Hey all

I'm wondering if someone implemented a graphical envelope generator
with mouse-draggable breakpoints. I think it probably could be done
using data structures, however my stumbling block is that I can't think
of a way to disallow point movement to x(n) > x(n+1), respectively x(n)
< x(n-1).

Preferably, it would allow to create new breakpoints in between
existing breakpoints (as opposed to new breakpoints being appended to
the end of the list). 

I'm not so much looking for the perfect solution, but wondering what is
already there.

Cheers
Roman