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

[Sebastian Wiesner <swiesner@lunaryorn.com>]

> Am 04.12.2014 um 08:30 schrieb 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.

So here I am.  How do I subscribe to this bug so that I get replies per mail?

>> 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.

I do not know about the OP, but I do not have any “font configuration”.  All that I do is `(set-frame-font "Source Code Pro-13" nil t)'.

Besides, I'm no font expert at all, so how am I supposed do “optimize” my fonts?  Shouldn't Emacs pick reasonable defaults by itself, and remember them?  I don't mean to blame anyone, but see, all other applications on my system work fine with my fonts…

>> 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.