实现3D引擎（七）- 模型视图投影变换

野性酷女 2024-04-18 08:39 13阅读 0赞

本文在前文[实现3D引擎（三）- 绘制三角形][3D_-]的基础上，添加模型视图投影变换。

渲染流水线上的各种变换如下：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpeWF6aGVuMjAxMQ_size_16_color_FFFFFF_t_70][]

首先，顶点着色器通过uniform变量接收上述三个变换矩阵。

uniform mat4 projectionMatrix; 
    uniform mat4 modelMatrix; 
    uniform mat4 viewMatrix;

顶点的坐标依次乘以模型，视图，投影矩阵。

gl_Position = projectionMatrix * viewMatrix * modelMatrix * vec4(position, 1.0);

其次，计算**模型变换**矩阵。将模型绕X轴旋转80度，放入世界坐标系中。

glm::mat4 model = glm::mat4(1.0f);
    model = glm::rotate(model, glm::radians(80.0f), glm::vec3(1.0f, 0.0f, 0.0f));

计算**视图变换**矩阵。相机位于原点，场景沿Z轴负方向移动3。

glm::mat4 view = glm::mat4(1.0f);
     view = glm::translate(view, glm::vec3(0.0f, 0.0f, -3.0f));

计算**投影变换**矩阵。视锥角度45度，屏幕长宽比800/600，近平面0.1f，远平面100.0f。

glm::mat4 projection = glm::mat4(1.0f);
    projection = glm::perspective(glm::radians(45.0f), (float)(800 / 600), 0.1f, 100.0f);

最后，将上述三个矩阵传递到顶点着色器。

glUniformMatrix4fv(glGetUniformLocation(shaderProgram, "modelMatrix"), 1, GL_FALSE, glm::value_ptr(model));
    glUniformMatrix4fv(glGetUniformLocation(shaderProgram, "viewMatrix"), 1, GL_FALSE, glm::value_ptr(view));
    glUniformMatrix4fv(glGetUniformLocation(shaderProgram, "projectionMatrix"), 1, GL_FALSE, glm::value_ptr(projection));

示例代码如下：

#include<iostream>
    #define GLEW_STATIC
    #include<GL/glew.h>
    #include<GLFW/glfw3.h>
    #include <glm/glm.hpp>
    #include <glm/gtc/matrix_transform.hpp>
    #include <glm/gtc/type_ptr.hpp>
    
    
    const char* vertexShaderSource =
    "#version 330 core                     \n"
    "layout(location = 0) in vec3 position; \n"
    "uniform mat4 projectionMatrix; \n"
    "uniform mat4 modelMatrix; \n"
    "uniform mat4 viewMatrix; \n"
    "void main() {                          \n"
    "		gl_Position = projectionMatrix * viewMatrix * modelMatrix * vec4(position, 1.0);} \n ";
    
    const char* fragmentShaderSource =
    "#version 330 core                   \n"
    "out vec4 color;                     \n"
    "void main(){                        \n"
    "	color = vec4(1.0f, 0.5f, 0.2f, 1.0f);}  \n";
    
    GLfloat vertices[] = {
        -0.5f, -0.5f, 0.0f,
        0.5f, -0.5f, 0.0f,
        0.0f,  0.5f, 0.0f
    };
    
    //key表示按下的键，action表示键按下/释放，mode表示是否有Ctrl、Shift、Alt等按钮操作
    void key_callback(GLFWwindow * window, int key, int scancode, int action, int mode)
    {
        //用户按下ESC键，设置窗口WindowShouldClose属性为true,关闭应用程序
        if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
            glfwSetWindowShouldClose(window, GL_TRUE);
    }
    
    int main()
    {
        glfwInit();
        glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);    //主版本号
        glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);    //次版本号
        glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);//核心模式
    
        GLFWwindow* window = glfwCreateWindow(800, 600, "OpenGL Game", NULL, NULL); //创建窗口
        if (window == NULL)
        {
            std::cout << "Open window failed!" << std::endl;
            glfwTerminate();
            return -1;
        }
        //将窗口的上下文设置为当前线程的主上下文
        glfwMakeContextCurrent(window);
    
        //GLEW是用来管理OpenGL的函数指针,调用任何OpenGL的函数之前都需要初始化GLEW
        glewExperimental = GL_TRUE;
        if (glewInit() != GLEW_OK)
        {
            std::cout << "Init Glew failed！" << std::endl;
            glfwTerminate();
            return -1;
        }
    
        int width, height;
        //从GLFW中获取视口大小
        glfwGetFramebufferSize(window, &width, &height);
        //窗口左下角的位置、宽度、高度
        glViewport(0, 0, width, height);
    
        //注册按键回调函数
        glfwSetKeyCallback(window, key_callback);
    
        //顶点数组对象
        unsigned int VAO;
        glGenVertexArrays(1, &VAO);
        glBindVertexArray(VAO);
    
        //顶点缓冲对象
        unsigned int VBO;
        glGenBuffers(1, &VBO);
        glBindBuffer(GL_ARRAY_BUFFER, VBO);
        //将顶点数据复制到缓冲中
        glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    
        //创建顶点着色器
        unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);
        glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
        glCompileShader(vertexShader);
    
        //创建片段着色器
        unsigned int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
        glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
        glCompileShader(fragmentShader);
    
        //创建着色器程序
        unsigned int shaderProgram = glCreateProgram();
        glAttachShader(shaderProgram, vertexShader);
        glAttachShader(shaderProgram, fragmentShader);
        glLinkProgram(shaderProgram);
    
        //顶点属性配置,告诉OpenGL该如何解析顶点数据
        glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
        glEnableVertexAttribArray(0);
    
        //启用着色器程序
        glUseProgram(shaderProgram);
        glm::mat4 model = glm::mat4(1.0f);
        model = glm::rotate(model, glm::radians(80.0f), glm::vec3(1.0f, 0.0f, 0.0f));
        glm::mat4 view = glm::mat4(1.0f);
        view = glm::translate(view, glm::vec3(0.0f, 0.0f, -3.0f));
        glm::mat4 projection = glm::mat4(1.0f);
        projection = glm::perspective(glm::radians(45.0f), (float)(800 / 600), 0.1f, 100.0f);
        glUniformMatrix4fv(glGetUniformLocation(shaderProgram, "modelMatrix"), 1, GL_FALSE, glm::value_ptr(model));
        glUniformMatrix4fv(glGetUniformLocation(shaderProgram, "viewMatrix"), 1, GL_FALSE, glm::value_ptr(view));
        glUniformMatrix4fv(glGetUniformLocation(shaderProgram, "projectionMatrix"), 1, GL_FALSE, glm::value_ptr(projection));
    
        //检查GLFW是否要求退出
        while (!glfwWindowShouldClose(window))
        {
            //检查是否触发事件（鼠标移动、键盘输入等），如果有则调用相应的回调函数
            glfwPollEvents();
            //渲染操作放入循环中
            //清屏
            glClearColor(0.2f, 0.3f, 0.3f, 1.0);
            glClear(GL_COLOR_BUFFER_BIT);    
            glBindVertexArray(VAO);  
            //绘制
            glDrawArrays(GL_TRIANGLES, 0, 3);
            //交换颜色缓冲
            glfwSwapBuffers(window);
        }
        //结束时释放资源
        glfwTerminate();
        return 0;
    }

运行结果：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpeWF6aGVuMjAxMQ_size_16_color_FFFFFF_t_70 1][]

[3D_-]: https://blog.csdn.net/liyazhen2011/article/details/86186971
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpeWF6aGVuMjAxMQ_size_16_color_FFFFFF_t_70]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/17/4982bb3398914ccdb82973900cd27dd6.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpeWF6aGVuMjAxMQ_size_16_color_FFFFFF_t_70 1]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/17/a3fb8af5f3a041808f719c82d32a9226.png