如何在 Unity 中存储对象在上一帧中的位置？

Question

我一直在试图弄清楚为什么这段代码没有像我想的那样工作。 “lastPosition”变量始终与“currentPosition”变量相同，尽管我认为我在“currentPosition”变量中缓存了当前帧上的 transform.position。我觉得这是一个非常简单的错误，但我不确定在哪里。这是我的代码：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
 
public class PlayerMovement : MonoBehaviour
{
    [SerializeField]
    private float moveSpeed = 2f;
 
    [SerializeField]
    private float currentSpeed;
 
    private Vector3 lastPosition;
 
 
    [SerializeField]
    private float strengthMultiplier;
 
    [SerializeField]
    private float strengthDiminisher = 7000f;
 
    private bool isRollingForwards;
 
    private bool isRollingBackwards;
 
    private bool isRollingLeft;
 
    private bool isRollingRight;
 
 
    private void Start()
    {
        lastPosition = transform.position;
    }
 
    private void Update()
    {
        Vector2 inputVector = new Vector2(0, 0);
 
        Vector3 currentPosition = transform.position;
 
 
        currentSpeed = (currentPosition - lastPosition).magnitude / Time.deltaTime;
 
 
        strengthMultiplier = currentSpeed / strengthDiminisher;
 
        if (Input.GetKey(KeyCode.W) || Input.GetKey(KeyCode.UpArrow))
        {
            inputVector.y = +1;
        }
 
        if (Input.GetKey(KeyCode.S) || Input.GetKey(KeyCode.DownArrow))
        {
            inputVector.y = -1;
        }
 
        if (Input.GetKey(KeyCode.A) || Input.GetKey(KeyCode.LeftArrow))
        {
            inputVector.x = -1;
        }
 
        if (Input.GetKey(KeyCode.D) || Input.GetKey(KeyCode.RightArrow))
        {
            inputVector.x = +1;
        }
 
       
        inputVector = inputVector.normalized;
 
        Vector3 moveDir = new Vector3(inputVector.x, 0f, inputVector.y);
 
        Vector3 playerVelocity = (currentPosition - lastPosition) / Time.deltaTime;
 
        Vector3 playerDir = playerVelocity.normalized;
 
     
 
        isRollingForwards =  currentPosition.z > lastPosition.z;
 
        isRollingBackwards = transform.rotation.x < 0f;
 
        isRollingLeft = transform.rotation.z > 0f;
 
        isRollingRight = transform.rotation.z < 0f;
 
 
        transform.position += moveDir * moveSpeed * strengthMultiplier * Time.deltaTime;
       
 
        lastPosition = transform.position;
 
    }
 
    public bool IsRollingForwards()
    {
        return isRollingForwards;
    }
 
    public bool IsRollingBackwards()
    {
        return isRollingBackwards;
    }
 
    public bool IsRollingLeft()
    {
        return isRollingLeft;
    }
 
    public bool IsRollingRight()
    {
        return isRollingRight;
    }
}

我尝试缓存对象的最后位置和当前位置，但它们总是相同的。

Answer 1

我认为你可以为此使用Unity的

LateUpdate()

功能。 LateUpdate() 所做的是在调用

Update()

函数后执行该函数内的所有内容。所以基本上，它在一帧的末尾执行代码。 （不完全在框架的末尾，但你明白了）。

你可以做的是这样的：

void Update()
{

    currentPosition = transform.position

}

void LateUpdate()
{

    //Make sure that lastPosition and currentPosition are both Vector3, then you can set it
    lastPosition = currentPosition;

}