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Deferred Shadow Maps
http://www.horde3d.org/forums/viewtopic.php?f=7&t=635
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Author:  swiftcoder [ 02.02.2009, 20:05 ]
Post subject:  Deferred Shadow Maps

http://www.ziggyware.com/readarticle.php?article_id=235

Seems to be a brand new technique, and it looks very promising to help reduce the complexity of material shaders, especially if you are already using a depth-prepass.

Author:  DarkAngel [ 03.02.2009, 00:21 ]
Post subject:  Re: Deferred Shadow Maps

I only had a quick skim over it, but it seems to suffer from the same problem as many deferred techniques - limited G-Buffer space.
If a shadow occlusion term is stored in the G-Buffer *for each light* then you will quickly run out of places to store them, which limits the number of lights which can use shadows.

In situations where you only need 1 to ~4 shadow-casters at a time though, it looks like a great way to solve the shader-permutation problem.

Author:  swiftcoder [ 03.02.2009, 01:19 ]
Post subject:  Re: Deferred Shadow Maps

DarkAngel wrote:
I only had a quick skim over it, but it seems to suffer from the same problem as many deferred techniques - limited G-Buffer space.
If a shadow occlusion term is stored in the G-Buffer *for each light* then you will quickly run out of places to store them, which limits the number of lights which can use shadows.

In situations where you only need 1 to ~4 shadow-casters at a time though, it looks like a great way to solve the shader-permutation problem.
I think the question becomes whether you truly need a separate shadow buffer per light - my inclination is that fairly decent shadowing could be implemented with a single shadow buffer for all lights. Basically just additively blend the shadow contribution into a single buffer, and use the final value as the opacity of the shadow at that pixel.

At that point, it becomes much closer to light pre-pass rendering, and the performance should be fairly decent.

Author:  marciano [ 03.02.2009, 09:00 ]
Post subject:  Re: Deferred Shadow Maps

swiftcoder wrote:
Seems to be a brand new technique, and it looks very promising to help reduce the complexity of material shaders, especially if you are already using a depth-prepass.

It is not quite a new technique but nevertheless very useful for forward rendering. Crysis is also using it:
http://ati.amd.com/developer/gdc/2007/Mittring-Finding_NextGen_CryEngine2(Siggraph07).pdf

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