[osg-users] ParallelSplitShadowMap ....

Adrian Egli 3dhelp at gmail.com
Thu Sep 27 23:44:47 PDT 2007


Thanks All,

exactly what i am looking for some days, why i have to use a negative
PolygonOffset. But i still not found the problem.
may i did a bad mistake in the code. i would like doing a review and of the
presented code. may there is a z-flip inside what would be
really bad. i don't know yet what's going wrong.

/adegli

2007/9/28, Terry Welsh <mogumbo at gmail.com>:
>
> I can't say what the problem is, but I doubt it is PolygonOffset.  On
> my own PSSM implementation and other simpler shadows that I have done
> everything works well with factor = 1.1 and units = 4.0.  These
> numbers come straight out of this document:
> http://www1.cs.columbia.edu/~ravir/6160/papers/shadowmaps.ppt
>
> Numbers as large as 10.0/20.0 really shouldn't be necessary, and I've
> never heard of using negative numbers for PolygonOffset.  That's a new
> one on me.  Anyway, I believe the problem lies somewhere other than
> PolygonOffset.
> --
> Terry Welsh - mogumbo 'at' gmail.com
> www.reallyslick.com  |  www.mogumbo.com
>
> > Message: 8
> > Date: Thu, 27 Sep 2007 13:41:51 +0100
> > From: "Robert Osfield" <robert.osfield at gmail.com>
> > Subject: Re: [osg-users] ParallelSplitShadowMap ....
> > To: "OpenSceneGraph Users" <osg-users at lists.openscenegraph.org>
> > Message-ID:
> >         <7ffb8e9b0709270541o2cae61d7v7674d63131ed70a4 at mail.gmail.com>
> > Content-Type: text/plain; charset=ISO-8859-1
> >
> > Thanks Adrian,
> >
> > Changes now merged and submitted to SVN.
> >
> > Visual quality is better with the suggested options in the README but
> > still not great, in particular I loose shadows when near to objects
> > and at shallow angles to the surfaces under shadow.  I've played
> > around with the polygonoffset and found that changing units makes no
> > difference for the models/views I've tested, but factor to to 4 or 5
> > seems sufficient to avoid the z fighting.  The values you've chosen
> > for NVidia look excessive.
> >
> > I am beginning to wonder about the value of using PolygonOffset in
> > this context, its just not reliable enough across hardware.
> > Alternatives to using PolygonOffset are tweaking the depth range via
> > osg::Depth or via a small tweak to the projection matrix.  Replacing
> > osg::PolygonOffset by osg::Depth might well be a useful thing to try.
> >
> > Robert.
> >
> > On 9/26/07, Adrian Egli <3dhelp at gmail.com> wrote:
> > > Hi Robert,
> > >
> > > please update the PSSM, i did some bug fixes and added new features to
> move
> > > the camera virtual against the view direction by applaying a simple
> distance
> > > factor (a), which is calculated camera eye - camera center distance.
> and we
> > > can move the "light camera" against the light direction (b).
> > >
> > > (a) some objects behind the camera can cast shadow
> > > (b) object aboive the camera can cast shadow
> > >
> > > then i fixed the shadow map orientation, now screen x coordinate
> alinged
> > > which improve the quality
> > >
> > >  /adegli
> > >
> > > --
> > > ********************************************
> > > Adrian Egli
> > > _______________________________________________
> > > osg-users mailing list
> > > osg-users at lists.openscenegraph.org
> > >
> http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
> > >
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-- 
********************************************
Adrian Egli
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