Re: Emacs and Gnome Canvas

[Jan Djärv]

Eli Zaretskii skrev 2010-07-15 10.59:
> > Date: Thu, 15 Jul 2010 10:48:12 +0200
> > From: Jan Djärv<address@hidden>
> > CC: address@hidden, address@hidden
> >
> > > > The changes that require redisplay would have to notify the Canvas that things
> > > > changed.  I think this style is more efficient.
> > >
> > > What do you mean by "changes that require redisplay"?  Suppose a
> > > character was inserted or deleted -- would that need to notify the
> > > Canvas?
> >
> > Yes.
>
> But the inserted character could be in the portion that is not
> displayed at all, in which case it does not "require redisplay".  Who
> should decide whether redisplay is necessary?  If that's Emacs, then
> it should know a lot about the display layout.  If its the Canvas,
> then it should know a lot about what portions of the buffer text are
> on the screen.

You probably have your text in an CanvasItem that has a GtkTextBuffer.  When a 
character is inserted, you insert in to the GtkTextBuffer.  The redisplay part 
is then handeled internally between GtkTextBuffer, GnomeCanvas(Rich)TextItem 
and GnomeCanvas.

As I said, it probably relies on having all text in the GtkTextBuffer.

> Besides, this mean a thorough redesign of Emacs objects.  Currently,
> they are totally unaware of the display engine, and don't request any
> redisplays.  They just modify themselves and that's it.
>
> > >   How about an arbitrary mouse move?
> >
> > If it resulted in a different highlightning of a link, yes.
>
> Again, how to know that?  Note that some mouse movements perform
> complex operations on Emacs objects, like popping up windows and
> frames.

Each CanvasItem can have callbacks for mouse move, click, key press and so on. 
 The idea is to have separate CanvasItems for the items that should react to 
mouse events and then register callbacks for those events.  The callback then 
pops up windows or whatever.

It is a more event driven approach, and that in itself is a big modification 
for Emacs which is more sequential in nature.

        Jan D.