Re: animate incredibly slow compared to 21.3

[Miles Bader]

On Fri, 11 Mar 2005 23:33:36 +0100, Kim F. Storm <address@hidden> wrote:
> I don't know the internals of X, but if done properly, the Xserver
> updates an internal bitmap and only transfers that to the screen when
> flushed by Xflush.

The historical function of Xflush is to flush the queue of requests to
the X server (like fflush does for a stream).  The actual drawing
happens after the xserver gets the requests.

The X server almost certainly doesn't do any kind of "duplicate
squashing" on the request stream -- it would be far too difficult.

I think the main effect of avoiding Xflush would be to avoid some
context switches and other latency.  So instead of Emacs - X - Emacs -
X - EMacs - X, it would be Emacs - Emacs -  Emacs - X - X - X.  There
would probably be _some_ speedup and reduction of flickering, but the
user might still perceive a lot of display activity.

It's possible that some X implementations use an internal bitmap, and
then periodically transfer the contents to the physical display; such
implementations may indeed arrange for some sort of coordination with
Xflush, but it's not the traditional function (I believe typically
such backend buffered display updates are mostly based on time
anyway).

-Miles
-- 
Do not taunt Happy Fun Ball.