Re: Apple II graphics

[dempson@actrix.gen.nz (David Empson)]

Jeff Blakeney <CUTjefbla@bconnex.net> wrote:

> On 16 Jul 1998 04:55:55 GMT, supertimer@aol.com (Supertimer) wrote:
> 
> >Gabriel Morales <Togega@concentric.net> wrote:
> >
> >>Now, could I subsequently call up these graphics in BASIC in order to
> >>produce simple animation, or is there a better way of doing this?
> >
> >Yes; the easiest way is to load up hires screens from the slot 3 RAM
> >disk.  Assuming your program is in slot 6, drive 1 and your graphics
> >are labeled gpx1 through gpx7, you can use the following program...

[program snipped]

> >The reason you want to load from s3,d2 is because of the speed
> >of the RAM disk.  If you have a larger RAM disk, you can add more
> >frames.
>
> That should be A$2000,L$1FF8 for a single hires image in hires page 1.
> For hi-res page 2 you would use A$4000,L$1FF8.  You can use L$2000 if
> you want but it will use an extra block on the disk that doesn't
> contain any image data.

Considering Supertimer's example assumes a RAM disk on S3,D2, this
implies ProDOS, and ProDOS doesn't waste an extra block if you save the
full $2000 bytes from a Hi-res graphics page.

(DOS 3.3 adds a load address and length at the start of a 'B' file, so
it ends up crossing an extra sector boundary.)

> However, I believe there was a suggestion to use Double Hi-Res
> graphics which makes things a little more difficult because DHR
> graphics use twice as much drive space.  This means it will take twice
> as long to load the image from disk and it will also take longer to
> display because you need to load one hi-res page, move it into Aux
> memory then load the second hi-res page and display the DHR screen.

It is possible to load a picture directly into DHR page 1 by playing
with the 80-column softswitches, avoiding the load-then-copy
requirement.
 
> Also, there is no page 2 for DHR graphics

Yes there is.  You just can't access the auxiliary memory half of it via
the 80STORE/PAGE1/PAGE2 soft switches.  On a IIe or IIc, you have to
make auxiliary memory active.

(It is easier on the IIgs, because you can do an indirect bank
reference.)

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand