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Dual Sphere-Unfolding/Omni-directional shadow maps


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#1 B_old   Members   -  Reputation: 667

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Posted 19 July 2012 - 07:07 AM

I'm curious what people are using for omni-directional shadow maps these days.
I think that dual paraboloid and cube map shadows are two typical choices. I have used the latter in the past. While looking for alternatives that might perform faster with comparable quality I came across Dual Sphere-Unfolding Shadow Maps, which are rendered in a single pass. Has anyone tried it? Is there a more detailed explanation of the method around? Any other methods that are worth looking into?

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#2 PixelSmasher   Members   -  Reputation: 415

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Posted 19 July 2012 - 05:19 PM

I tried this method in a recent project to fill a scene with 100 dynamic lights casting shadows. The theory is appealing and the results are not so bad...
BUT you'll want to have a very fine geometry in order to obtain accurate shadows: the projection used to store the whole shadow sphere in a single texture will highly bend the geometric data, thus leading to frequent artifacts during the depth comparison.
(Though I had to rush that project so I might have missed something)

Still, it was tremendously fast and produced cool shadows... If you don't stare at them too much Posted Image

Edited by PixelSmasher, 19 July 2012 - 05:21 PM.


#3 B_old   Members   -  Reputation: 667

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Posted 23 July 2012 - 08:23 AM

Interesting.
Are you aware of additional resources related to this technique?

#4 PixelSmasher   Members   -  Reputation: 415

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Posted 24 July 2012 - 03:12 AM

Unfortunately, I am not.
This technique seems to remain unnoticed (or people consider that such artifacts are unworthy of their time Posted Image).

There is this video, made by the author of Dual-Sphere Unfolding (It was my only help when implementing my demo), but nothing from the community.
If you ever find something, I would be greatly interested.

Edited by PixelSmasher, 25 July 2012 - 06:23 AM.


#5 CryZe   Members   -  Reputation: 768

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Posted 25 July 2012 - 09:43 AM

It's just simply sphere mapping. The only difference is, that they use 2 sphere maps and let the vertex shader decide on which one the vertex gets projected, based on whether the y axis is positive or negative. They say that it would be a one pass method, but I really doubt it. I don't think that a triangle that has vertices on both sides of the xz-plane wouldn't cause artifacts. You'd probably still need a geometry shader or 2 passes to render these shadow maps without artifacts. I think it's worse than dual paraboloid shadow mapping, but I'll give it a try.

#6 B_old   Members   -  Reputation: 667

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Posted 26 July 2012 - 04:47 AM

It's just simply sphere mapping. The only difference is, that they use 2 sphere maps and let the vertex shader decide on which one the vertex gets projected, based on whether the y axis is positive or negative. They say that it would be a one pass method, but I really doubt it. I don't think that a triangle that has vertices on both sides of the xz-plane wouldn't cause artifacts. You'd probably still need a geometry shader or 2 passes to render these shadow maps without artifacts. I think it's worse than dual paraboloid shadow mapping, but I'll give it a try.

It would be nice to see your results in case you find the time and implement it.

#7 Frenetic Pony   Members   -  Reputation: 1395

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Posted 26 July 2012 - 08:45 PM

I would also try single pass cubemapping using the geometry shader: http://devmaster.net/forums/topic/9367-render-to-cubemap-in-a-single-pass-really-useful/

The least amount of geometry warping that I know of, and still very efficient Posted Image

#8 B_old   Members   -  Reputation: 667

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Posted 30 July 2012 - 02:52 AM

I would also try single pass cubemapping using the geometry shader: http://devmaster.net...-really-useful/

The least amount of geometry warping that I know of, and still very efficient Posted Image

Last time I tried it, using the geometry shader for single pass cubemapping was slower on my machine than doing a pass for every cube face. Have you seen more encouraging results?




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