Re: ancient animation

[Michael Kennett <kennett@math.ubc.ca>]

> Chris Wicklein (chrisw@eagle.ais.net) wrote:
> : Bell Cecelia (cbell@Phoenix.kent.edu) wrote:
> : Bell Cecelia (cbell@Phoenix.kent.edu) wrote:
> : : Long long ago i saw a great Apple II cartoon featuring a guy dancing to turkey
> : : in the straw.
> : : The program took a long time drawing a living room and tv set then all
> : : of a sudden the little guy would appear and startd ancing.
> : : Is this program still around?
> : : Is it on Asimov or anywhere else?
> 
> :       You're thinking of Bob Bishop Presents....Apple Vision!
> 
> :       I wish I knew where I had a copy....Hmm......
> 
>    Apple-Vision was written in Integer BASIC. I have a copy somewhere, and
> am willing to help you get it, as long as it's legal?
> 
>         Stavros
> (skaratso@oucsace.cs.ohiou.edu)

Ages ago, I hacked around with this program. Even though it was
written in Integer BASIC, I recall that it used small machine
code routines. From memory, this program was significant in that
it showed the `double hi-res' mode of the apple ][ display.
Normally, the hi-res graphics of the ][ was 192x280. (This is from
memory - I haven't used the old ][+ my Dad owned for 5 years. Its
back in Australia (STILL WORKING!!!!!), and I'm now in Canada.
BIG ASIDE: Anyone in Vancouver with a ][ that I can play with...:-) )

Anyway, Bob Bishop's Apple Vision used the 2 different white colours
of the hires mode to achieve a resolution of 560x192. I was very
impressed with this trick - I had small successes in recreating it
with a few of my own programs.

Are there any ][ guru's who know the nitty-gritty details of the
hi-res display? From (rusty) memory, there were two hires pages,
hires1 ($2000-$3FFF) and hires2 ($4000-$5FFF). Each byte within
these memory blocks contained 7 pixels - bits 0->6 were used to
determine which pixels were `on' (1). The remaining bit, bit 7, was
the colour (OK OK - so I don't use the American spelling `color'.
No flames please :-) ) bit that determined what colours the pixels
in the byte were. There were complicated rules about how the image
could be composed, involving even/odd addressing within the display
byte. I recall that if two adjacent bits (amongst bits 0->6) were
set, then the colours of the pixels where WHITE. There were 2 white
colours, depending on bit 7 being set or not.

I believe these details are (in general) correct. Usual disclaimers...
this is all from memory, haven't used a ][ for ages, etc... However,
I would welcome discussion on the details behind the ][ display.

Addendum:
If the resolution of the hires screen is 280 x 192, then
	280x192 = 53760
different pixels are on the screen. Assuming further that the
length of display memory allocated is $2000 bytes(32 pages), and
that there are 7 pixels per display byte, have
	8192x7 = 57344
possible pixels on the screen. It all looks hunky-dory.