new: Set up a window

Nehe的教程确实太老了，不过我认为它也能够让我了解OpenGL3.2以前的管线渲染模式，即使它在现在已经不常见了。因为想要了解，所以我还是会看完Nehe的教程。

现在这是一个新的教程 - JoeyDeVries的教程，可以说是网上最好的OpenGL教程，现在一步一步地来学习。我会在每个新的教程标题前面附加new，旧的教程标题前面附加outdated。

glfw的函数都可以在这里找到。

在运行代码前，需要先在项目属性-链接器-输入-附加依赖项中添加glew32s.lib、glfw3.lib、opengl32.lib。

代码如下：

#include <iostream>

// GLEW
#define GLEW_STATIC
#include <GL/glew.h>

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

// Window dimensions
const GLuint WIDTH = 800, HEIGHT = 600;

void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode)
{
    std::cout << key << std::endl;
    // When a user presses the escape key, we set the WindowSouldlose propert to ture
    // closing the application
    if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
        glfwSetWindowShouldClose(window, GLFW_TRUE);
}

// The MAIN function, from here we start the application and run the game loop
int main()
{
    // Init GLFW
    glfwInit();
    // Set all the required options for GLFW
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);

    // Create a GLFWwindow object that we can use for GLFW's functions
    GLFWwindow* window = glfwCreateWindow(WIDTH, HEIGHT, "OpenGL", nullptr, nullptr);
    if (window == nullptr)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    // Set the required callback function
    glfwSetKeyCallback(window, key_callback);
    // Set this to true so GLEW knows to use a modern approach to retrieving 
    // function pointers and extensions
    glewExperimental = GL_TRUE;
    // Initialize GLEW to setup the OpenGL Function pointers
    if (glewInit() != GLEW_OK)
    {
        std::cout << "Failed to initialize GLEW" << std::endl;
        return -1;
    }

    // Define the viewport dimensions
    int width, height;
    glfwGetFramebufferSize(window, &width, &height);
    glViewport(0, 0, width, height);

    // Game loop
    while (!glfwWindowShouldClose(window))
    {
        // Check if any events have been activiated (key pressed, mouse moved etc.) 
        // and call corresponding response functions
        glfwPollEvents();

        glClearColor(0.2, 0.3, 0.4, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        // Swap the screen buffers
        glfwSwapBuffers(window);
    }

    // Terminate GLFW, clearing any resources allocated by GLFW.
    glfwTerminate();
    return 0;
}