[osg-users] Shadow techniques status

Adrian Egli OpenSceneGraph (3D) 3dhelp at gmail.com
Tue Jul 29 06:13:48 PDT 2008


2008/7/29 Jean-Sébastien Guay <jean-sebastien.guay at cm-labs.com>

> Hello Dan,
>
>  I'm looking at shadow techniques provided by the osgshadow nodekit for use
>> in a production project.  On the wiki it reads like only ShadowMap is
>> production
>> ready and all the others have problems.  Is this the case?  Or have the
>> others
>> been marked as experimental because they do not work across video cards?
>>
>
> Here is my opinion on the current shadow techniques in osgShadow. Please
> take these with a grain of salt. And bare in mind that it's pretty easy to
> compare them yourself in your environment, because in most cases once you
> have one shadow technique running you can just swap out the ShadowTechnique
> that you give to your ShadowedScene for another one. Some tweaks are
> technique-specific but that will give you a good idea of what they look like
> in your context.
>
>
> osgShadow::ShadowVolume is broken, I have never seen it work correctly even
> with simple test scenes. There are inverted shadows everywhere (which hints
> at a problem with the z-pass or z-fail implementation). If someone wants to
> fix it, it would be a nice alternative to other techniques in some
> situations.
>
> osgShadow::ShadowTexture is the simplest technique. It works well for
> planar shadows, but for anything more complex you'll want at least
> osgShadow::ShadowMap.
>
> osgShadow::ShadowMap is what I would call the main workforce of osgShadow
> at the moment. It works well, is well tested, and is flexible. The only
> downside is the heavy shadow map aliasing you get on medium to large
> environments, but this is to be expected from a simple technique like this.
> It's really just the basic shadow map, no bells or whistles.
>
> osgShadow::SoftShadowMap is ShadowMap augmented with a simple filtering of
> shadows. The look is not too realistic (it smooths everywhere uniformly
> instead of considering distance of occluder for the width of the penumbra,
> which would be more complex of course) but it alleviates the aliasing
> problem somewhat. It can still only go so far if the environments are large.
>
> osgShadow::ParallelSplitShadowMap is the first of the "next-gen" shadow
> mapping techniques integrated into OSG. Essentially, it uses several shadow
> maps and is view-dependent which reduces aliasing dramatically. It's less
> tested, and until recently was completely broken. It now should work on most
> machines, but I'm still not confident enough about it to use it in
> production (my personal opinion - try it out and see for yourself).
>

Parallel Split Shadow Map: it's still under *beta* release :-) i wait for a
review by a specialist, ... please review, test this algorithme, for
terrain, ... it's once of the most robust algorithm, but it has to be
tested.
***

>
>
> A few more techniques will soon be added (shortly after 2.6, hopefully)
> which are also view dependent, and will give some more choices to users.
> Essentially a shadow technique is a tool, and you just have to find the
> right one for your needs.
>
> If the wiki misrepresents this state of affairs, could you please update it
> or post the pages where there is outdated info here?
>
> Hope this helps,
>
> J-S
> --
> ______________________________________________________
> Jean-Sebastien Guay    jean-sebastien.guay at cm-labs.com
>                               http://www.cm-labs.com/
>                        http://whitestar02.webhop.org/
>
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>



-- 
********************************************
Adrian Egli
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