Fix shaping problems on iOS 14 / macOS 11

Detection of AAT fonts was exclusively based on the existence
of tables mort, morx and kerx. In the SF font (the UI default)
on iOS 14 and Big Sur, none of these tables actually exist, so
we would accidentally use the OpenType shaper for it. But there
are plenty of other AAT tables in the font and the OT shaper
can´t handle it. In particular, this caused us to get the wrong
advance for comma when it was followed by a space.

Looking at all the affected SF fonts on Big Sur, they all have
the trak table, so we expand the detection to include this.
This is possibly also the table used to determine the correct
glyph positions in this case.

In Qt 6, this already works as expected, because Harfbuzz has
built-in support for AAT and does not require the CoreText
fallback. Therefore, this is just a hotfix for the 5.15 series
and there is no need to upstream this patch.

[ChangeLog][macOS] Fixed shaping of default UI font on macOS 11
and iOS 14.

Fixes: QTBUG-88495
Change-Id: Ia2b3f45cbc0c32b93864760cb427ede6b0566e8f
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

2 files changed, 2 insertions, 2 deletions

diff --git a/src/3rdparty/harfbuzz-ng/src/hb-coretext.cc b/src/3rdparty/harfbuzz-ng/src/hb-coretext.cc
index d64cb7edbd..11b6deee04 100644
--- a/src/3rdparty/harfbuzz-ng/src/hb-coretext.cc
+++ b/src/3rdparty/harfbuzz-ng/src/hb-coretext.cc
@@ -1322,7 +1322,7 @@ struct hb_coretext_aat_shaper_face_data_t {};
 hb_coretext_aat_shaper_face_data_t *
 _hb_coretext_aat_shaper_face_data_create (hb_face_t *face)
 {
-  static const hb_tag_t tags[] = {HB_CORETEXT_TAG_MORX, HB_CORETEXT_TAG_MORT, HB_CORETEXT_TAG_KERX};
+  static const hb_tag_t tags[] = {HB_CORETEXT_TAG_MORX, HB_CORETEXT_TAG_MORT, HB_CORETEXT_TAG_KERX, HB_CORETEXT_TAG_TRAK};
 
   for (unsigned int i = 0; i < ARRAY_LENGTH (tags); i++)
   {
diff --git a/src/3rdparty/harfbuzz-ng/src/hb-coretext.h b/src/3rdparty/harfbuzz-ng/src/hb-coretext.h
index 4b0a6f01b6..12f7d2515b 100644
--- a/src/3rdparty/harfbuzz-ng/src/hb-coretext.h
+++ b/src/3rdparty/harfbuzz-ng/src/hb-coretext.h
@@ -43,7 +43,7 @@ HB_BEGIN_DECLS
 #define HB_CORETEXT_TAG_MORT HB_TAG('m','o','r','t')
 #define HB_CORETEXT_TAG_MORX HB_TAG('m','o','r','x')
 #define HB_CORETEXT_TAG_KERX HB_TAG('k','e','r','x')
-
+#define HB_CORETEXT_TAG_TRAK HB_TAG('t','r','a','k')
 
 HB_EXTERN hb_face_t *
 hb_coretext_face_create (CGFontRef cg_font);