[kepler-dev] scrollbar additions to kepler

[Chad Berkley]

Hi,

I've been working the last 4 days to add scrollbars to the vergil 
canvas.  I've had limited success and I've run into a couple problems. 
I wanted to see what others thought of this before I continue.

There are two different places where this functionality can be added. 
The first one (and probably the technically correct place) is in the 
Diva library.  Diva is the library ptolemy uses to provide all of the 
graph editing functionality.  Diva also provides the panner (the widget 
in the bottom left that allows you to move around the workspace).  The 
second place this functionality can be added is to the Vergil gui classes.

Placing the code in diva is probably the best way to do this because 
then it would integrate seamlessly into the current view and allow the 
scrollbars to interact with the panner.  Changing Diva to do this is not 
trivial.  Diva has it's own layer system built around AWT with some 
Swing components.  Also, if we change diva, it's going to be much harder 
to make this a "pluggable" change without making some architectural 
change to diva itself.

Placing the code in the BasicGraphFrame class of vergil is the most 
straight forward way to do it because the vergil gui uses all swing 
components and places diva widgets inside the swing components.  This is 
the way I have partially implemented the scrollbars now (using a 
JScrollPane).  There are several problems with this.  First of all, 
getting the scrollbars to interact with the panner correctly seems 
mostly impossible.  Basically, i have to remove the panner or else 
things get chaotic real quick.  If the user moves the workspace via the 
panner, there is no event to catch when this happens, so the scrollbars 
can't be updated accordingly.  I've also had to make major changes to 
the zoom code.  The two advantages of doing it this way are that it's 
easier to code since one can work with only swing components and i think 
it will be easier to make this a pluggable change since some people have 
said they don't want scrollbars on the canvas.

Another thing I thought of the other day while working with photoshop 
(which has scrollbars on it's canvas), is that we could add a "hand" 
tool which would serve one of the purposes of the panner (to let you 
move around the workspace).  I like the panner and don't really want to 
get rid of it anyway.  I think the panner, scrollbars and a potential 
hand tool would work well together.  It's just a matter of figuring out 
the best way to do it.  Ptolemy folks: how hard do you think it would be 
to add this to Diva?

thoughts?

chad