Path: utzoo!attcan!uunet!clyde.concordia.ca!jarvis.csri.toronto.edu!utgpu!barry
From: barry@gpu.utcs.utoronto.ca (Barry Lay)
Newsgroups: comp.sys.atari.st
Subject: Re: Fine scrollin'
Keywords: graphics atari helpx2
Message-ID: <1990Feb13.162107.2537@gpu.utcs.utoronto.ca>
Date: 13 Feb 90 16:21:07 GMT
References: <1199@elmgate.UUCP>
Organization: UTCS Public Access
Lines: 22

Jeff,
  I tried to mail to you directly the last time, but the message got sent back
"userid not known".  This seems to happen a lot on this network nowadays.
Hopefully others will be interested too.

Having done some playing around with scrolling methods, I would say that 
blitting is definitely the way to go.  Figure out the screen size in pixels,
subtract the offset of the scroll amount (1, in your case), and use a raster
copy opaque (vro_cpyfm(), if memory serves me right) to shift the screen by
the offset amount.  You will now need to overlay the "vacated" screen space.
If you are working within a window, v_gtext() will work fine.  It doesn't care
what pixel it starts on, although it is faster if it is snapped horizontally
to a byte boundary.  If you are dealing with the alpha screen, you are in for
some work, unless somebody in netland knows a quick way to do this.  I would
build the text line image in some buffer (alternate Logbase?) and blit a
portion of it into the screen.  I don't have much experience with the alpha
mode, so I will defer to better advice here.

If you would like to see a code fragment for a window, send me a note.  Perhaps
personal mail works better.

Barry