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fix: T-posing skinned models — autorig produced an orphan skin with no weights

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The model animated its skeleton but rendered a permanent T-pose: the mesh
wasn't skin-bound. Root cause was in autorig's binding, introduced while
chasing an earlier "skins:0" export:

- The earlier "skins:0" was actually caused by bone-heat weighting failing
  (0 weighted verts → empty skin gets dropped), NOT by the Armature modifier.
- The "fix" then stripped the Armature modifier and used parent_type=ARMATURE.
  That makes the glTF exporter emit a skin OBJECT but with no node.skin
  reference and no per-vertex JOINTS/WEIGHTS — an orphan skin. The mesh then
  renders its bind pose (T-pose) forever while the skeleton animates unseen.

Fix: keep the standard ARMATURE_AUTO result (Armature modifier + vertex
groups). With the nearest-bone fallback ensuring real weights, the exporter
now writes a COMPLETE skin (verified: meshnode.skin=0, JOINTS/WEIGHTS present).

Also:
- skinned_player_model: _ensure_meshes_bound() re-binds any skinned mesh whose
  skeleton NodePath doesn't resolve at load — graceful degradation instead of
  a silent T-pose for imperfect GLBs.
- smoke test now asserts the spawned player's mesh is bound to its skeleton,
  so this class of bug fails the test instead of shipping. 30/30 pass.
- regenerated miku_test.glb with the corrected pipeline.

Co-Authored-By: Claude Fable 5 <[email protected]>
This commit is contained in:
Nicholas Butzke
2026-07-06 18:11:26 -04:00
co-authored by Claude Fable 5
parent e2fbc424a7
commit 22cb0a58b7
4 changed files with 33 additions and 13 deletions
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debug/spawn_smoke_test.gd
+8
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@@ -79,6 +79,14 @@ func _test_spawn_with_skin(skin_id: String, expect_skinned: bool) -> void:
if _check(skinned != null, "SkinnedModel created for GLB skin"):
_check(skinned.loaded, "GLB model loaded")
_check(skinned.skeleton != null, "skeleton found in GLB")
# The mesh must be bound to the skeleton, else it renders its bind
# pose (T-pose) while the skeleton animates invisibly.
var bound := false
if skinned.skeleton:
for mi in skinned.find_children("*", "MeshInstance3D", true, false):
if mi.skin != null and mi.get_node_or_null(mi.skeleton) == skinned.skeleton:
bound = true
_check(bound, "skinned mesh is bound to the skeleton (won't T-pose)")
if skinned.animation_player:
_check(skinned.animation_player.is_playing(), "animation playing")
print(" clips resolved: ", skinned._resolved_clips)