[ot] Search globally for 'vert' feature if not found in specified script/lang

Fixes https://github.com/behdad/harfbuzz/issues/63

src/hb-ot-layout-private.hh

@@ -36,6 +36,15 @@
 #include "hb-set-private.hh"
 
 
+/* Private API corresponding to hb-ot-layout.h: */
+
+HB_INTERNAL hb_bool_t
+hb_ot_layout_table_find_feature (hb_face_t    *face,
+				 hb_tag_t      table_tag,
+				 hb_tag_t      feature_tag,
+				 unsigned int *feature_index);
+
+
 /*
  * GDEF
  */

src/hb-ot-layout.cc

@@ -291,6 +291,28 @@ hb_ot_layout_table_get_feature_tags (hb_face_t    *face,
   return g.get_feature_tags (start_offset, feature_count, feature_tags);
 }
 
+hb_bool_t
+hb_ot_layout_table_find_feature (hb_face_t    *face,
+				 hb_tag_t      table_tag,
+				 hb_tag_t      feature_tag,
+				 unsigned int *feature_index)
+{
+  ASSERT_STATIC (OT::Index::NOT_FOUND_INDEX == HB_OT_LAYOUT_NO_FEATURE_INDEX);
+  const OT::GSUBGPOS &g = get_gsubgpos_table (face, table_tag);
+
+  unsigned int num_features = g.get_feature_count ();
+  for (unsigned int i = 0; i < num_features; i++)
+  {
+    if (feature_tag == g.get_feature_tag (i)) {
+      if (feature_index) *feature_index = i;
+      return true;
+    }
+  }
+
+  if (feature_index) *feature_index = HB_OT_LAYOUT_NO_FEATURE_INDEX;
+  return false;
+}
+
 
 unsigned int
 hb_ot_layout_script_get_language_tags (hb_face_t    *face,

src/hb-ot-map-private.hh

@@ -154,9 +154,10 @@ struct hb_ot_map_t
 
 enum hb_ot_map_feature_flags_t {
   F_NONE		= 0x0000u,
-  F_GLOBAL		= 0x0001u,
-  F_HAS_FALLBACK	= 0x0002u,
-  F_MANUAL_ZWJ		= 0x0004u
+  F_GLOBAL		= 0x0001u, /* Feature applies to all characters; results in no mask allocated for it. */
+  F_HAS_FALLBACK	= 0x0002u, /* Has fallback implementation, so include mask bit even if feature not found. */
+  F_MANUAL_ZWJ		= 0x0004u, /* Don't skip over ZWJ when matching. */
+  F_GLOBAL_SEARCH	= 0x0008u  /* If feature not found in LangSys, look for it in global feature list and pick one. */
 };
 /* Macro version for where const is desired. */
 #define F_COMBINE(l,r) (hb_ot_map_feature_flags_t ((unsigned int) (l) | (unsigned int) (r)))

src/hb-ot-map.cc

@@ -216,6 +216,16 @@ hb_ot_map_builder_t::compile (hb_ot_map_t &m)
 						   info->tag,
 						   &feature_index[table_index]);
     }
+    if (!found && (info->flags & F_GLOBAL_SEARCH))
+    {
+      for (unsigned int table_index = 0; table_index < 2; table_index++)
+      {
+	found |= hb_ot_layout_table_find_feature (face,
+						  table_tags[table_index],
+						  info->tag,
+						  &feature_index[table_index]);
+      }
+    }
     if (!found && !(info->flags & F_HAS_FALLBACK))
       continue;
 

src/hb-ot-shape.cc

@@ -102,7 +102,11 @@ hb_ot_shape_collect_features (hb_ot_shape_planner_t          *planner,
 			 F_HAS_FALLBACK : F_NONE));
   else
   {
-    map->add_global_bool_feature (HB_TAG('v','e','r','t'));
+    /* We really want to find a 'vert' feature if there's any in the font, no
+     * matter which script/langsys it is listed (or not) under.
+     * See various bugs referenced from:
+     * https://github.com/behdad/harfbuzz/issues/63 */
+    map->add_feature (HB_TAG ('v','e','r','t'), 1, F_GLOBAL | F_GLOBAL_SEARCH);
   }
 
   if (planner->shaper->override_features)