From: lawrence bertoldi (lberto++at++md.prestige.net)
Date: 04/15/2002 13:00:47
On Linux... Some times yes, depending on what else is in the scene. for example
if the scene has more then one object with transparency in it there is no way to tell
when
things will be drawn( without sorting back to front) unless you create your own bins.
then you can set the order that things happen. The scene did draw your background
first and you can see it through the transparent parts of the second object to be
drawn.
so if the next object drawn is between the background and the 2nd object.. well you
get the picture!
See Ya ~;-}>
Lawrence Bertoldi Graphics Software Consultant
lberto++at++md.prestige.net Simagery Inc.
410.960.1623 Software Consulting For Hire
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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