david@jpl-devvax.JPL.NASA.GOV (David E. Smyth) (10/20/90)
Version 1.04 of the Widget Creation Library is now available
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Widget Creation Library,
Motif Resource Interpreter,
Athena Resource Interpreter:
An Easier Way to Develop Applications
using Motif and Athena Widgets.
Window-based applications are notoriously difficult to program. When
the Macintosh was introduced in early 1984, Bill Gates projected that
50% of Microsoft revenues would come from Mac application by October
1984. In reality, the first Mac applications were only beginning to be
shipped by that date.
When Steve Jobs left Apple and developed the NeXT computer, the window
environment was specifically designed to support a WYSIWYG interface
builder. NextStep and the NeXT IB were the results of this effort.
The X developers at MIT and DEC also needed an easy way to develop
windowed applications. Instead of developing a WYSIWYG tool like NeXT,
they developed a toolkit where interfaces were specified using C code,
and could be significantly modified via `resource files' using a
minimum number of attribute specifications. They provided an instance
attribute inheritance mechanism to propogate attributes throughout an
interface. This allows such simple specification as the following to
alter every font in an interface:
*font: 9x15
The toolkit is called the Xt Intrinsics. The windows, buttons, menus,
scrollbars, etc., are called Widgets. The Athena Widgets are one set
of user interface objects built upon the Xt Intrinsics. Motif is
another set of widgets.
As time went on, developers of widget-based applications found the
resource files to be more and more useful. For the fourth release of
the X11 window system, many of the example programs evolved to the
point that only the raw behavior of the applications were specified in
C, with most of the look and feel being specified using resource files.
At the fourth annual X Technical Conference, several people pointed
out that resource files could be used to specify everything about
a widget based user interface, except the actual "tree" of widgets,
their types, and bindings of behaviors to the user interface widgets.
Could the resource mechanism be enhanced to allow these to be specified
as well?
Martin Brunecky at Auto-Trol in Denver Colorado took up the challenge,
and posted a simple set of routines which he called WsXc, for "Window
System: Xrm Creation."
Xrm stands for X Resource Manager, which is a heirarchical database for
keeping arbitrary named data related to X window interfaces. The Xt
Intrinsics use Xrm for widget resources. The basic idea of WsXc is
to search the Xrm database, starting at the root, and pull out resources
which describe the widget heirarchy and bindings to callback functions.
Over the next several months, WsXc was repackaged as Mri (Motif
Resource Interpreter), and then Ari (Athena Resource Interpreter), and
finally generalized into the Widget Creation Library. The result provides
several significant benefits to the developer and the user:
o Rapid Prototyping: Arbitrarily complex widget interfaces
may be specified, and many common behaviors (pop-up,
change attributes, exit) can be specified for the
interface.
o Prototyping Environment is the Development Environment is
the Delivery Environment: There is no specific breaking
point between prototyping, developing, and tuning a
delivered program.
o Minimum Specifications: The Xrm and Xt Intrinsics instance
attribute inheritance mechanism is fully utilized, so
a minimum number of specifications can describe a
complete user interface.
o Extensible: Adding new widget types and callback routines
is trivial.
o Widget Set Independent: The C code which provides the
behavior of the application can frequently be
written in a widget set independent manner. This
allows an application to be written which supports
multiple look-and-feel definitions: Motif, OpenLook,
and Athena interfaces can all be front-ends to the
same underlying application.
o The user can make any change to the interface: Deeply nested
menus can be substituted for dialog boxes, or vice versa.
Any label or image can be altered, which supports inter-
nationalization.
The Widget Creation Library Distribution
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The distribution now consists of the tar file with all the
source and examples, and two postscript documents. The
Wcl.ps.Z document is sort of a user's guide, along with
some discussion on how to use Wcl in the context of a
software life cycle. The WclSlides.ps.Z is a set of
view graphs or slides which present the same information,
but it also has several examples with some discussion.
The distribution is available in several ways. The preferred
approach it for you to get the compressed tar file using
anonymous ftp from either of these ftp servers:
devvax.jpl.nasa.gov (128.149.1.143) pub/Wc1_04.tar.Z
expo.lcs.mit.edu (18.30.0.212) contrib/Wc1_04.tar.Z
If you have never used ftp, this is how it is done:
# ftp devvax.jpl.nasa.gov
Name: anonymous
Password: <anything non-null>
ftp> binary
ftp> cd pub
ftp> get Wc1_04.tar.Z
ftp> get Wcl.ps.Z
ftp> get WclSlides.ps.Z
ftp> quit
# uncompress *.Z
# lpr Wcl.ps WclSlides.ps
# tar xvf Wc1_04.tar
Using ftp to get the distribution from expo is similar, except that
you cd into contrib, not pub.
If you do not have ftp, I will can you the 11 shar files through
email.
Also, I can send the compressed tar file uuencoded. This is the
least reliable way, since the uuencoded file is 246547 bytes
long, which will cause some mailers to barf.
If you really don't know if you want the whole distribution,
I can send you a shar file which contains just the README
files.
If you send me mail asking for the shar files, the uuencoded
file, or the README shar file, my mail back to you may bounce.
If you don't hear anything for a couple of days, try again...
The distribution includes the following README files:
0thREADME Fixes and enhancements to this version
1stREADME Intro, credits, and build instructions
2ndREADME Minimimum information to use Wc from an application
3rdREADME Wc Resources
4thREADME Standard Callbacks
5thREADME Standard Actions
6thREADME Wc Widget Creation, Widget Registration, Callback
Registration, and Action Registration Functions
7thREADME Writing Callback Functions
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David Smyth david@jpl-devvax.jpl.nasa.gov
Senior Software Engineer, seismo!cit-vax!jpl-devvax!david
X and Object Guru. (818)393-0983
Jet Propulsion Lab, M/S 230-103, 4800 Oak Grove Drive, Pasadena, CA 91109
--------------------------- Quote of the Day: ---------------------------
"A Guru is not one who simply knows all the answers. Rather, a
Guru is like one who walks among the mountains, and by wandering
around abit, can see the horizon through long narrow canyons."
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