【小沐学OpenGL】Ubuntu环境下glad的安装和使用

文章目录

1、简介
- 1.1 OpenGL简介
- 1.2 glad简介
2、安装glad
- 2.1 手动安装glad
- 2.2 git安装glad
- 2.3 源码编译成glad单独库
3、测试glad
- 3.1 例子1
- 3.2 例子2
结语

1、简介

1.1 OpenGL简介

OpenGL作为图形界的工业标准，其仅仅定义了一组2D和3D图形接口API，而对于窗口管理、IO消息响应等并没有规定。也就是说，OpenGL依赖各平台提供用于渲染的context以及具体实现方式，而各平台提供的实现不尽相同。这些实现主要有：Windows平台下的WGL、Linux下的Mesa/GLX、Mac OS X下的Cocoa/NSGL，以及跨平台的GLUT、GLFW、SDL等等。

Mesa是Linux下的OpenGL实现。它提供了对AMD Radeon系列、Nvidia GPU、Intel i965, i945, i915以及VMWare虚拟GPU等多种硬件驱动的支持，同时也提供了对softpipe等多种软件驱动的支持。Mesa项目由Brian Paul于1993年8月创建，于1995年2月发布了第一个发行版，此后便受到越来越多的关注，如今Mesa已经是任何一个Linux版本首选的OpenGL实现。

GLX则是在Linux上用于提供GL与窗口交互、窗口管理等等的一组API。它的作用与Windows的WGL、Mac OS X的AGL以及针对OpenGL ES的EGL相似。在Linux上，窗口创建、管理等API遵循X Window接口，而GLX提供了OpenGL与X Window交互的办法。因此GLX也可以运用于其他使用X Window的平台，例如FreeBSD等。

在Debian/Ubuntu系统上，使用以下命令来安装Mesa和GLX：

sudo apt-get install libgl1-mesa-dev

安装OpenGL ES版本的Mesa：

sudo apt-get install libgles2-mesa-dev

对于OpenGL ES，EGL的安装如下：

sudo apt-get install libegl1-mesa-dev

查看安装的Mesa版本以及安装是否成功：

glxinfo | grep "OpenGL version"

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1.2 glad简介

Windows平台由于微软的Direct3D存在，微软对OpenGL的支持并不积极。在大多数微软操作系统中所支持OpenGL版本还是1.0和1.1，仅支持固定管线API，对于现代使用OpenGL开发的程序并不友好。不过通过OpenGL的ARB扩展机制可以让我们访问到OpenGL的高级特性接口。

GLAD 是一个用于加载 OpenGL 函数指针的库，它简化了 OpenGL 函数的调用。你可以从 GLAD 的官方网站下载并生成适合你需求的 GLAD 配置。通常，你需要指定 OpenGL 的版本和配置文件类型（通常是核心模式）。生成后，将包含的头文件和源文件添加到你的项目中。

GLAD使用步骤：GLAD可以使OpenGL基础渲染变得简单，流程如下：

1.初始化GLAD库，加载所有OpenGL函数指针。
2.创建着色器并附加到着色器程序。
3.构建缓冲对象并附加到顶点属性。
4.使用着色器程序，利用渲染接口将缓冲对象按照指定图元类型渲染出来。

初始化GLAD库：常用接口如下：

int gladLoadGLLoader(GLADloadproc load)：任何的OpenGL接口调用都必须在初始化GLAD库后才可以正常访问。如果成功的话，该接口将返回GL_TRUE，否则就会返回GL_FALSE。
其中GLADloadproc函数声明如下：
void* (GLADloadproc)(const char name)

2、安装glad

2.1 手动安装glad

配置GLAD需要设置OpenGL版本,可以通过glxinfo查看；

# 安装glxinfo
sudo apt install mesa-utils

# 查看OpenGL版本
glxinfo | grep "OpenGL version"

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可以看到笔者的是3.1。

https://glad.dav1d.de/

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下载glad源码如下：

通过CMake构建项目，其CMakeLists.txt添加如下代码：

add_library(glad glad/src/glad.c)
target_include_directories(glad  PUBLIC glad/include)
target_link_libraries(main glfw ${GL_LIBRARY} glad)

解压glad.zip如下：
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方法1：

cd glad/include
sudo mv glad/ /usr/local/include #将glad目录移动到/usr/local/include
sudo mv KHR/ /usr/local/include #将KHR目录移动到/usr/local/include

最后将glad/src目录下的glad.c文件拷贝一份到你的工程源码目录下，如跟main.cpp文件在同一个目录下。

方法2：
或者点击GENERRATE生成对应的zip文件并下载。解压这个zip文件,可以一个包含include和src的文件夹,将include下的文件移动到系统目录下:

sudo mv include/* /usr/local/include

src目录下的glad.c文件稍后放置在工程文件中。

mv <glad_path>/src/glad.c glad.c

2.2 git安装glad

git clone https://github.com/Dav1dde/glad.git
cd glad
cmake ./
make
sudo cp -a include /usr/local/

2.3 源码编译成glad单独库

（1）下载glad的include， src 到 3rdparty/glad/
（2）在 3rdparty/glad/里新建CMakeLists.txt文件如下：

cmake_minimum_required(VERSION 3.0)
project(Glad)

add_library(glad include/glad/glad.h src/glad.c)
target_include_directories(glad PUBLIC include/)

（3）在项目主 CMakeLists.txt 加入下面的代码.

cmake_minimum_required(VERSION 2.8.1)

project(my_app)

find_package(glfw3 REQUIRED)
add_subdirectory(3rdparty/glad)

add_executable(my_app main.cpp)
target_link_libraries(my_app glfw glad)

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3、测试glad

3.1 例子1

新建CMakeLists.txt内容如下：

CMakeLists.txt:

cmake_minimum_required(VERSION 2.8.1)

project(my_project)

find_package(OpenGL REQUIRED)
add_library(glad src/glad.c)
target_include_directories(glad  PUBLIC include/glad)

set (CMAKE_CXX_LINK_EXECUTABLE "${CMAKE_CXX_LINK_EXECUTABLE} -ldl")

add_executable(main main.cpp)
target_link_libraries(main glfw ${GL_LIBRARY} glad)

main.cpp

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

void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    glViewport(0, 0, width, height);
}

int main()
{
    glfwInit();
    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);

    GLFWwindow* window = glfwCreateWindow(800, 600, "Linux Opengl, yxy", NULL, NULL);
    if (window == NULL)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }
    glViewport(0, 0, 800, 600);

    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
    while(!glfwWindowShouldClose(window))
    {
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);
        glfwSwapBuffers(window);
        glfwPollEvents();
    }
    glfwTerminate();
    return 0;
}

编译如下：
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3.2 例子2

CMakeLists.txt:

CMakeLists.txt文件内容同上。

main.cpp

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

#include <iostream>

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow *window);

// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;

const char *vertexShaderSource = "#version 330 core\n"
                                 "layout (location = 0) in vec3 aPos;\n"
                                 "void main()\n"
                                 "{\n"
                                 "   gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);\n"
                                 "}\0";
const char *fragmentShaderSource = "#version 330 core\n"
                                   "out vec4 FragColor;\n"
                                   "void main()\n"
                                   "{\n"
                                   "   FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n"
                                   "}\n\0";

int main()
{
    // glfw: initialize and configure
    // ------------------------------
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

#ifdef __APPLE__
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // uncomment this statement to fix compilation on OS X
#endif

    // glfw window creation
    // --------------------
    GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
    if (window == NULL)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

    // glad: load all OpenGL function pointers
    // ---------------------------------------
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }


    // build and compile our shader program
    // ------------------------------------
    // vertex shader
    int vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);
    // check for shader compile errors
    int success;
    char infoLog[512];
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
    }
    // fragment shader
    int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    glCompileShader(fragmentShader);
    // check for shader compile errors
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
    }
    // link shaders
    int shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);
    // check for linking errors
    glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
    if (!success) {
        glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
    }
    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);

    // set up vertex data (and buffer(s)) and configure vertex attributes
    // ------------------------------------------------------------------
    float vertices[] = {
        0.5f,  0.5f, 0.0f,  // top right
        0.5f, -0.5f, 0.0f,  // bottom right
        -0.5f, -0.5f, 0.0f,  // bottom left
        -0.5f,  0.5f, 0.0f   // top left
    };
    unsigned int indices[] = {  // note that we start from 0!
        0, 1, 3,  // first Triangle
        1, 2, 3   // second Triangle
    };
    unsigned int VBO, VAO, EBO;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    glGenBuffers(1, &EBO);
    // bind the Vertex Array Object first, then bind and set vertex buffer(s), and then configure vertex attributes(s).
    glBindVertexArray(VAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);

    // note that this is allowed, the call to glVertexAttribPointer registered VBO as the vertex attribute's bound vertex buffer object so afterwards we can safely unbind
    glBindBuffer(GL_ARRAY_BUFFER, 0);

    // remember: do NOT unbind the EBO while a VAO is active as the bound element buffer object IS stored in the VAO; keep the EBO bound.
    //glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);

    // You can unbind the VAO afterwards so other VAO calls won't accidentally modify this VAO, but this rarely happens. Modifying other
    // VAOs requires a call to glBindVertexArray anyways so we generally don't unbind VAOs (nor VBOs) when it's not directly necessary.
    glBindVertexArray(0);


    // uncomment this call to draw in wireframe polygons.
    //glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);

    // render loop
    // -----------
    while (!glfwWindowShouldClose(window))
    {
        // input
        // -----
        processInput(window);

        // render
        // ------
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        // draw our first triangle
        glUseProgram(shaderProgram);
        glBindVertexArray(VAO); // seeing as we only have a single VAO there's no need to bind it every time, but we'll do so to keep things a bit more organized
        //glDrawArrays(GL_TRIANGLES, 0, 6);
        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
        // glBindVertexArray(0); // no need to unbind it every time

        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    // optional: de-allocate all resources once they've outlived their purpose:
    // ------------------------------------------------------------------------
    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);
    glDeleteBuffers(1, &EBO);

    // glfw: terminate, clearing all previously allocated GLFW resources.
    // ------------------------------------------------------------------
    glfwTerminate();
    return 0;
}

// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
void processInput(GLFWwindow *window)
{
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);
}

// glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    // make sure the viewport matches the new window dimensions; note that width and
    // height will be significantly larger than specified on retina displays.
    glViewport(0, 0, width, height);
}

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