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

#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>

#include <learnopengl/shader.h>
#include <learnopengl/camera.h>
#include <learnopengl/model.h>

#include <iostream>

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void mouse_callback(GLFWwindow* window, double xpos, double ypos);
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset);
void processInput(GLFWwindow *window);
unsigned int loadTexture(const char *path, bool gammaCorrection);
void renderQuad();
void renderCube();

// settings
const unsigned int SCR_WIDTH = 1280;
const unsigned int SCR_HEIGHT = 720;
bool bloom = true;
bool bloomKeyPressed = false;
float exposure = 1.0f;

// camera
Camera camera(glm::vec3(0.0f, 0.0f, 5.0f));
float lastX = (float)SCR_WIDTH / 2.0;
float lastY = (float)SCR_HEIGHT / 2.0;
bool firstMouse = true;

// timing
float deltaTime = 0.0f;
float lastFrame = 0.0f;

int main()
{
    // glfw: initialize and configure
    // ------------------------------
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

#ifdef __APPLE__
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // uncomment this statement to fix compilation on OS X
#endif

    // glfw window creation
    // --------------------
    GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
    if (window == NULL)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
    glfwSetCursorPosCallback(window, mouse_callback);
    glfwSetScrollCallback(window, scroll_callback);

    // tell GLFW to capture our mouse
    glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);

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

    // configure global opengl state
    // -----------------------------
    glEnable(GL_DEPTH_TEST);

    // build and compile shaders
    // -------------------------
    Shader shader("7.bloom.vs", "7.bloom.fs");
    Shader shaderLight("7.bloom.vs", "7.light_box.fs");
    Shader shaderBlur("7.blur.vs", "7.blur.fs");
    Shader shaderBloomFinal("7.bloom_final.vs", "7.bloom_final.fs");

    // load textures
    // -------------
    unsigned int woodTexture      = loadTexture(FileSystem::getPath("resources/textures/wood.png").c_str(), true); // note that we're loading the texture as an SRGB texture
    unsigned int containerTexture = loadTexture(FileSystem::getPath("resources/textures/container2.png").c_str(), true); // note that we're loading the texture as an SRGB texture

    // configure (floating point) framebuffers
    // ---------------------------------------
    unsigned int hdrFBO;
    glGenFramebuffers(1, &hdrFBO);
    glBindFramebuffer(GL_FRAMEBUFFER, hdrFBO);
    // create 2 floating point color buffers (1 for normal rendering, other for brightness treshold values)
    unsigned int colorBuffers[2];
    glGenTextures(2, colorBuffers);
    for (unsigned int i = 0; i < 2; i++)
    {
        glBindTexture(GL_TEXTURE_2D, colorBuffers[i]);
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB16F, SCR_WIDTH, SCR_HEIGHT, 0, GL_RGB, GL_FLOAT, NULL);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);  // we clamp to the edge as the blur filter would otherwise sample repeated texture values!
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
        // attach texture to framebuffer
        glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0 + i, GL_TEXTURE_2D, colorBuffers[i], 0);
    }
    // create and attach depth buffer (renderbuffer)
    unsigned int rboDepth;
    glGenRenderbuffers(1, &rboDepth);
    glBindRenderbuffer(GL_RENDERBUFFER, rboDepth);
    glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, SCR_WIDTH, SCR_HEIGHT);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, rboDepth);
    // tell OpenGL which color attachments we'll use (of this framebuffer) for rendering 
    unsigned int attachments[2] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1 };
    glDrawBuffers(2, attachments);
    // finally check if framebuffer is complete
    if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
        std::cout << "Framebuffer not complete!" << std::endl;
    glBindFramebuffer(GL_FRAMEBUFFER, 0);

    // ping-pong-framebuffer for blurring
    unsigned int pingpongFBO[2];
    unsigned int pingpongColorbuffers[2];
    glGenFramebuffers(2, pingpongFBO);
    glGenTextures(2, pingpongColorbuffers);
    for (unsigned int i = 0; i < 2; i++)
    {
        glBindFramebuffer(GL_FRAMEBUFFER, pingpongFBO[i]);
        glBindTexture(GL_TEXTURE_2D, pingpongColorbuffers[i]);
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB16F, SCR_WIDTH, SCR_HEIGHT, 0, GL_RGB, GL_FLOAT, NULL);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); // we clamp to the edge as the blur filter would otherwise sample repeated texture values!
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
        glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, pingpongColorbuffers[i], 0);
        // also check if framebuffers are complete (no need for depth buffer)
        if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
            std::cout << "Framebuffer not complete!" << std::endl;
    }

    // lighting info
    // -------------
    // positions
    std::vector<glm::vec3> lightPositions;
    lightPositions.push_back(glm::vec3( 0.0f, 0.5f,  1.5f));
    lightPositions.push_back(glm::vec3(-4.0f, 0.5f, -3.0f));
    lightPositions.push_back(glm::vec3( 3.0f, 0.5f,  1.0f));
    lightPositions.push_back(glm::vec3(-.8f,  2.4f, -1.0f));
    // colors
    std::vector<glm::vec3> lightColors;
    lightColors.push_back(glm::vec3(2.0f, 2.0f, 2.0f));
    lightColors.push_back(glm::vec3(1.5f, 0.0f, 0.0f));
    lightColors.push_back(glm::vec3(0.0f, 0.0f, 1.5f));
    lightColors.push_back(glm::vec3(0.0f, 1.5f, 0.0f));


    // shader configuration
    // --------------------
    shader.use();
    shader.setInt("diffuseTexture", 0);
    shaderBlur.use();
    shaderBlur.setInt("image", 0);
    shaderBloomFinal.use();
    shaderBloomFinal.setInt("scene", 0);
    shaderBloomFinal.setInt("bloomBlur", 1);

    // render loop
    // -----------
    while (!glfwWindowShouldClose(window))
    {
        // per-frame time logic
        // --------------------
        float currentFrame = glfwGetTime();
        deltaTime = currentFrame - lastFrame;
        lastFrame = currentFrame;

        // input
        // -----
        processInput(window);

        // render
        // ------
        glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        // 1. render scene into floating point framebuffer
        // -----------------------------------------------
        glBindFramebuffer(GL_FRAMEBUFFER, hdrFBO);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        glm::mat4 projection = glm::perspective(glm::radians(camera.Zoom), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f);
        glm::mat4 view = camera.GetViewMatrix();
        glm::mat4 model;
        shader.use();
        shader.setMat4("projection", projection);
        shader.setMat4("view", view);
        glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D, woodTexture);
        // set lighting uniforms
        for (unsigned int i = 0; i < lightPositions.size(); i++)
        {
            shader.setVec3("lights[" + std::to_string(i) + "].Position", lightPositions[i]);
            shader.setVec3("lights[" + std::to_string(i) + "].Color", lightColors[i]);
        }
        shader.setVec3("viewPos", camera.Position);
        // create one large cube that acts as the floor
        model = glm::mat4();
        model = glm::translate(model, glm::vec3(0.0f, -1.0f, 0.0));
        model = glm::scale(model, glm::vec3(12.5f, 0.5f, 12.5f));
        shader.setMat4("model", model);
        shader.setMat4("model", model);
        renderCube();
        // then create multiple cubes as the scenery
        glBindTexture(GL_TEXTURE_2D, containerTexture);
        model = glm::mat4();
        model = glm::translate(model, glm::vec3(0.0f, 1.5f, 0.0));
        model = glm::scale(model, glm::vec3(0.5f));
        shader.setMat4("model", model);
        renderCube();

        model = glm::mat4();
        model = glm::translate(model, glm::vec3(2.0f, 0.0f, 1.0));
        model = glm::scale(model, glm::vec3(0.5f));
        shader.setMat4("model", model);
        renderCube();

        model = glm::mat4();
        model = glm::translate(model, glm::vec3(-1.0f, -1.0f, 2.0));
        model = glm::rotate(model, glm::radians(60.0f), glm::normalize(glm::vec3(1.0, 0.0, 1.0)));
        shader.setMat4("model", model);
        renderCube();

        model = glm::mat4();
        model = glm::translate(model, glm::vec3(0.0f, 2.7f, 4.0));
        model = glm::rotate(model, glm::radians(23.0f), glm::normalize(glm::vec3(1.0, 0.0, 1.0)));
        model = glm::scale(model, glm::vec3(1.25));
        shader.setMat4("model", model);
        renderCube();

        model = glm::mat4();
        model = glm::translate(model, glm::vec3(-2.0f, 1.0f, -3.0));
        model = glm::rotate(model, glm::radians(124.0f), glm::normalize(glm::vec3(1.0, 0.0, 1.0)));
        shader.setMat4("model", model);
        renderCube();

        model = glm::mat4();
        model = glm::translate(model, glm::vec3(-3.0f, 0.0f, 0.0));
        model = glm::scale(model, glm::vec3(0.5f));
        shader.setMat4("model", model);
        renderCube();

        // finally show all the light sources as bright cubes
        shaderLight.use();
        shaderLight.setMat4("projection", projection);
        shaderLight.setMat4("view", view);

        for (unsigned int i = 0; i < lightPositions.size(); i++)
        {
            model = glm::mat4();
            model = glm::translate(model, glm::vec3(lightPositions[i]));
            model = glm::scale(model, glm::vec3(0.25f));
            shaderLight.setMat4("model", model);
            shaderLight.setVec3("lightColor", lightColors[i]);
            renderCube();
        }
        glBindFramebuffer(GL_FRAMEBUFFER, 0);

        // 2. blur bright fragments with two-pass Gaussian Blur 
        // --------------------------------------------------
        bool horizontal = true, first_iteration = true;
        unsigned int amount = 10;
        shaderBlur.use();
        for (unsigned int i = 0; i < amount; i++)
        {
            glBindFramebuffer(GL_FRAMEBUFFER, pingpongFBO[horizontal]);
            shaderBlur.setInt("horizontal", horizontal);
            glBindTexture(GL_TEXTURE_2D, first_iteration ? colorBuffers[1] : pingpongColorbuffers[!horizontal]);  // bind texture of other framebuffer (or scene if first iteration)
            renderQuad();
            horizontal = !horizontal;
            if (first_iteration)
                first_iteration = false;
        }
        glBindFramebuffer(GL_FRAMEBUFFER, 0);

        // 3. now render floating point color buffer to 2D quad and tonemap HDR colors to default framebuffer's (clamped) color range
        // --------------------------------------------------------------------------------------------------------------------------
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        shaderBloomFinal.use();
        glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D, colorBuffers[0]);
        glActiveTexture(GL_TEXTURE1);
        glBindTexture(GL_TEXTURE_2D, pingpongColorbuffers[!horizontal]);
        shaderBloomFinal.setInt("bloom", bloom);
        shaderBloomFinal.setFloat("exposure", exposure);
        renderQuad();

        std::cout << "bloom: " << (bloom ? "on" : "off") << "| exposure: " << exposure << std::endl;

        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    glfwTerminate();
    return 0;
}

// renderCube() renders a 1x1 3D cube in NDC.
// -------------------------------------------------
unsigned int cubeVAO = 0;
unsigned int cubeVBO = 0;
void renderCube()
{
    // initialize (if necessary)
    if (cubeVAO == 0)
    {
        float vertices[] = {
            // back face
            -1.0f, -1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 0.0f, 0.0f, // bottom-left
             1.0f,  1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 1.0f, 1.0f, // top-right
             1.0f, -1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 1.0f, 0.0f, // bottom-right         
             1.0f,  1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 1.0f, 1.0f, // top-right
            -1.0f, -1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 0.0f, 0.0f, // bottom-left
            -1.0f,  1.0f, -1.0f,  0.0f,  0.0f, -1.0f, 0.0f, 1.0f, // top-left
            // front face
            -1.0f, -1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 0.0f, 0.0f, // bottom-left
             1.0f, -1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 1.0f, 0.0f, // bottom-right
             1.0f,  1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 1.0f, 1.0f, // top-right
             1.0f,  1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 1.0f, 1.0f, // top-right
            -1.0f,  1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 0.0f, 1.0f, // top-left
            -1.0f, -1.0f,  1.0f,  0.0f,  0.0f,  1.0f, 0.0f, 0.0f, // bottom-left
            // left face
            -1.0f,  1.0f,  1.0f, -1.0f,  0.0f,  0.0f, 1.0f, 0.0f, // top-right
            -1.0f,  1.0f, -1.0f, -1.0f,  0.0f,  0.0f, 1.0f, 1.0f, // top-left
            -1.0f, -1.0f, -1.0f, -1.0f,  0.0f,  0.0f, 0.0f, 1.0f, // bottom-left
            -1.0f, -1.0f, -1.0f, -1.0f,  0.0f,  0.0f, 0.0f, 1.0f, // bottom-left
            -1.0f, -1.0f,  1.0f, -1.0f,  0.0f,  0.0f, 0.0f, 0.0f, // bottom-right
            -1.0f,  1.0f,  1.0f, -1.0f,  0.0f,  0.0f, 1.0f, 0.0f, // top-right
            // right face
             1.0f,  1.0f,  1.0f,  1.0f,  0.0f,  0.0f, 1.0f, 0.0f, // top-left
             1.0f, -1.0f, -1.0f,  1.0f,  0.0f,  0.0f, 0.0f, 1.0f, // bottom-right
             1.0f,  1.0f, -1.0f,  1.0f,  0.0f,  0.0f, 1.0f, 1.0f, // top-right         
             1.0f, -1.0f, -1.0f,  1.0f,  0.0f,  0.0f, 0.0f, 1.0f, // bottom-right
             1.0f,  1.0f,  1.0f,  1.0f,  0.0f,  0.0f, 1.0f, 0.0f, // top-left
             1.0f, -1.0f,  1.0f,  1.0f,  0.0f,  0.0f, 0.0f, 0.0f, // bottom-left     
            // bottom face
            -1.0f, -1.0f, -1.0f,  0.0f, -1.0f,  0.0f, 0.0f, 1.0f, // top-right
             1.0f, -1.0f, -1.0f,  0.0f, -1.0f,  0.0f, 1.0f, 1.0f, // top-left
             1.0f, -1.0f,  1.0f,  0.0f, -1.0f,  0.0f, 1.0f, 0.0f, // bottom-left
             1.0f, -1.0f,  1.0f,  0.0f, -1.0f,  0.0f, 1.0f, 0.0f, // bottom-left
            -1.0f, -1.0f,  1.0f,  0.0f, -1.0f,  0.0f, 0.0f, 0.0f, // bottom-right
            -1.0f, -1.0f, -1.0f,  0.0f, -1.0f,  0.0f, 0.0f, 1.0f, // top-right
            // top face
            -1.0f,  1.0f, -1.0f,  0.0f,  1.0f,  0.0f, 0.0f, 1.0f, // top-left
             1.0f,  1.0f , 1.0f,  0.0f,  1.0f,  0.0f, 1.0f, 0.0f, // bottom-right
             1.0f,  1.0f, -1.0f,  0.0f,  1.0f,  0.0f, 1.0f, 1.0f, // top-right     
             1.0f,  1.0f,  1.0f,  0.0f,  1.0f,  0.0f, 1.0f, 0.0f, // bottom-right
            -1.0f,  1.0f, -1.0f,  0.0f,  1.0f,  0.0f, 0.0f, 1.0f, // top-left
            -1.0f,  1.0f,  1.0f,  0.0f,  1.0f,  0.0f, 0.0f, 0.0f  // bottom-left        
        };
        glGenVertexArrays(1, &cubeVAO);
        glGenBuffers(1, &cubeVBO);
        // fill buffer
        glBindBuffer(GL_ARRAY_BUFFER, cubeVBO);
        glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
        // link vertex attributes
        glBindVertexArray(cubeVAO);
        glEnableVertexAttribArray(0);
        glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
        glEnableVertexAttribArray(1);
        glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(3 * sizeof(float)));
        glEnableVertexAttribArray(2);
        glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(6 * sizeof(float)));
        glBindBuffer(GL_ARRAY_BUFFER, 0);
        glBindVertexArray(0);
    }
    // render Cube
    glBindVertexArray(cubeVAO);
    glDrawArrays(GL_TRIANGLES, 0, 36);
    glBindVertexArray(0);
}

// renderQuad() renders a 1x1 XY quad in NDC
// -----------------------------------------
unsigned int quadVAO = 0;
unsigned int quadVBO;
void renderQuad()
{
    if (quadVAO == 0)
    {
        float quadVertices[] = {
            // positions        // texture Coords
            -1.0f,  1.0f, 0.0f, 0.0f, 1.0f,
            -1.0f, -1.0f, 0.0f, 0.0f, 0.0f,
             1.0f,  1.0f, 0.0f, 1.0f, 1.0f,
             1.0f, -1.0f, 0.0f, 1.0f, 0.0f,
        };
        // setup plane VAO
        glGenVertexArrays(1, &quadVAO);
        glGenBuffers(1, &quadVBO);
        glBindVertexArray(quadVAO);
        glBindBuffer(GL_ARRAY_BUFFER, quadVBO);
        glBufferData(GL_ARRAY_BUFFER, sizeof(quadVertices), &quadVertices, GL_STATIC_DRAW);
        glEnableVertexAttribArray(0);
        glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)0);
        glEnableVertexAttribArray(1);
        glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)(3 * sizeof(float)));
    }
    glBindVertexArray(quadVAO);
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
    glBindVertexArray(0);
}

// 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);

    if (glfwGetKey(window, GLFW_KEY_W) == GLFW_PRESS)
        camera.ProcessKeyboard(FORWARD, deltaTime);
    if (glfwGetKey(window, GLFW_KEY_S) == GLFW_PRESS)
        camera.ProcessKeyboard(BACKWARD, deltaTime);
    if (glfwGetKey(window, GLFW_KEY_A) == GLFW_PRESS)
        camera.ProcessKeyboard(LEFT, deltaTime);
    if (glfwGetKey(window, GLFW_KEY_D) == GLFW_PRESS)
        camera.ProcessKeyboard(RIGHT, deltaTime);

    if (glfwGetKey(window, GLFW_KEY_SPACE) == GLFW_PRESS && !bloomKeyPressed)
    {
        bloom = !bloom;
        bloomKeyPressed = true;
    }
    if (glfwGetKey(window, GLFW_KEY_SPACE) == GLFW_RELEASE)
    {
        bloomKeyPressed = false;
    }

    if (glfwGetKey(window, GLFW_KEY_Q) == GLFW_PRESS)
    {
        if (exposure > 0.0f)
            exposure -= 0.001f;
        else
            exposure = 0.0f;
    }
    else if (glfwGetKey(window, GLFW_KEY_E) == GLFW_PRESS)
    {
        exposure += 0.001f;
    }
}

// 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)
{
    // make sure the viewport matches the new window dimensions; note that width and 
    // height will be significantly larger than specified on retina displays.
    glViewport(0, 0, width, height);
}

// glfw: whenever the mouse moves, this callback is called
// -------------------------------------------------------
void mouse_callback(GLFWwindow* window, double xpos, double ypos)
{
    if (firstMouse)
    {
        lastX = xpos;
        lastY = ypos;
        firstMouse = false;
    }

    float xoffset = xpos - lastX;
    float yoffset = lastY - ypos; // reversed since y-coordinates go from bottom to top

    lastX = xpos;
    lastY = ypos;

    camera.ProcessMouseMovement(xoffset, yoffset);
}

// glfw: whenever the mouse scroll wheel scrolls, this callback is called
// ----------------------------------------------------------------------
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset)
{
    camera.ProcessMouseScroll(yoffset);
}

// utility function for loading a 2D texture from file
// ---------------------------------------------------
unsigned int loadTexture(char const * path, bool gammaCorrection)
{
    unsigned int textureID;
    glGenTextures(1, &textureID);

    int width, height, nrComponents;
    unsigned char *data = stbi_load(path, &width, &height, &nrComponents, 0);
    if (data)
    {
        GLenum internalFormat;
        GLenum dataFormat;
        if (nrComponents == 1)
        {
            internalFormat = dataFormat = GL_RED;
        }
        else if (nrComponents == 3)
        {
            internalFormat = gammaCorrection ? GL_SRGB : GL_RGB;
            dataFormat = GL_RGB;
        }
        else if (nrComponents == 4)
        {
            internalFormat = gammaCorrection ? GL_SRGB_ALPHA : GL_RGBA;
            dataFormat = GL_RGBA;
        }

        glBindTexture(GL_TEXTURE_2D, textureID);
        glTexImage2D(GL_TEXTURE_2D, 0, internalFormat, width, height, 0, dataFormat, GL_UNSIGNED_BYTE, data);
        glGenerateMipmap(GL_TEXTURE_2D);

        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

        stbi_image_free(data);
    }
    else
    {
        std::cout << "Texture failed to load at path: " << path << std::endl;
        stbi_image_free(data);
    }

    return textureID;
}
HI