Re: RGBA with 8 samples on IR

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Angus Dorbie (dorbie++at++bitch.reading.sgi.com)
Thu, 10 Oct 1996 10:43:46 +0100

On Oct 10, 9:39am, Orad Hi-Tec Systems wrote:
> Subject: Re: RGBA with 8 samples on IR
> Remi Arnaud wrote:
> >
> > Here is a message from Ziv Gigus <ziv++at++argus>
> >
> > IR's hardware was designed to support either 10 bit RGB (no A) or 12
> > bit RGBA. It was never designed to support 10 bit RGBA and no future
> > flavour of IR ever will.
> >
> WHY !?
> As was mentioned, the alpha in the framebuffer is mostly needed by
> applications in a video environment. Highest quality digital video
> is 10 bits, never 12. (Also on the monitor side, it was mentioned that
> the DACs dither to 10 bit). So what is really needed is 10 bit RGBA,
> not 12 bit RGBA.

But you may need more precision if you want to gamma correct before
the DACs which is exactly what you do on iR.

>
> > Due to bugs in imp8 it can not support 8 samples RGBA (12 bit). It
> > does support 8 sample RGB (10 bit) which are advertised in all pixels
> > depths.
> >
> What is imp8 ?
> Is it a ucode release? A hardware release?
> a programmable-hardware release?
> Is it now fixed? Is it in the process of being fixed?
> How will customers get this fixed?

It's the ASIC on the RMs which processes the pixel operations, I think
there are 80 of them per RM.
A bug in this context will be with the design of the ASIC, not the software.

InfiniteReality in Onyx2 may have different imps so there
is some hope of doing this in the new architecture but I don't
have that information.

You can forget about doing this on your existing hardware. Use the
methods described in earlier posts. The Onyx iR was not advertised
as being cabable of doing this.

Cheers,
Angus.

>
> > Finally, note that both on IR and RE we dither glSampleAlpha(...) over
> > 4 pixels, so with N samples you get 4N + 1 levels. This is done not
> > done for AlphaToMask, however.
> >
>
> Is this a bug or a feature?
>
> Moshe Nissim
> Orad Hi-Tec Systems
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