Re: Layer anomalies
Amaury LE LEYZOUR (amaury++at++caraibes.paris.sgi.com)
Wed, 21 Jun 1995 09:37:29 -0600
On Jun 20, 9:51am, John Rohlf wrote:
> Subject: Re: Layer anomalies
> >
> > >
> > > Performer uses displacepolygon() for fast rendering
> > >and stencil() for not-so-fast rendering of coplanar geometry.
> > >Unfortunately, IrisGL's displacepolygon() is inadequate in
> > >certain situations - you can see poke through when layers
> > >have large z-slopes and flimmering when they have small z-slopes.
> > >
> > > Note that if you specify PFDECAL_BASE_HIGH_QUALITY when
> > >building your Performer database (See pfLayerMode) you will always get
> > >accurate coplanar rendering. You need not call stensize() nor stencil().
> > >
> > > I am currently working on a fix for the
> > >displacepolygon() problem that will be available in 2.0
> > >and will experiment with your database.
> > >
> >
> > John Rohlf
> >
> > You are right PFDECAL_BASE_HIGH_QUALITY will render coplanar polygons
> > correctly on our database, we have tried that in our lab and it works on
> > an Onyx and Crimson.The problem is that we need this to work on a Indig^2
> > Extreme which supports 4 stencil planes. If I understand this correctly it
> > means that the Indigo^2 Extreme can support up to 16 layers. Well I find
> > hard to believe that we need more than that in our database so that it can
> > be rendered correctly.
>
>
> Performer needs only a single stencil plane for rendering
> any number of PFDECAL_BASE_STENCIL layers. However, base and
> layer geometry must be rendered sequentially which obviates any
> benefits from mode sorting.
>
> 2.0 has a pseudo-fix to the displacepolygon() poke-through
> problem but the real fix comes with OpenGL where glPolygonOffset
> has both a scale and an offset.
>
The OpenGL function is glPolygonOffsetEXT. This function is an extension for
OpenGL, and is not part of the OpenGL ARB at that moment. The EXT means that
some vendors (of cours including SGI) have implemented this function. But, be
careful, the names of those functions can change at any time ; and they may not
work on some workstations (see the man pages). If you work on SGI Reality
Engine, don't care if you are under IRIX 5.3.
--
# Office Location: SGI France
# Name: Amaury LE LEYZOUR
#
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