Re: AppleVision video?

BluPhoenyx

To: Michael J. Mahon
Michael J. Mahon wrote:
> Keith Rose wrote:
>> Paul Schlyter <> wrote:
>>
>>> The Applevision program was actually written in 6502 machine language.
>>> However, back then it was very common to embed machine language programs
>>> in Integer Basic program files, and Applevision was one of them.
>>
>>
>> One thing that I've always wondered about the AppleVision program, was
>> how the "HOME SWEET HOME" text was placed in the middle of the HIRES
>> screen. If I remember correctly, the only way to quit AppleVision was
>> to hit the RESET key, which dumped you out of HIRES mode. But when
>> you did that, the "HOME SWEET HOME" text was still there. As far as
>> I know the only way to mix HIRES and text was at the bottom of the
>> screen.
>>
>> Anybody know how that particular piece of magic was accomplished?
>
> It's likely that Bob used a hi-res character generator to write
> the text on the hi-res screen, and many of them use the PRINT
> interface and echo whatever text is written to the hi-res screen
> on the text screen.

I've used a number of these HRCG style programs and the technique works
well with (usually) one or two minor flaws. One, the text display slows
down a bit but is usually acceptable. Two, most don't scroll the
graphics window if the text window scrolls and the programmer must
account for this 'feature'. Programming is random sized memory windows
will acerbate the problem but might be quicker to refresh the screen. I
suppose screen swapping might eliminate the visibility issues.

One useful advantage is being able to read the text screen to capture
text which matches the text displayed in graphics memory.

At that time the Apple approved character generator was included on the
DOS 3.3 disks and I believe it uses this method. Of course this was some
time back and my memory bits have deteriorated over the years.

Cheers,
Mike T.