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shaq1106

Unit Cube Clipping for LisPSM

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Hi.
I'm reading about LisPSM and got some code
from nvidia.com
When apply unit cube clipping for LisPSM
the shadow quality is much better then before.

But I don't know what the code means.
I mean what the unit cube clipping means for LisPSM
and how to apply it for LisPSM.
There are other tech such as PSM,TSM.
But this time I want to focus on LisPSM first.

Thanks.

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I believe their unit cube clipping applies to PSM specifically.
At least this is the case if you are talking about the algorithm
in GPU Gems 1.

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imagine the light's pov

now instead of rendering from the light's pov (looking down z)
you use a lookat vector which is perpendicular to the light z vector
but with direction as close as possible to the view z vector

then after you calculate:

Pproj = mul(Pview, MworldViewProj)

you just swizzle it around

Pproj = Pproj.xzy; // for example

so you end up with linear z and non-linear x axis

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Hi.
I'm reading about LisPSM and got some code
from nvidia.com
When apply unit cube clipping for LisPSM
the shadow quality is much better then before.

But I don't know what the code means.
I mean what the unit cube clipping means for LisPSM
and how to apply it for LisPSM.
There are other tech such as PSM,TSM.
But this time I want to focus on LisPSM first.

Thanks.




I think you will find that the y divide for this technique seriously damages the z precision of the shadowmap, and you will still be left dealing with the dueling frusta cases unless you have a locked POV (say an isometric camera for an RTS style game).

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