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

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;

// 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;

float lerp(float a, float b, float f)
{
    return a + f * (b - a);
}

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 shaderGeometryPass("9.ssao_geometry.vs", "9.ssao_geometry.fs");
    Shader shaderLightingPass("9.ssao.vs", "9.ssao_lighting.fs");
    Shader shaderSSAO("9.ssao.vs", "9.ssao.fs");
    Shader shaderSSAOBlur("9.ssao.vs", "9.ssao_blur.fs");

    // load models
    // -----------
    Model nanosuit(FileSystem::getPath("resources/objects/nanosuit/nanosuit.obj"));

    // configure g-buffer framebuffer
    // ------------------------------
    unsigned int gBuffer;
    glGenFramebuffers(1, &gBuffer);
    glBindFramebuffer(GL_FRAMEBUFFER, gBuffer);
    unsigned int gPosition, gNormal, gAlbedo;
    // position color buffer
    glGenTextures(1, &gPosition);
    glBindTexture(GL_TEXTURE_2D, gPosition);
    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_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, gPosition, 0);
    // normal color buffer
    glGenTextures(1, &gNormal);
    glBindTexture(GL_TEXTURE_2D, gNormal);
    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_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT1, GL_TEXTURE_2D, gNormal, 0);
    // color + specular color buffer
    glGenTextures(1, &gAlbedo);
    glBindTexture(GL_TEXTURE_2D, gAlbedo);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, SCR_WIDTH, SCR_HEIGHT, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT2, GL_TEXTURE_2D, gAlbedo, 0);
    // tell OpenGL which color attachments we'll use (of this framebuffer) for rendering 
    unsigned int attachments[3] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1, GL_COLOR_ATTACHMENT2 };
    glDrawBuffers(3, attachments);
    // 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);
    // finally check if framebuffer is complete
    if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
        std::cout << "Framebuffer not complete!" << std::endl;
    glBindFramebuffer(GL_FRAMEBUFFER, 0);

    // also create framebuffer to hold SSAO processing stage 
    // -----------------------------------------------------
    unsigned int ssaoFBO, ssaoBlurFBO;
    glGenFramebuffers(1, &ssaoFBO);  glGenFramebuffers(1, &ssaoBlurFBO);
    glBindFramebuffer(GL_FRAMEBUFFER, ssaoFBO);
    unsigned int ssaoColorBuffer, ssaoColorBufferBlur;
    // SSAO color buffer
    glGenTextures(1, &ssaoColorBuffer);
    glBindTexture(GL_TEXTURE_2D, ssaoColorBuffer);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RED, SCR_WIDTH, SCR_HEIGHT, 0, GL_RGB, GL_FLOAT, NULL);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, ssaoColorBuffer, 0);
    if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
        std::cout << "SSAO Framebuffer not complete!" << std::endl;
    // and blur stage
    glBindFramebuffer(GL_FRAMEBUFFER, ssaoBlurFBO);
    glGenTextures(1, &ssaoColorBufferBlur);
    glBindTexture(GL_TEXTURE_2D, ssaoColorBufferBlur);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RED, SCR_WIDTH, SCR_HEIGHT, 0, GL_RGB, GL_FLOAT, NULL);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, ssaoColorBufferBlur, 0);
    if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
        std::cout << "SSAO Blur Framebuffer not complete!" << std::endl;
    glBindFramebuffer(GL_FRAMEBUFFER, 0);

    // generate sample kernel
    // ----------------------
    std::uniform_real_distribution<GLfloat> randomFloats(0.0, 1.0); // generates random floats between 0.0 and 1.0
    std::default_random_engine generator;
    std::vector<glm::vec3> ssaoKernel;
    for (unsigned int i = 0; i < 64; ++i)
    {
        glm::vec3 sample(randomFloats(generator) * 2.0 - 1.0, randomFloats(generator) * 2.0 - 1.0, randomFloats(generator));
        sample = glm::normalize(sample);
        sample *= randomFloats(generator);
        float scale = float(i) / 64.0;

        // scale samples s.t. they're more aligned to center of kernel
        scale = lerp(0.1f, 1.0f, scale * scale);
        sample *= scale;
        ssaoKernel.push_back(sample);
    }

    // generate noise texture
    // ----------------------
    std::vector<glm::vec3> ssaoNoise;
    for (unsigned int i = 0; i < 16; i++)
    {
        glm::vec3 noise(randomFloats(generator) * 2.0 - 1.0, randomFloats(generator) * 2.0 - 1.0, 0.0f); // rotate around z-axis (in tangent space)
        ssaoNoise.push_back(noise);
    }
    unsigned int noiseTexture; glGenTextures(1, &noiseTexture);
    glBindTexture(GL_TEXTURE_2D, noiseTexture);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB32F, 4, 4, 0, GL_RGB, GL_FLOAT, &ssaoNoise[0]);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);

    // lighting info
    // -------------
    glm::vec3 lightPos = glm::vec3(2.0, 4.0, -2.0);
    glm::vec3 lightColor = glm::vec3(0.2, 0.2, 0.7);

    // shader configuration
    // --------------------
    shaderLightingPass.use();
    shaderLightingPass.setInt("gPosition", 0);
    shaderLightingPass.setInt("gNormal", 1);
    shaderLightingPass.setInt("gAlbedo", 2);
    shaderLightingPass.setInt("ssao", 3);
    shaderSSAO.use();
    shaderSSAO.setInt("gPosition", 0);
    shaderSSAO.setInt("gNormal", 1);
    shaderSSAO.setInt("texNoise", 2);
    shaderSSAOBlur.use();
    shaderSSAOBlur.setInt("ssaoInput", 0);

    // 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. geometry pass: render scene's geometry/color data into gbuffer
        // -----------------------------------------------------------------
        glBindFramebuffer(GL_FRAMEBUFFER, gBuffer);
            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, 50.0f);
            glm::mat4 view = camera.GetViewMatrix();
            glm::mat4 model = glm::mat4(1.0f);
            shaderGeometryPass.use();
            shaderGeometryPass.setMat4("projection", projection);
            shaderGeometryPass.setMat4("view", view);
            // room cube
            model = glm::mat4(1.0f);
            model = glm::translate(model, glm::vec3(0.0, 7.0f, 0.0f));
            model = glm::scale(model, glm::vec3(7.5f, 7.5f, 7.5f));
            shaderGeometryPass.setMat4("model", model);
            shaderGeometryPass.setInt("invertedNormals", 1); // invert normals as we're inside the cube
            renderCube();
            shaderGeometryPass.setInt("invertedNormals", 0); 
            // nanosuit model on the floor
            model = glm::mat4(1.0f);
            model = glm::translate(model, glm::vec3(0.0f, 0.0f, 5.0));
            model = glm::rotate(model, glm::radians(-90.0f), glm::vec3(1.0, 0.0, 0.0));
            model = glm::scale(model, glm::vec3(0.5f));
            shaderGeometryPass.setMat4("model", model);
            nanosuit.Draw(shaderGeometryPass);
        glBindFramebuffer(GL_FRAMEBUFFER, 0);


        // 2. generate SSAO texture
        // ------------------------
        glBindFramebuffer(GL_FRAMEBUFFER, ssaoFBO);
            glClear(GL_COLOR_BUFFER_BIT);
            shaderSSAO.use();
            // Send kernel + rotation 
            for (unsigned int i = 0; i < 64; ++i)
                shaderSSAO.setVec3("samples[" + std::to_string(i) + "]", ssaoKernel[i]);
            shaderSSAO.setMat4("projection", projection);
            glActiveTexture(GL_TEXTURE0);
            glBindTexture(GL_TEXTURE_2D, gPosition);
            glActiveTexture(GL_TEXTURE1);
            glBindTexture(GL_TEXTURE_2D, gNormal);
            glActiveTexture(GL_TEXTURE2);
            glBindTexture(GL_TEXTURE_2D, noiseTexture);
            renderQuad();
        glBindFramebuffer(GL_FRAMEBUFFER, 0);


        // 3. blur SSAO texture to remove noise
        // ------------------------------------
        glBindFramebuffer(GL_FRAMEBUFFER, ssaoBlurFBO);
            glClear(GL_COLOR_BUFFER_BIT);
            shaderSSAOBlur.use();
            glActiveTexture(GL_TEXTURE0);
            glBindTexture(GL_TEXTURE_2D, ssaoColorBuffer);
            renderQuad();
        glBindFramebuffer(GL_FRAMEBUFFER, 0);


        // 4. lighting pass: traditional deferred Blinn-Phong lighting with added screen-space ambient occlusion
        // -----------------------------------------------------------------------------------------------------
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        shaderLightingPass.use();
        // send light relevant uniforms
        glm::vec3 lightPosView = glm::vec3(camera.GetViewMatrix() * glm::vec4(lightPos, 1.0));
        shaderLightingPass.setVec3("light.Position", lightPosView);
        shaderLightingPass.setVec3("light.Color", lightColor);
        // Update attenuation parameters
        const float constant  = 1.0; // note that we don't send this to the shader, we assume it is always 1.0 (in our case)
        const float linear    = 0.09;
        const float quadratic = 0.032;
        shaderLightingPass.setFloat("light.Linear", linear);
        shaderLightingPass.setFloat("light.Quadratic", quadratic);
        glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D, gPosition);
        glActiveTexture(GL_TEXTURE1);
        glBindTexture(GL_TEXTURE_2D, gNormal);
        glActiveTexture(GL_TEXTURE2);
        glBindTexture(GL_TEXTURE_2D, gAlbedo);
        glActiveTexture(GL_TEXTURE3); // add extra SSAO texture to lighting pass
        glBindTexture(GL_TEXTURE_2D, ssaoColorBufferBlur);
        renderQuad();


        // 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);
}

// 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);
}
HI