Lite: Standard material on gltf model causes broken rotation and scaling

Bugs
1

Replacing PBR material with standard material on a gltf model will lead to broken rotation and scaling.

2

Hi! Thanks for the clear repro :folded_hands:

This isnā€™t a rotation/scaling bug - itā€™s a missing feature. The Xbot.glb
model is a skinned (skeletal) mesh, and in Babylon Lite the skinning
(the bone transforms that pose each vertex) is handled inside the materialā€™s
vertex shader.

Right now:

  • PBR material has the skinning path built in, so the character poses correctly.
  • StandardMaterial doesnā€™t have a skinning path yet - so when you swap the
    PBR material for a StandardMaterial, the bone transforms are simply no longer
    applied. The vertices render in their raw positions, which looks like broken
    rotation and scaling.

So itā€™s not that StandardMaterial gets the math wrong - it just doesnā€™t do
skinning at all yet. Thatā€™s why your second (untouched) copy of the model looks
fine while the swapped one doesnā€™t.

Two ways we could go from here:

  1. Add skeletal skinning support to StandardMaterial so it works with skinned
    models too.
  2. At minimum, log a warning when a StandardMaterial is used on a skinned mesh,
    so itā€™s not a silent surprise.

CC @Deltakosh (when you are back :slight_smile: ) - what do you think? Worth adding skinning to StandardMaterial in Lite, or should we keep Standard lightweight and just warn?

3

Hereā€™s a PR to track: feat(standard): opt-in deform features (skeleton/vertex-color/uv-offset) + dynamic fog by PatrickRyanMS Ā· Pull Request #338 Ā· BabylonJS/Babylon-Lite Ā· GitHub, which contains skinning support for StandardMaterial. :slight_smile:

4

Yes Iā€™m adding it today or tomorrow

Ok just saw that @PatrickRyan started it :smiley:

5

Iā€™ll push it to the finish line today!

6

I see the PR is merged. Thanks for the huge work :grinning_face_with_smiling_eyes:

Will enableStandardSkeleton, enableStandardUvOffset, enableStandardVertexColors be exported as well?

7

Oh yeah I forgot. Please do a PR to export them! iā€™ll merge it

8

Sure, here it is:

9

merged!