From: jpc@tauon.ph.unimelb.edu.au (John Costella)
Newsgroups: sci.virtual-worlds
Subject: Re: PAPER: Galilean Antialiasing for VR, Part 01/04
Date: 10 Nov 92 19:19:30 GMT
Article-I.D.: u.1992Nov11.035532.17361
Organization: University of Washington
Originator: hlab@stein.u.washington.edu


Thanks, Jon, for some worthwhile comments.
 
>     My opinion is similar, that scan conversion is already a solved
> problem, and it will turn out to be easier to throw enough hardware at
> the front end to sustain 1 update/field than to solve the sampling and
> aliasing problems of a "galpixel" buffer. But I'll still offer an
> opposing viewpoint.

OK, to each his own. I don't know, though, if everyone would agree with 
a ``more dollars than sense'' approach <grin>. The simple fact is
that once you get 1 update/frame, you always feel like de-speccing 
down to 5 or 10 frames per update, to squeeze every last effective
drop out of your investment, in terms of image complexity. Gal antialiasing
lets you do this despeccing with a much less harsh visual impact.

>     First, note that the expense of updating a galpixel buffer doesn't
> vary with the image complexity. So the balance between frame buffer
> and rendering hardware will vary depending on how complex your
> database is.

Ah, yes, the glimmerings of understanding are starting to appear! <grin> 
The fact that the updating algorithm can be implemented in a pre-determined
fixed running time, and implemented with *simple* circuits (not even a
microprocessor in sight), is the reason it is worthwhile. I can draw
you a circuit schematic on the back of an envelope (er ... OK, an A3-size
envelope :), with nothing more complicated than MSI components and RAM. 
Of course, you wouldn't really do it this way in practice (stick it all 
onto VLSI instead), but you get the idea.
 
>     What I'd suggest the author do is trim this paper to about 20
> pages describing solely the galpixel concept, add some diagrams and a
> block level approach to implementing a G(2) frame buffer, and, most
> importantly, produce experimental evidence that Galilean antialiasing
> will indeed offer the claimed benefits. The other stuff about
> nonplanar displays belongs in a different paper.

I was awaiting these criticisms <grin>. It really did start off as a 
20-page thing, but then I started wondering about *who* was going to 
read it.  (Hell, no, don't worry about the reader <grin>.) Many people 
that *have* read it say:

- I liked these sections a lot
- These bits were OK
- I didn't quite follow these bits
- The following bits were not necessary
- These bits were total balderdash

However, *every* reader puts *different* parts of the paper in each of these
categories! So, in that sense, maybe I have covered the wide range of
backgrounds of readership reasonably ... different strokes for different 
folks. I also dislike dry (even if concise) mathematical treatises; so if 
that is what you want, then write your own! <grin>

OK, for the *justifiable* criticisms <large grin>: 

Experimental evidence: Well, I do have a software simulation that I can
provide, that shows precisely what the hardware would show (for a very
simple situation). Hardware experimental evidence: This is clearly 
required.  Unfortunately, I am not (politically and financially) in a 
position to carry this out. So the idea's out there for anyone at the 
big corporate labs to give a burl: if it flies, it's yours; if it doesn't, 
then you did something wrong <large grin>. I'm afraid that circumstances
do not allow me to do better than that.

Flat planar display: Yes, I know it's a sore thumb in there. The original
idea was to give *all* the beautiful material you suggest: block
diagrams, schematics, colour pictures <grin>; as well as the mathematical
formulae that compute the *software* side of things: taking derivatives
of the perspective transfomation for a moving viewpoint, derivatives of
the shading models, etc. This would have required using the perspective
transformation *explicitly* ... and that is why I wanted to first outline
at least ONE cartographical projection for dealing with wrap-around
displays, so that the maths could be demonstrated on *it*, too.

Of course, you know the rest: to make it understandable to a wide audience,
the text was fleshed out; the paper grew; and in the end it was a matter
of shutting the gate on the paper before it grew any further: anyone with 
a bit of nous can generate all of those other niceties pretty trivially.
So the paper, in its current form, is not what one would usually 
``publish'' ... I am hoping that the fact that we can discuss criticisms
in a matter of days (which, for even a journal like the mis-named _Physical_
_Review_Letters_, would by now have taken twelve months), means that it
can be more a starting-point than a complete tome. (OK, lame excuse. :)


My question to the group: 
------------------------
Who has one built by now? Stop lurking! <grin>

John

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John P. Costella              School of Physics, The University of Melbourne
jpc@tauon.ph.unimelb.edu.au         Tel: +61 3 543-7795, Fax: +61 3 347-4783
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