[linux-audio-dev] cross-toolkit host/plugins: significant news

[Paul Davis]

its been a productive evening/night. or has it?

i hacked up a small test that runs Qt as a host, and loads a shared
object that uses GTK+ as its GUI. the host loads the shared object,
and runs its GUI, in addition to its own. cool, eh?

well, not so fast. i am now wondering what in the hell all the fuss
was about in the first place. and as the main progenitor of "you can't
do this", i feel responsible for cleaning up the mess.

why? i don't see anything in what i've done that is at all clever. the
only slightly tricky part is running the GTK+ GUI in its own thread,
and routing requests to instantiate a new GUI to that thread via a
pipe that is hooked into the GTK+ event loop. i can't see any reason
why *any* toolkit couldn't be used in this way (assuming it can do
this kind of "add an fd to the event loop" thing, and AFAIK they all
can). i even removed all the stuff i added to open a dedicated X
Display - it just isn't necessary. Qt and GTK+ both have their own
connection to the X Server, and there are separate event loops
handling windows created by each toolkit, each running in its own
thread. all you have to avoid is a plugin calling QApplication::exec()
or gtk_main() etc., which will different and odd effects on each
toolkit. 

AFAICT, there are two things the host can't really do. one is to snoop
on events for other toolkit's loops. so, a host that relies on
snooping keyboard events (e.g. ardour) is out of luck when it comes to
events occuring in plugin GUI windows using a non-host-toolkit. the
host also cannot get access to the toplevel windows of the
non-host-toolkit, so it can't add the kind of generic widgets that you
tend to see on TDM/VST plugin GUIs for "bypass", "save" and so forth.

but to return to the core issue here. what the f*ck have i been
ranting on about all this time?  unless its just the issue of globals
in Xlib, but i really don't believe they are there anymore, at least
not in XFree86 ... yes, the toolkits can't share an X Display, but fer
chrissakes! they don't even try to!!

to put in bluntly, it appears that i have been totally and utterly
full of crap, and have unnecessarily delayed the advent of decent
plugin GUIs on linux by a year or more.

if anybody wants to see the code for my little demo, i'll tar it up. i
hate the way Qt takes over the build process. It reminds me too much
of Oracle in this respect. Anyway, i need to get to bed. I feel glad
that this can be made to work, but embarrased about what i may have
done here.

--p