fontselect: coretext: get fallback font family name via FreeType

Since commit be0d1613f79a95073d18d96a60e1394abf9316a2,
get_fallback can return a name from Core Text that is different
from all names that match_fonts registers for the same font.
This causes font fallback to fail as find_fonts fails to
find any font having the name received from get_fallback.
(Moreover, libass will keep retrying fallback for other glyphs,
and the coretext match_fonts will keep readding the same fonts
over and over again.)

Commit 152d0484e98f118d01987138695cf40579c9e297 attempted
to fix font fallback by getting a full name from Core Text
instead of a family name when it was noticed that Core Text's
family name can come from TT_NAME_ID_TYPOGRAPHIC_FAMILY
in addition to TT_NAME_ID_FONT_FAMILY, which we fetch in
get_font_info, but the problem goes deeper: Core Text can return
Macintosh-platform names that don't match Microsoft-platform
names, or the font might have no Microsoft-platform names at all.
Furthermore, returning a full name breaks style matching:
get_fallback does not know about weight, slant etc. and is
expected to return a whole family of fonts that will be
lazy-loaded in its entirety (if applicable) and searched
through for the best stylistic match by find_fonts.

To fix fallback while preserving maximum name portability
in the spirit of be0d1613f79a95073d18d96a60e1394abf9316a2,
use the same API in get_fallback as is used in match_fonts
to look up a family name.

Note: this could be more efficient if ass_get_font_info
could be told to return just an arbitrary family name.

This fixes https://github.com/libass/libass/issues/457.

1 files changed, 25 insertions, 7 deletions

diff --git a/libass/ass_coretext.c b/libass/ass_coretext.c
index 49a96ff..f1063ba 100644
--- a/libass/ass_coretext.c
+++ b/libass/ass_coretext.c
@@ -246,8 +246,11 @@ static void match_fonts(void *priv, ASS_Library *lib, ASS_FontProvider *provider
     SAFE_CFRelease(cfname);
 }
 
-static char *get_fallback(void *priv, const char *family, uint32_t codepoint)
+static char *get_fallback(void *priv, ASS_Library *lib,
+                          const char *family, uint32_t codepoint)
 {
+    FT_Library ftlib = priv;
+
     CFStringRef name = CFStringCreateWithBytes(
         0, (UInt8 *)family, strlen(family), kCFStringEncodingUTF8, false);
     CTFontRef font = CTFontCreateWithName(name, 0, NULL);
@@ -256,17 +259,32 @@ static char *get_fallback(void *priv, const char *family, uint32_t codepoint)
         0, (UInt8*)&codepointle, sizeof(codepointle),
         kCFStringEncodingUTF32LE, false);
     CTFontRef fb = CTFontCreateForString(font, r, CFRangeMake(0, 1));
-    CFNumberRef cfformat = CTFontCopyAttribute(fb, kCTFontFormatAttribute);
-    CFStringRef cfname = is_postscript_font_format(cfformat) ?
-        CTFontCopyPostScriptName(fb) : CTFontCopyFullName(fb);
-    char *res_name = cfstr2buf(cfname);
+    CTFontDescriptorRef fontd = CTFontCopyFontDescriptor(fb);
+
+    char *res_name = NULL;
+    char *path = NULL;
+    ASS_FontProviderMetaData meta = {0};
+    if (get_font_info_ct(lib, ftlib, fontd, &path, &meta))
+        res_name = meta.families[0];
+
+    for (int i = 1 /* skip res_name */; i < meta.n_family; i++)
+        free(meta.families[i]);
+
+    for (int i = 0; i < meta.n_fullname; i++)
+        free(meta.fullnames[i]);
+
+    free(meta.families);
+    free(meta.fullnames);
+
+    free(meta.postscript_name);
+
+    free(path);
 
     SAFE_CFRelease(name);
     SAFE_CFRelease(font);
     SAFE_CFRelease(r);
     SAFE_CFRelease(fb);
-    SAFE_CFRelease(cfformat);
-    SAFE_CFRelease(cfname);
+    SAFE_CFRelease(fontd);
 
     return res_name;
 }