Re: Redisplay issue

[Eli Zaretskii <eliz@gnu.org>]

> Date: Fri, 27 Nov 2015 14:31:55 -0800
> From: Yuan MEI <yuan.mei.list@gmail.com>
> 
>     Sometimes when I switch to another virtual desktop then come back
> to emacs

What is a "virtual desktop" in this case?

> the entire frame shows only the background color, no letter
> or only part of the frame is visible.  This does not happen all the
> time though.  I just happened to capture a screenshot (attached, I
> hope the mailing server accepts it.)

The screenshot shows a text-mode Emacs frame, AFAICT.  Does this
happen only with text-mode frames, or do you see that in GUI frames as
well?

If this happens with text-mode frames only, then that's not an Emacs
problem.  It's a problem with the terminal emulator (xterm etc.) you
are using: it should sense the switch and redraw the display on the
low level.

When Emacs runs on a TTY, it doesn't listen to any expose or conceal
messages sent by the windowing system, so it has no idea that its
display was concealed or exposed, and cannot initiate a redisplay in
these situations.  From the Emacs POV, a TTY frame is the only thing
displayed by the console device, and the only way such a frame can be
concealed and exposed is by stopping Emacs (with the likes of "C-z")
and then resuming it.  And these are the only cases a TTY frame will
be completely redrawn.

GUI frames are different: Emacs gets expose events for them, and
should react by redrawing the exposed portion(s) of the frame.