentPath);
        std::stringstream vShaderStream, fShaderStream;
        // read file's buffer contents into streams
        vShaderStream << vShaderFile.rdbuf();//<<箭头的方向指向流的方向
        fShaderStream << fShaderFile.rdbuf();//直接获取ifstream的底层缓冲区//缓冲区（Buffer）
                                             //在流对象（如文件流、网络流等）与硬件设备
                                             //（如磁盘、网卡等）之间的交互中减少流对象访问
                                             // 硬件设备的次数
        // close file handlers
        vShaderFile.close();
        fShaderFile.close();
        // convert stream into string
        vertexCode = vShaderStream.str();
        fragmentCode = fShaderStream.str();
    }
    catch (std::ifstream::failure& e)
    {
        std::cout << "ERROR::SHADER::FILE_NOT_SUCCESSFULLY_READ: " << e.what() << std::endl;
    }//e是我们的异常对象，.what()则返回描述错误原因的字符串如"failed to open file"
    const char* vShaderCode = vertexCode.c_str();//c_str()的作用将string类型字符串转换为c风格字符
                                                 //串，一般只有需要与C接口交互时才会使用
    const char* fShaderCode = fragmentCode.c_str();
    // 2. compile shaders
    unsigned int vertex, fragment;
    // vertex shader
    vertex = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertex, 1, &vShaderCode, NULL);
    glCompileShader(vertex);
    checkCompileErrors(vertex, "VERTEX");//着色器的流程：Create->Source->Compile，分别代表创建
                                         //着色器，着色器绑定源码，编译着色器，检查着色器状态
    // fragment Shader
    fragment = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragment, 1, &fShaderCode, NULL);
    glCompileShader(fragment);
    checkCompileErrors(fragment, "FRAGMENT");
    // shader Program
    ID = glCreateProgram();//ID是整个着色器程序的识别符
    glAttachShader(ID, vertex);
    glAttachShader(ID, fragment);
    glLinkProgram(ID);
    checkCompileErrors(ID, "PROGRAM");
    // delete the shaders as they're linked into our program now and no longer necessary
    glDeleteShader(vertex);
    glDeleteShader(fragment);//链接后就可以删除之前的顶点着色器和片元着色器了

}

ID就是我们在程序这一侧的着色器识别符，然后是我们Shader的有参构造，我们先定义了两个string对象和两个ifstream对象用来读取我们自定义的shader文件，这里调用了ifstream自带的抛出异常方法：发生failbit或者badbit就抛出异常（failbit代表逻辑错误但流本身没有损坏，badbit则代表更严重的错误如文件无法打开等导致流异常）。然后我们用一个try、catch来防止读取文件时报错，我们按照文件路径打开输入流后创建两个stringstream来获取ifstream中的rdbuf（rdbuf是我们的ifstream与存储在硬件设备之间的缓冲区，如果没有缓冲区我们每次想要得到ifstream中的数据都要对硬件设备发起一次访问，而有了缓冲区可以大大减少访问次数）,之后进行类型转换即可。这里可以注意catch执行：我们调用ifstream返回的异常类型中的what()函数获得异常类型（.what()返回描述异常类型的字符串）。

一切正常的话，我们就可以得到自定义的顶点着色器和片元着色器的定义内容，在这里我们要进行c_str类型的转换，也就是c风格的字符串，这是因为我们需要去调用c语言写好的接口，不过一般情况下我们还是不转换为好。接着就是我们定义着色器的老步骤：定义一个ID，绑定源码，编译，检测编译是否正常。最后我们还要将我们的ID，也就是总的着色器运行程序的识别符绑定，然后链接上我们的着色器并检测是否有异常，最后将之前生成的两个已链接的着色器删除即可。

在这里我们介绍如何检测着色器编译和链接过程是否异常：

void checkCompileErrors(GLuint shader, std::string type)
{
    GLint success;
    GLchar infoLog[1024];
    if (type != "PROGRAM")
    {
        glGetShaderiv(shader, GL_COMPILE_STATUS, &success);//glGetShaderiv获取整个着色器状态
                                                           //检查编译阶段
        if (!success)
        {
            glGetShaderInfoLog(shader, 1024, NULL, infoLog);
            std::cout << "ERROR::SHADER_COMPILATION_ERROR of type: " << type << "\n" << infoLog << "\n -- --------------------------------------------------- -- " << std::endl;
        }
    }
    else
    {
        glGetProgramiv(shader, GL_LINK_STATUS, &success);//检查链接阶段
        if (!success)
        {
            glGetProgramInfoLog(shader, 1024, NULL, infoLog);
            std::cout << "ERROR::PROGRAM_LINKING_ERROR of type: " << type << "\n" << infoLog << "\n -- --------------------------------------------------- -- " << std::endl;
        }
    }
}

在这里可以补充一下GLint类型和普通int的区别：

不难看出我们的关键在于我们的glGetShaderiv函数，这个函数准确地说是用来查询着色器状态的，我们的三个参数分别代表指定查询的着色器对象，查询的着色器具体属性，以及指向存储查询结果的整型变量的指针。如果返回的success为false我们将错误信息打印出来。

现在我们已经知道了如何从自定义的shader文件中读取代码并创建、汇编、链接，现在要学习如何去使用shader了。

 void use() const
 {
     glUseProgram(ID);//激活着色器
 }
 // utility uniform functions//后续的函数统一设置着色器的uniform变量
 // ------------------------------------------------------------------------
 void setBool(const std::string& name, bool value) const
 {
     glUniform1i(glGetUniformLocation(ID, name.c_str()), (int)value);
 }
 // ------------------------------------------------------------------------
 void setInt(const std::string& name, int value) const
 {
     glUniform1i(glGetUniformLocation(ID, name.c_str()), value);
 }
 // ------------------------------------------------------------------------
 void setFloat(const std::string& name, float value) const
 {
     glUniform1f(glGetUniformLocation(ID, name.c_str()), value);
 }

我们封装一个use函数，其中使用glUseProgram(ID)来激活着色器的运行程序。后续的一系列set系列函数则是我们定义如何修改着色器定义中的uniform变量：也就是着色器定义中的常量，都是一个模板：获取着色器的uniform变量并绑定给定的值即可。

上述的是我们的shader.h文件的内容，现在让我们来看看如何一些基本的着色器的定义。

顶点着色器（vertexShader）:

#version 330 core
layout (location = 0) in vec3 aPos;

uniform mat4 model;
uniform mat4 view;
uniform mat4 projection;

void main()
{
	gl_Position = projection * view * model * vec4(aPos, 1.0);
}

片元着色器：

#version 330 core
out vec4 FragColor;
  
uniform vec3 objectColor;
uniform vec3 lightColor;

void main()
{
    FragColor = vec4(lightColor * objectColor, 1.0);
}

可以看到着色器最开始的一行语句都是先定义好我们的版本号和运行模式（核心模式见前文），定义好输入和输出的变量，函数。

我们在源程序中通过下列语句即可实现着色器的使用：

Shader ourShader("4.2.texture.vs", "4.2.texture.fs");

......

ourShader.use(); // don't forget to activate/use the shader before setting uniforms!
    // either set it manually like so:
    glUniform1i(glGetUniformLocation(ourShader.ID, "texture1"), 0);
    // or set it via the texture class
    ourShader.setInt("texture2", 1);

我们将文件的名字作为构造函数的参数传入，使用use()函数激活着色器之后设置uniform变量即可。

纹理

我们设置的纹理的代码如下：

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow *window);

// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;

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);

    // glad: load all OpenGL function pointers
    // ---------------------------------------
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }

    // build and compile our shader zprogram
    // ------------------------------------
    Shader ourShader("4.2.texture.vs", "4.2.texture.fs");

    // set up vertex data (and buffer(s)) and configure vertex attributes
    // ------------------------------------------------------------------
    float vertices[] = {
        // positions          // colors           // texture coords
         0.5f,  0.5f, 0.0f,   1.0f, 0.0f, 0.0f,   1.0f, 1.0f, // top right
         0.5f, -0.5f, 0.0f,   0.0f, 1.0f, 0.0f,   1.0f, 0.0f, // bottom right
        -0.5f, -0.5f, 0.0f,   0.0f, 0.0f, 1.0f,   0.0f, 0.0f, // bottom left
        -0.5f,  0.5f, 0.0f,   1.0f, 1.0f, 0.0f,   0.0f, 1.0f  // top left 
    };
    unsigned int indices[] = {
        0, 1, 3, // first triangle
        1, 2, 3  // second triangle
    };
    unsigned int VBO, VAO, EBO;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    glGenBuffers(1, &EBO);

    glBindVertexArray(VAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

    // position attribute
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);
    // color attribute
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(3 * sizeof(float)));
    glEnableVertexAttribArray(1);
    // texture coord attribute
    glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(6 * sizeof(float)));
    glEnableVertexAttribArray(2);


    // load and create a texture 
    // -------------------------
    unsigned int texture1, texture2;
    // texture 1
    // ---------
    glGenTextures(1, &texture1);
    glBindTexture(GL_TEXTURE_2D, texture1); 
     // set the texture wrapping parameters
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);	// set texture wrapping to GL_REPEAT (default wrapping method)
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    // set texture filtering parameters
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    // load image, create texture and generate mipmaps
    int width, height, nrChannels;
    stbi_set_flip_vertically_on_load(true); // tell stb_image.h to flip loaded texture's on the y-axis.
    // The FileSystem::getPath(...) is part of the GitHub repository so we can find files on any IDE/platform; replace it with your own image path.
    unsigned char *data = stbi_load(FileSystem::getPath("resources/textures/container.jpg").c_str(), &width, &height, &nrChannels, 0);
    if (data)
    {
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, data);
        glGenerateMipmap(GL_TEXTURE_2D);
    }
    else
    {
        std::cout << "Failed to load texture" << std::endl;
    }
    stbi_image_free(data);
    // texture 2
    // ---------
    glGenTextures(1, &texture2);
    glBindTexture(GL_TEXTURE_2D, texture2);
    // set the texture wrapping parameters
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);	// set texture wrapping to GL_REPEAT (default wrapping method)
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    // set texture filtering parameters
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    // load image, create texture and generate mipmaps
    data = stbi_load(FileSystem::getPath("resources/textures/awesomeface.png").c_str(), &width, &height, &nrChannels, 0);
    if (data)
    {
        // note that the awesomeface.png has transparency and thus an alpha channel, so make sure to tell OpenGL the data type is of GL_RGBA
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);
        glGenerateMipmap(GL_TEXTURE_2D);
    }
    else
    {
        std::cout << "Failed to load texture" << std::endl;
    }
    stbi_image_free(data);

    // tell opengl for each sampler to which texture unit it belongs to (only has to be done once)
    // -------------------------------------------------------------------------------------------
    ourShader.use(); // don't forget to activate/use the shader before setting uniforms!
    // either set it manually like so:
    glUniform1i(glGetUniformLocation(ourShader.ID, "texture1"), 0);
    // or set it via the texture class
    ourShader.setInt("texture2", 1);



    // render loop
    // -----------
    while (!glfwWindowShouldClose(window))
    {
        // input
        // -----
        processInput(window);

        // render
        // ------
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        // bind textures on corresponding texture units
        glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D, texture1);
        glActiveTexture(GL_TEXTURE1);
        glBindTexture(GL_TEXTURE_2D, texture2);

        // render container
        ourShader.use();
        glBindVertexArray(VAO);
        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);

        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    // optional: de-allocate all resources once they've outlived their purpose:
    // ------------------------------------------------------------------------
    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);
    glDeleteBuffers(1, &EBO);

    // glfw: terminate, clearing all previously allocated GLFW resources.
    // ------------------------------------------------------------------
    glfwTerminate();
    return 0;
}

// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
void processInput(GLFWwindow *window)
{
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);
}

// glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    // make sure the viewport matches the new window dimensions; note that width and 
    // height will be significantly larger than specified on retina displays.
    glViewport(0, 0, width, height);
}

我们只说说相比之前内容的新东西即可：

    unsigned int texture1, texture2;
    // texture 1
    // ---------
    glGenTextures(1, &texture1);
    glBindTexture(GL_TEXTURE_2D, texture1); 
     // set the texture wrapping parameters
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);	// set texture wrapping to GL_REPEAT (default wrapping method)
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    // set texture filtering parameters
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    // load image, create texture and generate mipmaps
    int width, height, nrChannels;
    stbi_set_flip_vertically_on_load(true); // tell stb_image.h to flip loaded texture's on the y-axis.
    // The FileSystem::getPath(...) is part of the GitHub repository so we can find files on any IDE/platform; replace it with your own image path.
    unsigned char *data = stbi_load(FileSystem::getPath("resources/textures/container.jpg").c_str(), &width, &height, &nrChannels, 0);
    if (data)
    {
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, data);
        glGenerateMipmap(GL_TEXTURE_2D);
    }
    else
    {
        std::cout << "Failed to load texture" << std::endl;
    }
    stbi_image_free(data);
    // texture 2
    // ---------
    glGenTextures(1, &texture2);
    glBindTexture(GL_TEXTURE_2D, texture2);
    // set the texture wrapping parameters
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);	// set texture wrapping to GL_REPEAT (default wrapping method)
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    // set texture filtering parameters
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    // load image, create texture and generate mipmaps
    data = stbi_load(FileSystem::getPath("resources/textures/awesomeface.png").c_str(), &width, &height, &nrChannels, 0);
    if (data)
    {
        // note that the awesomeface.png has transparency and thus an alpha channel, so make sure to tell OpenGL the data type is of GL_RGBA
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);
        glGenerateMipmap(GL_TEXTURE_2D);
    }
    else
    {
        std::cout << "Failed to load texture" << std::endl;
    }
    stbi_image_free(data);

可以看到我们的纹理本质上和着色器的定义也类似：创建一个标识符，绑定纹理，设置参数，加载纹理数据（如图像），如果存在就将图像数据传给我们的纹理并生成多级渐远纹理，绘制完成后就释放加载的纹理数据。

我们从设置参数的glTexParameteri函数开始讲起：

在我们的代码中可以看到设置了纹理目标的四个参数，分别代表：

加载纹理的函数是：stbi_load，显然这是一个stb_image.h头文件的函数。

我们再来看看我们的顶点着色器和片元着色器的定义：

#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec3 aColor;
layout (location = 2) in vec2 aTexCoord;

out vec3 ourColor;
out vec2 TexCoord;

void main()
{
	gl_Position = vec4(aPos, 1.0);
	ourColor = aColor;
	TexCoord = vec2(aTexCoord.x, aTexCoord.y);
}

以及：

#version 330 core
out vec4 FragColor;

in vec3 ourColor;
in vec2 TexCoord;

// texture samplers
uniform sampler2D texture1;
uniform sampler2D texture2;

void main()
{
	// linearly interpolate between both textures (80% container, 20% awesomeface)
	FragColor = mix(texture(texture1, TexCoord), texture(texture2, TexCoord), 0.2);
}

顶点着色器就是把传入的颜色、坐标、纹理坐标应用即可，而片元着色器还做了一个纹理的混合处理

然后是将图像数据传输给我们的纹理的函数：glTexImage2D。

这些OpenGL内部实现好的函数我们不用去背，反正也背不下来，但是我们要记得具体的执行流程，到用的时候得心里有数。

在这里得介绍一下多级渐远纹理的概念：简单地说就是近大远小导致看见远处的事物小，虽然实际构建的过程中每个物体的像素按理说是一样多的，但是远处的物体可能我们能看到的只有一两个像素，却依然照本宣科地一个像素一个像素地去渲染，也不过是对计算资源多余的浪费罢了，还会导致一些采样问题如摩尔纹。多级渐远纹理就是为了处理这样一种情况而存在的，对于越来越远的物体，我们的纹理会越来越“模糊”，其实就是对像素的采样率在不断降低，分辨率在降低，这样提高观感的同时还能减小资源的浪费。

我们用glGenerateMipmap函数来实现多级渐远纹理的生成。

得到结果图：

变换

聊到变换，就离不开我们的线性代数，比如我们的平移，翻转，旋转等操作的实质其实都是通过矩阵的计算得到的。变换这个词本身就是线性代数的一种应用，在这里我就不再赘述数学的基础部分，不了解的大家可以自行去查阅，我放一些比较重要的结论供后续代码使用时解释：

在数学上讨论如何生成这样的矩阵仍然超出了本节内容。但是记住，即使这样一个矩阵也不能完全解决万向节死锁问题（尽管会极大地避免）。避免万向节死锁的真正解决方案是使用四元数(Quaternion)，它不仅更安全，而且计算会更有效率。四元数可能会在后面的教程中讨论。

在这里我想讨论的是两个东西：齐次坐标系与万向锁。

齐次坐标系的引入主要是为了克服同维度下我们平移时无法用一个矩阵来表示的问题（比如你想斜上方平移2个单位，你必须先向右平移再向上平移，需要两个矩阵），而多引入一个维度后我们就可以统一用矩阵的乘法来做（斜上方变成了），这样所有的变换操作都可以用矩阵的乘法来做；

万向锁则是一个经典问题，简单来说，当我们沿着俯仰角旋转九十度后，你会发现你的另外两个轴重合了，这就导致你会失去一个可以操作的轴。正如上文所述，解决万向锁的方法就是四元数。

我们先实现一个简单的变换程序来作为下一节的引子：

while (!glfwWindowShouldClose(window))
    {
        // input
        // -----
        processInput(window);

        // render
        // ------
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        // bind textures on corresponding texture units
        glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D, texture1);
        glActiveTexture(GL_TEXTURE1);
        glBindTexture(GL_TEXTURE_2D, texture2);

        // create transformations
        glm::mat4 transform = glm::mat4(1.0f); // make sure to initialize matrix to identity matrix first
        transform = glm::translate(transform, glm::vec3(0.5f, -0.5f, 0.0f));
        transform = glm::rotate(transform, (float)glfwGetTime(), glm::vec3(0.0f, 0.0f, 1.0f));

        // get matrix's uniform location and set matrix
        ourShader.use();
        unsigned int transformLoc = glGetUniformLocation(ourShader.ID, "transform");
        glUniformMatrix4fv(transformLoc, 1, GL_FALSE, glm::value_ptr(transform));

        // render container
        glBindVertexArray(VAO);
        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);

        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

可以看到这是我们的render loop，其中我们先生成了一个变换矩阵transform，然后分别调用了glm库中的translate和rotate函数来实现一个平移和旋转的效果。

坐标系统

变换只是一些基本的操作，真正重要的是现在要介绍的：坐标系统。

还记得我们渲染管线的步骤吗？我们需要将一些现实世界的三维坐标转换成我们屏幕上的二维坐标，这个过程其实涉及到坐标系的不断变换。

看起来确实很复杂，我们来一步步地理清：

首先我们拥有的是一个局部空间：这个空间内定义了你的物体在局部空间的相对距离，比如你的物体在局部空间的正z轴上；然后我们通过一个模型变换矩阵（Model）从局部空间变换为世界空间坐标系，这个坐标系里不仅有你的物体，还有别的物体如摄像机，光源等；然后我们通过一个观察矩阵（View）将我们的坐标系从世界坐标系转化为观察坐标系，更准确地说，其实就是以摄像机为基准进行观察的坐标系；然后我们还需要一个透视变换矩阵（Projection）将摄像机可看到的空间进行裁剪，超出裁剪空间的部分不可见；最后通过视口变换就可以得到我们在屏幕上可以看见的东西了。

让我们看看具体的代码实现是如何实现的吧：

// create transformations
        glm::mat4 model         = glm::mat4(1.0f); // make sure to initialize matrix to identity matrix first
        glm::mat4 view          = glm::mat4(1.0f);
        glm::mat4 projection    = glm::mat4(1.0f);
        model = glm::rotate(model, glm::radians(-55.0f), glm::vec3(1.0f, 0.0f, 0.0f));
        view  = glm::translate(view, glm::vec3(0.0f, 0.0f, -3.0f));
        projection = glm::perspective(glm::radians(45.0f), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f);
        // retrieve the matrix uniform locations
        unsigned int modelLoc = glGetUniformLocation(ourShader.ID, "model");
        unsigned int viewLoc  = glGetUniformLocation(ourShader.ID, "view");
        // pass them to the shaders (3 different ways)
        glUniformMatrix4fv(modelLoc, 1, GL_FALSE, glm::value_ptr(model));
        glUniformMatrix4fv(viewLoc, 1, GL_FALSE, &view[0][0]);
        // note: currently we set the projection matrix each frame, but since the projection matrix rarely changes it's often best practice to set it outside the main loop only once.
        ourShader.setMat4("projection", projection);

我们先将M,V,P矩阵都初始化为单位矩阵，然后我们将M矩阵沿着x轴旋转-55度，其实也就是向下倾斜（OpenGL是右手坐标系），V矩阵向z轴方向移动-3个单位，其实就是摄像机整体向后移动了三个单位，P矩阵的参数里的45度代表的是FOV，也就是视野角度，然后是宽高比，近裁面和远裁面的大小，然后我们要将我们的MVP矩阵的定义传递给我们着色器中的uniform变量。

现在的代码中还缺少一个非常重要的参数：深度，也就是在z轴上的差异。

如果没有深度，本质上来说虽然我们是在三维空间进行处理，但是无法处理不同z值会导致远近重叠，所以我们还要去设置Z缓冲。OpenGL存储它的所有深度信息于一个Z缓冲(Z-buffer)中，也被称为深度缓冲(Depth Buffer)。GLFW会自动为你生成这样一个缓冲（就像它也有一个颜色缓冲来存储输出图像的颜色）。深度值存储在每个片段里面（作为片段的z值），当片段想要输出它的颜色时，OpenGL会将它的深度值和z缓冲进行比较，如果当前的片段在其它片段之后，它将会被丢弃，否则将会覆盖。这个过程称为深度测试(Depth Testing)，它是由OpenGL自动完成的。

开启深度测试后的三维物体be like：

摄像机

我们从后往前推进，先看一下写好的camera.h文件：

#ifndef CAMERA_H
#define CAMERA_H

#include <glad/glad.h>
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>

// Defines several possible options for camera movement. Used as abstraction to stay away from window-system specific input methods
enum Camera_Movement {
    FORWARD,
    BACKWARD,
    LEFT,
    RIGHT
};

// Default camera values
const float YAW = -90.0f;//水平旋转角度
const float PITCH = 0.0f;//竖直旋转角度
const float SPEED = 2.5f;//移动速度
const float SENSITIVITY = 0.01f;//鼠标灵敏度
const float ZOOM = 45.0f;//视野角度（FOV）


// An abstract camera class that processes input and calculates the corresponding Euler Angles, Vectors and Matrices for use in OpenGL
class Camera
{
public:
    // camera Attributes
    glm::vec3 Position;
    glm::vec3 Front;
    glm::vec3 Up;
    glm::vec3 Right;
    glm::vec3 WorldUp;
    // euler Angles
    float Yaw;
    float Pitch;
    // camera options
    float MovementSpeed;
    float MouseSensitivity;
    float Zoom;

    // constructor with vectors
    Camera(glm::vec3 position = glm::vec3(0.0f, 0.0f, 0.0f), glm::vec3 up = glm::vec3(0.0f, 1.0f, 0.0f), float yaw = YAW, float pitch = PITCH) : Front(glm::vec3(0.0f, 0.0f, -1.0f)), MovementSpeed(SPEED), MouseSensitivity(SENSITIVITY), Zoom(ZOOM)
    {
        Position = position;
        WorldUp = up;
        Yaw = yaw;
        Pitch = pitch;
        updateCameraVectors();
    }
    // constructor with scalar values
    Camera(float posX, float posY, float posZ, float upX, float upY, float upZ, float yaw, float pitch) : Front(glm::vec3(0.0f, 0.0f, -1.0f)), MovementSpeed(SPEED), MouseSensitivity(SENSITIVITY), Zoom(ZOOM)
    {
        Position = glm::vec3(posX, posY, posZ);
        WorldUp = glm::vec3(upX, upY, upZ);
        Yaw = yaw;
        Pitch = pitch;
        updateCameraVectors();
    }

    // returns the view matrix calculated using Euler Angles and the LookAt Matrix
    glm::mat4 GetViewMatrix()
    {
        return glm::lookAt(Position, Position + Front, Up);//LookAt函数，三个参数分别为摄像机位置
                                                           //目标点和上方向
    }

    // processes input received from any keyboard-like input system. Accepts input parameter in the form of camera defined ENUM (to abstract it from windowing systems)
    void ProcessKeyboard(Camera_Movement direction, float deltaTime)
    {
        float velocity = MovementSpeed * deltaTime;
        if (direction == FORWARD)
            Position += Front * velocity;
        if (direction == BACKWARD)
            Position -= Front * velocity;
        if (direction == LEFT)
            Position -= Right * velocity;
        if (direction == RIGHT)
            Position += Right * velocity;
    }

    // processes input received from a mouse input system. Expects the offset value in both the x and y direction.
    void ProcessMouseMovement(float xoffset, float yoffset, GLboolean constrainPitch = true)
    {
        xoffset *= MouseSensitivity;
        yoffset *= MouseSensitivity;

        Yaw += xoffset;
        Pitch += yoffset;//更新偏航角和俯仰角

        // make sure that when pitch is out of bounds, screen doesn't get flipped
        if (constrainPitch)
        {
            if (Pitch > 89.0f)
                Pitch = 89.0f;
            if (Pitch < -89.0f)
                Pitch = -89.0f;
        }//限制俯仰角放置反转

        // update Front, Right and Up Vectors using the updated Euler angles
        updateCameraVectors();//更新摄像机方向向量
    }

    // processes input received from a mouse scroll-wheel event. Only requires input on the vertical wheel-axis
    void ProcessMouseScroll(float yoffset)
    {
        Zoom -= (float)yoffset;
        if (Zoom < 10.0f)
            Zoom = 10.0f;
        if (Zoom > 45.0f)
            Zoom = 45.0f;
    }

private:
    // calculates the front vector from the Camera's (updated) Euler Angles
    void updateCameraVectors()
    {
        // calculate the new Front vector
        glm::vec3 front;
        front.x = cos(glm::radians(Yaw)) * cos(glm::radians(Pitch));//radians将度数转换为弧度
        front.y = sin(glm::radians(Pitch));
        front.z = sin(glm::radians(Yaw)) * cos(glm::radians(Pitch));
        Front = glm::normalize(front);
        // also re-calculate the Right and Up vector
        Right = glm::normalize(glm::cross(Front, WorldUp));  // normalize the vectors, because their length gets closer to 0 the more you look up or down which results in slower movement.
        Up = glm::normalize(glm::cross(Right, Front));
    }
};
#endif

这个.h文件中有三个地方值得一提：

    // returns the view matrix calculated using Euler Angles and the LookAt Matrix
    glm::mat4 GetViewMatrix()
    {
        return glm::lookAt(Position, Position + Front, Up);//LookAt函数，三个参数分别为摄像机位置
                                                           //目标点和上方向
    }

我们获取视图矩阵（View矩阵）可以直接通过glm库自带的LookAt函数来得到。

// processes input received from a mouse input system. Expects the offset value in both the x and y direction.
void ProcessMouseMovement(float xoffset, float yoffset, GLboolean constrainPitch = true)
{
    xoffset *= MouseSensitivity;
    yoffset *= MouseSensitivity;

    Yaw += xoffset;
    Pitch += yoffset;//更新偏航角和俯仰角

    // make sure that when pitch is out of bounds, screen doesn't get flipped
    if (constrainPitch)
    {
        if (Pitch > 89.0f)
            Pitch = 89.0f;
        if (Pitch < -89.0f)
            Pitch = -89.0f;
    }//限制俯仰角放置反转

    // update Front, Right and Up Vectors using the updated Euler angles
    updateCameraVectors();//更新摄像机方向向量
}

我们有两种移动摄影机的方式：键盘输入和鼠标输入，这里需要注意的是对于OpenGL来说外部设备的输入是统一处理的，但是本身键盘的输入的数值和鼠标输入的数值并不相等，你可以假设按下键盘的按键输入的值较小而移动鼠标输入的值较大，所以我们针对两种输入方法需要写两个方法，这里设置了一个偏航角的限制（-89°，89°），防止相机翻转（翻转后你按左会变成右，方向也完全相反了）。

    void updateCameraVectors()
    {
        // calculate the new Front vector
        glm::vec3 front;
        front.x = cos(glm::radians(Yaw)) * cos(glm::radians(Pitch));//radians将度数转换为弧度
        front.y = sin(glm::radians(Pitch));
        front.z = sin(glm::radians(Yaw)) * cos(glm::radians(Pitch));
        Front = glm::normalize(front);
        // also re-calculate the Right and Up vector
        Right = glm::normalize(glm::cross(Front, WorldUp));  // normalize the vectors, because their length gets closer to 0 the more you look up or down which results in slower movement.
        Up = glm::normalize(glm::cross(Right, Front));
    }
};

这里是我们每次对摄像机进行操作后都要执行的更新摄像机参数的函数，我们会根据俯仰角和偏航角来实时计算我们的相机的正前方、正右方和正上方，这里面涉及到一些几何上的计算：

我们可以根据俯仰角直接乘以sin得到我们的y轴上的值，同时也可以得到方向向量在x-z平面的一个分量。

我们再来到x-z平面根据偏航角即可计算出具体x值和z值：

这样我们就得到了一个摄像机的向前的角度，那我们如何得到摄像机的向右角度和向上角度呢？

这个时候就需要我们的叉乘出场，如果还有人记得叉乘的作用的话：两个向量的叉乘得到的是垂直于这两个向量组成平面的向量。所以我们用世界坐标系中的上方向和我们的摄像机的前方向进行叉乘就能得到我们的摄像机右方向，而摄像机的右方向和前方向再叉乘就能得到我们的摄像机的上方向。

这是还没有将摄像机写成.h文件的代码：

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);

// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;

// camera
glm::vec3 cameraPos   = glm::vec3(0.0f, 0.0f, 3.0f);
glm::vec3 cameraFront = glm::vec3(0.0f, 0.0f, -1.0f);
glm::vec3 cameraUp    = glm::vec3(0.0f, 1.0f, 0.0f);

bool firstMouse = true;
float yaw   = -90.0f;	// yaw is initialized to -90.0 degrees since a yaw of 0.0 results in a direction vector pointing to the right so we initially rotate a bit to the left.
float pitch =  0.0f;
float lastX =  800.0f / 2.0;
float lastY =  600.0 / 2.0;
float fov   =  45.0f;

// timing
float deltaTime = 0.0f;	// time between current frame and last frame
float lastFrame = 0.0f;

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 mouse
    glfwSetInputMode(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 ourShader("7.3.camera.vs", "7.3.camera.fs");

    // set up vertex data (and buffer(s)) and configure vertex attributes
    // ------------------------------------------------------------------
    float vertices[] = {
        -0.5f, -0.5f, -0.5f,  0.0f, 0.0f,
         0.5f, -0.5f, -0.5f,  1.0f, 0.0f,
         0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
         0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
        -0.5f,  0.5f, -0.5f,  0.0f, 1.0f,
        -0.5f, -0.5f, -0.5f,  0.0f, 0.0f,

        -0.5f, -0.5f,  0.5f,  0.0f, 0.0f,
         0.5f, -0.5f,  0.5f,  1.0f, 0.0f,
         0.5f,  0.5f,  0.5f,  1.0f, 1.0f,
         0.5f,  0.5f,  0.5f,  1.0f, 1.0f,
        -0.5f,  0.5f,  0.5f,  0.0f, 1.0f,
        -0.5f, -0.5f,  0.5f,  0.0f, 0.0f,

        -0.5f,  0.5f,  0.5f,  1.0f, 0.0f,
        -0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
        -0.5f, -0.5f, -0.5f,  0.0f, 1.0f,
        -0.5f, -0.5f, -0.5f,  0.0f, 1.0f,
        -0.5f, -0.5f,  0.5f,  0.0f, 0.0f,
        -0.5f,  0.5f,  0.5f,  1.0f, 0.0f,

         0.5f,  0.5f,  0.5f,  1.0f, 0.0f,
         0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
         0.5f, -0.5f, -0.5f,  0.0f, 1.0f,
         0.5f, -0.5f, -0.5f,  0.0f, 1.0f,
         0.5f, -0.5f,  0.5f,  0.0f, 0.0f,
         0.5f,  0.5f,  0.5f,  1.0f, 0.0f,

        -0.5f, -0.5f, -0.5f,  0.0f, 1.0f,
         0.5f, -0.5f, -0.5f,  1.0f, 1.0f,
         0.5f, -0.5f,  0.5f,  1.0f, 0.0f,
         0.5f, -0.5f,  0.5f,  1.0f, 0.0f,
        -0.5f, -0.5f,  0.5f,  0.0f, 0.0f,
        -0.5f, -0.5f, -0.5f,  0.0f, 1.0f,

        -0.5f,  0.5f, -0.5f,  0.0f, 1.0f,
         0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
         0.5f,  0.5f,  0.5f,  1.0f, 0.0f,
         0.5f,  0.5f,  0.5f,  1.0f, 0.0f,
        -0.5f,  0.5f,  0.5f,  0.0f, 0.0f,
        -0.5f,  0.5f, -0.5f,  0.0f, 1.0f
    };
    // world space positions of our cubes
    glm::vec3 cubePositions[] = {
        glm::vec3( 0.0f,  0.0f,  0.0f),
        glm::vec3( 2.0f,  5.0f, -15.0f),
        glm::vec3(-1.5f, -2.2f, -2.5f),
        glm::vec3(-3.8f, -2.0f, -12.3f),
        glm::vec3( 2.4f, -0.4f, -3.5f),
        glm::vec3(-1.7f,  3.0f, -7.5f),
        glm::vec3( 1.3f, -2.0f, -2.5f),
        glm::vec3( 1.5f,  2.0f, -2.5f),
        glm::vec3( 1.5f,  0.2f, -1.5f),
        glm::vec3(-1.3f,  1.0f, -1.5f)
    };
    unsigned int VBO, VAO;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);

    glBindVertexArray(VAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    // position attribute
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);
    // texture coord attribute
    glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)(3 * sizeof(float)));
    glEnableVertexAttribArray(1);


    // load and create a texture 
    // -------------------------
    unsigned int texture1, texture2;
    // texture 1
    // ---------
    glGenTextures(1, &texture1);
    glBindTexture(GL_TEXTURE_2D, texture1);
    // set the texture wrapping parameters
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    // set texture filtering parameters
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    // load image, create texture and generate mipmaps
    int width, height, nrChannels;
    stbi_set_flip_vertically_on_load(true); // tell stb_image.h to flip loaded texture's on the y-axis.
    unsigned char *data = stbi_load(FileSystem::getPath("resources/textures/container.jpg").c_str(), &width, &height, &nrChannels, 0);
    if (data)
    {
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, data);
        glGenerateMipmap(GL_TEXTURE_2D);
    }
    else
    {
        std::cout << "Failed to load texture" << std::endl;
    }
    stbi_image_free(data);
    // texture 2
    // ---------
    glGenTextures(1, &texture2);
    glBindTexture(GL_TEXTURE_2D, texture2);
    // set the texture wrapping parameters
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    // set texture filtering parameters
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    // load image, create texture and generate mipmaps
    data = stbi_load(FileSystem::getPath("resources/textures/awesomeface.png").c_str(), &width, &height, &nrChannels, 0);
    if (data)
    {
        // note that the awesomeface.png has transparency and thus an alpha channel, so make sure to tell OpenGL the data type is of GL_RGBA
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);
        glGenerateMipmap(GL_TEXTURE_2D);
    }
    else
    {
        std::cout << "Failed to load texture" << std::endl;
    }
    stbi_image_free(data);

    // tell opengl for each sampler to which texture unit it belongs to (only has to be done once)
    // -------------------------------------------------------------------------------------------
    ourShader.use();
    ourShader.setInt("texture1", 0);
    ourShader.setInt("texture2", 1);


    // render loop
    // -----------
    while (!glfwWindowShouldClose(window))
    {
        // per-frame time logic
        // --------------------
        float currentFrame = static_cast<float>(glfwGetTime());
        deltaTime = currentFrame - lastFrame;
        lastFrame = currentFrame;

        // input
        // -----
        processInput(window);

        // render
        // ------
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 

        // bind textures on corresponding texture units
        glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D, texture1);
        glActiveTexture(GL_TEXTURE1);
        glBindTexture(GL_TEXTURE_2D, texture2);

        // activate shader
        ourShader.use();

        // pass projection matrix to shader (note that in this case it could change every frame)
        glm::mat4 projection = glm::perspective(glm::radians(fov), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f);
        ourShader.setMat4("projection", projection);

        // camera/view transformation
        glm::mat4 view = glm::lookAt(cameraPos, cameraPos + cameraFront, cameraUp);
        ourShader.setMat4("view", view);

        // render boxes
        glBindVertexArray(VAO);
        for (unsigned int i = 0; i < 10; i++)
        {
            // calculate the model matrix for each object and pass it to shader before drawing
            glm::mat4 model = glm::mat4(1.0f); // make sure to initialize matrix to identity matrix first
            model = glm::translate(model, cubePositions[i]);
            float angle = 20.0f * i;
            model = glm::rotate(model, glm::radians(angle), glm::vec3(1.0f, 0.3f, 0.5f));
            ourShader.setMat4("model", model);

            glDrawArrays(GL_TRIANGLES, 0, 36);
        }

        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    // optional: de-allocate all resources once they've outlived their purpose:
    // ------------------------------------------------------------------------
    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);

    // glfw: terminate, clearing all previously allocated GLFW resources.
    // ------------------------------------------------------------------
    glfwTerminate();
    return 0;
}

// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
void processInput(GLFWwindow *window)
{
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);

    float cameraSpeed = static_cast<float>(2.5 * deltaTime);
    if (glfwGetKey(window, GLFW_KEY_W) == GLFW_PRESS)
        cameraPos += cameraSpeed * cameraFront;
    if (glfwGetKey(window, GLFW_KEY_S) == GLFW_PRESS)
        cameraPos -= cameraSpeed * cameraFront;
    if (glfwGetKey(window, GLFW_KEY_A) == GLFW_PRESS)
        cameraPos -= glm::normalize(glm::cross(cameraFront, cameraUp)) * cameraSpeed;
    if (glfwGetKey(window, GLFW_KEY_D) == GLFW_PRESS)
        cameraPos += glm::normalize(glm::cross(cameraFront, cameraUp)) * cameraSpeed;
}

// glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    // make sure the viewport matches the new window dimensions; note that width and 
    // height will be significantly larger than specified on retina displays.
    glViewport(0, 0, width, height);
}

// glfw: whenever the mouse moves, this callback is called
// -------------------------------------------------------
void mouse_callback(GLFWwindow* window, double xposIn, double yposIn)
{
    float xpos = static_cast<float>(xposIn);
    float ypos = static_cast<float>(yposIn);

    if (firstMouse)
    {
        lastX = xpos;
        lastY = ypos;
        firstMouse = false;
    }

    float xoffset = xpos - lastX;
    float yoffset = lastY - ypos; // reversed since y-coordinates go from bottom to top
    lastX = xpos;
    lastY = ypos;

    float sensitivity = 0.1f; // change this value to your liking
    xoffset *= sensitivity;
    yoffset *= sensitivity;

    yaw += xoffset;
    pitch += yoffset;

    // make sure that when pitch is out of bounds, screen doesn't get flipped
    if (pitch > 89.0f)
        pitch = 89.0f;
    if (pitch < -89.0f)
        pitch = -89.0f;

    glm::vec3 front;
    front.x = cos(glm::radians(yaw)) * cos(glm::radians(pitch));
    front.y = sin(glm::radians(pitch));
    front.z = sin(glm::radians(yaw)) * cos(glm::radians(pitch));
    cameraFront = glm::normalize(front);
}

// glfw: whenever the mouse scroll wheel scrolls, this callback is called
// ----------------------------------------------------------------------
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset)
{
    fov -= (float)yoffset;
    if (fov < 1.0f)
        fov = 1.0f;
    if (fov > 45.0f)
        fov = 45.0f;
}

可以看到大多数的功能都已经解释过了，但是这里还有几行代码是不得不提的：

    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
    glfwSetCursorPosCallback(window, mouse_callback);
    glfwSetScrollCallback(window, scroll_callback);

    // tell GLFW to capture our mouse
    glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);

这几行代码就是为我们glfw可以读取来自外部设备输入设置回调函数，最上面的函数是我们的老朋友帧缓冲回调函数，而后续的分别是鼠标的回调函数，滚轮的回调函数以及隐藏我们的鼠标。

综上所述，我们就能得到一个可以在三维空间内自由移动的摄像机了。