[subset] Add no subset tables and passthrough unrecognized tables to the subset api.

Matches fontTools options.

src/hb-subset-input.cc

@@ -50,6 +50,7 @@ hb_subset_input_create_or_fail ()
   hb_set_add (input->name_languages, 0x0409);
   input->layout_features = hb_set_create ();
   input->drop_tables = hb_set_create ();
+  input->no_subset_tables = hb_set_create ();
   input->drop_hints = false;
   input->desubroutinize = false;
   input->retain_gids = false;
@@ -58,6 +59,7 @@ hb_subset_input_create_or_fail ()
   input->notdef_outline = false;
   input->no_prune_unicode_ranges = false;
   input->retain_all_layout_features = false;
+  input->passthrough_unrecognized = false;
 
   hb_tag_t default_drop_tables[] = {
     // Layout disabled by default
@@ -83,9 +85,24 @@ hb_subset_input_create_or_fail ()
     HB_TAG ('S', 'i', 'l', 'f'),
     HB_TAG ('S', 'i', 'l', 'l'),
   };
-
   input->drop_tables->add_array (default_drop_tables, ARRAY_LENGTH (default_drop_tables));
 
+  hb_tag_t default_no_subset_tables[] = {
+    HB_TAG ('a', 'v', 'a', 'r'),
+    HB_TAG ('f', 'v', 'a', 'r'),
+    HB_TAG ('g', 'a', 's', 'p'),
+    HB_TAG ('c', 'v', 't', ' '),
+    HB_TAG ('f', 'p', 'g', 'm'),
+    HB_TAG ('p', 'r', 'e', 'p'),
+    HB_TAG ('V', 'D', 'M', 'X'),
+    HB_TAG ('D', 'S', 'I', 'G'),
+    HB_TAG ('M', 'V', 'A', 'R'),
+    HB_TAG ('c', 'v', 'a', 'r'),
+    HB_TAG ('S', 'T', 'A', 'T'),
+  };
+  input->no_subset_tables->add_array (default_no_subset_tables,
+                                      ARRAY_LENGTH (default_no_subset_tables));
+
   //copied from _layout_features_groups in fonttools
   hb_tag_t default_layout_features[] = {
     // default shaper
@@ -276,6 +293,11 @@ hb_subset_input_drop_tables_set (hb_subset_input_t *subset_input)
   return subset_input->drop_tables;
 }
 
+HB_EXTERN hb_set_t *
+hb_subset_input_no_subset_tables_set (hb_subset_input_t *subset_input)
+{
+  return subset_input->no_subset_tables;
+}
 
 HB_EXTERN hb_bool_t
 hb_subset_input_get_flag (hb_subset_input_t *input,
@@ -293,6 +315,8 @@ hb_subset_input_get_flag (hb_subset_input_t *input,
       return input->name_legacy;
     case HB_SUBSET_FLAG_SET_OVERLAPS_FLAG:
       return input->overlaps_flag;
+    case HB_SUBSET_FLAG_PASSTHROUGH_UNRECOGNIZED:
+      return input->passthrough_unrecognized;
     default:
       return false;
   }
@@ -320,6 +344,9 @@ hb_subset_input_set_flag (hb_subset_input_t *input,
     case HB_SUBSET_FLAG_SET_OVERLAPS_FLAG:
       input->overlaps_flag = value;
       break;
+    case HB_SUBSET_FLAG_PASSTHROUGH_UNRECOGNIZED:
+      input->passthrough_unrecognized = value;
+      break;
     default:
       // Do nothing.
       break;

src/hb-subset-input.hh

@@ -42,6 +42,7 @@ struct hb_subset_input_t
   hb_set_t *glyphs;
   hb_set_t *name_ids;
   hb_set_t *name_languages;
+  hb_set_t *no_subset_tables;
   hb_set_t *drop_tables;
   hb_set_t *layout_features;
 
@@ -54,6 +55,8 @@ struct hb_subset_input_t
   hb_bool_t notdef_outline;
   hb_bool_t no_prune_unicode_ranges;
   hb_bool_t retain_all_layout_features;
+  hb_bool_t passthrough_unrecognized;
+
   /* TODO
    *
    * features

src/hb-subset-plan.cc

@@ -427,6 +427,7 @@ hb_subset_plan_create (hb_face_t	 *face,
   plan->notdef_outline = input->notdef_outline;
   plan->prune_unicode_ranges = !input->no_prune_unicode_ranges;
   plan->retain_all_layout_features = input->retain_all_layout_features;
+  plan->passthrough_unrecognized = input->passthrough_unrecognized;
   plan->unicodes = hb_set_create ();
   plan->name_ids = hb_set_copy (input->name_ids);
   _nameid_closure (face, plan->name_ids);
@@ -434,6 +435,7 @@ hb_subset_plan_create (hb_face_t	 *face,
   plan->layout_features = hb_set_copy (input->layout_features);
   plan->glyphs_requested = hb_set_copy (input->glyphs);
   plan->drop_tables = hb_set_copy (input->drop_tables);
+  plan->no_subset_tables = hb_set_copy (input->no_subset_tables);
   plan->source = hb_face_reference (face);
   plan->dest = hb_face_builder_create ();
 

src/hb-subset-plan.hh

@@ -48,6 +48,7 @@ struct hb_subset_plan_t
   bool notdef_outline : 1;
   bool prune_unicode_ranges : 1;
   bool retain_all_layout_features : 1;
+  bool passthrough_unrecognized : 1;
 
   // For each cp that we'd like to retain maps to the corresponding gid.
   hb_set_t *unicodes;
@@ -64,6 +65,9 @@ struct hb_subset_plan_t
   //glyph ids requested to retain
   hb_set_t *glyphs_requested;
 
+  // Tables which should not be processed, just pass them through.
+  hb_set_t *no_subset_tables;
+
   // Tables which should be dropped.
   hb_set_t *drop_tables;
 

src/hb-subset.cc

@@ -244,9 +244,22 @@ _should_drop_table (hb_subset_plan_t *plan, hb_tag_t tag)
   }
 }
 
+static bool
+_passthrough (hb_subset_plan_t *plan, hb_tag_t tag)
+{
+  hb_blob_t *source_table = hb_face_reference_table (plan->source, tag);
+  bool result = plan->add_table (tag, source_table);
+  hb_blob_destroy (source_table);
+  return result;
+}
+
 static bool
 _subset_table (hb_subset_plan_t *plan, hb_tag_t tag)
 {
+  if (plan->no_subset_tables->has (tag)) {
+    return _passthrough (plan, tag);
+  }
+
   DEBUG_MSG (SUBSET, nullptr, "subset %c%c%c%c", HB_UNTAG (tag));
   switch (tag)
   {
@@ -288,10 +301,11 @@ _subset_table (hb_subset_plan_t *plan, hb_tag_t tag)
 #endif
 
   default:
-    hb_blob_t *source_table = hb_face_reference_table (plan->source, tag);
-    bool result = plan->add_table (tag, source_table);
-    hb_blob_destroy (source_table);
-    return result;
+    if (plan->passthrough_unrecognized)
+      return _passthrough (plan, tag);
+
+    // Drop table
+    return true;
   }
 }
 

src/hb-subset.h

@@ -41,11 +41,12 @@ typedef struct hb_subset_input_t hb_subset_input_t;
 
 typedef enum
 {
-  HB_SUBSET_FLAG_HINTING =	     1,
-  HB_SUBSET_FLAG_RETAIN_GIDS =	     2,
-  HB_SUBSET_FLAG_DESUBROUTINIZE =    3,
-  HB_SUBSET_FLAG_NAME_LEGACY =	     4,
-  HB_SUBSET_FLAG_SET_OVERLAPS_FLAG = 5,
+  HB_SUBSET_FLAG_HINTING =		    1,
+  HB_SUBSET_FLAG_RETAIN_GIDS =		    2,
+  HB_SUBSET_FLAG_DESUBROUTINIZE =	    3,
+  HB_SUBSET_FLAG_NAME_LEGACY =		    4,
+  HB_SUBSET_FLAG_SET_OVERLAPS_FLAG =	    5,
+  HB_SUBSET_FLAG_PASSTHROUGH_UNRECOGNIZED = 6,
 } hb_subset_flag_t;
 
 HB_EXTERN hb_subset_input_t *
@@ -79,8 +80,10 @@ HB_EXTERN hb_bool_t
 hb_subset_input_get_retain_all_features (hb_subset_input_t *subset_input);
 
 HB_EXTERN hb_set_t *
-hb_subset_input_drop_tables_set (hb_subset_input_t *subset_input);
+hb_subset_input_no_subset_tables_set (hb_subset_input_t *subset_input);
 
+HB_EXTERN hb_set_t *
+hb_subset_input_drop_tables_set (hb_subset_input_t *subset_input);
 
 HB_EXTERN hb_bool_t
 hb_subset_input_get_flag (hb_subset_input_t *input,