Hello Triangle

使用OpenGL绘制图形的步骤

1. 一般来说，顶点着色器和片段着色器需要我们自定义的。所以首先自定义顶点着色器和片段着色器，按照格式写出他们的源码。
2. 使用GLFW完成窗口的初始创建。
3. 使用GLAD加载所有OpenGL函数指针。
4. 创建着色器，并检查他们是否创建成功。
5. 创建连接程序。我觉得就是把渲染管线搭好。检查是否搭好，然后就能把之前创建的着色器都删除了。
6. 架子搭好了，然后就应该塞数据了。创建顶点缓冲对象，顶点数组对象；绑定顶点数组对象；绑定顶点缓冲对象；往顶点缓冲对象里边塞数据；设置顶点属性；解绑。
7. 然后while循环进行绘制。
8. 窗口销毁后，删除顶点数组对象，顶点缓冲对象。

代码

#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);
}

void processInput(GLFWwindow* window)
{
    if (glfwGetKey(window,GLFW_KEY_ESCAPE) == GLFW_PRESS)
    {
        glfwSetWindowShouldClose(window, true);
    }
}

//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初始化
    glfwInit();
    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(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
    if (!window)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

    //glad: 加载所有OpenGL函数的指针
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return - 1;
    }

    //窗口初始化完成，并加载了OpenGL的函数，下面进行OpenGL相关的操作

    //着色器
    //----------------------------------------------------
    //创建顶点着色器
    int vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);
    //检查顶点着色器是否创建成功
    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;
    }
    //创建片段着色器
    int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    glCompileShader(fragmentShader);
    //检查片段着色器是否创建成功
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
    }

    //创建完顶点着色器和片段着色器之后，我们应该把他们链接到一起
    int shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);
    //检查是否链接成功
    glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
    if (!success)
    {
        glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << std::endl;
    }
    //链接成功，删除创建的Shaders
    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);

    //至此，OpenGL渲染管线已经搭建完毕，我们要塞数据了
    //----------------------------------------------------------------------------------------------
    //设置三个顶点
    float vertices[] = {
        -0.5f, -0.5f, 0.0f, // left  
         0.5f, -0.5f, 0.0f, // right 
         0.0f,  0.5f, 0.0f  // top   
    };
    //创建顶点缓冲对象，顶点数组对象
    unsigned int VBO, VAO;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    //绑定顶点数组对象，然后绑定并设置顶点缓冲，之后再设置顶点属性
    //-------------------------------------------------------------------
    //绑定顶点数组对象
    glBindVertexArray(VAO);
    //绑定顶点缓冲对象
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    //往顶点缓冲对象里边塞数据
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), &vertices, GL_STATIC_DRAW);
    //设置顶点属性
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);
    //解绑？
    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindVertexArray(0);

    while (!glfwWindowShouldClose(window))
    {
        processInput(window);
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);
        //开始绘制三角形！
        glUseProgram(shaderProgram);
        glBindVertexArray(VAO);
        glDrawArrays(GL_TRIANGLES, 0, 3);

        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);

    glfwTerminate();
    return 0;

}

效果