triangle

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

// Vertex Shader source code
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";
//Fragment Shader source code
const char* fragmentShaderSource = "#version 330 core\n"
"out vec4 FragColor;\n"
"void main()\n"
"{\n"
"   FragColor = vec4(0.8f, 0.3f, 0.02f, 1.0f);\n"
"}\n\0";

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);
}

int main()
{
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    // Tell GLFW we are using the CORE profile, So that means we only have the modern functions
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    GLFWwindow* window = glfwCreateWindow(800, 600, "LearnOpenGL", NULL, NULL);
    // Error check if the window fails to create
    if (window == NULL)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    // Introduce the window into the current context
    glfwMakeContextCurrent(window);

    // Load GLAD so it configures OpenGL or use th method gladLoadGL();
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }
    // gladLoadGL();

    // glViewport(0, 0, 800, 600);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

    // Create Vertex Shader Object and get its reference
    GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
    // Attach Vertex Shader source to the Vertex Shader Object
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    // Compile the Vertex Shader into machine code
    glCompileShader(vertexShader);
    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;
        return -1;
    }

    // Create Fragment Shader Object and get its reference
    GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    // Attach Fragment Shader source to the Fragment Shader Object
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    // Compile the Vertex Shader into machine code
    glCompileShader(fragmentShader);

    // Create Shader Program Object and get its reference
    GLuint shaderProgram = glCreateProgram();
    // Attach the Vertex and Fragment Shaders to the Shader Program
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    // Wrap-up/Link all the shaders together into the Shader Program
    glLinkProgram(shaderProgram);
    glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
    if (!success) {
        glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
        return -1;
    }

    // Delete the now useless Vertex and Fragment Shader objects
    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);

    // Vertices coordinates
    GLfloat vertices[] =
    {
        -0.5f, -0.5f * float(sqrt(3)) / 3, 0.0f, // Lower left corner
        0.5f, -0.5f * float(sqrt(3)) / 3, 0.0f, // Lower right corner
        0.0f, 0.5f * float(sqrt(3)) * 2 / 3, 0.0f, // Upper corner
        -0.5f / 2, 0.5f * float(sqrt(3)) / 6, 0.0f, // Inner left
        0.5f / 2, 0.5f * float(sqrt(3)) / 6, 0.0f, // Inner right
        0.0f, -0.5f * float(sqrt(3)) / 3, 0.0f, // Inner down
    };

    GLuint indices[] =
    {
        0, 3, 5,
        3, 2, 4,
        5, 4, 1,
    };

    // Create reference containers for the Vartex Array Object and the Vertex Buffer Object
    GLuint VAO, VBO, EBO;

    // Generate the VAO and VBO with only 1 object each
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    glGenBuffers(1, &EBO);

    // Make the VAO the current Vertex Array Object by binding it
    glBindVertexArray(VAO);

    // Bind the VBO specifying it's a GL_ARRAY_BUFFER
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    // Introduce the vertices into the 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);

    // Configure the Vertex Attribute so that OpenGL knows how to read the VBO
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
    // Enable the Vertex Attribute so that OpenGL knows to use it
    glEnableVertexAttribArray(0);

    // Bind both the VBO and VAO to 0 so that we don't accidentally modify the VAO and VBO we created
    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindVertexArray(0);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);

    while (!glfwWindowShouldClose(window))
    {
        processInput(window);
        // rendering commands here
        // Specify the color of the background
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        // Clean the back buffer and assign the new color to it
        glClear(GL_COLOR_BUFFER_BIT);
        // Tell OpenGL which Shader Program we want to use
        glUseProgram(shaderProgram);
        // Bind the VAO so OpenGL knows to use it
        glBindVertexArray(VAO);
        // Draw the triangle using the GL_TRIANGLES primitive
        // glDrawArrays(GL_TRIANGLES, 0, 3);
        glDrawElements(GL_TRIANGLES, 9, GL_UNSIGNED_INT, 0);
        // check and call events and swap the buffers
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    // Delete all the objects we've created
    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);
    glDeleteBuffers(1, &EBO);
    glDeleteProgram(shaderProgram);
    // Delete window before ending the program
    glfwDestroyWindow(window);
    // Terminate GLFW before ending the program
    glfwTerminate();
    return 0;
}