Re: Suggest installing more fonts?

[Gregory Heytings via "Emacs development discussions." <emacs-devel@gnu.org>]

>>>> Apparently it's not clear, so I'll say one last time that the feature 
>>>> I propose does _not_ require to install Unifont system-wide.  It is 
>>>> to include Unifont in Emacs (say in etc/unifont), and to offer it as 
>>>> an additional option for glyphless-char-display, along with hex-code, 
>>>> empty-box, thin-space, and zero-width.  The bitmap data would be used 
>>>> to draw the glyph in produce_glyphless_glyph() .
>>>
>>> I don't understand this proposal.  Are you saying Emacs can already 
>>> use a font that is not installed?  If so, can you tell how to do that?
>>
>> I don't (yet) know, but I'd be surprised if this could not be done. 
>> Emacs already creates glyphs dynamically for tofus
>
> No, Emacs doesn't create any glyphs dynamically for tofus, it simply 
> uses a smaller font in a box it itself draws.  See 
> xterm.c:x_draw_glyphless_glyph_string_foreground for how this is done on 
> X (w32 and ns do it very similarly).
>

Yes, but Emacs draws the box itself, and I suppose that if it can draw a 
box, it could instead draw a small black-and-white (8x16 or 16x16) bitmap. 
Emacs already does this for fringe bitmaps AFAIU.

>>> The way Emacs uses fonts is by using various system libraries, such as 
>>> Fontconfig, to find fonts that match certain criteria (script, 
>>> encoding, character codepoint, size, slant, etc.).  How do you propose 
>>> to do that if, for example, Fontconfig knows nothing about a font?
>>
>> The proposal is not to change anything to the way Emacs uses fonts, but 
>> to change something to the way Emacs behaves when it does not find an 
>> appropriate font to display a character.  In that case Emacs would 
>> display a "degraded" glyph (from Unifont), and would issue a warning 
>> that the user should install another font.
>
> I don't see how this can be done without serious changes in the code 
> that finds and uses fonts.  We _need_ the Fontconfig functionality.
>

With the proposal, there is no need to find the font, it is already 
included, and only used as a fallback when no appropriate font has been 
found.  Unifont is just a long sequence of small bitmaps, Emacs only has 
to pick the bitmap corresponding to a given character in that list and to 
draw it.  For example, the character "A" in Unifont is the 8x16 bitmap 
"0000000018242442427E424242420000" which occupies only 16 bytes.