Re: Apple][VGA - finally available

["Michael J. Mahon" <mjmahon@aol.com>]

geoff wrote:
>   To: Michael J. Mahon
> TYhe Second Sight performs various functions, including an Apple II/IIgs video 
> to VGA converter (this is how most Second Sight owners use their card).
>
> The nice thing about the Second Sight is that if you don't like the RGB 
> display is generated, you can write your software code to make it do something 
> different.  You don't have to burn your ROM--just write a driver when the OS 
> boots.  Jut because nobody has done this doesn't mean that it doesn't have the 
> capability.  It becomes really easy to support enhancements when no hardware 
> changes are needed.

The fact that nobody has done this is a testament to the difference
between making a thing *possible* and making it *probable*.  ;-)

That this possibility is even discussed sounds like saying "it's
programmable, so if the designer(s) didn't make it work well, you
can fix it yourself".  ;-)

> If you want to immediately make HGR look horrible by adding NTSC artifacts, 
> there is nothing to prevent you :)

Actually, I think you would find that the Second Sight doesn't have
nearly enough processing to provide proper NTSC effects digitally.

You may be missing some of the context...

This is part of a protracted and intermittent discussion on how to best
and most economically provide the capability of connecting an Apple IIgs
to a modern VGA display--both because of fears of analog RGB monitors
failing and because of the convenience of being able to share monitors
with modern machines.

As with any engineering problem, there are several possible approaches.

One is to tap into the RGB signals (digital preferred, but analog OK)
inside the IIgs and, with as little fuss as possible, use them to
create a VGA RGB stream.  A few have had good success with converters
using "NTSC" scan standards RGB in and providing VGA RGB out.  There
have been experiments using the digital RGB in a similar way, but no
product yet.  (Critical issues are the relation of the sampling clock
to the Apple dot clock, and the bandwidth of the video processing--not
too much, not too little.)

Another method is to eavesdrop on the Apple II peripheral bus and
completely recreate Apple II/IIgs graphics modes using another
processor and frame buffer, from which VGA video is generated.
This has the advantage of extreme versatility, combined with the
disadvantage of extreme versatility.  ;-)  It invites the invention
of graphics modes with no support on the Apple II platforms.  To the
degree that is simply aims to emulate the native Apple II graphics
modes, it takes on the responsibility of a full emulation--ideally even
including frame buffer timing for "mixed mode" displays--which is quite
complex and apparently was never fully done...

If it isn't clear  ;-), I think that the latter approach--the one taken
by the Second Sight card--is a failed strategy.

There is no value in offering modes that are not supported by any
meaningful software base or tools.  And the job of fully emulating
native modes is much more subtle than designers first realize.

Finally, the vast majority of Apple II graphics are not IIgs graphics--
they are Apple II graphics designed to be viewed on analog composite
monitors, where the subtleties of color and the pleasant lack of
detail (that cannot be represented in Apple II video) is an artistic
match to the designer's intent.

I certainly wouldn't want to use it for text displays, but there are
hundreds of hi-res screens that only represent their designer's intent
when viewed with limited color bandwidth, and that look positively
gruesome in standard RGB modes (think dithering).  So any VGA converter
should offer the *option* of processing the video with NTSC artifacts.
Not offering this option would mean that I would need another monitor
on my desk just to view these graphics properly.

Put another way, Woz designed the Apple II to make color on the
rather imperfect analog NTSC monitors of the day, and legions of
game designers designed their graphics for these monitors, since
they knew that practically all of their customers would be using
similar monitors to view them.

> Geoff
>
>  > Dave Althoff, Jr. wrote:
>  > > Ferdinan Meyer-hermann 
>  > > <ferdinan.meyer-hermann@a2central.com.remove-rw3-this> wrote: :  > Why 
>  > > did you not add support for the IIGS?
>  > > : So you'll have to wait until someone designs a "GS2VGA"...
>  > > : A real GS2VGA would also have the advantage of being cheaper and 
>  > > drawing less : power than a combined solution. And it is likely to cause 
>  > > less trouble
>  > 
>  > > Anybody remember the Second Sight board?  8-)
>  > 
>  > That's not a IIgs video to VGA converter.
>
>  > The Second Sight was a much more problematic "VGA card for the IIgs"
>  > with the consequent need to support new graphics modes, as opposed
>  > to simply converting IIgs RGB video into VGA video.
>
>  > The trickiest part of such a conversion would be a mode to handle NTSC-like 
>  > color rendition (instead of the much higher bandwidth and,
>  > for many graphics, less attractive "digital RGB" modes) for Apple II video.

-michael

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