bug#11822: 24.1; emacsclient terminal mode captures escape characters as text

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: raeburn@permabit.com,  11822@debbugs.gnu.org
> Date: Tue, 08 Sep 2015 14:52:22 -0400
> 
> > In any case, I think the issue at hand is that more than one frame is
> > being redisplayed when only one should suffice.
> 
> Agreed (tho it's probably 2 instead, but the other one's redisplay
> should be fairly simple and efficient: just redraw the modeline to
> reflect its new non-selected status).

Perhaps so, but note that this particular use case (i.e. a client
frame displayed via a slow network) gives a rather new meaning to
"redisplay optimizations": where normally we mainly try to avoid
redrawing the parts of any window that didn't change, here we need to
try to avoid even considering those parts, or at least minimize the X
calls while we consider them.  I think until now the assumption was
that the most expensive parts of redisplay are those that regenerate
glyph matrices and those that actually send data to the glass; here
the expensive parts are elsewhere.

So if redrawing the mode line involves recomputing all the basic
faces, it might still be too expensive over a slow network.  We need
to avoid that recomputation where possible.