Jurassic Park
Hi Mark,
Well, I think it'd be *possible* to use metaballs in a poly modeler…!
Metaballs and blobby modeling both fall under "implicit
modeling"…using algebraic expressions (instead of a listing of poly
vertices, or a parametric patchmesh description, or quadrics) to
describe a shape. The "sphere of influence" that Jim Roof describes
is a special case of this, but not the only way it can be used! The
hard part is figuring out the equations needed for a certain shape,
and I think that may be why most of the action is on the blobby
methods now — it's easier for designers to interface with.
But it's tough to render these equations. One popular way is to first
polygonize the data, and then send it out to a normal renderer.
Paradoxically, it's easier to fit poly vertices to a specified shape
than it is to fit a spline patch to it — the tradeoff is lower
fidelity vs. quicker development. But blobs->polys is being done
today! (And isn't this "zone of influence" idea similar to the way
that bones deform vertice positions?)
It seems metaball computation is a bear, though…takes significant
time even on a workstation. There's already a PC program (it's either
Poly-Ray or POV-Ray) that uses Blinn-style blobby modeling…haven't
fired it up yet myself…more info in GraphDev. And there's what
sounds to be a hot class on Implicit Modeling at SIGGRAPH this year,
with many of the folks who've done the basic research.
Odds are that we'll be able to use this stuff "soon" — cool! Anyone
have more info?