Subject: Re: NeWS and X

From: [email-masked] (Robert Reed)
Date: Thu, 21 May 87 23:59:26 EDT

Date: 21 May 87 20:40:23 GMT
From: [email-masked]  (Robert Reed)

In article <[email-masked]> [email-masked] (Derek Fluker) writes:

    ... many Mac programs ... put glyphs on the screen to denote which
    mode the user is in (MacPaint and MacDraw have glyphs on the left hand
    side that denote what operation the user is allowed to perform; what
    mode he is in.  This requires constant moving over [and] pressing the
    glyphs to change allowable operations.)  If the number of [discrete
    modes needed] is three or less, is it not better to [assign] them to
    specific mouse buttons allowing the user to change context with a
    minimal amount of motor action?

A set of applications running on a windowed system is rarely limited to
three distinct operating states.  If there were only three that you ever had
to deal with, then such an approach might be reasonable.  However, as soon
as you go over three, you are stuck in the same situation as the Mac with
one button--you must be able to reassign the function of a mouse button (or
buttons) on user demand.  If button functions change, then you must still
represent the current state in some way, such as the way the Mac does it.

There is a little more subtlety to be considered here.  The Mac mouse button
is actually at least bi-functional in that it is sensitive to certain
regions of the display, and when invoked in those areas operates at a higher
level to effect a change of function.  Outside these areas, button events go
to the function currently invoked.  On three button mice, even if there were
only three distinct functions required, the mental exercise of remembering
which button does what is too much to expect of the casual user.  Such a
system would still require some display (even if it is labels on the keys)
to act as a reminder for the functionality of the application.

A more conventional solution with mouse buttons is to assign some generic
operation to each which does not vary despite the number of available
functions.  The smallTalk example of left = select, middle = local popup,
right = window manager popup, is typical of the assignment choices made.

The usefulness of an interaction scheme where the selection of a menu symbol
then causes the symbol to be highlighted, is not limited to environments
where you have access to only a single mouse button.  In particular, use of
a three button mouse does not nullify the value of this technique.
--
Robert Reed, Tektronix CAE Systems Division, [email-masked]