LearnOpenGL (2) 绘制三角形

 #include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <iostream>

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;

float vertices[] = {        //三角形的三个顶点
    -0.5f, -0.5f, 0.0f,     //顶点1
     0.5f, -0.5f, 0.0f,     //顶点2
     0.0f,  0.5f, 0.0f      //顶点3
};
// 顶点着色器程序
const char* vertexShaderSource = "#version 330 core\n"
"layout (location = 0) in vec3 aPos;\n"
"void main()\n"
"{\n"
"   gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);\n"
"}\0";
// 片段着色器程序
const char* fragmentShaderSource = "#version 330 core\n"
"out vec4 FragColor;\n"
"void main()\n"
"{\n"
"   FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n"
"}\n\0";

int main()
{
    //实例化GLFW窗口
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    GLFWwindow* window = glfwCreateWindow(800, 600, "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是用来管理OpenGL的函数指针的，在调用任何OpenGL的函数之前我们需要初始化GLAD。
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }

    // 建立顶点着色器对象
    unsigned int vertexShader;
    vertexShader = glCreateShader(GL_VERTEX_SHADER);
    // 将顶点着色器源码附加到着色器对象上
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    // 编译顶点着色器源码
    glCompileShader(vertexShader);
    // 检查是否编译成功
    int  success;
    char infoLog[512];
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
    }

    // 创建片段着色器对象
    unsigned int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    // 将片段着色器程序附加到片段着色器对象上
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    // 编译片断着色器程序
    glCompileShader(fragmentShader);
    // 检查是否编译成功
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
    }

    // 创建着色器程序对象
    unsigned int shaderProgram = glCreateProgram();
    // 把编译完成的顶点着色器和片段着色器附加到着色器程序对象上
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    // 将顶点着色器和片段着色器链接起来，构成一个可执行的着色器程序
    glLinkProgram(shaderProgram);
    // 检查是否链接成功
    glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
    if (!success) {
        glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
    }
    // 此时可以安全的删除着色器对象
    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);

    // 生成一个VAO对象
    unsigned int VAO;
    glGenVertexArrays(1, &VAO);
    // 绑定VAO
    glBindVertexArray(VAO);
    // 生成一个VBO对象
    unsigned int VBO;
    glGenBuffers(1, &VBO);
    //绑定VBO到 GL_ARRAY_BUFFER 上，从这一刻起，我们使用的任何（在GL_ARRAY_BUFFER目标上的）缓冲调用都会用来配置当前绑定的缓冲(VBO)。
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    //把顶点数据复制到VBO内存中。
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    //现在我们已经把顶点数据储存在显卡的内存中，用VBO这个顶点缓冲对象管理。
    // 告诉opengl应该如何解释顶点数据，即把数据应用到顶点属性上。
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
    // 顶点属性默认是禁用的， 需要启用。
    glEnableVertexAttribArray(0);

    // 解绑VBO
    glBindBuffer(GL_ARRAY_BUFFER, 0);
    // 解绑VAO
    glBindVertexArray(0);




    //渲染循环
    while (!glfwWindowShouldClose(window))
    {
        // 处理输入事件
        processInput(window);

        // 设置颜色缓冲区的默认颜色
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        // 清空屏幕颜色缓冲区并设置成我们上面设置的颜色
        glClear(GL_COLOR_BUFFER_BIT);

        // 使用着色器程序对象
        glUseProgram(shaderProgram);
        // 绑定VAO，调用设置的一组状态
        glBindVertexArray(VAO);
        // 绘制三角形
        glDrawArrays(GL_TRIANGLES, 0, 3);
        // 不需要每次解绑VAO，因为调用glBindVertexArray会自动解绑上次绑定的VAO.

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

    // 释放资源
    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);
    glDeleteProgram(shaderProgram);

    glfwTerminate();
	return 0;
}

// 处理键盘事件
void processInput(GLFWwindow* window)
{
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);
}

void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    // 根据窗口大小改变视口大小
    glViewport(0, 0, width, height);
}