Re: Help needed: Emulation of AppleII Graphic modes

[Holger Picker <pickerh@uni-muenster.de>]

Hello,

thanks a lot for your replies.

On 14 Feb 2003, Lazarus I. Long wrote:
> you have guessed correctly.  I actually use a 5 pixel window, since 4
> pixels is not enough information in certain cases.  when looking at a
> 5 pixel window, the one you're coloring is the center one.
Hmm... I've used this kind of technique for my emulator, too, when writing
the code for a "sharp" hi-res output. It's just that I looked at three
hi-res (1/280) pixel instead. :-)

> and you assume that there are 2 extra pixels on each side, with value 0.
This also corresponds to what Mr. Mahon wrote:
"Generally, you would be safe to assume that the bits
'shifted in' before and after the ends of the line are 0 (black)."
And, I have to agree, it really seems to be some kind of art "how one
simulates this 'artifact' NTSC color on a PC display". :-)
Having quoted that, well, forgive me, Mr. Long, but I've seen you posting on
this matter several times now, and I have also visited your web site before
where you compare the results of different algorithms.
> happy to send you the code if you want it.
Well, would you mind, if I send you a (perhaps a bit longer) email about the
code?

> > a) What size do the hires pixel have (I assume 1/280 i.e. 2/560, not 1/560)
> correct
>
> > b) What happens if there are two bytes, the first with highbit on, the second with highbit off, like 0000001-1 0000000-0?
>
> you will loose the 2nd 1/560 pixel.  it just "goes away"  IIRC and you
> get lowrez color there
>
> :)
Ah, I see. Thanks for that information. I've kept wondering about this kind of
thing for quite a while.

Kind regards

  Holger