Thanks for explaining.

It rises some questions, but if there is a detailed documentation for this, please give me the link, but I am unsure if I was able to find it.

To understand it properly, let's have the following example:
We have a bone A, animations1-3 and 3 tracks.
Track 0 - empty or unset (in our case, several empty tracks waiting for specific animations)
Track 1 - animation1 that animates bone A (has keys for A) which is interrupted in the middle, mixed to other animation2 which has no keys for A
Track 2 - another third animation3 that has no keys for A

What is the correct and expected behavior? After the mixing, should bone A have keys from setup or from interrupted animation1 (depending on when we started mixing)?

And please note that from my observation, this behavior changed with the previous code change in the first post. And that what I see in Spine Preview (trying to simulate something very similar) is different from the Unity runtime. There is still a small chance that something is bad in my code, but as I said it was working ok before runtime update. Also I need to be sure what is the correct behavior before diving deeper.

Another edge case might be what happens when on track 1 or 2 happens mixing during mixing, or calling update or anything special like that (there are some cases like this, difficult to simulate in Spine editor preview). May I ask if you have any test projects for testing these layering cases? Maybe I can try it on them?

Didn't know about the Layered tick box! That sounds very useful, can you please share a more detailed info or docs link on it?

Harald If this is not your result, you might have discovered a bug. Could you please describe what result you get?

After the runtime update, I see the key from mixed out animation is preserved in the following example, no to the setup pose. It stays in the the position where mixing started. Now the question is if it is related purely to runtime or something in my code. I will try to investigate more.
Do you have any test examples pre-ready for these?

Harald When selecting an animation in the Tree view, you have options Export and Layered.

Yeah, I found it, just wanted to read some more detailed info how exactly the Layeredworks.

Ok, when trying to isolate the problem it looks like that in very basic scenario it works like intended. Now I need to dive deeper to see what is specific to my setup.

Here is code for an isolated problem, see the last lines with TODO and comments. I would like to hear your thoughts on this?

using Spine;
using Spine.Unity;
using UnityEngine;

public class AnimationTest : MonoBehaviour
{
    private const int MainTrack = 0;
    private const int HeadTrack = 1;

    [SerializeField] private SkeletonAnimation skeletonAnimation;
    [SerializeField] private AnimationReferenceAsset idleAnimation; // idle with keyed bone
    [SerializeField] private AnimationReferenceAsset walkAnimation; // walk without keyed bone
    [SerializeField] private AnimationReferenceAsset headAnimation; // head animation without keyed bone

    private void Start()
    {
        // Start idle
        skeletonAnimation.AnimationState.SetAnimation(MainTrack, idleAnimation, true);

        // Watch animations start
        skeletonAnimation.AnimationState.Start += AnimationStateOnStart;
    }

    private void Update()
    {
        if (Input.GetKeyDown(KeyCode.T))
        {
            // Start walking
            // AnimationStateOnStart will be fire and head animation set
            var mainTrackEntry = skeletonAnimation.AnimationState.SetAnimation(MainTrack, walkAnimation, true);
            mainTrackEntry.MixDuration = 0;
        }

        if (Input.GetKeyDown(KeyCode.U))
        {
            // Back to idle
            skeletonAnimation.AnimationState.SetAnimation(MainTrack, idleAnimation, true);
            skeletonAnimation.AnimationState.SetEmptyAnimation(HeadTrack, 0);
        }
    }

    private void AnimationStateOnStart(TrackEntry trackEntry)
    {
        // Checking if animation that needs independent head (like walk) started
        if (trackEntry.TrackIndex == MainTrack && trackEntry.Animation == walkAnimation.Animation)
        {
            var headTrackEntry = skeletonAnimation.AnimationState.SetAnimation(HeadTrack, headAnimation, true);
            headTrackEntry.MixDuration = 0;

            skeletonAnimation.Update(0); // TODO: This is causing the problem!
            // When Update(0) is called, the bone stays in idleAnimation position where it was interrupted
            // When Update(0) is not called, the bone mix to setup position as intended
            // This behavior changed after spine runtime update
            // Update(0) is here to prevent missing heads for one frame in some specific cases, but not sure if should be needed?
        }
    }
}

Hi Harald,

Thanks, you are looking into it. The thing now is that I need to understand the change and how it works and if I should update my code or wait if you will be making some changes.
Because I can see that I can probably remove the Update call, which definitely was there for some reason, but I can't find any problems when removing it, so maybe something else was fixed in between?

So I don't need a quick fix, I better need to understand the issue properly and what is a general good practice.

The related question is if calls to Update(0) should ever be needed? I can see multiple calls to this in my code, usually fixing blinking for one frame as some logic changed something and animation is updated one frame later. So calling Update(0) fixes these and everything looks as it should. But maybe this is a bad practice in general and there is some better way?

Harald in general a valid call to immediately reflect certain performend changes within the same frame

Well, thanks, then I am waiting for your investigation

Hi, Thanks for detailed explanation! Now I got it, I think in that case I will fix it just by removing the Update call.

Still, there might be (and apparently there was before) a reason to call Update in OnAnimationStart. The Update was called not alone but with using another SetAnimation there. But now I see that would need a different pattern to be sure it is always called after setting trackEntry properties.

My minor notes to this:

1. It would be great to have an option to set these trackEntry properties right with the SetAnimation call (before the start event is fired). This order of actions that SetAnimation (and thus OnAnimationStart) is always called before we can manipulate mixDuration was already misleading a few times before, and I need to create some hacks around that. Or am I again missing some option to set it?
2. I am still not sure what exactly was changed in the runtime that changed my behavior. But I assume that now I understand it more deeply and if there will be again some visual changes, I will dive into it to understand it before doing dirty hacks. Generally, I am just a little concerned about the runtime always providing reliable identical outcome.

Thanks again for taking time to deep dive into it, I truly appreciate it!