Re: How do I set up font fallback in a robust way?

[Eli Zaretskii <eliz@gnu.org>]

> Cc: emacs-devel@gnu.org
> From: Clément Pit--Claudel <clement.pit@gmail.com>
> Date: Sat, 9 Apr 2016 16:01:27 -0400
> 
> On 04/09/2016 03:46 PM, Eli Zaretskii wrote:
> > The default fontset already defines specific blocks to be handled by
> > these fonts, see fontset.el.  What problems, specifically, do you have
> > with the default setup and the current emacs-25 branch?
> 
> I get relatively inconsistent results in terms of which font is chosen to display a given symbol.

I don't think I understand well enough what that means.  This issue
must be dealt with by presenting specific examples.

> The pair of fonts that I mentioned (Ubuntu Mono and Symbola) was just an example; my question is about configuring fallbacks for any given pair of fonts: it could be Source Code Pro and Asana Math instead of Ubuntu Mono and Symbola, for example.

I answered the general question already.  You can find examples of
that in fontset.el.

> >> What's the proper way to configure font fallback?
> > 
> > In general: find the characters you want to change and augment the
> > default fontset to use the font you want for them.
> 
> Is it enough to augment the default fontset? Changing the :height of the 'default font creates a new fontset, which doesn't respect the fallbacks that I configure.

Again, please provide specific examples, because I don't think I
understand how changing height could get in the way.

> >> *Note*: for testing purposes, here are a few math characters: `ℕ𝓟⧺×≠≥≤±¬∨∧∃∀λ⟿⟹⊥⊤⊢`
> > 
> > Which, if any, of those give you trouble with the default fontset?
> 
> 𝓟 is displayed using `Latin Modern Math' in emacs -Q, it seems.

Is that not okay for some reason?  If so, why?