Unity2D I can't change the TrailRenderer material of a cloned object-CodePudding

In the game I'm making, I clone a Ball object whenever a "split ball" power-up is acquired. Everything works as intended except the TrailRenderer material. The Ball prefab has a default material used for TrailRenderer in the beginning. This, however, changes when the ball hits an object controlled by the player (which is called a "bumper"). The material changes work perfectly on collision. Here is the shortened script for the Ball object:

[NonSerialized]
public TrailRenderer trailRenderer;

[SerializeField]
private Material defaultTrailMaterial;


void Start()
{
    trailRenderer = GetComponent<TrailRenderer>();
    trailRenderer.material = defaultTrailMaterial;
}

private void OnCollisionEnter2D(Collision2D collision)
{
    if (CollidedObjectIsABumper(collision))
    {
        // SetTrailColorToBumperColor() is called along other calculations
    }
}

private bool CollidedObjectIsABumper(Collision2D collision)
{
    return collision.gameObject.CompareTag("Bumper");
}

private void SetTrailColorToBumperColor()
{
    trailRenderer.material = lastCollidedBumper.material;
}

I discarded a few things for clarity.

Now, here is the shortened script for the split ball power-up:

void OnTriggerEnter2D(Collider2D collision)
    {
        if (!CollidedWithABall(collision))
            return;

        Ball mainBall = collision.gameObject.GetComponent<Ball>();

        // I added this part as a desperate attempt, didn't work.
        mainBall.trailRenderer.material = mainBall.lastCollidedBumper.material;
        Ball splitBall = Instantiate(mainBall, pos, Quaternion.identity);
        splitBall.tag = "Split Ball";
        splitBall.GetComponent<TrailRenderer>().material = mainBall.lastCollidedBumper.material;

        Destroy(gameObject);
    }

    private bool CollidedWithABall(Collider2D collision)
    {
        return collision.gameObject.CompareTag("Ball") || collision.gameObject.CompareTag("Split Ball");
    }

pos is a Vector3 variable that is declared in the cut portion. After getting the power-up, this is how the game scene looks like:

None of the balls touched a bumper after getting the power-up. I expect the split ball to have a red trail but it doesn't. I'm sure I'm missing something with Instantiate() but I don't know what.

One thing I assumed was that Instantiate() used the prefab of the main ball, in which case the trail would have a neutral color, but I added an assignment statement after Instantiate() so I don't think that's the only problem here. For reference, the split ball DOES change its trail color when it hits a bumper.

Thank you and please let me know if you need additional information.

CodePudding user response：

As mentioned this is a timing issue.

You have

void Start()
{
    trailRenderer = GetComponent<TrailRenderer>();
    trailRenderer.material = defaultTrailMaterial;
}

which overwrites your material.

The call of Start on new instantiated objects is delayed until the beginning the next frame for the purpose of being able to still change some field values right after Instantiate before Start is called.

So you set the material in

splitBall.GetComponent<TrailRenderer>().material = mainBall.lastCollidedBumper.material;

But then it is later changed again by Start.

Awake however is called right away.

So either you change it to

void Awake()
{
    trailRenderer = GetComponent<TrailRenderer>();
    trailRenderer.material = defaultTrailMaterial;
}

so this is done first and then the line

splitBall.GetComponent<TrailRenderer>().material = mainBall.lastCollidedBumper.material;

can correctly overwrite the material or alternatively you could also make

public Material defaultTrailMaterial;

and instead of directly setting the material in

splitBall.GetComponent<TrailRenderer>().material = mainBall.lastCollidedBumper.material;

you rather only set

splitBall.GetComponent<YourComponent>().defaultTrailMaterial = mainBall.lastCollidedBumper.material;

and then let Start do the job as currently.