Re: how to detect that current font does not have particular unicode char

[Eli Zaretskii]

> From: yyoncho <yyoncho@gmail.com>
> Date: Sat, 19 Dec 2020 13:33:05 +0200
> Cc: emacs-devel <emacs-devel@gnu.org>
> 
>  What kind of fallback?  
> 
> I want to detect if char is visible and use a different one. E. g. bulb can 
> be replaced with "!". 

But that's misleading, isn't it?  The user could think the character
really was "!".

You could instead set up the glyphless-char-display char-table to have
"!" in the slot for U+1F4A1, then Emacs will display the "!" character
inside a box, which at least cannot dupe the user.

>  > I tried to use char-displayable-p but it seems like it is not
>  > what I am looking for.
> 
>  I believe you want font-get-glyphs.
> 
> I will try that out. I am not sure what FONT-OBJECT parameter stands for?

The return value of one of functions that return such objects.  I
think in your case font-at will be useful in that role.