Hi Matthew,
My current theory is that we're observing an artifact of the design of
ly:one-page-breaking. But I have to investigate. (It's interesting to
note what happens if we remove the tagline = ##f setting!)
It turns out that a possible workaround is making sure that the markup
has top coordinate zero. Try this:
#(define-markup-command (show-extent layout props arg) (markup?)
(let ((stil (interpret-markup layout props arg)))
(ly:message "X: ~a\nY: ~a\n\n"
(ly:stencil-extent stil X)
(ly:stencil-extent stil Y))
stil))
\markup
\show-extent
\general-align #Y #UP
{ \box \line { \vspace #3 text } }
(The show-extent command is only for displaying the stencil extent of a
markup; the actual change is in calling \general-align.)
I still don't understand the mechanics involved, and of course it's not
desirable for you to have to put all of your markups in a \general-align
command. (Even though this could probably be automated by manipulating
the top level markup handlers.)
Lukas
