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// Copyright (c) 2022-2023 Magic Leap, Inc. All Rights Reserved.
// Use of this file is governed by the Magic Leap 2 Software License Agreement, located here: https://www.magicleap.com/software-license-agreement-ml2  
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using UnityEngine;

namespace MagicLeap.Spectator
{
    public class LazyBillboard : MonoBehaviour
    {
        #region Public variables

        [Tooltip("The forwards distance from the camera that this object should be placed.")]
        public float CanvasDistanceForwards = 1.5f;

        [Tooltip("The upwards distance from the camera that this object should be placed.")]
        public float CanvasDistanceUpwards = 0.0f;

        [Tooltip("The right distance from the camera that this object should be placed.")]
        public float CanvasDistanceRight = 0.0f;

        [Tooltip("The speed at which this object changes its position.")]
        public float PositionLerpSpeed = 5f;

        [Tooltip("The speed at which this object changes its rotation.")]
        public float RotationLerpSpeed = 5f;

        #endregion

        #region Private varibles

        // The camera this object will be in front of
        private Camera _camera;

        #endregion

        #region MonoBehaviour methods

        void Awake()
        {
            _camera = Camera.main;
        }

        private void OnEnable()
        {
            transform.position = _camera.transform.position + 
                (_camera.transform.forward * CanvasDistanceForwards) + 
                (_camera.transform.up * CanvasDistanceUpwards) + 
                (_camera.transform.right * CanvasDistanceRight);
        }

        void Update()
        {
            // Move the object CanvasDistance units in front of the camera.
            float posSpeed = Time.deltaTime * PositionLerpSpeed;
            Vector3 posTo = _camera.transform.position + 
                (_camera.transform.forward * CanvasDistanceForwards) +
                (_camera.transform.up * CanvasDistanceUpwards) +
                (_camera.transform.right * CanvasDistanceRight);
            transform.position = Vector3.SlerpUnclamped(transform.position, posTo, posSpeed);

            // Rotate the object to face the camera.
            float rotSpeed = Time.deltaTime * RotationLerpSpeed;
            Quaternion rotTo = Quaternion.LookRotation(transform.position - _camera.transform.position);
            transform.rotation = Quaternion.Slerp(transform.rotation, rotTo, rotSpeed);
        }

        #endregion
    }
}