[OPENGL learning] glfw+glad environment construction and the first window program

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1. What is opengl?

 OpenGL（全写Open Graphics Library）是指定义了一个跨编程语言、跨平台的编程接口规格的专业的图形程序接口。它用于三维图像（二维的亦可），是一个功能强大，调用方便的底层图形库

2. Use steps

1. Import library

The whole process is based on the website: https://learnopengl-cn.github.io/ to learn, thank you for sharing. The website currently recommends using glfw and glad (currently, it may be updated in the future).

The first step must be to have a vs2019.

The second step is to download glfw and glad.
1. First, the download address of glfw: http://www.glfw.org/download.html
Download the things in the red box

and then decompress the incluse folder and lib-vc2019 of the decompressed package, and I will decompress them here .

2. Download glad, download address: https://glad.dav1d.de/
Because glfw does not support versions prior to opengl3.0, so I downloaded version 4.6 here.
Unzip the include file in glad.zip to the same directory as the include folder of glfw and lib-vc2019.

3. Create a c++ project with vs2019, then right-click the project to select properties, find the include directory and library directory in vc++, and enter the decompressed file path

5. There is waiting to add glfw3.lib in the connector

6. Finally, put the glad.c file in glad.zip into the project. , otherwise the compiler will say that the function of glad cannot be linked externally

7. The good environment is set up, and the work will start below.

2. Don't talk about it, just upload the code

The code is as follows (example):

#include<glad/glad.h> //glad的引入必须要在glfw的上面
#include<GLFW/glfw3.h>
#include<iostream>

using namespace std;

//窗口的宽度
static int width = 800;
//窗口高度
static int height = 600;
//窗口的名字
static char  window_name[] = "opengl window";

void framebuffer_size_callback(GLFWwindow*,int,int);
void processInput(GLFWwindow*);
void renderOrder();

int main() {
    
    
	cout << "opengl progaming start......" << "\n";
	//函数库的初始化
	glfwInit();
	//设定opengl版本为3.3
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	//设定opengl为核心模式
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
	//苹果的系统下需要进行兼容的设置
#ifdef _apple_
	glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif
	//创建窗口对象
	GLFWwindow* window = glfwCreateWindow(width, height, window_name, NULL, NULL);
	if (window == NULL) {
    
    
		cout << "opengl window start fail!gl progaming will terminate....." << endl;
		glfwTerminate(); //终结掉gl程序
		return -1;
	}
	//设定当前剩下文
	glfwMakeContextCurrent(window);
	//注册窗口大小改变回调
	glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
	//初始化gladLoader
	if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) {
    
    
		//如果无法获取到glfw指针就相当于失败，并且终止掉gl程序
		cout << "can`t get glfw pointer address!gl progaming will terminate....." << endl;
		glfwTerminate();
		return -1;
	}
	//执行到这里就是默认完成了所有初始化
   //glfw没有执行结束的时候就一直是死循环
	while (!glfwWindowShouldClose(window))
	{
    
    
		processInput(window);
		renderOrder();
		//缓冲区交互
		//关于双缓存的补充:
		//如果使用单缓存的渲染模式，那么游戏画面可以会出现闪烁现象，原因是图形渲染出一帧的画面时，每一个像素点不是同时渲染出来的，
		//而是遵循流水线，由左往右，由上往下来进行渲染的。所以这个时候采用双缓存，当前缓存显示完，直接把后缓存的画面交换上去，则就可以避免游戏闪烁现象。
		//并且使用glfeSwapBuffers()函数进行交换。
		glfwSwapBuffers(window);
		//执行被触发的事件
		glfwPollEvents();
	}
	return 0;
}

/// <summary>
/// 回调函数。窗口大小改变时。
/// </summary>
void framebuffer_size_callback(GLFWwindow* window, int wid, int het) {
    
    
   //这是控制视口的函数。
   //前面两个参数是指视口的左下角的坐标偏移位置。(opengl的视口窗口默认左下角为原点0,0)
   //后面两个参数是指视口的宽度和高度
	glViewport(0, 0, wid, het);
	cout << "opengl window resolution change!" << "wid:" << wid << "  " << "het:" << het << endl;
}
/// <summary>
/// 输入函数
/// </summary>
void processInput(GLFWwindow* window){
    
    
	if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS){
    
    
		glfwSetWindowShouldClose(window,true);
	}
}
/// <summary>
/// 渲染指令
/// </summary>
void renderOrder() {
    
    
	//深绿色
	glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
	//关于glfwClear函数，这是一个清屏的函数。当前是去掉颜色缓存区
   //如果传入参数GL_DETCH_BUFFER_BIT(深度缓存区)和GL_STENCIL_BUFFER_BIT(模板缓存区)就是清掉对应的缓存区
	glClear(GL_COLOR_BUFFER_BIT);
}

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Summarize

It is mainly to set up a good environment and write a window program for opengl.
Regarding the selection of versions: early opengl was rendered using immediate mode (fixed rendering pipeline). Starting from version 3.2 of OpenGL, OpenGL has removed the immediate mode and switched to the core mode, and encourages developers to use this mode. Most developers choose the early opengl version, because the new opengl version basically adds new features on the original basis, or implements (optimizes) the same function in a better way. The new features are likely to be provided by a new version of the graphics card driver, and an earlier version of opengl is selected for better compatibility.