From octave-graphics-request at bevo dot che dot wisc dot edu  Fri Mar 12 05:28:39 1999
Subject: Canvas vs Plot Widget 
From: Rafael Laboissiere <rafael at icp dot inpg dot fr>
To: octave-graphics at bevo dot che dot wisc dot edu
Date: 12 Mar 1999 12:28:37 +0100


I had thought about the Plot Widget implementation, as well as the
necessity of a canvas widget.  I will try to reply to some posts in this
mailing list regarding these issues.

>>>>> "JK" == Jonathan King <kingjw at missouri dot edu> writes:

    JK> Another very desirable thing if you want to do interactive plots
    JK> and "handle" like graphics is a good Canvas widget.  Tk has one;
    JK> gtk might have one if you roll gnome into the mix, and I'm not
    JK> sure about wxWindows.  The Tk canvas widget is great because you
    JK> can embed almost anything in it from images to text to menubars,
    JK> and, for better or for worse, it's easy to see how you could
    JK> implement satanic handle graphics for it.

If I understand correctly, having a canvas widget would enable us to easier
emulate some aspects of Handle Graphics, like the association of callbacks
to mouse actions on plot objects (lines, axis, whatever).  I have written
some programs in Matlab that exploit this, but they all suck.  User-written
mouse interaction in Matlab is a way too slow.  Furthermore, from the point
of view of programming, the combination of the interpreted language +
set/get constructs is just evil (some would say satanic ;-)

My idea was to create a simple Plot Widget that contains essentially a
pixmap.  This is to answer JWE's question:

>>>>> "JWE" == John W Eaton <jwe at bevo dot che dot wisc dot edu> writes:

    JWE> I think it would be nice if we had a widget that could be used as
    JWE> part of the GUI toolkit we choose.  Then the graphics widget could
    JWE> be used as part of the GUI too.  Perhaps some existing graphics
    JWE> library (the GNU one, or plplot, or gnuplot) could be adapted?

According to the design that I have in mind, a plotting library would be
used to tell to the Plot Widget where to put the pixels that correspond to
axes, ticks, labels, lines, points, etc.  This widget would have some basic
functionalities like scrolling and zooming (and eventually saving the plot
as a PostScript file), but not much more than that.  I really do not see
how to completely emulate handle graphics in this framework, as it will not
be possible to associate a bunch of pixels in the pixmap with a specific
graphical objects (at least if we are going to use PLplot as the plotting
engine).

Of course, this widget could be packed in a window widget, along with
other widgets like menus, buttons and the like.  

Do you guys think that this design is too constraining?  

I am trying to implement these ideas with PLplot and Gtk, just as a proof
of concept.  I will be extremely busy until the end of March and it will be
hard to generate any useful code till there.  As soon as I have something
decent, I will post here.

--
Rafael Laboissiere
Institut de la Communication Parlee | Email: rafael at icp dot inpg dot fr
UPRESS A CNRS 5009 / INPG           | Voice: +33 4.76.57.48.49
46, av. Felix Viallet               |   Fax: +33 4.76.57.47.10
F-38031 Grenoble CEDEX 1 France     |   URL: http://www.icp.inpg.fr/~rafael