a broad question

[Paul Davis <pbd op net>]

i'm about to embark on an attempt to implement an API for a GUI
"toolkit" called libvstgui, used to implement GUI's for plugins used
in Steinberg's Virtual Studio Technology system. a bunch of us on the
Linux Audio Development mailing list feel that adopting libvstgui for
the Linux audio plugin system known as LADSPA is a highly beneficial
move all around. we've spent over a year knocking around proposals to
use XML to specify GUI's in a portable fashion, and many other ideas.
some of us have given up: there are some really cool plugins that
already use libvstgui, and its an excellent design and very
cross-platform in its outlook.

the question arises: at what level to implement libvstgui? its a GUI
toolkit based on primitives (and not very many of them) that allow the
plugin to create a highly customized (frequently "chromed") appearance
for its GUI. rather than using any standard widget appearances,
plugins using libvstgui generally use bit/pixmaps to control how
various control and display elements appear. its also a C++ API.

it would be much faster to use an existing high level toolkit and just
bolt libvstgui over the top of that. actually, the Canvas comes to
mind in a number of ways too. 

but there is a serious disadvantage in doing that. it means that
applications that want to host these plugins but that don't use the
chosen toolkit are completely out of luck - they will be running a
main event loop that is incompatible with the one expected by the port
of libvstgui (and the underlying toolkit).

looking at the API (its very well documented; the headers are
available and even contain some useful stuff) it appears that it
wouldn't be incredibly painful to use Xlib directly. but then again,
doing anything directly with Xlib tends to be fairly painful. it would
delightful to use GDK, but i have a strong feeling that GDK is
thoroughly rooted in the g_main_loop() abstraction, and so is not
suitable. doing it in Xlib would allow the library to be used by any
application using X, regarding of which toolkit it was based on.

if anyone has any thoughts on this, they would be very welcome.

--p