Re: GS/OS Hires/Double-Hires File Recognition Problem

[rubywand@aol.com (RUBYWAND)]

In article <Pine.SUN.3.91.951224011938.27106E-100000@owens>, Cyrus Roton
<croton@ridgecrest.ca.us> writes:

>
>If a true hires file is saved (BSAVE) with length less than $2000, then
it 
>will be missing some pixels. I seem to remember something about extra, 
>unused, bytes at the end of each hires line, and some program to save the

>picture without those extra bytes. I feel sure that, if that is the case,

>you would have to have a special program to load the file back into 
>memory with all the data bytes going into the proper places. However, 
>such a file would be considerably smaller than $1FFF.
>
>I do not see how a hires picture can be saved with length $1FF8, but 
>would be interested in finding out. Have you tried to BLOAD the file and 
>then BSAVE it with the proper length? If you do, BLOAD into the hires 
>area of memory (after selecting that area for viewing) and see if really 
>is a hires pic.
>

    No problem. BSAVEing hires pics at length $1FF8 is an ancient trick of
DOS 3.3 users. (It saves an extra sector of disk space.)  The explanation
is that the hires display hardware does not use $2000 bytes. In fact,
there are quite a few non-displayed bytes in a "hires page". One run of
undisplayed bytes is the last eight in hires page memory-- i.e.
$3FF8-$3FFF in hires page 1 and $5FF8-$5FFF in hires page 2.