Re: How to determine if a font is a fallback font?

[Urs Liska]

Am 28.04.2015 um 12:18 schrieb Werner LEMBERG:
> On my openSuSE GNU/Linux box, I get different results.
>
> > Given font name: Emmentaler-13
> > Determined font file: /usr/share/fonts/TTF/mplus-1c-medium.ttf
> > Actual font in that file: mplus-1c-medium
> > Given font is present: #f
>    Given font name: Emmentaler-13
>    Determined font file: 
> /usr/local/share/lilypond/2.19.16/fonts/otf/emmentaler-13.otf
>    Actual font in that file: Emmentaler-13
>    Given font is present: 
> #t/usr/local/share/lilypond/2.19.16/fonts/otf/emmentaler-13.otf
>    Emmentaler-13
>
> > Given font name: Alegreya
> > Determined font file: /usr/share/fonts/TTF/mplus-1c-medium.ttf
> > Actual font in that file: mplus-1c-medium
> > Given font is present: #f
>    Given font name: Alegreya
>    Determined font file: /usr/share/fonts/truetype/Alegreya-Regular.ttf
>    Actual font in that file: Alegreya-Regular
>    Given font is present: #f/usr/share/fonts/truetype/Alegreya-Regular.ttf
>    Alegreya-Regular
>
> Note that `ly:ttf-ps-name' returns the font's *PostScript* name.  This
> is *not* what fontconfig normally operates on (but see below).
>
> > Given font name: DejaVu Sans
> > Determined font file: /usr/share/fonts/TTF/mplus-1c-medium.ttf
> > Actual font in that file: mplus-1c-medium
> > Given font is present: #f/usr/share/fonts/TTF/mplus-1c-medium.ttf
> > mplus-1c-medium
>    Given font name: DejaVu Sans
>    Determined font file: /usr/share/fonts/truetype/DejaVuSans.ttf
>    Actual font in that file: DejaVuSans
>    Given font is present: #f/usr/share/fonts/truetype/DejaVuSans.ttf
>    DejaVuSans
>
> Same as above: `DejaVuSans' != `DejaVu Sans'.
>
> Since FontConfig version 2.11 (released October 2013), however, it is
> possible to search for PostScript names also.  Example:
>
>    $ fc-match "Alegreya"
>    Alegreya-Regular.ttf: "Alegreya" "Regular"
>
>    $ fc-match "AlegreyaRegular"
>    arial.ttf: "Arial" "Normal"
>
>    $ fc-match ":postscriptname=AlegreyaRegular"
>    Alegreya-Regular.ttf: "Alegreya" "Regular"
>
> Maybe lilypond's `display_fontset' function (in font-config-scheme.cc)
> can be extended to display PS names also.  And perhaps it makes sense
> to extend lilypond's font loading function to accept a font's PS name
> – or to provide a Scheme function wrapper for FontConfig to access a
> given font's PS name.
>
>
>      Werner

I think I have found something.

After some experimenting with a copy of font-config-get-font-file and 
trying different approaches I could guess from the documentations 
available I found that replacing an item in the FcPatternGetString call 
this function returns the font name and not the Postscript name or the 
font file.

The following preliminary function (if added to font-config-scheme.cc) 
returns either the Font Name (if the font exists) or "Emmentaler-11" (on 
my system) if it doesn't exist. I assume it would return other names on 
other systems:

LY_DEFINE (ly_font_config_font_exists, "ly:font-config-font-exists", 1, 
0, 0,
           (SCM name),
           "Determing if font @var{name} exists.")
{
  LY_ASSERT_TYPE (scm_is_string, name, 1);

  FcPattern *pat = FcPatternCreate ();
  FcValue val;

  val.type = FcTypeString;
  val.u.s = (const FcChar8 *)ly_scm2string (name).c_str (); // 
FC_SLANT_ITALIC;
  FcPatternAdd (pat, FC_FAMILY, val, FcFalse);

  FcResult result;
  SCM scm_result = SCM_BOOL_F;

  FcConfigSubstitute (NULL, pat, FcMatchFont);
  FcDefaultSubstitute (pat);

  pat = FcFontMatch (NULL, pat, &result);
  FcChar8 *str = 0;
  if (FcPatternGetString (pat, FC_FAMILY, 0, &str) == FcResultMatch)
    scm_result = scm_from_utf8_string ((char const *)str);

  FcPatternDestroy (pat);
  return scm_result;
}

Now I get stuck with C++ basics, namely types, references and pointers, 
but it should be possible to achieve something with the following approach:
In the line
scm_result = scm_from_utf ...

"str" holds the result from this match.
If this matches the originally passed "name" argument the return value 
should be set to SCM_BOOL_T.
This should be dead easy, but I don't know to perform this comparison.

If someone gives me a helping hand here we would get a function 
ly:font-config-font-exists that returns #t or #f depending on the 
existence of the font.

Please ...

Best
Urs
 set the return value to SCM_BOOL_T if