Re: help with DHR plotting

[nparker@cie-2.uoregon.edu (Neil Parker)]

In article <Pine.SUN.3.91.951210100139.4708B-100000@owens> Cyrus Roton
<croton@ridgecrest.ca.us> writes:
>I need help in debugging a double hi-res plotting routine. The following
>program steps are used in setting up for DHR plotting:
>
>LDA $C057    ;hires
>LDA $C052    ;mixclr
>LDA $C050    ;txtclr
>LDA $C002    ;mainread
>LDA $C004    ;mainwrt
>STA $C001     ;store80
>STA $C00D     ;0n80col
>LDA $C05E     ;an3off
>
>Subsequently, plotting to main or auxmem is selected by 
>
>LDA $C054    or   LDA $C055
>
>The problem is that certain programs (not all of them) which use 80 columns,
>seem to leave some softswitch or another set to interfere with this plotting.
>The result is thin vertical bands on the plot. I can load and view DHR
>properly, I just can't plot properly.
>
> The only way I have found to eliminate the problem is to shut off and
>reboot and don't run those other programs prior to DHR plotting. Reset does
>not help, nor does playing around with the normal 80 col/40 col keyboard
>commands.

This differs slightly from the symptoms I've experienced, but I'll risk
a guess anyway.

Is your computer by any chance a IIGS?  And are the "certain programs" you
mention by any chance Appleworks 2.0?

I've observed that on my IIGS, Appleworks 2.0 turns off some of the the
graphics screen shadowing controls (probably for speed reasons--that way the
system doesn't have to wait for a write to shadowed memory to synchronize with
the slow RAM), and doesn't turn them back on when it exits.

When graphics screen shadowing is off, you can bank-switch the DHR pages all
you want, and never succeed in displaying anything on the screen, because
the screen memory isn't there anymore--it's been pulled out from under you.


I haven't tested any other versions of Appleworks to see if they suffer from
the same quirk.

               - Neil Parker
-- 
Neil Parker                       | No cute quote, no cute ASCII art, no cute
nparker@cie-2.uoregon.edu         | disclaimer, no deposit, no return....
nparker@cie.uoregon.edu           | (This space intentionally left blank:
http://cie-2.uoregon.edu/~nparker |                                           )