Thread: [Empyrean-devel] In the hopes JL is around...

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Anyone know how to merge geometry in Maya while keeping bone influences on the 
vertices?

Chad

On Fri, 12 Nov 2004, Chad Austin wrote:

> Anyone know how to merge geometry in Maya while keeping bone influences
> on the vertices?

I have no doubt that it is possible, although I don't think Maya supports
it directly -- you'd have to do some pretty involved scripting to automate
the process.  To do any sort of modification to skin geometry, you first
have to detach the skin (Skin | Detach Skin), which loses the skin
weights, which is annoying if you have edited them from their default
values.  Maya's workaround for this is to first export the skin weights
(Skin | Edit Smooth Skin | Export Skin Weight Maps), then detach the skin,
edit the geometry, rebind the skin, and import the skin weight maps again.
The skin weight maps are a directory of image files, one for each joint,
that indicate, via a greyscale texture map, the influence of each joint on
geometry vertices.

The problem with using this technique to merge two pieces of geometry is
two-fold:  (1) Exporting the skin weights of the original geometry
produces two directories of weight map images which somehow need to be
merged into one.  Simply adding the image values together would work,
assuming that: (2) The original pieces of geometry don't overlap in UV
space.

So, one way to do the merge might be to:
- Scale both pieces of geometry in UV space so that each occupies one half
  of the texture space.
- Export the weight maps of each piece of geometry.
- Manually merge each weight map image (via the "screen" blending mode in
  Photoshop, for instance).
- Merge the geometry.
- Rebind the skin.
- Import the merged weight maps.

Of course, the success of this method also depends on the weight map
resolution, and maybe other stuff.  A more exact and automated solution
would be to write a custom MEL script to perform the merge
programmatically, although I'm not sure how one would go about this.

                                --=o0o=--
Joe Lee -- jc...@cs...

You gonna be on IRC this weekend?  I'm about to submit our entry, but tomorrow 
I'm going to be working on the Cal3D exporter some more.  It mostly works, but 
I'd like to discuss some stuff about your robot.  (And maybe have you show me 
how you baked it.  Annie's fish isn't baked, so only half of it animates in Cal3D.)

About to pass out,
Chad

Joe Lee wrote:
> On Fri, 12 Nov 2004, Chad Austin wrote:
> 
> 
>>Anyone know how to merge geometry in Maya while keeping bone influences
>>on the vertices?
> 
> 
> I have no doubt that it is possible, although I don't think Maya supports
> it directly -- you'd have to do some pretty involved scripting to automate
> the process.  To do any sort of modification to skin geometry, you first
> have to detach the skin (Skin | Detach Skin), which loses the skin
> weights, which is annoying if you have edited them from their default
> values.  Maya's workaround for this is to first export the skin weights
> (Skin | Edit Smooth Skin | Export Skin Weight Maps), then detach the skin,
> edit the geometry, rebind the skin, and import the skin weight maps again.
> The skin weight maps are a directory of image files, one for each joint,
> that indicate, via a greyscale texture map, the influence of each joint on
> geometry vertices.
> 
> The problem with using this technique to merge two pieces of geometry is
> two-fold:  (1) Exporting the skin weights of the original geometry
> produces two directories of weight map images which somehow need to be
> merged into one.  Simply adding the image values together would work,
> assuming that: (2) The original pieces of geometry don't overlap in UV
> space.
> 
> So, one way to do the merge might be to:
> - Scale both pieces of geometry in UV space so that each occupies one half
>   of the texture space.
> - Export the weight maps of each piece of geometry.
> - Manually merge each weight map image (via the "screen" blending mode in
>   Photoshop, for instance).
> - Merge the geometry.
> - Rebind the skin.
> - Import the merged weight maps.
> 
> Of course, the success of this method also depends on the weight map
> resolution, and maybe other stuff.  A more exact and automated solution
> would be to write a custom MEL script to perform the merge
> programmatically, although I'm not sure how one would go about this.
> 
>                                 --=o0o=--
> Joe Lee -- jc...@cs...
> 
> 
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On Sat, 13 Nov 2004, Chad Austin wrote:

> You gonna be on IRC this weekend?

I'll be around.

> (And maybe have you show me how you baked it.  Annie's fish isn't baked,
> so only half of it animates in Cal3D.)

If I recall correctly, I selected all the joints in the Outliner (via
control-clicking each), then I used Edit | Keys | Bake Simulation -- you
can check out the options, but I just used the defaults.  I believe what
this does is sample the values for each channel of the selected items for
each time step, then hooks up a new animation curve to the channel based
on these values, overriding any previous animation or connections.

                                --=o0o=--
Joe Lee -- jc...@cs...