Re: Multisample Masks
Rob Jenkins (robj++at++quid)
Fri, 28 Feb 1997 13:06:38 -0800
On Feb 28, 3:01pm, Moshe Nissim wrote:
> Subject: Re: Multisample Masks
> Ran Yakir wrote:
> >
> > On Feb 26, 1:57pm, Sharon Clay wrote:
> > > Subject: Re: Multisample Masks
> > >
> > > ->There is a *very* annoying SGI hardware bug which prevents the setup
> > > ->of n=8 multisamples coexisting with alpha bit-planes (no such visual
> > > ->exists). You can only do n=4 multisamples with alpha bit-planes.
> > > ->This is *independent* of your framebuffer memory size (number of RM6
> > > ->boards).
> > >
> > > Just to clarify to avoid possible confusion here, destination alpha
planes
> > > are not needed to implement the fade techniques discussed - they only use
> > > source (in-coming) alpha.
> > >
> > So they do. However, in broadcast applications, using the Sirius, you use
the
> > alpha planes to send a mask for the chromakeyer, so that you can perform
> > obstructions of real video by virtual objects, in the chromakeyer. This is
the
> > reason why we must use alpha bitplanes, and therefore suffer from this bug.
I
> > must agree with Orad on this matter - this is really a very annoying bug.
>
> Thanks.
>
> We have raised this problem when the iR came out, but so far, it seems
> that
> this is not a priority with SGI. Maybe SGI is not interested in the
> broadcast
> market? ;) Their marketing indicates otherwise ...
>
Absolutely. I know we've discussed this problem and some potential workarounds
before. I also know that the workarounds are not ideal but the fact remains
that this problem is caused by a *HW* bug, it's not intentional. The
possibility of fixing it has been looked at and various things tried to no
avail.
> Anyone, please confirm/deny that this bug still exists in the Onyx2 iR
> pipe?
>
The last time this came up I checked, and yes it was still there in Onyx2 iR.
I'm not aware of any change to that but I'll confirm again.
Cheers
Rob
--
________________________________________________________________
Rob Jenkins mailto:robj++at++csd.sgi.com
Silicon Graphics, Mtn View, California, USA
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on Mon Aug 10 1998 - 17:54:46 PDT