Re: removing flickering in emacs

[Jan D.]

Michal Maruška wrote:

> Hello,
> I have written a patch for CVS emacs as a proof-of-concept for my method of
> removing flickering caused by using background (pixel or pixmap) of windows in
> X11, flickering which happens on Exposure, and on resizing.
>
> The method is described at
>
>   http://maruska.dyndns.org/wiki/anti-flicker-method
>
> I don't know Xt, so I limit myself to xlib, and I tested the patch with 
> ./configure  --with-x-toolkit=no --without-gtk  (--with-png --with-jpeg --without-xim)
>
>
> I would appreciate comments from people who know the display code.
>
>
> The patch itself is:
> http://maruska.dyndns.org/comp/packages/cvs-emacs-flicker-free.patch


I find the patch hard to follow, there are too much #if 0 and code that 
is commented out. But reading your anti-flicker-method page it seem that 
the theory is to use window background None and explicitly write the 
background yourself. I can not see how that would improve things, 
instead of having the X server clear the background itself, you are 
doing it from the client. This introduces more client to server calls 
and no visible advantage.

You wonder about Gtk+ on you page. IMHO they have taken the proper 
approach to flikering by using double buffering everywhere. 
Unfortunately Emacs compiled for GTK can not use this feature, except 
for menus, scrollbars and toolbars. But as a principle, double buffering 
is easier to implement (no need to keep track of intersecting areas) and 
is sure to remove flicker.

As a side not, I haven't seen much flicker in Emacs, and the time that 
there where some, those places where bugs that has been fixed. Can you 
supply a test case where flickering in Emacs can be clearly seen?

Jan D.