# learn-opengl

**Repository Path**: zmx0142857/learn-opengl

## Basic Information

- **Project Name**: learn-opengl
- **Description**: learn opengl
- **Primary Language**: Unknown
- **License**: Not specified
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 1
- **Forks**: 0
- **Created**: 2021-06-15
- **Last Updated**: 2024-02-25

## Categories & Tags

**Categories**: Uncategorized

**Tags**: demo

## README

# Learn OpenGL

https://learnopengl.com/Getting-started/OpenGL

## quick start

安装 GLFW, 这个库用于绘制窗口. 类似的库还有 GLUT, SDL, SFML 等.

    $ sudo pacman -S glfw-x11

安装 OpenGL 发行版, 如 Mesa, NVidia, AMD 的任一个.

    $ sudo pacman -S mesa

现在 `/usr/lib` 目录下应该有 `libglfw.so` 和 `libGL.so` 两个文件.

运行 `glxinfo | grep version` 查看 OpenGL 版本, 确保为 3.3 或更高.

下载 GLM (OpenGL Mathematics) 库, 然后把 `glm/glm` 目录拷贝到
`learn-opengl/include` 目录中.

    $ git clone https://github.com/g-truc/glm --depth=1

编译并运行:

    $ make # 编译
    $ bin/main # 运行

## starter code

### GLAD

下载 GLAD: 打开 https://glad.dav1d.de/, 选择
- Language: C/C++
- Specification: OpenGL
- API: gl: Version 3.3 或者更高
- Profile: Core
- Options: Generate a loader

生成并下载 `glad.zip` (`include` 和 `src` 目录已经包含在内).

```text
glad
├── include
│   ├── glad
│   │   └── glad.h
│   └── KHR
│       └── khrplatform.h
├── Makefile
└── src
    ├── glad.c
    └── main.cpp
```

### 编写代码

`Makefile`
```Makefile
CC = g++
IDIR = include
CFLAGS = -I$(IDIR)
LINKS = -lglfw -lGL -lX11 -lpthread -lXrandr -lXi -ldl

# $@ 表示目标
# $^ 表示所有依赖
bin/main: obj/main.o obj/glad.o
	mkdir -p bin
	$(CC) $(LINKS) -o $@ $^

obj/glad.o: src/glad.c
	mkdir -p obj
	$(CC) $(CFLAGS) -c -o $@ $^

obj/main.o: src/main.cpp
	mkdir -p obj
	$(CC) $(CFLAGS) -c -o $@ $^
```

`src/main.cpp`
```c++
#include <glad/glad.h>
#include <GLFW/glfw3.h>

int main()
{
    return 0;
}
```

> Be sure to include GLAD before GLFW. The include file for GLAD includes
> the required OpenGL headers behind the scenes (like GL/gl.h) so be sure
> to include GLAD before other header files that require OpenGL (like
> GLFW).

运行 `make`, 尝试编译项目.

### 一个黑窗口

继续修改代码:

`src/main.cpp`
```c++
#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <iostream>

const int width = 800;
const int height = 600;

// 窗口大小改变时的回调
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    glViewport(0, 0, width, height);
}

int main()
{
    glfwInit();

    // 配置 GLFW
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    //glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // for MacOS

    // 创建窗口
    GLFWwindow* window = glfwCreateWindow(width, height, "LearnOpenGL", NULL, NULL);
    if (!window) {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);

    // 初始化 GLAD
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }

    // 初始化 viewport
    glViewport(0, 0, width, height);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

    // 既然是图形程序, 就要有消息循环
    while (!glfwWindowShouldClose(window)) {
        glfwSwapBuffers(window); // 双缓冲
        glfwPollEvents(); // 派发事件
    }

    glfwTerminate();

    return 0;
}
```

编译并运行, 如果一切顺利, 将出现一个黑窗口.

### 输入控制与渲染

`src/main.cpp`
```c++
void processInput(GLFWwindow *window)
{
    // 按下 esc 关闭窗口
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);
}

void render(GLFWwindow *window)
{
    glClearColor(0.2f, 0.3f, 0.3f, 1.0f); // rgba
    glClear(GL_COLOR_BUFFER_BIT); // or GL_DEPTH_BUFFER_BIT, GL_STENCIL_BUFFER_BIT
}

    while (!glfwWindowShouldClose(window)) {
+       processInput(window); // 处理输入
+       render(window); // 渲染
        glfwSwapBuffers(window); // 双缓冲
        glfwPollEvents(); // 派发事件
    }
```

这个程序将得到一个蓝色背景.