Unity 2D撞机卡在墙上？

Question

I have just updated Unity to version 5.2.1 from 5.0.0 this morning and I experienced a few problems. After Unity translated the game to work for the new version, I tested the game. Everything worked fine, except that when I shot a bullet in my game, they would stick to the walls instead of bouncing off of them, but only at certain angles and distances. It was like the bullet was so fast that it skipped hitting the collider and got stuck inside of the collider. That would make a little bit of sense, but the weird part is that I have a C# script for slow motion in the game. Whenever I turn the slow motion on and then turn it off again, the problem with bullets sticking goes away. I cannot seem to figure out what is causing the problem and it definitely wasn't there before I updated the software. Can anyone help me out with this? Thanks. I'll post the bullet script and the slow motion script below. The bullet is instantiated inside the player script by the way.

Bullet Script:

using UnityEngine;
using System.Collections;

public class Bullet : MonoBehaviour {

public float bulletSpeed;
public float bulletOpacity;
public bool fadeOut;

Animator anim;
Rigidbody2D rigidbod;
SpriteRenderer spriterend;

public GameObject player;
public float aimRotation;

// Use this for initialization
void Start () {

    anim = GetComponent<Animator> ();
    rigidbod = GetComponent<Rigidbody2D> ();
    spriterend = GetComponent<SpriteRenderer> ();

    rigidbod.velocity = transform.right * bulletSpeed;
    rigidbod.gravityScale = 0;

    bulletOpacity = 1;

}

// Update is called once per frame
void Update () {

    Destroy (gameObject, 3f);

    spriterend.color = new Color (1f, 1f, 1f, bulletOpacity);

    if (fadeOut == true)
        bulletOpacity -= 0.03f;

    if (bulletOpacity <= 0)
        Destroy (gameObject);

    aimRotation = player.GetComponent<Player> ().aimRotation;

}

void OnTriggerEnter2D (Collider2D bulletHit) {

    /*if (bulletHit.gameObject.layer == LayerMask.NameToLayer ("vulnerableLayer")) {

    }*/
    rigidbod.gravityScale = 1;
    rigidbod.drag = 1;
    fadeOut = true;

}

}

Slow Motion Script:

using UnityEngine;
using System.Collections;

public class SlowMotion : MonoBehaviour {

public float currentLongevity = 0f;
public float slowAmount = 0.2f;
public float normalTime = 1f;
public float slowLongevity = 0.4f;


// Use this for initialization
void Start () {

}

// Update is called once per frame
void Update () {

    if (Input.GetMouseButtonDown (1)) {
        Time.fixedDeltaTime = 0.0f * Time.timeScale;
        if (Time.timeScale == normalTime)
            Time.timeScale = slowAmount;
    }

    if (Time.timeScale == slowAmount) {
        currentLongevity += Time.deltaTime;
    }

    if (currentLongevity > slowLongevity) {
        currentLongevity = 0;
        Time.timeScale = normalTime;
    }

}
}

Answer 1

Since you indicated that the 'weird' bullet behavior ceases after the SlowMotion script is run, I would suggest that the issue has to do with setting Time.fixedDeltaTime as you are doing in the Update() method of the SlowMotion script. This is also supported by your later comment that the 'weird' behavior no longer appears when you set the rigidBody2D's collision detection to continuous (the bullet's RigidBody2D I assume).

Continuous RididBody2D collision detection enables determining if contact occurred between updates , where as Discrete collision detection registers a collision during a physics update . In your SlowMotion script, the following line (in the Update() method) sets fixedDeltaTime to zero :

Time.fixedDeltaTime = 0.0f * Time.timeScale;

Since Time.fixedDeltaTime is the interval in seconds at which physics and other fixed frame rate updates are performed , there must be some minimum value at which the frame rate is realistically run, (0.0 cannot be an actual frame-rate update interval). When Time.fixedDeltaTime == 0.0, Unity may use a default minimum value or use this to indicate that frame updates run as often as possible, (though I have not tested this). Since the Bullet script calls Update() rather than FixedUpdate(), there is no guarantee that the actual interval between the frame updates is uniform . I suspect that when you run the SlowMotion script, and set Time.fixedDeltaTime to 0.0, Unity runs with the smallest possible frame update interval and following this, it does render the expected bullet behavior.

One way to test this would be to set your initial Time.fixedDeltaTime to 0.0 in the editor (and your collision detection behavior back to discrete for the bullet's RididBody2D).

To set Time Manager fixedDeltaTime in the editor: main menu -> Edit -> Project Settings -> Time

If you find a fixedDeltaTime that works, you can set this in the editor and retrieve the initial value in your SlowMotion script in the Awake() method to initialize the base fixedDeltaTime. I would not recommend using fixedDeltaTime == 0.0 since there is no indication in the documentation of a consistent behavior for a time interval of 0.0 and it may be bound more to the underlying hardware and could result in more unexpected behavior.

Hope this helps, cheers!