The FBX SDK absolutely claims that there is a normal layer to each
FbxShape, with non-trivial data, even when the corresponding FBX file,
upon visual inspection, explicitly contains nothing but zeroes. The only
conclusion I can draw is that the SDK is computing normals from
geometry, without being asked to, which seems kind of sketchy.
These computed normals are often not at all what the artist wanted, they
take up a lot of space -- often pointlessly, since if they're computed,
we could just as well compute them on the client -- and at least in the
case of three.js their inclusion uses up many of the precious 8 morph
target slots in the shader.
So, they are now opt-in, at least until we can solve the mystery of just
what goes on under the hood in the SDK.
This adds blend shape / morph target functionality.
At the FBX level, a mesh can have a number of deformers associated with it. One such deformer type is the blend shape. A blend shape is a collection of channels, which do all the work. A channel can consist of a single target shape (the simple case) or multiple (a progressive morph). In the latter case, the artist has created in-between shapes, the assumption being that linear interpolation between a beginning shape and an end shape would be too crude. Each such target shape contains a complete set of new positions for each vertex of the deformed base mesh.
(It's also supposed to be optionally a complete set of normals and tangents, but I've yet to see that work right; they always come through as zeroes. This is something to investigate in the future.)
So the number of glTF morph targets in a mesh is the total number of FBX target shapes associated with channels associated with blend shape deformers associated with that mesh! Yikes.
The per-vertex data of each such target shape is added to a vector in RawVertex. A side effect of this is that vertices that participate in blend shapes must be made unique to the mesh in question, as opposed to general vertices which are shared across multiple surfaces.
Blend Shape based animations become identical glTF morph target animations..
Fixes#17.
Pär Winzell
Par Winzell