CNA-GAP-040: A skinned glTF model cannot also carry rigid scene-node animation: tracks not driven by its skins are dropped

CNA snapshot 009d40f5 · Known Issues › Functional gaps · source links pinned to 009d40f5

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Evidence basis: source-verified at the pinned commit; tests exist (not executed for this page). Claims on this page were checked by reading the CNA source at commit 009d40f5; unless a sentence says otherwise, nothing here was built or executed. Nothing on this page was executed unless the Evidence section says so.

Model::Tag holds SkinningData for a skinned model, so scene-node clips whose tracks are not carried by a skin palette are dropped with the rigid-animation-dropped-on-skinned-model diagnostic.

Identifier: CNA-GAP-040
Category: Functional gap
Subsystem: Models & glTF
Status: Open
Verified against: CNA 009d40f5 (009d40f5dd085c4e674d3479675fac84b12b3e0a)
Evidence basis: Source-verified: read at TARGET, not executed
Tests touching this area: Yes: see Current tests
Affected contract: ContentManager::Load<Model> on glTF files that animate non-joint nodes of a skinned model

Expected behaviour

A glTF file may animate both a skin's joints and ordinary nodes; both kinds of track should reach the application.

Actual behaviour at TARGET

ContentManager.cpp attaches rigid clips (ModelAnimationsEXT) only to an unskinned model. For a skinned one it counts the scene-node tracks not carried by the skins, logs a GLTF-295 warning and calls AppendGltfRigidAnimationDropEXT (GltfImportCore.cpp), which records rigid-animation-dropped-on-skinned-model: “cannot be retained because Model::Tag already contains SkinningData”. Tracks on nodes that belong to a skin palette are kept through the skin.

Source locations

modules/content/src/Xna/ContentManager.cpp — ReadGltfModel: GLTF-294/GLTF-295 branches
modules/content/src/GltfImport/GltfImportCore.cpp — AppendGltfRigidAnimationDropEXT

Evidence

Checked by reading at 009d40f5; not executed.

Focused reproduction

No focused reproduction is known. Nothing has been invented here; the evidence above is what exists.

Current tests

GltfImportReportTests.cpp covers the diagnostic; no test expects the rigid tracks to survive.

Regression test

If a second carrier is added (a property rather than Tag), a fixture with a skinned mesh and an animated prop node expecting both clips.

Blast radius

Skinned characters whose files also animate props, cameras or other rigid nodes.

Workaround

Split the rigid parts into a separate unskinned file.

The same subject is explained at several altitudes. These are the neighbouring pages at each one.

User guide: Model loading: runtime glTF
Deep dives: Skinning and animation: clips
Known issues: Functional gap index