Re: Database Tearing/Channel Clear Problem

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Brian Furtaw (brian++at++sgi.com)
Wed, 26 Mar 1997 09:55:12 -0500

I think what you are describing is a problem with the Esky mode you are using.
In some modes the screen is not actually cleared but instead colored polygons
are drawn just short of the far clipping planes. If you specify PFES_SKY it
will only draw in the upper portion of the screen assuming that you are going
to repaint the bottom yourself. Here's an excerpt from pfEarthSky man page,

               PFES_SKY
                    Causes a sky and horizon backdrop to be drawn. These are
                    drawn using large polygons that are recalculated each
                    frame, using information about the clipping planes, field
                    of view, and eyepoint vertical position for the selected
                    channel. They are drawn instead of a screen clear,
                    forcing the Z buffer to a known state. If the viewpoint
                    goes below the ground plane, the area below the horizon
                    will not be cleared. In the case of PFES_SKY, the screen
                    is never cleared below the lower edge of the horizon.

Is this what you are seeing can you provide a simple test case which
demonstrates your problem? You could modify
/usr/share/Performer/src/pguide/libpf/C++/earthsky.C to add the channel offsets
and make use of some of the databases in /usr/share/Performer/data .

Brian

On Mar 25, 4:21pm, Julia Ellery wrote:
> Subject: Database Tearing/Channel Clear Problem
> To anyone,
>
> We have come across a problem with multichannel use that we think may be
> due to the EarthSky model.
>
> When we have a large roll, the off centre channels do not appear to
> clear properly and a staggered layering effect is seen.
>
> If we remove our call to pfChanESky then all seems ok.
>
> We have 3 channels with the side channels offset by +/- 45 degrees.
>
> Does anyone know what is going on and if so, what we can do to get round
> it? We need the EarthSky model for fog effects and also for real-time
> sky colour changes.
>
> Thanks,
>
> --
>
> Regards,
>
> Julia Ellery,
> Senior Visual Software Engineer,
> Intersim Limited, Units 7-8, Thorgate Road, Littlehampton. Sussex. UK
> Tel: +44 (0)1903 733428 Fax: +44 (0)1903 730246
> email: modellers++at++intersim.co.uk Internet: http://www.intersim.co.uk
>
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>-- End of excerpt from Julia Ellery

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Brian Furtaw  (brian++at++sgi.com)	
VisSim  Technical  Consultant
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