[Plib-devel] [Fwd: Model / 3D Object format that is easy to use, yet powerful? (fwd)]

[Steve B. <sjb...@ai...>]

I spotted this on the Opengl-Gamedev list, it seemed like
it may be of some interest to this list.

It's talking about the ASE file format - and some
known problems with the 3DS ASE writer...

> ---------- Forwarded message ----------
> From: Joe Demers <JD...@nv...>

> Having worked on a couple projects that made extensive use of the .ASE
> format,
> I personally wouldn't choose to use that format for anything again.
> 
> The problems we ran into mainly stemmed from the fact that
> the .ase exporter is just a sample plugin, and wasn't intended as a real
> file format.
> As such, it is ridden with bugs, and completely unsupported.
> (That wasn't intended as a cut on the author - I mentioned it's just a
> sample plugin)
> 
> Anyways, here are the main problems we ran into:
> 1) transformations - .ase has the transformations stored in a full matrix,
>    plus the components of the matrix (rotation, scale, etc.)
>    which just happen to not match up.
>    (One of them is just totally wrong - and I don't remember which)
> 2) no documentation - there are several completely unintuitive things
>    about the 3ds max architecture that you become exposed to but using .ase.
>    For example:
>    2a) normals - normals are sometimes in world space, and sometimes in
> object space,
>        and the space they're in is determined by whether they're being
> animated,
>        whether their parent transforms are being animated, etc.
>    2b) ignore rotation flags - there are a couple flags on each matrix
>        that specify whether or not to inherit its parent's
> rotation/scale/translation,
>        which is awkward for the programmer, albeit useful for the artist.
>        The problem is, the flag means exactly the opposite of what it's
> named.
>        (inheritRotation true -> don't inherit parent's rotation)
> 3) animation - keyframes for mesh animation and transform animation aren't
> sync'ed,
>    so if you have an animation with both, you need to untransform all the
> mesh animations
>    at each transform animation keyframes, which requires you to exactly
> mimic
>    the interpolation going on within max - which isn't trivial for TCB
> interpolated quaternions. ;)
>    (We were able to do this last only after bugging the developers for their
> 3dsmax
>    TCB interpolation code - Ugh - most of the comments in the batch of 10
> files
>    were commented out code, and the one classic: "However, I think this code
> is incorrect.")
> 
> I might suggest the .obj file format,
> for which there are free exporters available from max,
> although, of course, it won't export animation or skeletons.
> It's trivial to read, but again, it's probably not
> as fully functional as you may need.
> 
> The best alternative is, given the time and motivation,
> is to write a plugin that exports the data you want,
> but even this isn't foolproof, given the bug in max
> that causes IK to be unavailable to any plugin.
> 
> Oops, my coworked just corrected my list of problems.
> The normals problem is actually part of a larger one:
> 
> transforms and vertices are in global space,
> normals are usually in local space, unless they're below a space warp,
> (which isn't written into the .ase file, so there's no way to know this)
> in which case they're also in global space.
> 
> mesh keyframes are in local space,
> transformation keyframes are in global space,
> and rotational transformation keyframes are in global space,
> but every keyframe except the first is a relative keyframe.
> (all other keyframes (mesh and non-rotational transformation) are absolute.
> 
> Whew.
> Sorry for the novel,
> but that's finally it.
> 
> So, I'd suggest using .obj (and .mtl) if you can,
> and if not, seriously consider spending the time
> writing a 3dsmax plugin. (or a Maya plugin, or whatever)

-- 
Steve Baker                  http://web2.airmail.net/sjbaker1
sjb...@ai... (home)  http://www.woodsoup.org/~sbaker
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