text: #ifndef CAMERA_H
  #define CAMERA_H
  
  #include <glm/glm.hpp>
  #include <glm/gtc/matrix_transform.hpp>
  
  #include <vector>
  
  // Defines several possible options for camera movement. Used as abstraction to stay away from window-system specific input methods
  enum Camera_Movement {
      FORWARD,
      BACKWARD,
      LEFT,
      RIGHT
  };
  
  // Default camera values
  const float YAW         = -90.0f;
  const float PITCH       =  0.0f;
  const float SPEED       =  2.5f;
  const float SENSITIVITY =  0.1f;
  const float ZOOM        =  45.0f;
  
  
  // An abstract camera class that processes input and calculates the corresponding Euler Angles, Vectors and Matrices for use in OpenGL
  class Camera
  {
  public:
      // camera Attributes
      glm::vec3 Position;
      glm::vec3 Front;
      glm::vec3 Up;
      glm::vec3 Right;
      glm::vec3 WorldUp;
      // euler Angles
      float Yaw;
      float Pitch;
      // camera options
      float MovementSpeed;
      float MouseSensitivity;
      float Zoom;
  
      // constructor with vectors
      Camera(glm::vec3 position = glm::vec3(0.0f, 0.0f, 0.0f), glm::vec3 up = glm::vec3(0.0f, 1.0f, 0.0f), float yaw = YAW, float pitch = PITCH) : Front(glm::vec3(0.0f, 0.0f, -1.0f)), MovementSpeed(SPEED), MouseSensitivity(SENSITIVITY), Zoom(ZOOM)
      {
          Position = position;
          WorldUp = up;
          Yaw = yaw;
          Pitch = pitch;
          updateCameraVectors();
      }
      // constructor with scalar values
      Camera(float posX, float posY, float posZ, float upX, float upY, float upZ, float yaw, float pitch) : Front(glm::vec3(0.0f, 0.0f, -1.0f)), MovementSpeed(SPEED), MouseSensitivity(SENSITIVITY), Zoom(ZOOM)
      {
          Position = glm::vec3(posX, posY, posZ);
          WorldUp = glm::vec3(upX, upY, upZ);
          Yaw = yaw;
          Pitch = pitch;
          updateCameraVectors();
      }
  
      // returns the view matrix calculated using Euler Angles and the LookAt Matrix
      glm::mat4 GetViewMatrix()
      {
          return glm::lookAt(Position, Position + Front, Up);
      }
  
      // processes input received from any keyboard-like input system. Accepts input parameter in the form of camera defined ENUM (to abstract it from windowing systems)
      void ProcessKeyboard(Camera_Movement direction, float deltaTime)
      {
          float velocity = MovementSpeed * deltaTime;
          if (direction == FORWARD)
              Position += Front * velocity;
          if (direction == BACKWARD)
              Position -= Front * velocity;
          if (direction == LEFT)
              Position -= Right * velocity;
          if (direction == RIGHT)
              Position += Right * velocity;
      }
  
      // processes input received from a mouse input system. Expects the offset value in both the x and y direction.
      void ProcessMouseMovement(float xoffset, float yoffset, GLboolean constrainPitch = true)
      {
          xoffset *= MouseSensitivity;
          yoffset *= MouseSensitivity;
  
          Yaw   += xoffset;
          Pitch += yoffset;
  
          // make sure that when pitch is out of bounds, screen doesn't get flipped
          if (constrainPitch)
          {
              if (Pitch > 89.0f)
                  Pitch = 89.0f;
              if (Pitch < -89.0f)
                  Pitch = -89.0f;
          }
  
          // update Front, Right and Up Vectors using the updated Euler angles
          updateCameraVectors();
      }
  
      // processes input received from a mouse scroll-wheel event. Only requires input on the vertical wheel-axis
      void ProcessMouseScroll(float yoffset)
      {
          Zoom -= (float)yoffset;
          if (Zoom < 1.0f)
              Zoom = 1.0f;
          if (Zoom > 45.0f)
              Zoom = 45.0f; 
      }
  
  private:
      // calculates the front vector from the Camera's (updated) Euler Angles
      void updateCameraVectors()
      {
          // calculate the new Front vector
          glm::vec3 front;
          front.x = cos(glm::radians(Yaw)) * cos(glm::radians(Pitch));
          front.y = sin(glm::radians(Pitch));
          front.z = sin(glm::radians(Yaw)) * cos(glm::radians(Pitch));
          Front = glm::normalize(front);
          // also re-calculate the Right and Up vector
          Right = glm::normalize(glm::cross(Front, WorldUp));  // normalize the vectors, because their length gets closer to 0 the more you look up or down which results in slower movement.
          Up    = glm::normalize(glm::cross(Right, Front));
      }
  };
  #endif