I am rendering shadows using depth stencil buffers and a shadow map.
I am using a floating point texture for the shadow map. The shadow
map size is 1024. On older video cards, or cards that have only 256MB
ram, everything works fine. However, when I try to render the shadows
to a newer card with more than 256MB, the shadows flicker and exhibit
something that looks like Z-fighting. I was able to cure this, by
explicitly disabling fixed function Z buffering in my pixel shader
(ZEnable = FALSE). But this then led to the shadows showing through
all objects, whether the occluder was in front of them or not. This
effect makes it look like objects who have a shadow cast on them, are
transparent! You can see shadows straight through them.

So, I either get nasty flickering, or objects that are transparent
with regard to shadows.
But in cards that are older and less advanced, it works perfect as
long as I comment out the ZENABLE = FALSE!? If ZEnable is left at
FALSE, then shadows show through objects in both types of graphics
cards.
GeForce 6800 GO Ultra(256MB) - works GeForce 8300 GS - flicker or
transparency

First of all, the technique you're presenting here
doesn't use stencil-shadowing (that's the thing
with geometry of shadow casters beeing extruded in
light-direction to the frustrum's bounds, then even/odd
testing the number of shadow-surfaces actually drawn
behind the scene).

Also it looks like you're using the non-hw sccelerated
version of shadow maps (FP-Textures carrying depth,
instead of real hardware depth-buffers, moving the
depth-comparison and weighting step the the hardware).

So if you disable Z-testing, the outcome should
look like always when you disabkle z-testing, at least
without any respect to shadows.

Maybe you should first take a look at wich format
your shadow maps are really using (does it depend
on the cards used?).

Gruss

Jan Bruns

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