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

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

In article <Pine.SUN.3.91.951224011938.27106E-100000@owens>,
Cyrus Roton  <croton@ridgecrest.ca.us> wrote:
> 
> If a true hires file is saved (BSAVE) with length less than $2000, then it 
> will be missing some pixels.

No it won't.

> 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. 

It works the same way as the text screen: there are eight "screen
hole" bytes at the end of each run of 128 bytes.  These bytes have no
effect on the displayed picture in any way.

One of the graphics formats (FOT, file type 8) uses the first group of
screen holes to store additional information about the graphic, such
as whether it is monochrome or colour.

The last eight bytes ($3FF8 to $3FFF) are rarely used by any program
that makes use of hi-res graphics.  They certainly aren't used by the
picture, so there is no point saving them.

> 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. 

8192 divided by 128 multiplied by 120 = 7680 bytes instead of 8192 bytes.

Hardly worth the effort, since you would have to do a messy update
when reloading it.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand