Re: Hourglass only for X-windows?

["Eli Zaretskii" <eliz@gnu.org>]

> From: "Lennart Borgman" <lennart.borgman.073@student.lu.se>
> Date: Sun, 27 Feb 2005 18:57:08 +0100
> 
> I am trying to understand the implementation around hourglass cursors. When
> I look through eval.c, fns.c, keyboard.c, lread.c and minibuf.c I see in
> many places something like:
> 
>     #ifdef HAVE_X_WINDOWS
>       if (display_hourglass_p)
>         cancel_hourglass ();
>     #endif
> 
> Is this really correct?

Yes, I think so.

> It looks like displaying an hourglass cursor should only happen if x
> windows is available.

What other systems?  If you refer to Windows, then please see
w32fns.c, where the timer-related hourglass code is ifdef'ed away
(probably because Windows doesn't emulate well Posix timers that raise
asynchronous signals).  The Windows implementation of hourglass
cursor, if I understand it correctly, is synchronous, i.e. the
redisplay code and the idle loop set and reset it.

Of other non-X ports, the MSDOS port doesn't support this feature at
all (you cannot change the Windows mouse pointer shape from a DOS
program running on Windows, and doing so on plain DOS involves
undesirable complications).

As for MacOS X, I don't know.

> Maybe it would be better to remove these ifdefs and require every Emacs
> implementation to compile the lines? Does not most systems actually have the
> possibility to display hourglass cursors? If they do not could the
> implementation not just supply some dummies for the required functions?

That'd not be a good idea, I think: firing SIGALRM signals by the
timers complicates things (e.g., you get to handle the problem of
interrupted system calls), so it shouldn't be done without a good
reason.