[sldev] Sculpties: Vacuum-Forming, Skittering, Zone Linking

[Dale Mahalko]

I am looking for some sort of 3D editor that is optimized to work with the
sculptie concept. I know what features need to exist in a proper sculptie
editor but I don't know enough about what's available to know if it already
exists or not. At this point what I'm looking for probably does not exist,
and so I'm putting this here to plant a seed, hopefully for its eventual
creation.. :-)


1. Vacuum-Forming

A sculptie is best defined as a balloon. It is a continuous shape that is
extremely flexible, and pliable, that can be poked and prodded and molded
into practically any shape. The difficulty in working with a sculptie is
finding ways to manipulate this balloon.

One of the easiest ways to make complex meshes and individual prims
translate into a sculptie, is to treat the sculptie as if it were being made
in a vacuum-forming machine. To do this, traditional meshes and prims are
placed inside a sculptie "inflated" to its maximum size, and the
sculptie is then programmatically "deflated" so that it surrounds and
conforms to the shape of the meshes/prims within.

http://video.google.com/videoplay?docid=8573678537143717206


2. Skittering

A sculptie has some special properties beyond traditional vacuum-forming, in
that it can be stretched without limit to the maximum distance possible
between points without tearing or pulling apart. In order for a sculptie to
best conform to the shape of an object, and to optimize control point
distribution, it would be useful for the points to be able to move around
the surface of the formed shape to concentrate the points into areas of
highest detail. This I refer to as the Skitter function.

Across a large flat space there is relatively little detail and therefore a
need for relatively few control points to define the shape. The control
points can be allowed to stretch out and skitter away from the flat surface
to accumulate around the edges where higher detail is needed. When modeling
a skull as a sculptie, it is best if the control points skitter towards and
concentrate on the face and ears, while also skittering away from the back
and top of the skull, so that the points are concentrated in the areas where
higher detail is required.

 To assist in the shaping of the sculpty around the objects within, it might
be displayed as a transparent sheet draping over the objects inside, with
recesses that are not properly matched by the sculpty given a highlight
color so the user knows to skitter more points towards that location.

Automatic optimized skittering is potentially an intensively computational
problem, but can be assisted by allowing the user to manually control how
points are distributed. A default sculptie mesh is deflated around a set of
target meshes or prims, and the user is then able to "touch" the surface of
the sculptie to define whether mesh points should skitter away or towards
the touch point. The editor then programmatically distributes points towards
or away from the center of the location touched, based on the strengthening
and weakening of the elastic lines connecting the points together.

Direct repositioning of the surface mesh is also possible by allowing the
used to grab a point and then drag it across the surface of the prims below,
causing all other points to stretch or contract around the point that the
user is holding, and then setting a new "stretch memory" for all the elastic
lines between points when the user lets go. In this way a mesh can be
deformed, but then attempts to retain the deformed shape as additional
deformations are applied. Being able to pin control points to the defined
surface so that they cannot move would further assist in the economizing of
point distribution.


3. Zone Linking

Because sculpties can overlap and self-intersect without any problems, it is
possible to create a hole in a sculptie by wrapping it around an open space
and having the sculptie self-intersect when it has wrapped completely around
the open area. Special handling is needed to allow for the creation of
overlaps inside a deflation-capable editor, and one way to deal with this is
to use Zone Linking.

The internal objects which build up the sculptie are linked together to
create zones of deflation. The sculptie deflation begins with objects being
defined within a single zone, ignoring all other objects not selected as
part of the initial zone. To extend out a wrap-around tentacle from the
initial zone, a new zone is defined that links off from one of the objects
within the primary zone. Points are then skittered across the first zone to
spread out across the new, additional zone. The overtlap is formed by
defining still more links and zones that reselect objects from the previous
zones, and continuing to skitter the control points to spread out across the
expanding chain.

 The key to making this work is that the base object from which a
self-intersecting sculptie is to be formed, needs to be built up using
separate meshes or prims so that each section of the object can be split off
into its own zone. This method cannot work with a complex mesh that has
already a hole cut through it, because the sculptie vacuum-forming can only
wrap completely around the outside of each object within each zone..



Skittering and Zone Linking can make complex sculptie objects such as an
octopus relatively easy to produce by defining an initial body zone, and
then defining tentacled zones that link off from objects in the main body.

A traditional wooden rocking chair can potentially be modeled with a single
sculptie by defining the seat as the initial zone, and then each of the
wooden legs, rockers, and back-rest posts defined as a separate tentacled
zone extending off from the seat base. Each tentacled post zone overlaps
into other tentacle zones at the end of each post or plate, to form what
appears to be a single solid object with multiple open spaces between the
leg posts and back-rest posts.

Other possibilities include making a gift box lid with a flower-shaped bow
on top, and each loop of the bow is defined as a separate zone and sculptie
tentacle extending off from the base of the bow, with each bow loop tentacle
overlapping in the center of the bow so as to appear to be continuous.

A mesh grille sculptie is simply rows and columns of zoned tentacles which
cross through each other and extend off from a base zone formed from one
column and one row along the edge of the grille.


So far I don't know of any 3D editor which offers scultpie design methods
like this.

- Scalar Tardis, aka Dale Mahalko
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