[subset-plan] Keep a reverse-gid vector

To speed up iteration.

src/hb-ot-hmtx-table.hh

@@ -211,15 +211,17 @@ struct hmtxvmtx
     }
 
     auto it =
-    + hb_range (c->plan->num_output_glyphs ())
-    | hb_map ([c, &_mtx, mtx_map] (unsigned _)
+    + hb_enumerate (c->plan->new_to_old_gid_list)
+    | hb_map ([c, &_mtx, mtx_map] (const hb_pair_t<hb_codepoint_t, hb_codepoint_t> &_)
 	      {
-	        hb_pair_t<unsigned, int> *v = nullptr;
-		if (!mtx_map->has (_, &v))
+		hb_codepoint_t new_gid = _.first;
+		hb_codepoint_t old_gid = _.second;
+		if (old_gid == HB_MAP_VALUE_INVALID)
+		  return hb_pair (0u, 0);
+
+		hb_pair_t<unsigned, int> *v = nullptr;
+		if (!mtx_map->has (new_gid, &v))
 		{
-		  hb_codepoint_t old_gid;
-		  if (!c->plan->old_gid_for_new_gid (_, &old_gid))
-		    return hb_pair (0u, 0);
 		  int lsb = 0;
 		  if (!_mtx.get_leading_bearing_without_var_unscaled (old_gid, &lsb))
 		    (void) _glyf_get_leading_bearing_without_var_unscaled (c->plan->source, old_gid, !T::is_horizontal, &lsb);

src/hb-subset-plan-member-list.hh

@@ -35,6 +35,8 @@
 HB_SUBSET_PLAN_MEMBER (hb_set_t, unicodes)
 HB_SUBSET_PLAN_MEMBER (hb_sorted_vector_t E(<hb_pair_t<hb_codepoint_t, hb_codepoint_t>>), unicode_to_new_gid_list)
 
+HB_SUBSET_PLAN_MEMBER (hb_vector_t<hb_codepoint_t>, new_to_old_gid_list)
+
 // name_ids we would like to retain
 HB_SUBSET_PLAN_MEMBER (hb_set_t, name_ids)
 

src/hb-subset-plan.cc

@@ -755,7 +755,6 @@ _populate_gids_to_retain (hb_subset_plan_t* plan,
 
   _remove_invalid_gids (&plan->_glyphset, plan->source->get_num_glyphs ());
 
-
 #ifndef HB_NO_VAR
   if (!drop_tables->has (HB_OT_TAG_GDEF))
     _collect_layout_variation_indices (plan);
@@ -783,6 +782,7 @@ _create_old_gid_to_new_gid_map (const hb_face_t *face,
                                 const hb_map_t  *requested_glyph_map,
 				hb_map_t	*glyph_map, /* OUT */
 				hb_map_t	*reverse_glyph_map, /* OUT */
+				hb_vector_t<hb_codepoint_t> *new_to_old_gid_list /* OUT */,
 				unsigned int	*num_glyphs /* OUT */)
 {
   unsigned pop = all_gids_to_retain->get_population ();
@@ -863,6 +863,12 @@ _create_old_gid_to_new_gid_map (const hb_face_t *face,
   | hb_sink (glyph_map)
   ;
 
+  auto &l = *new_to_old_gid_list;
+  l.resize (*num_glyphs);
+  hb_memset (l.arrayZ, 0xff, l.length * sizeof (l[0]));
+  for (auto _ : *reverse_glyph_map)
+    l[_.first] = _.second;
+
   return true;
 }
 
@@ -1086,6 +1092,7 @@ hb_subset_plan_t::hb_subset_plan_t (hb_face_t *face,
           &input->glyph_map,
           glyph_map,
           reverse_glyph_map,
+	  &new_to_old_gid_list,
           &_num_output_glyphs))) {
     return;
   }