OpenGL编写着色程序，并演示使用

• 用到少量的OPENGLSL语言
• 实现简单的顶点着色器
• 实现简单的片段着色器
• 使用VAO储存vertex attributes
• 演示如何链接顶点着色器和片段着色器并创建一个着色程序
• 最后，输入了一组顶点数据，绘制了一个三角形

可以使用此小程序创建各种图形，只需要多加几个顶点。

#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <iostream>
using namespace std;
const unsigned int screen_width = 800;
const unsigned int screen_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"
                            "}\0";

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

int main()
{
    //initialization and setting
    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);

    //Creating window and checking whether it is created or not;
    GLFWwindow * window = glfwCreateWindow(screen_width, screen_height, "MyWindow", nullptr, nullptr);
    if(window == nullptr)
    {
        cout << "Fail to create window." << endl;
        glfwTerminate();

        return -1;
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

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

    //Creating vertexshader compiler
    int vertexShader;
    vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, nullptr);
    glCompileShader(vertexShader);
    int sucess;
    char infoLog[512];
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &sucess);
    if(!sucess)
    {
        glGetShaderInfoLog(vertexShader, 512, nullptr, infoLog);
        cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << endl;
    }

    //Creating fragmentShader compiler
    int fragmentShader;
    fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, nullptr);
    glCompileShader(fragmentShader);
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &sucess);
    if(!sucess)
    {
        glGetShaderInfoLog(fragmentShader, 512, nullptr, infoLog);
        cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << endl;
    }


    //Link vertex shader and fragement shader
    int shaderPragram;
    shaderPragram = glCreateProgram();
    glAttachShader(shaderPragram, vertexShader);
    glAttachShader(shaderPragram, fragmentShader);
    glLinkProgram(shaderPragram);
    glGetProgramiv(shaderPragram, GL_LINK_STATUS, &sucess);
    if(!sucess)
    {
        glGetProgramInfoLog(shaderPragram, 512, nullptr, infoLog);
        cout << "Fail to link shaders." << endl;
    }
    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);


    float vertices[] = {
    -0.5f, -0.5f, 0.0f,
     0.5f, -0.5f, 0.0f,
     0.0f,  0.5f, 0.0f
    };
    
    //Create vertex buffer to store data.
    unsigned int VBO, VAO;
    glGenBuffers(1, &VBO);
    glGenVertexArrays(1, &VAO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBindVertexArray(VAO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3*sizeof(float), (void *)0);
    glEnableVertexAttribArray(0);

    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindVertexArray(0);


    
   
   //building a rendor loop
    while(!glfwWindowShouldClose(window))
    {
        inputProcess(window);

        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        glUseProgram(shaderPragram);
        glBindVertexArray(VAO);
        glDrawArrays(GL_TRIANGLES, 0, 3);

        glfwPollEvents();
        glfwSwapBuffers(window);
        
    }

    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);
    
    glfwTerminate();
    return 0;
}

//building a viewport which can be changed.
void framebuffer_size_callback(GLFWwindow * window, int width, int height)
{
    glViewport(0,0, width, height);
}

//process input
void inputProcess(GLFWwindow * window)
{
    if(glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
    {
        glfwSetWindowShouldClose(window, true);
    }
}