main.cpp

#define STB_IMAGE_IMPLEMENTATION

#include "stb_image.h"
#include <fstream>
#include <sstream>
#include <string>
#include <iostream>

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


// === Global Variables ===

// Window Properties
const unsigned int windowWidth = 800;
const unsigned int windowHeight = 800;
const char* windowTitle = "GLFW Window (OpenGL)";

std::string readFile(const char* path);
void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow* window);

// === Main Function ===
int main()
{
	// Initialise GLFW
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 6);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

#ifdef __APPLE__
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif

    // Create GLFW window
    GLFWwindow* window = glfwCreateWindow(windowWidth, windowHeight, windowTitle, NULL, NULL);
    if (window == NULL)
    {
        std::cout << "Failed to create GLFW window!" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

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

    int success;
    char infoLog[512];

    // ==================================================================
    // Build and compile the shader program
    // ==================================================================

    std::string vertexCode = readFile("shaders/vertex.glsl");
    std::string fragmentCode = readFile("shaders/fragment.glsl");

    const char* vertexShaderSource = vertexCode.c_str();
    const char* fragmentShaderSource = fragmentCode.c_str();

    // Vertex Shader
    unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);
    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
    unsigned int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    glCompileShader(fragmentShader);
    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
    unsigned int shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    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;
    }
    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);

    // ==================================================================
    // Set up vertex data (and buffer(s)) and configure vertex attributes
    // ==================================================================

    float vertices[] = {
        // positions          // colors           // tex coords
         0.0f,  0.0f, 0.0f,   1.0f, 1.0f, 1.0f,   0.5f, 0.5f,
         0.5f,  0.5f, 0.0f,   1.0f, 0.0f, 0.0f,   1.0f, 1.0f,
         0.5f, -0.5f, 0.0f,   0.0f, 1.0f, 0.0f,   1.0f, 0.0f,
        -0.5f, -0.5f, 0.0f,   0.0f, 0.0f, 1.0f,   0.0f, 0.0f,
        -0.5f,  0.5f, 0.0f,   1.0f, 1.0f, 0.0f,   0.0f, 1.0f
    };

    unsigned int indices[] = {
        0, 1, 2,  // center ¡æ top right ¡æ bottom right
        0, 2, 3,  // center ¡æ bottom right ¡æ bottom left
        0, 3, 4,  // center ¡æ bottom left ¡æ top left
        0, 4, 1   // center ¡æ top left ¡æ top right
    };

    const unsigned int indexCount = sizeof(indices) / sizeof(indices[0]);

    unsigned int VBO, VAO, EBO;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    glGenBuffers(1, &EBO);
    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);

    // Position attribute
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);
    // Color attribute
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(3 * sizeof(float)));
    glEnableVertexAttribArray(1);
    // Texture coordinate attribue
    glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(6 * sizeof(float)));
    glEnableVertexAttribArray(2);

    glBindBuffer(GL_ARRAY_BUFFER, 0);

    glBindVertexArray(0);

    // Draw in wireframe
    //glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);

    // ==================================================================
    // Load Texture
    // ==================================================================

    unsigned int texture;

    glGenTextures(1, &texture);
    glBindTexture(GL_TEXTURE_2D, texture); // all upcoming GL_TEXTURE_2D operations now have effect on this texture object

    // Texture wrapping
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);

    // Texture filtering
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    // Flip texture
    stbi_set_flip_vertically_on_load(true);

    // load image, create texture and generate mipmaps
    int width, height, nrChannels;
    unsigned char* data = stbi_load("Texture.png", &width, &height, &nrChannels, 0);
    if (data)
    {
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);
        glGenerateMipmap(GL_TEXTURE_2D);
    }
    else
    {
        std::cout << "Failed to load texture" << std::endl;
    }
    stbi_image_free(data);


    // ==================================================================
    // Render loop
    // ==================================================================

    while (!glfwWindowShouldClose(window))
    {
        // Handle input
        processInput(window);

        // Clear color
        glClearColor(0.15f, 0.15f, 0.15f, 1.0f); // Set the color used to clear the color buffer
        glClear(GL_COLOR_BUFFER_BIT); // Clear the color buffer using the current clear color

        // Draw our first triangle
        glUseProgram(shaderProgram);
        glBindTexture(GL_TEXTURE_2D, texture);
        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
        glDrawElements(GL_TRIANGLES, indexCount, GL_UNSIGNED_INT, 0);

        // Swap buffers and poll IO events
        glfwSwapBuffers(window);
        glfwPollEvents();
    }
    
    glfwTerminate(); // Terminante and clear all previously allocated GLFW resources
	return 0;
}

// === Other Functions ===

// Read file
std::string readFile(const char* path)
{
    std::ifstream file(path, std::ios::in);
    if (!file.is_open())
    {
        std::cerr << "ERROR::SHADER::FILE_NOT_READ: " << path << std::endl;
        return "";
    }

    std::stringstream buffer;
    buffer << file.rdbuf();
    file.close();

    return buffer.str();
}

// 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)
{
    glViewport(0, 0, width, height);
}