From: Marcin Romaszewicz (marcin++at++sgi.com)
Date: 04/15/2002 16:22:33
In order to sort transparent geosets back to front, performer has to know
that they contain transparent geometry. To tell performer, you have to
call gstate->setMode(PFSTATE_TRANSPARENCY, PFTR_ON) and you can explicitly
put your trees into the transparent bin. Doing either of these things
should force back-to-front sorting. Performer does not sort back-to-front
within geosets, so if you have one geoset with a bunch of trees, they will
not be sorted with respect to each other, so only put one per geoset. Do
your trees have transparency enabled but dont get sorted?
-- Marcin
On Mon, 15 Apr 2002, Andreas Ekstrand wrote:
> Hi Yair,
>
> I thought that Performer used a special bin for all transparent geometry
> and sorted it from back to front. However, I tried an explicit setup
> like that and it still didn't work.
>
> Cut-out trees are not sufficient for me I'm afraid, I would like the
> alpha edges to blend nicely with the background. So I realize that the
> rendering order is of importance. But I can't see why this is happening
> if the background trees actually are rendered before the foreground
> trees? Do I have to assign special bins just for these trees? Isn't it
> enough to use the transparent bin?
>
> Regards,
> Andreas
>
>
> Yair Kurzion wrote:
> >
> > Hello Andreas !
> >
> > By default, IR/IR2/IR3 use a different transparency method than Octane/Octane2.
> > For correct semi-transparency, Octane/Octane2 require sorting of objects
> > from farthest to nearest.
> >
> > It looks like your trees are not sorted back-to-front. Do you assign
> > special bins to the tree geometry ?
> >
> > Trees are a special case of transparency. You normally don't want to see
> > semi-transparent pixels. Each pixel is either completely transparent or
> > completely opaque (the tree texture defines a cut-out of the polygon).
> > If all you want is cut-out trees, read on ...
> >
> > You can fix the tree edge problem without sorting back-to-front: Take a look
> > at pfGeoState modes: PFSTATE_ALPHAREF and PFSTATE_ALPHAFUNC. They let you
> > control what alpha values of a polygon are skipped while rendering.
> > Take a look at man pfAlphaFunc for more info on this.
> >
> > -yair
> >
> > > I have noticed that polygons with alpha textures (e.g. flat trees or
> > > bushes) become somewhat strangely rendered when viewed in front of each
> > > other. If you're viewing such a polygon in front of another, you can
> > > actually see through the second polygon through the edges between the
> > > alpha and non-alpha texels of the first polygon.
> > >
> > > I know, this might sound a bit confusing, but I'm sure this is a common
> > > problem and has been noticed by many Performers out there. It doesn't
> > > happen on IR/IR2/IR3, but it does with Octane/Octane2 as well as with
> > > Geforce2/Geforce3. I have attached an image that shows the problem quite
> > > clearly. Could anyone describe why this is happening and if you could
> > > avoid it?
> >
> > --
> > \_________ \_____ \__ \__ \_____
> > \_________ \_____ \__ \__ \_____ Yair Kurzion
> > \__ \__ \____\__ \__ yair++at++sgi.com
> > \__ \__ \__ (650) 933-6502
> > \__ \__ \__
> > \__ \__ \__
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>
> --
> ---------------------------------------------------------
> FDM-AE Andreas Ekstrand |E-mail: Andreas.Ekstrand++at++saab.se
> Saab AB |Phone: +46 (0)13 - 18 40 42
> SE-581 88 Linkoping |Fax: +46 (0)13 - 18 41 77
> SWEDEN |
> ---------------------------------------------------------
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> -----------------------------------------------------------------------
> ITEC 2002 Friends of Performer Meeting: Wednesday April 10 17:00h
> Hainaut Room, Lille Grand Palais, Lille, France
>
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