[mcclim-devel] new graph type: first drawf

[rpgoldman at real-time.com]

I have developed a tentative first version of a new graph type, which
is a tree with cross-edges.  I.e., you have a graph which is basically
a tree, but where you are allowed to have cross edges.  The cross
edges are NOT the same as graph edges, and in particular, don't cause
additions to the PARENT/CHILD relationships, nor (for this reason) do
they cause depths to be incremented.  Note that these cross-edges do
NOT have to be only one one level of the tree --- they can cross
levels.  To build such a graph you need to add two more arguments to
format-graph-from-roots:

:CROSS-ARC-DRAWER

a function that takes all the arguments accepted by a normal
arc-drawer, but also an edge-type keyword argument, which it is free
to ignore.

:CROSS-ARC-PRODUCER

a function that takes a graph-node as argument, like
inferior-producer, but that returns two values: a list of destination
nodes and (optionally) a list of type-designators, that can be passed
to the cross-arc-drawer, as the value of the :edge-type keyword
argument.

I have posted the source for this to the following URL, hoping that it
will attract comments and suggestions:

http://rpgoldman.real-time.com/lisp/tree-with-cross-edges.lisp

I'd love to see this integrated into McCLIM some day!

KNOWN BUGS:

1.  Currently only works on :horizontal orientation (I don't have the arc
routing for vertical yet).

2.  Only draws straight lines for cross edges.  It would be nice if the
cross edges would swoop around intervening nodes, but I haven't read
enough of the CLIM spec to figure out how to do this yet.

3.  If you have a depth-bounded tree, probably something very ugly
will happen!

I'll try to assemble some screendumps and post them, but for now it's
weekend...

Best,
R