Re: Emacs and Gnome Canvas

[YAMAMOTO Mitsuharu]

>>>>> On Sun, 18 Jul 2010 09:10:18 +0200, Jan Djärv <address@hidden> said:

>> You've rather been talking about an alternative double-buffering
>> that is for drawing during redisplay (i.e., outside the expose
>> handler), and said that is how GTK+ operates all the time.

> I think you misunderstood.  You said doing copying of the whole
> window from double buffering for small changes is too slow.  I said
> it can't be because Gtk+ does it.  Thats it.

GTK+ can make such copying efficient because it does drawing inside
the expose handler, which is called with the clipping region as
exposed area.  But if double buffering is done outside the expose
handler we don't know which area is updated.  So it has to copy the
whole area, or each drawing operation must take care about which area
is updated.  The latter is no easier than calculating dirty region.

> BTW, you would have to invent syntactic expose events for X, Xt and
> TTY unless you plan to have two display engines.

We don't need to change drawing code for TTY.  It just draws during
redisplay as in the current code.

                                     YAMAMOTO Mitsuharu
                                address@hidden