如何正确使用Physics.autoSimulation？

Question

我试图用Physics.autoSimulation来预测游戏对象的位置(游戏对象有一个刚体)。问题是，当我触发模拟时，物体会有某种闪烁。如下所示：

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我读过这个thread。我开始认为我没有正确地使用autoSimulation。这是我的密码：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class TestBall : MonoBehaviour {


    public float timeCheck = 3f;
    public float force = 10f;

    private Rigidbody rb;

    void Start () {

        rb = GetComponent<Rigidbody>();

    }//end Start



    void Update () {

        if (Input.GetKeyDown(KeyCode.Space)) {

            //Starts the simulation...
            Physics.autoSimulation = false;
            rb.AddForce(Vector3.right * force, ForceMode.Impulse);
            Vector3 futurePosition = CheckPosition(rb);    
            print("Future position at " + futurePosition);

            //...and move the GameObject for real
            rb.AddForce(Vector3.right * force, ForceMode.Impulse);

        }//end if

    }//end Update



    Vector3 CheckPosition (Rigidbody defaultRb) {

        Vector3 defaultPos = defaultRb.position;
        Quaternion defaultRot = defaultRb.rotation;

        float timeInSec = timeCheck;

        while (timeInSec >= Time.fixedDeltaTime) {

            timeInSec -= Time.fixedDeltaTime;
            Physics.Simulate(Time.fixedDeltaTime);

        }//end while

        Vector3 futurePos = defaultRb.position;

        Physics.autoSimulation = true;

        defaultRb.velocity = Vector3.zero;
        defaultRb.position = defaultPos;
        defaultRb.rotation = defaultRot;

        return futurePos;

    }//end CheckPosition

}//end TestBall

就像在一个很小的时刻，游戏对象在模拟结束时移动，然后返回，因为位置重置在CheckPosition函数中。

谢谢你的帮助！

Answer 1

您正确地使用了Physics.autoSimulation。问题是你如何重新设置这个位置。

修改刚体的位置和旋转与改变其变换的位置和旋转是不同的。您希望用转换而不是刚体重置对象的转换，这样移动就不会在多个帧上立即发生，因为这将使它在屏幕上可见。

取代：

defaultRb.position = defaultPos;
defaultRb.rotation = defaultRot;

使用

defaultRb.transform.position = defaultPos;
defaultRb.transform.rotation = defaultRot;

而且，由于这是一个滚动球，设置velocity并不足以阻止它。您还必须设置它的angularVelocity，因为球是旋转的，并且也是平移的：

defaultRb.velocity = Vector3.zero;
defaultRb.angularVelocity = Vector3.zero;

这是您的新CheckPosition函数，没有闪烁：

Vector3 CheckPosition(Rigidbody defaultRb)
{

    Vector3 defaultPos = defaultRb.position;
    Quaternion defaultRot = defaultRb.rotation;

    float timeInSec = timeCheck;

    while (timeInSec >= Time.fixedDeltaTime)
    {

        timeInSec -= Time.fixedDeltaTime;
        Physics.Simulate(Time.fixedDeltaTime);

    }//end while

    Vector3 futurePos = defaultRb.position;


    Physics.autoSimulation = true;

    defaultRb.velocity = Vector3.zero;
    defaultRb.angularVelocity = Vector3.zero;

    defaultRb.transform.position = defaultPos;
    defaultRb.transform.rotation = defaultRot;

    return futurePos;

}//end CheckPosition

最后，您的当前代码没有在旧的强制之上添加强制。这意味着，如果您按下空格键，并再次按它，力不会添加到旧的力量之上。相反，对象被停止，然后添加一个新的力。旧的丢了。

如果您想在旧力的基础上添加新的力，则必须在仿真之前存储当前的速度和angularVelocity，然后将它们应用到仿真后的刚体中。物体的速度应该随着时间的推移而增加。

这与您的问题无关，只是代码中的另一个bug。下面是对此的修复(新的Update和CheckPosition函数)：

void Update()
{
    if (Input.GetKeyDown(KeyCode.Space))
    {
        //Get current velocity and angularVelocity
        Vector3 defaultVelocity = rb.velocity;
        Vector3 defaultAngularVelocity = rb.angularVelocity;

        //Starts the simulation...
        Physics.autoSimulation = false;
        rb.AddForce(Vector3.right * force, ForceMode.Impulse);
        Vector3 futurePosition = CheckPosition(rb, defaultVelocity, defaultAngularVelocity);
        print("Future position at " + futurePosition);

        //...and move the GameObject for real
        rb.AddForce(Vector3.right * force, ForceMode.Impulse);

    }//end if

}//end Update



Vector3 CheckPosition(Rigidbody defaultRb, Vector3 defaultVelocity, Vector3 defaultAngularVelocity)
{

    Vector3 defaultPos = defaultRb.position;
    Quaternion defaultRot = defaultRb.rotation;

    float timeInSec = timeCheck;

    while (timeInSec >= Time.fixedDeltaTime)
    {
        timeInSec -= Time.fixedDeltaTime;
        Physics.Simulate(Time.fixedDeltaTime);

    }//end while

    Vector3 futurePos = defaultRb.position;


    Physics.autoSimulation = true;

    //Stop object force
    defaultRb.velocity = Vector3.zero;
    defaultRb.angularVelocity = Vector3.zero;

    //Reset Position
    defaultRb.transform.position = defaultPos;
    defaultRb.transform.rotation = defaultRot;

    //Apply old velocity and angularVelocity
    defaultRb.velocity = defaultVelocity;
    defaultRb.angularVelocity = defaultAngularVelocity;

    return futurePos;

}//end CheckPosition