Re: gtk_widget_draw()

[Paul Davis <paul linuxaudiosystems com>]

On Fri, Aug 20, 2010 at 8:32 PM, Jose Gonzalez <jose_ogp juno com> wrote:
>  When it comes to the question of the desirability of some notion
> of a canvas (or scene-graph if you like), it should be clear that
> whatever such a thing might be it's best if it were a local rather
> than global construct, ie. it's far more flexible if gtk *had* a
> canvas widget than for it to *be* a canvas.

i think this is fundamentally wrong and fundamentally at odds with the
evolution of GTK and with the evolution of other toolkits on both X
Window and other platforms. put differently, and to paraphrase
something said about unix: those who don't understand scene graphs are
condemned to reinvent them, poorly.

so no, i don't agree that this is clear, and in fact, i don't even
agree that its correct. the gains from having a single drawing model
and single event propagation model that extended from the simplest
elements of the toolkit up the the most complex (probably the treeview
at this time) are huge.

>  Now, just what might a useful canvas notion be? Well, I'd suggest
> the rather simple one of a gtk container widget which imposes no
> constraints on the positioning/geometry of its child widgets. What
> further properties it might allow is dependent on what you want
> (likely wanted are compositing & transforming of the child widgets, etc).

we have such widgets, but they are hampered by the fact that existing
GTK widgets are rooted in the fundamental GTK axiom that widgets
themselves do not overlap. but it really doesn't matter: this doesn't
address the question of whether or not the internal model of GTK
reflects its long term trajectory toward a scene graph model. and i
really mean this. look at everything that has happened with the
fundamental internals of GTK over the 10+ years that i've used it for
application development, and they all either trend toward a scene
graph model or have no relationship at all to this evolution (e.g.
input methods).

i would almost be to wager a bet: if GTK is not substantially
implemented as a scene graph within 4 years, i'll eat the hat that i
still haven't eaten from my bet that JACK (http://jackaudio.org/)
could not work well on Windows :)