OpenGL entry (a): Creating a simple window using GLFW

If you use the QT, then create an OpenGL rendering window is actually very easy, but for beginners point of view, the use of GLFW library to create a new window.

1. Download and configure GLFW

GLFW specifically for OpenGL is a C language library that provides a number of rendering objects required minimal interface, and supports cross-platform.

First, we need to start its official website to download: https://www.glfw.org/ .
After the download source, extract. It provides CMakeLists.txt can find documents, then we will be able to easily use cmake to compile it (recommended vs2015 under windows).

After compiling, we need these things:

• Compile glfw3.lib generated;
• include folder;
• deps folder.

In the new project ourselves created, these files will join in, and configure the header file directories and search library search directory, then the configuration work had been completed.
Also to note is that we need to depsdirectory under glad_gl.cadded to the compiled code .

2. Write test program

Source follows, the key function made the comment:

#include <iostream>

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

#pragma comment(lib, "glfw3.lib")

//窗口大小变化时，重新设置视口
void framebuff_size_callback(GLFWwindow* window, int width, int height) {
    glViewport(0, 0, width, height);
}

//处理输入
void process_input_callabck(GLFWwindow *window, int key, int scancode, int action, int mods) {
    if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS) {
        glfwSetWindowShouldClose(window, true);
    }
}

int main() {
    glfwInit();     //初始化GLFW

    //指明OpenGL版本
    //glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    //glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    //glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    //创建窗口
    GLFWwindow* window = glfwCreateWindow(800, 600, "OpenGLTest", NULL, NULL);
    if (window == NULL) {
        std::cout << "Failed to create GLFW window " << std::endl;
        //销毁所有窗口
        glfwTerminate();
        return -1;
    }
    //将该窗口作为当前线程的主上下文
    glfwMakeContextCurrent(window);

    //处理输入
    glfwSetKeyCallback(window, process_input_callabck);

    //GLAD是管理OpenGL指针的，在调用任何OpenGL的函数之前需要初始化GLAD
    if (!gladLoadGL(glfwGetProcAddress)) {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }

    //设置视口Viewport
    //前两个参数控制渲染窗口左下角的相对位置，第三和第四个参数控制渲染窗口的宽度和高度
    //OpenGL会在此窗口大小范围内进行坐标变换
    glViewport(0, 0, 800, 600);

    //监听窗口大小变化
    glfwSetFramebufferSizeCallback(window, framebuff_size_callback);
    
    //循环渲染，在退出前一直不断地绘制图像
    while (!glfwWindowShouldClose(window)) {
        //清屏
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        //将存储在缓冲区中的像素颜色进行绘制，这里涉及到双缓冲的问题
        glfwSwapBuffers(window);
        //检查有没有触发什么事件（键盘输入、鼠标移动等)、窗口改变
        glfwPollEvents();
    }
    
    // 退出前清理
    glfwTerminate();
    return 0;
}

After operating results:

There is at GLFW source examplesdirectory, there will be some more fun examples below.