Re: Emacs and Gnome Canvas

[YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp>]

>>>>> On Sat, 17 Jul 2010 10:00:40 +0900, YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp> said:

>> Is it really worth our while to optimize that?  What would be the
>> situation where we will get frequent expose events?

> If we change drawing during redisplay to addition of dirty area,
> then expose occurs on every window-system-level event handling or
> explicit flush.

... if redisplay had involved some updates, of course.

BTW, one reason several toolkits are adopting this strategy is that it
fits with transparency.  Consider that some transparent widget (such
as canvas where some lines and possibly translucent rectangles are
drawn) is overlaid above the Emacs "widget".  If we drew the Emacs
contents during redisplay, then the canvas would have no way to know
which part needs to be redrawn.  If redisplay marks the area dirty
instead of drawing, this can also be propagated to the canvas widget:
the toolkit sends redraw requests to the widgets intersecting the
dirty area in back-to-front order.

				     YAMAMOTO Mitsuharu
				mituharu@math.s.chiba-u.ac.jp