commit 38889c3ad6d3b917d5d4ea5247cedaef916e4829
author Behdad Esfahbod <behdad@behdad.org> Tue Mar 18 00:54:46 2025 -0600
committer Behdad Esfahbod <behdad@behdad.org> Tue Mar 18 03:28:44 2025 -0600
tree 7e69a1aa28eb7c2a442bc9e38e5fae625b4bac30
parent 472e65dd0f4a3fb8e56b3e92849e6ce6351be155

[coretext] Fix loading named instances

Needs tests...

TTC indices > 0 can't be loaded with CoreText API it seems.

Fixes https://github.com/harfbuzz/harfbuzz/issues/5158

src/hb-coretext.cc

diff --git a/src/hb-coretext.cc b/src/hb-coretext.cc
index deb3878..0280528 100644
--- a/src/hb-coretext.cc
+++ b/src/hb-coretext.cc
@@ -158,10 +158,17 @@
 }
 
 CGFontRef
-create_cg_font (CFArrayRef ct_font_desc_array, unsigned int index)
+create_cg_font (CFArrayRef ct_font_desc_array, unsigned int named_instance_index)
 {
-  auto ct_font_desc = (CFArrayGetCount (ct_font_desc_array) > index) ?
-		      (CTFontDescriptorRef) CFArrayGetValueAtIndex (ct_font_desc_array, index) : nullptr;
+  if (named_instance_index == 0)
+  {
+    // Default instance. We don't know which one is it. Return the first one.
+    // We will set the correct variations on it later.
+  }
+  else
+    named_instance_index--;
+  auto ct_font_desc = (CFArrayGetCount (ct_font_desc_array) > named_instance_index) ?
+		      (CTFontDescriptorRef) CFArrayGetValueAtIndex (ct_font_desc_array, named_instance_index) : nullptr;
   if (unlikely (!ct_font_desc))
   {
     CFRelease (ct_font_desc_array);
@@ -187,12 +194,21 @@
   if (unlikely (!blob_length))
     DEBUG_MSG (CORETEXT, blob, "Empty blob");
 
-  if (unlikely (index != 0))
+  unsigned ttc_index = index & 0xFFFF;
+  unsigned named_instance_index = index >> 16;
+
+  if (ttc_index != 0)
+  {
+    DEBUG_MSG (CORETEXT, blob, "TTC index %d not supported", ttc_index);
+    return nullptr; // CoreText does not support TTCs
+  }
+
+  if (unlikely (named_instance_index != 0))
   {
     auto ct_font_desc_array = CTFontManagerCreateFontDescriptorsFromData (CFDataCreate (kCFAllocatorDefault, (const UInt8 *) blob_data, blob_length));
     if (unlikely (!ct_font_desc_array))
       return nullptr;
-    return create_cg_font (ct_font_desc_array, index);
+    return create_cg_font (ct_font_desc_array, named_instance_index);
   }
 
   hb_blob_reference (blob);
@@ -393,7 +409,16 @@
     return nullptr;
   }
 
-  auto cg_font = create_cg_font (ct_font_desc_array, index);
+  unsigned ttc_index = index & 0xFFFF;
+  unsigned named_instance_index = index >> 16;
+
+  if (ttc_index != 0)
+  {
+    DEBUG_MSG (CORETEXT, nullptr, "TTC index %d not supported", ttc_index);
+    return nullptr; // CoreText does not support TTCs
+  }
+
+  auto cg_font = create_cg_font (ct_font_desc_array, named_instance_index);
   CFRelease (url);
 
   hb_face_t *face = hb_coretext_face_create (cg_font);
@@ -401,6 +426,8 @@
   if (unlikely (hb_face_is_immutable (face)))
     return nullptr;
 
+  hb_face_set_index (face, index);
+
   return face;
 }
 
@@ -433,6 +460,8 @@
   if (unlikely (hb_face_is_immutable (face)))
     return nullptr;
 
+  hb_face_set_index (face, index);
+
   return face;
 }
 

util/font-options.hh

diff --git a/util/font-options.hh b/util/font-options.hh
index bacd7bc..8c7ce1c 100644
--- a/util/font-options.hh
+++ b/util/font-options.hh
@@ -101,7 +101,8 @@
   hb_font_set_scale (font, scale_x, scale_y);
 
 #ifndef HB_NO_VAR
-  hb_font_set_var_named_instance (font, named_instance);
+  if (named_instance != HB_FONT_NO_VAR_NAMED_INSTANCE)
+    hb_font_set_var_named_instance (font, named_instance);
   hb_font_set_variations (font, variations, num_variations);
 #endif