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MultiSplitPane: Splitting Without Nesting [Shameless Plug]

Posted by hansmuller on March 23, 2006 at 8:23 AM PST

One aspect of many docking GUIs is support for reconfiguring tiled
subwindows by dragging shared subwindow edges. MultiSplitPane and
MultiSplitLayout support arbitraily complex tiled layouts that can be
reconfigured interactively and programatically.

As introductory paragraphs go, the previous one has to set a new
record for "not catchy". It always seems easier to start these things
with a personal story or recollection. So how about this:

Earlier this year I was arguing with

Tim Boudreau
about docking
frameworks and how best to compute an initial layout, when it occurred
to me that a tree structured model would be a nice way to encode the
relative sizes and positions of the tiles. If nodes in the tree
corresponded to tiles arranged in rows and columns, and if tiles were
allocated space proportionally, it seemed like only a small project to
build a two dimensional analag of JSplitPane. Tim suggested that my
project estimating skills were suspect and besides, there were more
important things to do. He was right on both counts, and yet.
Sometimes, when you're orbiting around an idea, headed somewhere else,
you find yourself captured by the idea's gravitational field. As it
turns out, I was in the software-idea equivalent of a tractor beam.

Over the next two days, I implemented the idea. Since subwindow tiles
were always allocated a fixed percentage of the available space, it
was easy to write a recursive layout algorithm that arranged the rows
and columns. As I was just finishing up,

Josh Marinacci
dropped by,
and so I proudly demo'd my creation. The nice way to respond to
someone's new demo, on Friday afternoon, is to smile, deliver a bland
compliment, and suggest that it's time for a cold one. Josh said:
"that's nice, but I don't think anyone would really want to use it".
After I stopped crying, he pointed out that people expect subwindow
tile boundaries to stay put when the window is resized. This is true,
and it makes the problem substantially more difficult. It means
that growing and shrinking the layout aren't symmetrical, and it
implies that the layout should honor preferred tile sizes, until
the user has indicated otherwise by dragging an edge. So, with tears
in my eyes, I started over again.

Version two of the layout algorithm took considerably longer than the
original version. The result is the aforementioned MultiSplitPane and
MultiSplitLayout classes, a small set of demos, a smattering of unit
tests, javadoc, a nod to accessibility (more on that later), and an
article that explains how it all works. The article bows today on, it's called

MultiSplitPane: Multi-Way Splitting Without
. I hope you'll find the time to read it. The classes will
become part of the SwingLabs project now and perhaps be incorporated
into a future Java release.


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