SkeletonGraphic rendering behavior changes with Multiple CanvasRenderers

1013912584

SkeletonGraphic does not render the `idle` animation after `active` unless Multiple CanvasRenderers is enabled

I'm using Spine 4.2 in Unity, and I've encountered a rendering issue with SkeletonGraphic.

The artist created an animation with an active animation followed by an idle animation.

My playback code is simply:

Spine.AnimationState.SetAnimation(0, "active", false);
Spine.AnimationState.AddAnimation(0, "idle", true, 0f);

Observed behavior

When I play the animations using SkeletonAnimation, everything works as expected:

active plays correctly.
idle starts immediately after active finishes.
The idle animation is rendered correctly and loops normally.

However, when I use SkeletonGraphic, the behavior is different:

active plays and is rendered correctly.
After active finishes, the idle animation is correctly added and starts playing.
I can confirm from the logs/debugging that the idle animation is actually being played and its timeline is being updated.
However, nothing is visible on screen during idle.

This makes it seem like a rendering problem rather than an animation-state problem.

The strange part

If I enable Multiple CanvasRenderers on the SkeletonGraphic component, the problem completely disappears.

With Multiple CanvasRenderers enabled, the exact same animation and playback code works correctly:

Spine.AnimationState.SetAnimation(0, "active", false);
Spine.AnimationState.AddAnimation(0, "idle", true, 0f);

active renders correctly, and idle is also rendered correctly afterward.

If I disable Multiple CanvasRenderers, active still renders correctly, but idle becomes invisible after the transition.

So the behavior can be summarized as:

| Component | Multiple CanvasRenderers | Result |
| ------------------- | -----------------------: | ------------------------------------------ |
| SkeletonAnimation | N/A | Works |
| SkeletonGraphic | Enabled | Works |
| SkeletonGraphic | Disabled | active renders, idle becomes invisible |

My questions

Is this a known bug or limitation of SkeletonGraphic in Spine 4.2?

Why would enabling Multiple CanvasRenderers change the rendering result in this situation?

Since the animation state and timelines continue to update correctly, I'm particularly interested in understanding what is different in the rendering path between:

SkeletonAnimation
SkeletonGraphic with Multiple CanvasRenderers = false
SkeletonGraphic with Multiple CanvasRenderers = true

I have attached the animation files/project data so that the issue can hopefully be reproduced directly.

Any explanation of what causes idle to become invisible, or what I should check in the Spine/Unity setup, would be greatly appreciated.

win.zip

217kB

Spinebot

This is a known rendering issue with SkeletonGraphic in certain configurations. Let me explain what's likely happening and why the behavior differs across the three cases.

Why SkeletonAnimation works fine

SkeletonAnimation uses Unity's MeshRenderer and MeshFilter components, which render directly via the standard Unity rendering pipeline. It has no dependency on the Unity UI/Canvas system, so there are no canvas-specific rendering quirks.

What SkeletonGraphic does differently

SkeletonGraphic is a Unity UI Graphic component, meaning it renders via the Canvas system. Without Multiple CanvasRenderers, it uses a single CanvasRenderer and must batch all skeleton geometry (potentially from multiple atlas pages or blend modes) into a single mesh. This is where the limitation lies.

Why idle becomes invisible without Multiple CanvasRenderers

The most common cause of this specific symptom — where an animation plays correctly according to state/logs but is not visible — is a material/submesh count mismatch between the two animations. Specifically:

If the active animation uses attachments that require a certain number of submeshes or a specific material setup, and the idle animation requires a different configuration (e.g., fewer or more atlas regions, different blend modes, or uses attachments from a different atlas page), the single CanvasRenderer may fail to update or rebuild its mesh correctly for the new configuration.
Without Multiple CanvasRenderers, SkeletonGraphic can only submit one material/texture. If the idle animation's attachments fall outside what was set up during active, they may silently produce an empty or invisible mesh.

Why enabling Multiple CanvasRenderers fixes it

When Advanced - Multiple Canvas Renderers is enabled, SkeletonGraphic creates a separate CanvasRenderer child object for each submesh/material. This allows it to handle varying numbers of materials and atlas pages between animations correctly, because each renderer is rebuilt independently per frame rather than being constrained to a single batched mesh.

What to check in your setup

Here are the most productive things to investigate:

Atlas page usage: Check whether active and idle use attachments from different atlas pages or have different blend modes. If idle uses an atlas page that wasn't active during active, the single CanvasRenderer path may not handle the transition correctly.
Slot visibility / attachment state: Confirm that the idle animation explicitly keys the slots/attachments it needs. If active hides certain slots and idle doesn't re-show them (because it has no key for those slots), they remain hidden. This is a general Spine animation issue but is worth ruling out. See Animation changes for more on this.
SkeletonGraphic Inspector - Advanced section: Take a look at the Advanced settings on your SkeletonGraphic component, particularly:
- Update When Invisible
- Multiple Canvas Renderers
Workarounds if you cannot use Multiple CanvasRenderers:
- Pack your atlas so that both animations use attachments on the same atlas page with the same blend mode.
- Use Multiple CanvasRenderers = true (this is the most straightforward fix and is the recommended approach when your skeleton uses multiple materials).

If you'd like a deeper investigation, you can send your minimal Unity project as a zip to contact@esotericsoftware.com so the issue can be reproduced directly against your specific atlas/skeleton data.

1013912584

Spinebot

Thanks for the detailed explanation. However, I have already checked the points you mentioned, and the issue does not appear to be related to any of them.

In particular:

active and idle do not use different atlas pages or different blend modes.
There is no material/submesh configuration change between the two animations that would explain the behavior.
The slots and attachments used by idle are not left hidden by active. I have also verified the attachment/slot state while idle is playing.
Update When Invisible is not the cause of the issue.

The important point here is that the animation itself is working correctly. AnimationState transitions from active to idle as expected, and the idle animation continues to update normally. The problem is specifically that the result is not rendered by SkeletonGraphic when Multiple CanvasRenderers is disabled.

What makes this particularly interesting is that the exact same skeleton, atlas, animations, and playback code work correctly with SkeletonAnimation, and simply enabling Multiple CanvasRenderers on SkeletonGraphic makes the problem disappear.

Also, I don't think Multiple CanvasRenderers should be considered the expected solution here. My understanding is that this option is intended for specific rendering configurations, rather than being something that should generally be required for a normal SkeletonGraphic.

So what I would really like to understand is:

What exactly changes internally in SkeletonGraphic when Multiple CanvasRenderers is enabled that makes this animation render correctly?

If the skeleton does not actually require multiple materials/atlas pages for this animation, why does enabling Multiple CanvasRenderers change the rendering result at all?

I can provide the Spine animation files attached to this report, and the issue should be reproducible with them. I think investigating the difference between the single-CanvasRenderer and multiple-CanvasRenderer rendering paths would be more relevant than checking atlas pages, blend modes, or slot visibility, since those have already been ruled out.

Harald

@1013912584 Thanks for the detailed reply, sorry to hear that the issue persists.

1013912584 What makes this particularly interesting is that the exact same skeleton, atlas, animations, and playback code work correctly with SkeletonAnimation, and simply enabling Multiple CanvasRenderers on SkeletonGraphic makes the problem disappear.

This is what would normally 100% hint at multiple Materials being required, either due to different atlas pages used (by the two animations, a different one each), or multiple blend modes used at the same time.

1013912584 Also, I don't think Multiple CanvasRenderers should be considered the expected solution here. My understanding is that this option is intended for specific rendering configurations, rather than being something that should generally be required for a normal SkeletonGraphic.

It's the proper solution and required as soon as your skeleton requires multiple materials (see above). The optimal configuration would be to ensure your skeleton has the atlas packed in a way that requires only a single atlas page at any time.

Admittedly having this option as opt-in is maybe not perfectly intuitive. This is mainly for historical reasons and backwards compatibility, as on old spine-unity versions there was no support for multiple atlas pages or blend modes. Still it would be encouraged to use just a single atlas page.

1013912584 So what I would really like to understand is:

What exactly changes internally in SkeletonGraphic when Multiple CanvasRenderers is enabled that makes this animation render correctly?

It uses multiple separate CanvasRenderer GameObjects then. Each one can draw only one Material / atlas page due to CanvasRenderer limitations. Also see the documentation here, or depending on your native language, see the Japanese and Chinese documentation page.

I can provide the Spine animation files attached to this report, and the issue should be reproducible with them. I think investigating the difference between the single-CanvasRenderer and multiple-CanvasRenderer rendering paths would be more relevant than checking atlas pages, blend modes, or slot visibility, since those have already been ruled out.

Yes, please do send us a minimal Unity reproduction project which still shows this issue. You can send it as a zip file to contact@esotericsoftware.com, briefly mentioning this forum thread URL. Then we can have a look at it.