OpenGL Tutorial 2 : The first triangle

教程地址：http://www.opengl-tutorial.org/beginners-tutorials/tutorial-2-the-first-triangle/

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代码备忘：

// Include standard headers
#include 
#include 

// Include GLEW
#include 

// Include GLFW
#include 
GLFWwindow* window;

// Include GLM
#include 
using namespace glm;
// Include shader
#include 

int main(void)
{

    // Initialise GLFW
    // 初始化GLFW
    if (!glfwInit())
    {
        fprintf(stderr, "Failed to initialize GLFW\n");
        getchar();
        return -1;
    }

    glfwWindowHint(GLFW_SAMPLES, 4);// 4x antialiasing，4倍反锯齿
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);// We want OpenGL 3.3
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // To make MacOS happy; should not be needed
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    // Open a window and create its OpenGL context
    // 创建窗口
    window = glfwCreateWindow(1024, 768, "MyOpenGL", NULL, NULL);
    if (window == NULL) {
        fprintf(stderr, "Failed to open GLFW window. If you have an Intel GPU, they are not 3.3 compatible. Try the 2.1 version of the tutorials.\n");
        getchar();
        glfwTerminate();
        return -1;
    }

    // 创建OpenGL上下文
    glfwMakeContextCurrent(window);

    // Initialize GLEW
    // GLEW是用来管理OpenGL的函数指针的，所以在调用任何OpenGL的函数之前我们需要初始化GLEW
    glewExperimental = true; // Needed for core profile

    // 初始化GLEW
    if (glewInit() != GLEW_OK) {
        fprintf(stderr, "Failed to initialize GLEW\n");
        getchar();
        glfwTerminate();
        return -1;
    }

    // Ensure we can capture the escape key being pressed below
    // 捕捉键盘
    glfwSetInputMode(window, GLFW_STICKY_KEYS, GL_TRUE);


    // Ensure we can capture the escape key being pressed below
    glfwSetInputMode(window, GLFW_STICKY_KEYS, GL_TRUE);


    // Grey background
    // 背景颜色 RGBA表示
    glClearColor(0.0f, 0.0f, 0.4f, 0.0f);

    GLuint VertexArrayID;
    glGenVertexArrays(1, &VertexArrayID);
    glBindVertexArray(VertexArrayID);

    // Create and compile our GLSL program from the shaders
    // 创建两个着色器
    GLuint programID = LoadShaders("SimpleVertexShader.vertexshader", "SimpleFragmentShader.fragmentshader");


    // An array of 3 vectors which represents 3 vertices
    // 临时定义三角形的顶点坐标
    static const GLfloat g_vertex_buffer_data[] = {
        -1.0f, -1.0f, 0.0f,
        1.0f, -1.0f, 0.0f,
        0.0f, 1.0f, 0.0f,
    };

    // This will identify our vertex buffer
    // GLuint相当于unsigned int
    GLuint vertexbuffer;

    // Generate 1 buffer, put the resulting identifier in vertexbufferID
    // 获取buffer的ID
    glGenBuffers(1, &vertexbuffer);

    // The following commands will talk about our 'vertexbufferID' buffer
    // 指定缓冲区
    glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);

    // Give our vertices to OpenGL.
    // 将缓冲区的三角形传给opengl
    glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data, GL_STATIC_DRAW);

    do {
        // Clear the screen. It's not mentioned before Tutorial 02, but it can cause flickering, so it's there nonetheless.
        // 清除颜色缓冲
        glClear(GL_COLOR_BUFFER_BIT);


        // Use our shader
        // 使用加载的着色器
        glUseProgram(programID);

        // 1rst attribute buffer : vertices
        // 启用着色器
        glEnableVertexAttribArray(0);
        glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);

        glVertexAttribPointer(
            0,                  // attribute 0. No particular reason for 0, but must match the layout in the shader.
            3,                  // size
            GL_FLOAT,           // type
            GL_FALSE,           // normalized?
            0,                  // stride
            (void*)0            // array buffer offset
        );

        // Draw the triangle !
        // 画三角形
        glDrawArrays(GL_TRIANGLES, 0, 3); // Starting from vertex 0; 3 vertices total -> 1 triangle

        glDisableVertexAttribArray(0);

        // Swap buffers
        glfwSwapBuffers(window);
        glfwPollEvents();

    } 

    // Check if the ESC key was pressed or the window was closed
    while (glfwGetKey(window, GLFW_KEY_ESCAPE) != GLFW_PRESS && glfwWindowShouldClose(window) == 0);

    // Cleanup VBO
    glDeleteBuffers(1, &vertexbuffer);
    glDeleteVertexArrays(1, &VertexArrayID);
    glDeleteProgram(programID);

    // Close OpenGL window and terminate GLFW
    glfwTerminate();

    return 0;
}