From: Andreas Ekstrand (Andreas.Ekstrand++at++saab.se)
Date: 04/15/2002 07:48:11
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?
>
> --
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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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