[iyonix-support] Re: Colour swapping (was: Re: Graphic cards and noise - warning)
- From: Terje Slettebø <tslettebo@xxxxxxxxxxxx>
- To: iyonix-support@xxxxxxxxxxxxx
- Date: Sun, 22 Oct 2006 20:07:15 +0200
>From: "David J. Ruck" <druck@xxxxxxxxxxxx>
> On 22 Oct 2006 Terje Sletteb=F8 <tslettebo@xxxxxxxxxxxx> wrote:
> > I've heard about this colour swapping thing. Could anyone give me an
> > overview of what the issue is, or provide a pointer? Googling for it di=
> dn't
> > result in much, and neither have I found it in any FAQ.
>
> Its quite simple, RISC OS expects a different order of red green and bits=
> than the graphics card.
>
> > Might it be possible to rewrite the relevant parts of RISC OS to
> > accommodate the apparent standard among the graphics cards, or is the
> > problem perhaps that some applications assume the order of the colours =
> in a
> > pixel, and is so, can you even change it in software (without possibly =
> a
> > significant performance hit)?
>
> All OS modules and applications that do any manipulation of image data ex=
> pect
> the order of RGB tbits o be as specified in the PRMs, and will not work
> otherwise.
Thanks for your reply. I'm a little "rusty" having been away from the
platform 10 years or so, does anyone know where in the PRM this order is
stated? I didn't find it with some searching.
Anyway, I did a quick test on my Iyonix with the FX5200 graphics card, using
BASIC to write directly to the video memory, and it appears that the
graphics card, in 32-bit mode, has the word layout &BBGGRR, or might it be
that this write is trapped and reversed, in software?
> > What I'm getting at is that, if possible, we should get a solution that=
> > minimises or avoids run-time overhead, if possible.
>
> That solution is already in place, except for little used 32K modes.
Ok, so I'm trying to find out exactly what this solution does, i.e. if it's
transparent for the programmer, even working directly with the video memory,
or if it only works with higher-level abstractions.
Regards,
Terje
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