#include <iostream>  // GLEW  #define GLEW_STATIC  #include <GL/glew.h>  // GLFW  #include <GLFW/glfw3.h> // Function prototypes  void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode);// Window dimensions  const GLuint WIDTH = 800, HEIGHT = 600;// Shaders  const GLchar* vertexShaderSource = "#version 330 core\n""layout (location = 0) in vec3 position;\n""void main()\n""{\n"    "gl_Position = vec4(position.x, position.y, position.z, 1.0);\n""}\0";const GLchar* fragmentShaderSource = "#version 330 core\n""out vec4 color;\n""void main()\n""{\n"    "color = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n""}\n\0";// The MAIN function, from here we start the application and run the game loop  int main(){    std::cout << "Starting GLFW context, OpenGL 3.3" << std::endl;    // Init GLFW      glfwInit();    // Set all the required options for GLFW      glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);    glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);    // Create a GLFWwindow object that we can use for GLFW‘s functions      GLFWwindow* window = glfwCreateWindow(WIDTH, HEIGHT, "LearnOpenGL", nullptr, nullptr);    glfwMakeContextCurrent(window);    // Set the required callback functions      glfwSetKeyCallback(window, key_callback);    // Set this to true so GLEW knows to use a modern approach to retrieving function pointers and extensions      glewExperimental = GL_TRUE;    // Initialize GLEW to setup the OpenGL Function pointers      glewInit();    // Define the viewport dimensions      int width, height;    glfwGetFramebufferSize(window, &width, &height);    glViewport(0, 0, width, height);    // Build and compile our shader program      // Vertex shader      GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);    glCompileShader(vertexShader);    // Check for compile time errors      GLint success;    GLchar 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      GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);    glCompileShader(fragmentShader);    // Check for compile time 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      GLuint 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 attribute pointers      //GLfloat vertices[] = {      //  // First triangle      //   0.5f,  0.5f,  // Top Right      //   0.5f, -0.5f,  // Bottom Right      //  -0.5f,  0.5f,  // Top Left       //  // Second triangle      //   0.5f, -0.5f,  // Bottom Right      //  -0.5f, -0.5f,  // Bottom Left      //  -0.5f,  0.5f   // Top Left      //};       GLfloat 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       };    GLuint indices[] = {  // Note that we start from 0!          0, 1, 3,  // First Triangle          1, 2, 3   // Second Triangle      };    GLuint 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 attribute pointer(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(GLfloat), (GLvoid*)0);    glEnableVertexAttribArray(0);    glBindBuffer(GL_ARRAY_BUFFER, 0); // Note that this is allowed, the call to glVertexAttribPointer registered VBO as the currently bound vertex buffer object so afterwards we can safely unbind      glBindVertexArray(0); // Unbind VAO (it‘s always a good thing to unbind any buffer/array to prevent strange bugs), remember: do NOT unbind the EBO, keep it bound to this VAO      // Uncommenting this call will result in wireframe polygons.      //glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);      // Game loop      while (!glfwWindowShouldClose(window))    {        // Check if any events have been activiated (key pressed, mouse moved etc.) and call corresponding response functions          glfwPollEvents();        // Render          // Clear the colorbuffer          glClearColor(0.2f, 0.3f, 0.3f, 1.0f);        glClear(GL_COLOR_BUFFER_BIT);        // Draw our first triangle          glUseProgram(shaderProgram);        glBindVertexArray(VAO);        //glDrawArrays(GL_TRIANGLES, 0, 6);          glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);        glBindVertexArray(0);        // Swap the screen buffers          glfwSwapBuffers(window);    }    // Properly de-allocate all resources once they‘ve outlived their purpose      glDeleteVertexArrays(1, &VAO);    glDeleteBuffers(1, &VBO);    glDeleteBuffers(1, &EBO);    // Terminate GLFW, clearing any resources allocated by GLFW.      glfwTerminate();    return 0;}// Is called whenever a key is pressed/released via GLFW  void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode){    if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)        glfwSetWindowShouldClose(window, GL_TRUE);}