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Path: utzoo!watmath!clyde!burl!ulysses!gamma!epsilon!mb2c!umich!pla
From: pla@umich.UUCP (Paul Anderson)
Newsgroups: net.micro.amiga
Subject: Quirk in AmigaBasic SCROLL command
Message-ID: <600@umich.UUCP>
Date: Wed, 21-May-86 19:57:46 EDT
Article-I.D.: umich.600
Posted: Wed May 21 19:57:46 1986
Date-Received: Sat, 24-May-86 17:58:04 EDT
Distribution: net
Organization: University of Michigan, EECS Dept., Ann Arbor, MI
Lines: 41

My apologies if this problem has already surfaced:

I have found a quirk in the operation of the
SCROLL command in Amiga Basic by MicroSoft.
The following sample program sets up a screen
with a little bit of random stuff on it, and
then prompts for a scroll amount.  With small
negative numbers, it seems to work as we expect,
but in other combinations, the area filled in
after the scroll is larger than it should be.

I would be grateful if anyone can comment on
what is happening, and if there is anything
that I can do about it.  I realize that I can
do a GET to and a PUT from an array to achieve
much the same thing, but it takes too much memory.

--------------------cut here----------------
LINE (0,0)-(616,186),3,bf
LINE (100,50)-(300,150),2,bf

LINE (100,100)-STEP(200,5),1,bf
LINE (200,50)-STEP(10,100),1,bf

INPUT "Enter delta x, delta y";dx,dy
SCROLL (125,60)-(275,140),dx,dy

REM Positive deltas seem to result in 
REM the background fill extending to
REM the edge of the window.

REM Negative deltas over about -15 or
REM -20 (i.e. -30,-30) drag part of the
REM window boundary

END

--------------------end of example----------

Thanks very much,
  Paul Anderson, University of Michigan EECS dept