Re: Emacs and Gnome Canvas

[Jan Djärv]

Eli Zaretskii skrev 2010-07-16 12.39:
> > Date: Fri, 16 Jul 2010 19:15:25 +0900
> > From: YAMAMOTO Mitsuharu<address@hidden>
>
> > For example, it does not accept multiple rectangles for exposed area
> > that is necessary for minimal redrawing.
>
> Don't we get a single expose event for each exposed rectangular area?
> If we do, what would be the gain from processing multiple rectangles
> at once?

There is an X extension for that, DAMAGE.  But if that is not used, you would 
get just one rectangle.  Since the extension exist and programs use it, I 
assume people found that it gave and advantage.

> > It also reuses functions primarily designed for drawing during
> > redisplay and that does not necessarily efficient for exposure
> > handing.
>
> Are you talking about draw_glyphs?  If so, how is it biased in favor
> of redisplay, and what would be a more efficient way of drawing glyphs
> in a specified area of the display than what draw_glyphs does?

If you for example have double buffer, you can split expose from update 
display.  When an expose comes, you just copy the area from the backing store 
to the window.  But for updating the display, you draw normally, but to the 
backing store.  Then when you are done, you copy it to the window.

But I don't think optimizing for expose is worth it.  Expose iis very rare 
compared to update.

        Jan D.