From: koopman@sgi84.ctc.com (Michael G. Koopman)
Subject: Re: INFO: Metaballs?
Date: Wed, 30 Jun 93 18:16:29 -0400



In article to Sci.VW, Bernie Roehl writes:

>  As I recall, a metaball is a kind of "equipotential surface" around a
>  point.  You specify a point, a radius, and an "intensity" for each
>  ball; when balls come close, their shapes blend to form a smooth
>  equipotential surface.

I had the opportunity for a brief chat with the developers at the last
SIGGRAPH, which is a 'long time' ago relative to software. :-) My
understanding was that the "balls" were ellipsoids of revolution with
shape control, in the core software, by definition of the foci loci.
I am awaiting an article (in Japanese) regarding the "stickiness"
control which determines the severity in the curvature of conics which
provide surface blends tangential to adjacent, connected metaballs.  I
believe "soft bond" 'deformation' and dynamic associativity of the
balls, as well as, "hard bond" 'rigidity' constraining kinematics are
available.  The surfaces are quadrics, therefore, some systems support
the basic polygon mesh form as a primitive, e.g., OpenGL.
Non-proportional scaling of these may also be implemented in METABALLS
(not yet in OpenGL, as far as I know).

>  I haven't used them, so this is all third-hand.  They can be rendered
>  by most raytracing packages (I believe they're also called "blobs" or
>  "soft spheres" or "fuzzy spheres"), but they can't be rendered in
>  real-time (so they're not useful for VR, at least not yet).

Some "really cool" capabilities come out in the rendering.  I believe
some neat tricks (magic?) to obtain transparency based on the viewed
volume (prismatic material) are used in raytracing of "mushy,
translucent" stuff.  'Real-time' raytracing of prismatic materials was
recently accomplished; NOT.  But, textured polygon METABALL quadrics
should be readily incorporated into several systems out there today.

Please regard this information as solidly founded on conjecture. ;-)

Michael Koopman (mike)                e-mail:  koopman@ctc.com
Concurrent Technologies Corporation    phone: +1-814-269-2637
1450 Scalp Avenue                    telefax: +1-814-269-2666
Johnstown, PA  15904-3321  USA          ICBM:  40-15'N-78-50'W