From 2124ad8906bb77eee099071dccc49d3c60fe331f Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Sun, 17 Jul 2022 21:32:27 -0600
Subject: [PATCH] [aat/morx] Implement language-specific forms

Test on Mac with, eg.

$ hb-view /Library/Fonts/BigCaslon.ttf -u 107
vs
$ hb-view /Library/Fonts/BigCaslon.ttf -u 107 --language pl

Fixes https://github.com/harfbuzz/harfbuzz/issues/1373
---
 src/hb-aat-layout-morx-table.hh | 7 +++++++
 src/hb-aat-map.hh               | 6 ++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/hb-aat-layout-morx-table.hh b/src/hb-aat-layout-morx-table.hh
index 3d053cb13..73ab5204a 100644
--- a/src/hb-aat-layout-morx-table.hh
+++ b/src/hb-aat-layout-morx-table.hh
@@ -980,6 +980,13 @@ struct Chain
 	  setting = HB_AAT_LAYOUT_FEATURE_SELECTOR_LOWER_CASE_SMALL_CAPS;
 	  goto retry;
 	}
+	else if (type == HB_AAT_LAYOUT_FEATURE_TYPE_LANGUAGE_TAG_TYPE && setting &&
+		 /* TODO: Rudimentary language matching. */
+		 map->face->table.ltag->get_language (setting - 1) == map->props.language)
+	{
+	  flags &= feature.disableFlags;
+	  flags |= feature.enableFlags;
+	}
       }
     }
     return flags;
diff --git a/src/hb-aat-map.hh b/src/hb-aat-map.hh
index 5a0fa7054..976a2cda2 100644
--- a/src/hb-aat-map.hh
+++ b/src/hb-aat-map.hh
@@ -52,8 +52,9 @@ struct hb_aat_map_builder_t
   public:
 
   HB_INTERNAL hb_aat_map_builder_t (hb_face_t *face_,
-				    const hb_segment_properties_t *props_ HB_UNUSED) :
-				      face (face_) {}
+				    const hb_segment_properties_t *props_) :
+				      face (face_),
+				      props (*props_) {}
 
   HB_INTERNAL void add_feature (hb_tag_t tag, unsigned int value=1);
 
@@ -87,6 +88,7 @@ struct hb_aat_map_builder_t
 
   public:
   hb_face_t *face;
+  hb_segment_properties_t props;
 
   public:
   hb_sorted_vector_t<feature_info_t> features;