[x3d-public] HAnim skinned deformation

Andreas Plesch andreasplesch at gmail.com
Thu Jul 12 05:18:02 PDT 2018

Before diving into an HAnim skinned deformation for x3dom, there are a few


Is there a proto implementation for skinned deformation, eg. the skin
related fields ?


Are there examples in addition to Joes kicking player ?


This field modulates the transformation applied to the indexed coords by a
factor ranging from 0 to 1. It is not quite clear how the factor should be
applied. The spec. focuses on the amount of rotation but scaling and
translation presumably should also be affected.

Should scaling and translation be weighted ?

The most straightforward way would be to just scale all the components of
the transformation matrix. However, that does not work for the rotational
components. Is there a recommended way to apply the weights to the complete
transformation matrix ? Multiply all the individually weighted field
matrixes ? That would be a lot of matrix multiplications, for each coord
for each frame of an animation.


The spec. only refers to the skinCoords as being affected by the weighted
transform. Presumably the skinNormals also need to be transformed ?
If so, it seems to make sense to only apply the rotational component, and
ignore scaling and translation ?

Mix of skeletal and skinned bodies

It is possible to have geometry both in the skin and the skeleton (within
segments) fields.
In this case it seems the full transform would be always applied to the
segment geometries. That may lead to out of sync movement during animation
but such mixed representation may not be intended to be fully supported.
How should an implementation deal with such humanoids ?
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