Re: Which way is up?

[Dan Hoey <hoey@nrl-aic.arpa>]

    Date: Mon, 3 Aug 87 08:59 EDT
    From: Richard Billington <Buff@cis.upenn.edu>

    ...If you started out with (0,0) in the bottom left corner, what would
    the next line be, (0,-1)?  Then all windows would run from (0,750) to
    (0,-SomeBigY)....

Don't be silly.  Start with (0,0) in the top left corner of these windows.

    Personally, I prefer consistancy [sic!].

Consistency is a good reason for having the same handedness of coordinate
system for text, graphics, and textbooks.

    Date: Mon, 3 Aug 87 15:27 EDT
    From: Mike McMahon <MMcM@STONY-BROOK.SCRC.Symbolics.COM>

    ...Even as an old style window **MORE**'s at the bottom and wraps around,
    the new output is in fact a continuation of the old.  It is a cause of
    major inconvenience in such windows that the coordinate system resets
    itself as the result of this essentially unpredictable event....

This is why graphics (which you show how to do later in your message)
and text should have the same system.  Mike McDonnell has made an
excellent case for this being Y-down.  Given that absolute
Y-coordinates in scrolling windows tend to approach bignums anyway,
having them be negative is no big deal.  Graphics will be relative to
the current cursor position anyway.

    In the improved graphics substrate which Symbolics is developing for a
    future release, all drawing is done through a general affine transform.
    This provides the basis for just the facility you are looking for.

It is unclear whether all the other software will know enough to write
through this transform.  If it is possible to make all my windows
appear to use a Y-down coordinate system for graphics and text, this is
just what is desired.  Somehow, I expect to find some software that
can't deal with the fact that TERPRI will decrease the y-coordinate of
the text cursor.

Dan Hoey
HOEY@NRL-AIC.ARPA