Cursors and masks

[Christoph North-Keys]

On Fri.d.3.Mar.1989 Skip Montanaro misstated the use of cursors and masks
as used in X and, perhaps, NeWS.  In general, bichromatic cursors consist
of the following:

    1. A rectangular image (allowing for blitter) of the cursor.
    2. A rectangular mask specifying which parts of the cursor are
       to be (a) displayed or (b) transparent.

Most people who have created cursors this way in X quickly discovered that
a cursor of only one color was invisible over a like-coloured region, and
altered the mask to allow a contrasting border to show through from the
cursor bitmap.  Unfortunately this simple technique was not used in
SunView.   This causes the OS4.0[.1] WHITE arrows used in some alert boxes
to be invisible on white windows, etc.  There may have been a further bug
involved, since even knowing this we were sometimes unable to find the
alert box arrow.

This same masking technique is used on some systems for icons.  In both
cases it can be expanded to allow for multicolour cursors and icons,
masked so that non-square objects can be created without having to go
through obnoxious processes like trying to match the background pattern,
as in SunView.

Montanaro's (snide) comment about NeWS causes me to wonder if these simple
graphics features, available on $1k systems, have been made available to
programmers in NeWS.  Has anybody been fortunate enough to find out?  Does
anyone know how to change the default SunView cursor?  Is there a way to
use masking on icons and/or cursors in SunView?

-Christopher North-Keys (harp%mcc.com at uunet.uu.net)
 Systems Administrator
 M.C.C. Packaging/Interconnect