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From: braner@batcomputer.TN.CORNELL.EDU (braner)
Newsgroups: net.micro.atari16
Subject: Re: New way to post binaries - discussion on format
Message-ID: <1322@batcomputer.TN.CORNELL.EDU>
Date: Wed, 29-Oct-86 12:58:44 EST
Article-I.D.: batcompu.1322
Posted: Wed Oct 29 12:58:44 1986
Date-Received: Thu, 30-Oct-86 22:21:38 EST
References: <2035@dalcs.UUCP> <2844@watmath.UUCP>
Reply-To: braner@batcomputer.UUCP (braner)
Distribution: net
Organization: Theory Center, Cornell University, Ithaca NY
Lines: 40
Keywords: compression
Summary: New way to code PICTURES - & problems

[]

By now I have a working AL RAM-resident program that, upon Alt-Help,
saves the screen in a file in a format that is BOTH compressed and
in a text (modem-able) form.  Doing both in one algorithm
is not only convenient, it is essential for getting the most compact
final product.  A typical desktop yields a TEXT FILE of about 7600
chars: 25% of the length of the bit map!

(Details on the coding algorithm used do not belong here,
It is similar to uuencode, but does not
use space chars nor is it sensitive to added/deleted control
chars or spaces.)

I am now working on a decoding program, to view such files, and on
a translator from the compressed format to Postscript (my intended
use of this whole mess is to send ST graphics to be printed on a
remote Laserwriter...).  I'll post it all when done.

Problems:

The coding program (I call it scode, or perhaps sencode?)
works fine from the desktop, but hangs if Alt-Help is pressed inside
Micro-C-Shell.  Why?  (When first run, the program replaces the screen
dump vector at $502, then does Ptermres() to stay in RAM.)
(I also bite hard and do OS TRAP calls from my code, even though it
is called from the Alt-Help interrupt handler.  I don't really have
a choice, do I?)

Also:  At the end of the ROM screen dump routine, it has:

	ADDQ.L	#4,A7
	RTS

If I end my dump routine with the same or with just plain RTS, it
works the same.  What's going on?

Any advice would be appreciated.

- Moshe Braner