Re: Emacs and Gnome Canvas

[Jan Djärv]

YAMAMOTO Mitsuharu skrev 2010-07-16 04.14:

>    1. Don't draw during redisplay, but mark the updated area dirty so
>       the upcoming exposure event can trigger the actual redraw for the
>       area to be updated.

If some characters change attribute for example foreground color, you have to 
draw it, there will be no expose.

>    2. Restrict the actual drawings to those in response to exposure
>       events.  This is the standard way in GTK+ and Cocoa.  That would
>       make double-buffering straightforward in GTK+ builds.

This is good, but can the current redisplay engine really update just a part 
of the display area?  Maybe we can set clipping to the expose area?
But most redrawings are not because of expose events, but of buffer changes, 
so I don't know if this would be such a big improvement.  If you have double 
buffering, then you can just copy over the buffer when expose happens.

>    3. Make expose_window etc. more efficient.  For example, the
>       foreground of same row might currently be redrawn three times for
>       some cases in order to handle overlaps between rows with minimal
>       flickering.  This can be eliminated if double-buffering is
>       introduced and whole the background is drawn at once and then
>       whole the foreground is drawn afterwards.

Are there many of these "reduce flicker" drawings going on?  Double buffer 
would be nice, I think it could help with images also (now images are drawn to 
a pixmap first, then copied to the frame).

>    4. Scrolling in redisplay (x_shift_glyphs_for_insert and
>       x_scroll_run) might require special treatment because copied area
>       might be marked dirty at the time of scrolling.

        Jan D.