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.

5 files changed, 32 insertions, 10 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;
 }
diff --git a/libass/ass_directwrite.c b/libass/ass_directwrite.c
index 49ab2d9..0ad9118 100644
--- a/libass/ass_directwrite.c
+++ b/libass/ass_directwrite.c
@@ -424,7 +424,8 @@ static int encode_utf16(wchar_t *chars, uint32_t codepoint)
     }
 }
 
-static char *get_fallback(void *priv, const char *base, uint32_t codepoint)
+static char *get_fallback(void *priv, ASS_Library *lib,
+                          const char *base, uint32_t codepoint)
 {
     HRESULT hr;
     ProviderPrivate *provider_priv = (ProviderPrivate *)priv;
diff --git a/libass/ass_fontconfig.c b/libass/ass_fontconfig.c
index 1e33106..a4ffb42 100644
--- a/libass/ass_fontconfig.c
+++ b/libass/ass_fontconfig.c
@@ -220,7 +220,8 @@ static void cache_fallbacks(ProviderPrivate *fc)
     FcPatternDestroy(pat);
 }
 
-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)
 {
     ProviderPrivate *fc = (ProviderPrivate *)priv;
     FcResult result;
diff --git a/libass/ass_fontselect.c b/libass/ass_fontselect.c
index 6b62511..3013f4a 100644
--- a/libass/ass_fontselect.c
+++ b/libass/ass_fontselect.c
@@ -717,7 +717,7 @@ char *ass_font_select(ASS_FontSelector *priv, ASS_Library *library,
         if (!search_family || !*search_family)
             search_family = "Arial";
         char *fallback_family = default_provider->funcs.get_fallback(
-                default_provider->priv, search_family, code);
+                default_provider->priv, library, search_family, code);
 
         if (fallback_family) {
             res = select_font(priv, library, fallback_family, bold, italic,
diff --git a/libass/ass_fontselect.h b/libass/ass_fontselect.h
index d029b0b..942ea00 100644
--- a/libass/ass_fontselect.h
+++ b/libass/ass_fontselect.h
@@ -144,12 +144,14 @@ typedef void    (*SubstituteFontFunc)(void *priv, const char *name,
  * fallbacks.
  *
  * \param priv font provider private data
+ * \param lib ASS_Library instance
  * \param family original font family name (try matching a similar font) (never NULL)
  * \param codepoint Unicode codepoint (UTF-32)
  * \return output font family, allocated with malloc(), must be freed
  *         by caller.
  */
 typedef char   *(*GetFallbackFunc)(void *priv,
+                                   ASS_Library *lib,
                                    const char *family,
                                    uint32_t codepoint);