Skin Attachment issue

Yimec

Hello everyone,

I'm having issues when changing skins in my game.

The initial skin has a slot whose skin placeholders are empty, but another upgraded skin contains shoulder pads. The problem is that the shoulder pads are not visible after switching skins. Strangely, the attachments for the first placeholder skin (E) and the last one (W) are visible, but the attachments for the other directions are not.

The animation has an initial keyframe that enables and disables attachments depending on the character's facing direction. In both skins, the shoulder-pad slot attachments are animated and keyed because the animations are exactly the same for both skins. However, once I add the skins and switch between them, some of the attachments stop appearing.

What is most confusing to me is that this only happens from certain viewing directions.

I've attached screenshots showing the slot setup in both the unarmored skin and the armored skin so you can see how everything is structured in Spine.

The script used to change skins is the following (it applies the change to multiple skeletons because there are several copies of the same character that need to be updated simultaneously):

using Spine;
using Spine.Unity;
using UnityEngine;
using Sirenix.OdinInspector;

public class SpineCombinedSkins : MonoBehaviour
{
    [SerializeField] SkeletonAnimation[] skeletonAnimations;
    private Skin mixAndMatchSkin = new Skin("custom-skin");

    [SpineSkin("", "", false, false, true, false)]
    public string baseSkinName;

    [SpineSkin("", "", false, false, true, false)]
    public string weaponSkinName;

    void Start()
    {
        UpdateSkins();
    }

    [Button]
    public void UpdateSkins()
    {
        var skeleton = skeletonAnimations[0].Skeleton;
        var skeletonData = skeleton.Data;

        mixAndMatchSkin.Clear();
        mixAndMatchSkin.AddSkin(skeletonData.FindSkin(baseSkinName));
        mixAndMatchSkin.AddSkin(skeletonData.FindSkin(weaponSkinName));

        foreach (var animation in skeletonAnimations)
        {
            animation.Skeleton.SetSkin(mixAndMatchSkin);
            animation.Skeleton.SetToSetupPose();
        }
    }
}

Harald

Sorry to hear it's not resolved by the above postings.

Yimec The animation has an initial keyframe that enables and disables attachments depending on the character's facing direction. In both skins, the shoulder-pad slot attachments are animated and keyed because the animations are exactly the same for both skins. However, once I add the skins and switch between them, some of the attachments stop appearing.

To understand your situation better: do you have the attachment key at the start of your animation, and start this animation before the skin is changed and the new skin is applied? In other words, is the attachment key applied before you change the skin?

Spinebot

Based on my knowledge, the issue you're experiencing with shoulder pad attachments not showing after switching skins is related to how Spine handles skin changes when animations have attachment keys.

The Problem

When you switch skins and the animation has keyframes that control attachment visibility, you need to ensure the animation state reapplies those keys after the skin change. Currently, your code calls SetToSetupPose(), but this doesn't reapply the current animation's attachment keys.

The Solution

After changing the skin, you need to tell the animation state to reapply the current animation. Modify your UpdateSkins() method like this:

[Button]
public void UpdateSkins()
{
    var skeleton = skeletonAnimations[0].Skeleton;
    var skeletonData = skeleton.Data;

    mixAndMatchSkin.Clear();
    mixAndMatchSkin.AddSkin(skeletonData.FindSkin(baseSkinName));
    mixAndMatchSkin.AddSkin(skeletonData.FindSkin(weaponSkinName));

    foreach (var animation in skeletonAnimations)
    {
        animation.Skeleton.SetSkin(mixAndMatchSkin);
        animation.Skeleton.SetSlotsToSetupPose();
        animation.AnimationState.Apply(animation.Skeleton);
    }
}

Key Changes:

Changed SetToSetupPose() to SetSlotsToSetupPose() - this only resets the slots to setup pose without affecting bones
Added animation.AnimationState.Apply(animation.Skeleton) - this reapplies the current animation, including all attachment keys

Why This Works

The proper sequence for skin changes when animations control attachments is:

Set the new skin
Reset slots to setup pose (to get base attachments from the new skin)
Apply the animation state (to activate attachments based on the current animation frame)

This ensures that attachments controlled by your animation keyframes are correctly shown from the new skin, regardless of viewing direction.

Yimec

Just to clarify, I tried what SpineBot suggests and it's still not working.

What I've achieved is to set the initial skin the one with the shoulderpads, overwrite on start this skin with the one without armor and, once updated to the armor skin, shoulderpads appear, but they are not "rigged" as they don't follow the animation (they are properly attached and animated in spine)

Spinebot

I understand the issue better now. The problem is that when you switch skins and the animation has attachment keys, those keys are referencing attachment names that need to exist in the new skin. Since your shoulder pad slot is empty in the initial skin but has attachments in the armored skin, the animation keys aren't properly connecting to the new attachments.

The Real Problem

When animations have attachment keys, they set attachments by name. If a slot starts empty (no attachment) in one skin and then you switch to a skin with attachments, the animation keys need to be reapplied, but there's an additional issue: the attachments might not be deforming properly because the skeleton's current pose isn't being updated after the skin change.

Try This Solution

[Button]
public void UpdateSkins()
{
    var skeleton = skeletonAnimations[0].Skeleton;
    var skeletonData = skeleton.Data;

    mixAndMatchSkin.Clear();
    mixAndMatchSkin.AddSkin(skeletonData.FindSkin(baseSkinName));
    mixAndMatchSkin.AddSkin(skeletonData.FindSkin(weaponSkinName));

    foreach (var animation in skeletonAnimations)
    {
        animation.Skeleton.SetSkin(mixAndMatchSkin);
        animation.Skeleton.SetSlotsToSetupPose();
        animation.AnimationState.Apply(animation.Skeleton);
        animation.skeleton.UpdateWorldTransform();
        animation.Update(0); // Force an update
    }
}

If that doesn't work, try this alternative approach:

[Button]
public void UpdateSkins()
{
    var skeleton = skeletonAnimations[0].Skeleton;
    var skeletonData = skeleton.Data;

    mixAndMatchSkin.Clear();
    mixAndMatchSkin.AddSkin(skeletonData.FindSkin(baseSkinName));
    mixAndMatchSkin.AddSkin(skeletonData.FindSkin(weaponSkinName));

    foreach (var animation in skeletonAnimations)
    {
        var currentTime = animation.AnimationState.GetCurrent(0)?.TrackTime ?? 0f;
        var currentAnimation = animation.AnimationState.GetCurrent(0)?.Animation;
        
        animation.Skeleton.SetSkin(mixAndMatchSkin);
        animation.skeleton.SetSlotsToSetupPose();
        
        if (currentAnimation != null)
        {
            animation.AnimationState.ClearTracks();
            animation.AnimationState.SetAnimation(0, currentAnimation.Name, true);
            animation.AnimationState.Update(currentTime);
            animation.AnimationState.Apply(animation.Skeleton);
        }
    }
}

This second approach actually restarts the animation at its current time position, which should ensure all attachment keys are properly evaluated with the new skin.

Can you also confirm: are the shoulder pad attachments mesh/weighted attachments or region attachments? If they're weighted meshes, there might be an additional issue with bone weights not being properly initialized.

Yimec

They are mesh weighted with physics bones (in case this is relevant).

None of both SpineBot suggestions actually work.

In case this is relevant, we are using latest 4.2 spine version with Unity 6000.3.14f1

Yimec

Harald Hola Harald, voy a probar a escribir en Español que es mi idioma aprovechando que parece que el foro se traduce automáticamente, espero que puedas leer bien mi mensaje.

La animación se reproduce en bucle y se reinicia cada vez que el jugador hace input para cambiar de dirección (hay un sistema de animaciones con 8 vistas montado y cada vez que el personaje se mueve en esa dirección se llama a la animación correspondiente). Por tanto, se llama constantemente al primer keyframe de cada animación que incluye los attachments correspondientes a cada vista.
Una captura del primer keyframe (en ambas skins ya que es la misma animación):

Voy a hablar con el director técnico del proyecto para intentar crear ese proyecto mínimo, mientras tanto, todo lo que pueda responderte lo intentaré hacer yo mismo.

Harald

@Yimec Anyway, could you perhaps send us a minimal Unity project which still shows your issue (please remove anything that is not necessary)? You can send it as a zip file to contact@eso, briefly mentioning this forum thread URL. Then this might be easier to diagnose.

Yimec

@Harald I'm sending an email with a simple scene to check the problem. Let me know if this helps.

Misaki

Yimec Thank you for sending us the Unity project file that reproduces the issue. However, the .zip file you shared was 994 MB, so it was by no means a minimal reproduction project.
Please note that only the Assets, Packages, and ProjectSettings folders are needed. The Library, Logs, and UserSettings folders can be removed without any problem.
I would greatly appreciate it if you could replace it with a smaller .zip file so that Harald can review it later.

From what I tested on my end, the behavior seems to differ depending on whether the same mixAndMatchSkin instance is cleared and reused, or whether a new Skin instance is created each time.

After commenting out the field-level private Skin mixAndMatchSkin = new Skin("custom-skin"); declaration and creating a new local Skin instance inside each method, it worked correctly on my end:

public void SetArmor()
{
    var skeleton = skeletonAnimations[0].Skeleton;
    var skeletonData = skeleton.Data;
    var mixAndMatchSkin = new Skin("custom-skin");
    mixAndMatchSkin.AddSkin(skeletonData.FindSkin(armorSkinName));
    mixAndMatchSkin.AddSkin(skeletonData.FindSkin(weaponSkinName));
    foreach (var animation in skeletonAnimations)
    {
        animation.Skeleton.SetSkin(mixAndMatchSkin);
        animation.Skeleton.SetSlotsToSetupPose();
    }
}

public void SetVillager()
{
    var skeleton = skeletonAnimations[0].Skeleton;
    var skeletonData = skeleton.Data;
    var mixAndMatchSkin = new Skin("custom-skin");
    mixAndMatchSkin.AddSkin(skeletonData.FindSkin(baseSkinName));
    mixAndMatchSkin.AddSkin(skeletonData.FindSkin(weaponSkinName));
    foreach (var animation in skeletonAnimations)
    {
        animation.Skeleton.SetSkin(mixAndMatchSkin);
        animation.Skeleton.SetSlotsToSetupPose();
    }
}

@Harald will likely be able to provide a more detailed answer, so please wait a little longer.

Yimec

Hello @Misaki.

Thanks for your reply. I updated the google drive link removing all unnecesary items from the .zip.

I'm sorry about that.

Harald

@Misaki Thanks very much for discovering the cause of the issue already!

[Edit: removed previous suggestion as it leads to potentially other issues with different skins]

Harald

@Yimec Please create a new Skin object for now, clearing the Skin and adding other skins and then assigning it would not work properly. So what Misaki suggested above remains the recommended fix.

I will discuss with the team if we can make the 4.3 API support assigning the same reused skin again after modification.

Yimec

Harald Hello Harald,
our technical team is still working on this as this solution partially works due to other systems they developed to render characters (something that is out of my comprehension area).

I'll let you know if they solve this issue with your help and guidance.

Thank you!

Harald

@Yimec Thanks for the update. Please note that creating a new Skin is the only ¹ viable solution currently to set a different combined skin, as otherwise the skeleton would no longer know which attachments were previously equipped (important e.g. when one of five mouth shapes was active). We are discussing it with the team how we can best prevent incorrect use and still keep things efficient.

[1] More correctly, assigning and then modifying the same skin and re-assigning it is not supported currently. You could theoretically use double-buffering and create two skins via new Skin and then assign them in alternating sequence, this would behave correctly as well.