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From: bammi@curie.ces.cwru.edu (Jwahar R. Bammi)
Newsgroups: comp.sys.atari.st
Subject: Re: How do you create non-scrolling screen regions?
Message-ID: <BAMMI.90Mar8012815@curie.ces.cwru.edu>
Date: 8 Mar 90 06:27:05 GMT
References: <2344@ultb.isc.rit.edu>
Sender: news@usenet.ins.cwru.edu
Organization: Case Western Reserve University
Lines: 37
In-reply-to: ajy2208@ultb.isc.rit.edu's message of 6 Mar 90 22:07:13 GMT

In article <2344@ultb.isc.rit.edu> ajy2208@ultb.isc.rit.edu (A.J. Yarusso) writes:
>   Hopefully I won't have to write custom screen i/o routines to do

	No you wont have to! there is an advertised lineA variable (V_CEL_MY)
just to do this: the short (16 bit) at offset -0x2a (-42 decimal) bytes from
the lineA base can be set to a number N to get effectively a N+1 line
scrolling region vt52. For instance if you want the N'th line to
be a status line, and have a (N-1)x80 vt52, you would set

	char *linea_base = (base of lineA from linea0 (0xA000));

	short *V_CEL_MY = (short *)(linea_base - 42L);
	short save;
	save = *V_CEL_MY;
	*V_CEL_MY = save - 1;

	....
	and before terminating:
	*V_CEL_MY = save;

its probably not a good idea to assume that the screen is 25 lines
high (or even 80 wide (with can be determined from V_CEL_MX at offset -44)).

To write to the bottom line(s):
	- you can use something like v_gtext()
	- or you can change *V_CEL_Y, write to the line using
	Bcon/Ccon traps, and change *V_CEL_Y back, and so on..

Some of this stuff is documented in <line.h> that i posted here a while
back, or in the more current version of that file that comes  with the
Gnu C library (available via FTP from dsrgsun.ces.crwu.edu).

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