bug#19266: 24.4; Font-related window redrawing delays on OS X

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 4 Dec 2014 02:13:30 -0500
> From: Kirill Ignatiev <kirill.ignatiev@gmail.com>
> 
> [This is a copy of this question on Emacs.SE:
> http://emacs.stackexchange.com/questions/4061]
> At least one other person has the same problem.

Please ask those persons to report here directly, and to read the
responses and discussions.

> Often when I'm editing a file with many uncommon unicode symbols (e.g.,
> in languages like haskell, julia or c++), and (I think) especially with
> an ornate color theme, I experience delays of maybe about five seconds
> when switching between buffers. Running emacs under lldb show a stack
> trace below; I get a similar stack trace from running `emacs -Q` and
> typing `C-h h` (`view-hello-file`), which takes quite a while to display
> the hello file.

AFAICT, these delays are due to Emacs searching the system for
appropriate fonts needed to display those unusual symbols.

> What can I do about these window redrawing delays? I am not sure what I
> have misconfigured.

Optimize your font configuration, so that the font search becomes
faster.

> Does emacs reload all fonts every time I switch to a different frame or
> buffer? It also seems to have a delay sometimes when a previously
> invisible overlay is shown.

Emacs only looks for a font when it needs to display something.  when
previously invisible portion is about to be displayed, Emacs needs the
fonts to display it.