Tween startValue is not applied immediately (setImmediately)

[MikeMuorte]

Hi, I was doing some tests with Sequences to see if PrimeTween could replace DoTween in my project, and surprise—on the very first try, I ran into a possible bug.

Here’s the test code I used:

    public Image barA;
    public Image barB;

    Sequence sq;

    public void AnimateSequence()
    {
        if (sq.isAlive)
        {
            Debug.Log("Sequence is Alive");
            return;
        }

        var tA = Tween.UIFillAmount(barA, 0, 1, 2);
        var tB = Tween.UIFillAmount(barB, 0, 1, 2);

        sq = Sequence.Create()
             .ChainCallback(() => Debug.Log("A"))
             .Chain(tA)
             .ChainCallback(() => Debug.Log("B"))
             .ChainDelay(2)
             .ChainCallback(() => Debug.Log("C"))
             .Chain(tB)
             .ChainCallback(() => Debug.Log("D"));
    }

    private void Update()
    {
        if (!sq.isAlive)
        {
            AnimateSequence();
        }
    }

It's about two Images that fill up in sequence, one after the other with a delay in between, and a few Logs along the way.

If we set the Fill value of both Images to 0 in the scene and then hit Play to start the test, the first time the bars fill up as expected.

However, on subsequent plays, the second bar remains filled from the beginning of the sequence (meaning it doesn't reset).

You can fix it with a small trick right after creating the Sequence to get the expected behavior. It seems like the system isn’t evaluating the full sequence before starting it—and doing this trick forces the internal tweens to evaluate.

sq.isPaused = true;
sq.progress = 1;
sq.progress = 0;
sq.isPaused = false;

On the other hand, if we configure the same sequence to run in Restart cycles, the expected behavior is properly observed.

sq = Sequence.Create(cycles: 2, cycleMode: CycleMode.Restart)

I hope the effort I put into testing and writing this helps improve PrimeTween.

Thank you very much for your time.

[MikeMuorte]

I'm using PrimeTween v1.2.2 (Asset Store) and Unity 6 (6000.0.26f1)

[KyryloKuzyk]

Hey, thank you for creating a detailed report with examples!

This behaviour is by design: PrimeTween doesn't assume you wish to apply the startValue immediately upon creation of the tween because that's not what the user wants in 100% of cases.

The simplest example of this problem is this one:

Sequence.Create()
    .ChainDelay(1f)
    .Chain(Tween.PositionX(transform, 0f, 10f, duration: 1f));

What the above code should do?

1. Wait 1 second, then play the animation from 0 to 10.
2. Set position.x immediately to 0f, then wait for 1 second, then play the animation from 0 to 10.

PrimeTween selects option 1 because it gives the user full control over how the animation behaves. If the user wants the behaviour of option 2, they can modify the position.x immediately at the same time they create the sequence.

So, to achieve the desired behavior in your case, simply add this line before creating the sequence:

barB.fillAmount = 0f;

PrimeTween also comes with DOTween adapter, which supports .From() extension that behaves the way you want.

On the other hand, if we configure the same sequence to run in Restart cycles, the expected behavior is properly observed.

Yeah, I can see how it may seem inconsistent in this particular example. Restart is a special case that resets all tweens in a sequence when a new cycle begins, so you observe the "correct" behaviour. But we can't assume that when a sequence has one cycle, like in your case, we should always apply all startValues immediately upon creation.

I need to think more about this in the meantime, but I'm afraid it would be too risky to change the default behavior because PrimeTween already has thousands of users, and such a change may break their projects.

Related question: https://discussions.unity.com/t/primetween-high-performance-animations-and-sequences/926420/300

[MikeMuorte]

Of course, totally understandable. it’s hard to guess what everyone is trying to do.
So, what I want to understand is whether the first run of the sequence behaves somewhat like a cycle configured as Incremental?

With your explanation, I now understand that the behavior is intentional, so I’ll know to account for it in advance.
It might be interesting to consider adding an option to the sequence constructor, or a method or parameter, to manually configure this behavior.

Thanks so much for taking the time to explain this to me.

[KyryloKuzyk]

So, what I want to understand is whether the first run of the sequence behaves somewhat like a cycle configured as Incremental?

I can't say that the first cycle is Incremental either. I would better describe the behaviour as tweens in a sequence are waiting for their order to start the animation during the first cycle. And when the second cycle begins, Sequence reset all animations to their startValue.

It might be interesting to consider adding an option to the sequence constructor, or a method or parameter, to manually configure this behavior.

Yeah, that's a good idea. I need to think more about it 👍