I am creating a Java tool that reverse engineers PHP scripts to
produce UML Sequence Diagrams from them. I have handled all the
parsing of the PHP code etc, and currently am in a state where I have
the necessary objects and information to draw a full sequence diagram.
What I am looking for however, is some sort of open source package
that I can use to physically draw the sequence diagrams from the
information I have. I.e. basically boxes, lines and annotations etc

Planning and presenting the diagrams in the interface myself is quite
a lengthy task, so if anyone has any suggestions at packages or tools
they think I could in corporate, then that would be appreciated. They
don't have to be UML tools specifically, but any sort of code/package
for drawing that you think I might be able to modify to my advantage
that gives me the ability to control the creation of diagram elements
(or drawing elements that I can turn in to my diagram elements) and
their positions, features etc.

Thanks in advance,

JH.