bug#13727: 24.3.50; terminal emacs flickers when redrawing frame

["Jose A. Ortega Ruiz" <jao@gnu.org>]

On Thu, Feb 21 2013, Eli Zaretskii wrote:

>> From: "Jose A. Ortega Ruiz" <jao@gnu.org>
>> Cc: 13727@debbugs.gnu.org
>> Date: Thu, 21 Feb 2013 18:51:19 +0100
>> 
>> In Gnus, the redrawing is more apparent because there are 3 buffers and
>> hence 3 modelines, and the flicker is more visible when it happens in
>> modelines (when browsing email folders in Gnus, the three modelines
>> sometimes change simultaneously).  The flickering there doesn't need the
>> same buffer open in two different frame types.
>
> Do all the 3 buffers change simultaneously, due to some Gnus command
> you run?

It's a 3 pane configuration.  On the left you have a list of mail
groups.  On the right, there are 2 windows: top one with a list of
messages, bottom with the current message.

You navigate messages on the top right window.  When you hit the end of
the list for the current group, it goes to the next one: at that point,
the left window with the list of groups is updated (to mark the current
group), the top left window is updated (to show the new list of
messages) and the bottom left window is updated to show the newly
selected message contents.

None of the window sizes changes at all.

> If so, then the flickering is expected: redisplay due to
> simultaneous changes in several buffers is not optimized in Emacs, it
> usually results in all windows on all frames being redisplayed.

Well, the flickering most definitely doesn't happen for emacs 24.2, and
hasn't happened for me since the emacs 19.x times.  What's more, it
wasn't happening for snapshots until recently, and it does not happen in
X mode, only in terminal windows (i would expect the redraw to be slower
in X mode than in an xterm, but i might of course be wrong).