[Rosegarden-devel] file merging

[Chris C. <ca...@al...>]

I've just wasted some time trying to work up a nice generic way of=20
merging one file (of any supported type) into the current=20
composition, and have ended up realising not only that the subject is=20
rather problematic but also that our current MIDI file merge is=20
somewhat broken too.

The problem is in the Studio.  At the moment the Composition and the=20
Studio both belong to a document.  When we load a file, at the=20
moment, we generate a new Composition and then swap its contents into=20
the document's existing Composition.  For the Studio stuff, however,=20
we always just refer to the document's Studio from the outset.  So=20
for example in MIDI file import and merge, one of the first things we=20
do is clear the document's Studio's instruments in preparation for=20
replacing them with the new file's instruments.  When we're merging,=20
of course, we don't want to do that.  I can fix that for MIDI merge,=20
but:

My scheme for generic merging was initially based on the wrong=20
assumption that a Studio belonged to a Composition, not a document. =20
So I started writing a merge method into Composition=20
("mergeFrom(const Composition &)") that looked at the MIDI program=20
values for the instruments in the other Composition and from them=20
assigned new instruments in its own Studio in order to create new=20
Tracks to copy the other Composition's data into.  This obviously=20
can't work because the Composition turns out not to own the Studio. =20

Either the merge method will have to be in the document class=20
("mergeFrom(const RosegardenGUIDoc &)"), which will cause=20
difficulties because we do not at the moment create a new document=20
when we load something, or else we have to assume that we're happy=20
for the file we're merging in to blast the current Studio, or else we=20
have to modify all of the file load methods so that they can be told=20
that they're merging and not clear out the Studio in that case.

Obviously the second of these is unsatisfactory, but the question is:=20
should we take this as an opportunity to do file load correctly (i.e.=20
with a new document, instead of this idiotic=20
create-new-Composition-and-swap() crap that we do at the moment), or=20
shall we continue with that shitty old hack but instead add some=20
logic to all of the file load methods so that they know they're doing=20
a merge and so not to blitz the Studio before they begin?

Nah, that's what I thought.


Chris