RE: [Algorithms] Perspective Shadow Mapping

[Rusch, M. <MRusch@EA.com>]

I echo your shifts from optimism to pessimism to optimism etc.  It seems
like every time I overcome one obstacle 5 more fall into my way.  I'll
try and post some of my findings once I get out of the 80 hour week
cycle and back into a normal schedule, hopefully someone will find them
useful.  Drawing the frustum and where it hits the unit cube (or unit
half-cube in the D3D case) was infinitely helpful.  That 2d app you made
has given me some other ideas.  Eventually I think these things can be
made to work as a pretty general lighting solution in the outdoors at
least.

Matt

-----Original Message-----
From: Thatcher Ulrich [mailto:tu...@tu...]=20
Sent: Friday, May 30, 2003 10:20 PM
To: gda...@li...
Subject: Re: [Algorithms] Perspective Shadow Mapping

On May 30, 2003 at 06:45 -0700, Peter-Pike Sloan wrote:

> Perspective shadow maps use the one degree of freedom that is left
> with shadow zbuffers - how the film plane intersects the frustum.

Wow, that's a pretty cool insight.  But -- is this only true of point
lights?  I.e. it seems like a directional light has parallel lines in
world-space, so the film plane angle is irrelevant.  In
post-perspective space of course the direction light becomes a point
light, and the film-plane insight holds, but the perspective transform
is also in effect.  So I'm not sure how to think of the extra degree
of freedom for directional lights.

> Steven Gortler has an undergrad (Hamilton Chong) who has analyzed
> perspective shadow maps in a more general manner (just in flat land
> so far), it is available at:
>=20
> http://people.deas.harvard.edu/~sjg/papers.html
>=20
> "Real-Time Perspective Optimal Shadow Maps"
>=20
> (near the bottom of the page...)
>=20
> They look at more general sampling problems (ie: what if you know
> the dominant receiver, etc.)

Looks like excellent stuff.

This thread inspired me to post some of my recent thoughts &
experiments, including a very simple "flatland" viz app, see:

http://tulrich.com/geekstuff/psm_notes.html

--=20
Thatcher Ulrich
http://tulrich.com


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