RE: [Algorithms] Current state of shadow maps?

[<c.s...@ph...>]

Shadowbuffering with PSM and derivatives are very useful for top-down, =
constrained views with (read: RTS games) with a fixed single directional =
light source (aka. the sun). For this purpose, PSM alone is great and =
all you need to have. Their usefulness vanishes the more freedom the =
user camera needs to have, ie. when you cannot forbid the user to get =
into a dueling frustum.=20

If you need ultimate robustness and must handle all cases on a =
consistent basis, I know of no other method other than Tom style =
multiple buffers or going stencil, that can guarantee to deliver it.

It seems that an opinion I held is still valid

Shadowbuffers win the outdoor, daylight scenario:
- you will need shadows from trees, which you cannot get with stencil =
volumes
- the sun covers all screen area and all geometry for which stencil is =
expensive
- the sun is a directional light source, for which PSM and derivatives =
are most effective.

Stencil volumes win the indoor/urban, night scenarios (think doom3, or =
neverwinter nights for the record)
- shadows from vegetation can be neglected.
- many omnidirectional light sources, or lightsources with large =
frustra, for which shadowbuffer is unoptimal (too many render targets)
- most light sources have small screen space extent and world extent, so =
stencil is not expensive


However shadowbuffers have other qualities that make them attractive =
(image based, soft edges), so it would be desireable to use them for all =
purposes. It's just a pity that they are so unfeasible for omni lights =
(I imagine an army with torches here ...).




-----Original Message-----
From: gda...@li... =
[mailto:gda...@li...] On Behalf Of Remy =
Saville
Sent: Wednesday, September 07, 2005 3:50 AM
To: gda...@li...
Subject: [Algorithms] Current state of shadow maps?


I'm going to start looking at improving our shadow system which uses
plain old shadow maps.

I thought I'd ping the list for opinions on what is best these days.  It
seems Nvidia had a good paper in GPU Gems; Perspective Shadow Maps: Care
and Feeding that takes care of most of the PSM issues.  However Light
Space Perspective Shadow Maps from
http://www.cg.tuwien.ac.at/research/vr/lispsm/ seem like they might be
even better.

Does anybody have any opinions on PSM or LSPSM?  I didn't see a lot of
LSPSM discussion in the archives.


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