Merge pull request #3610 from googlefonts/subset_create_tables_face

[subset] fix subsetting of faces created via hb_face_create_for_tables.

src/hb-subset.cc

@@ -78,6 +78,108 @@ using OT::Layout::GSUB::GSUB;
  * retain glyph ids option and configure the subset to pass through the layout tables untouched.
  */
 
+/*
+ * The list of tables in the open type spec. Used to check for tables that may need handling
+ * if we are unable to list the tables in a face.
+ */
+static hb_tag_t known_tables[] {
+  HB_TAG ('a', 'v', 'a', 'r'),
+  HB_OT_TAG_BASE,
+  HB_OT_TAG_CBDT,
+  HB_OT_TAG_CBLC,
+  HB_OT_TAG_cff1,
+  HB_OT_TAG_cff2,
+  HB_OT_TAG_cmap,
+  HB_OT_TAG_COLR,
+  HB_OT_TAG_CPAL,
+  HB_TAG ('c', 'v', 'a', 'r'),
+  HB_TAG ('c', 'v', 't', ' '),
+  HB_TAG ('D', 'S', 'I', 'G'),
+  HB_TAG ('E', 'B', 'D', 'T'),
+  HB_TAG ('E', 'B', 'L', 'C'),
+  HB_TAG ('E', 'B', 'S', 'C'),
+  HB_TAG ('f', 'p', 'g', 'm'),
+  HB_TAG ('f', 'v', 'a', 'r'),
+  HB_TAG ('g', 'a', 's', 'p'),
+  HB_OT_TAG_GDEF,
+  HB_OT_TAG_glyf,
+  HB_OT_TAG_GPOS,
+  HB_OT_TAG_GSUB,
+  HB_OT_TAG_gvar,
+  HB_OT_TAG_hdmx,
+  HB_OT_TAG_head,
+  HB_OT_TAG_hhea,
+  HB_OT_TAG_hmtx,
+  HB_OT_TAG_HVAR,
+  HB_OT_TAG_JSTF,
+  HB_TAG ('k', 'e', 'r', 'n'),
+  HB_OT_TAG_loca,
+  HB_TAG ('L', 'T', 'S', 'H'),
+  HB_OT_TAG_MATH,
+  HB_OT_TAG_maxp,
+  HB_TAG ('M', 'E', 'R', 'G'),
+  HB_TAG ('m', 'e', 't', 'a'),
+  HB_TAG ('M', 'V', 'A', 'R'),
+  HB_TAG ('P', 'C', 'L', 'T'),
+  HB_OT_TAG_post,
+  HB_TAG ('p', 'r', 'e', 'p'),
+  HB_OT_TAG_sbix,
+  HB_TAG ('S', 'T', 'A', 'T'),
+  HB_TAG ('S', 'V', 'G', ' '),
+  HB_TAG ('V', 'D', 'M', 'X'),
+  HB_OT_TAG_vhea,
+  HB_OT_TAG_vmtx,
+  HB_OT_TAG_VORG,
+  HB_OT_TAG_VVAR,
+  HB_OT_TAG_name,
+  HB_OT_TAG_OS2
+};
+
+static bool _table_is_empty (const hb_face_t *face, hb_tag_t tag)
+{
+  hb_blob_t* blob = hb_face_reference_table (face, tag);
+  bool result = (blob == hb_blob_get_empty ());
+  hb_blob_destroy (blob);
+  return result;
+}
+
+static unsigned int
+_get_table_tags (const hb_subset_plan_t* plan,
+                 unsigned int  start_offset,
+                 unsigned int *table_count, /* IN/OUT */
+                 hb_tag_t     *table_tags /* OUT */)
+{
+  unsigned num_tables = hb_face_get_table_tags (plan->source, 0, nullptr, nullptr);
+  if (num_tables)
+    return hb_face_get_table_tags (plan->source, start_offset, table_count, table_tags);
+
+  // If face has 0 tables associated with it, assume that it was built from
+  // hb_face_create_tables and thus is unable to list its tables. Fallback to
+  // checking each table type we can handle for existence instead.
+  auto it =
+      hb_concat (
+          + hb_array (known_tables)
+          | hb_filter ([&] (hb_tag_t tag) {
+            return !_table_is_empty (plan->source, tag) && !plan->no_subset_tables->has (tag);
+          })
+          | hb_map ([] (hb_tag_t tag) -> hb_tag_t { return tag; }),
+
+          plan->no_subset_tables->iter ()
+          | hb_filter([&] (hb_tag_t tag) {
+            return !_table_is_empty (plan->source, tag);
+          }));
+
+  it += start_offset;
+
+  unsigned num_written = 0;
+  while (bool (it) && num_written < *table_count)
+    table_tags[num_written++] = *it++;
+
+  *table_count = num_written;
+  return num_written;
+}
+
+
 static unsigned
 _plan_estimate_subset_table_size (hb_subset_plan_t *plan,
 				  unsigned table_len,
@@ -224,6 +326,14 @@ _subset (hb_subset_plan_t *plan, hb_vector_t<char> &buf)
 static bool
 _is_table_present (hb_face_t *source, hb_tag_t tag)
 {
+
+  if (!hb_face_get_table_tags (source, 0, nullptr, nullptr)) {
+    // If face has 0 tables associated with it, assume that it was built from
+    // hb_face_create_tables and thus is unable to list its tables. Fallback to
+    // checking if the blob associated with tag is empty.
+    return !_table_is_empty (source, tag);
+  }
+
   hb_tag_t table_tags[32];
   unsigned offset = 0, num_tables = ARRAY_LENGTH (table_tags);
   while ((hb_face_get_table_tags (source, offset, &num_tables, table_tags), num_tables))
@@ -388,7 +498,8 @@ hb_subset_plan_execute_or_fail (hb_subset_plan_t *plan)
   unsigned offset = 0, num_tables = ARRAY_LENGTH (table_tags);
   hb_vector_t<char> buf;
   buf.alloc (4096 - 16);
-  while ((hb_face_get_table_tags (plan->source, offset, &num_tables, table_tags), num_tables))
+
+  while ((_get_table_tags (plan, offset, &num_tables, table_tags), num_tables))
   {
     for (unsigned i = 0; i < num_tables; ++i)
     {
@@ -400,7 +511,7 @@ hb_subset_plan_execute_or_fail (hb_subset_plan_t *plan)
     }
     offset += num_tables;
   }
-end:
 
+end:
   return success ? hb_face_reference (plan->dest) : nullptr;
 }

test/api/test-subset.c

@@ -193,6 +193,42 @@ test_subset_plan (void)
   hb_face_destroy (face_ac);
 }
 
+static hb_blob_t*
+_ref_table (hb_face_t *face, hb_tag_t tag, void *user_data)
+{
+  return hb_face_reference_table ((hb_face_t*) user_data, tag);
+}
+
+static void
+test_subset_create_for_tables_face (void)
+{
+  hb_face_t *face_abc = hb_test_open_font_file ("fonts/Roboto-Regular.abc.ttf");
+  hb_face_t *face_ac = hb_test_open_font_file ("fonts/Roboto-Regular.ac.ttf");
+  hb_face_t *face_create_for_tables = hb_face_create_for_tables (
+      _ref_table,
+      face_abc,
+      NULL);
+
+  hb_set_t *codepoints = hb_set_create();
+  hb_set_add (codepoints, 97);
+  hb_set_add (codepoints, 99);
+
+  hb_subset_input_t* input = hb_subset_test_create_input (codepoints);
+  hb_set_destroy (codepoints);
+
+  hb_face_t* face_abc_subset = hb_subset_or_fail (face_create_for_tables, input);
+
+  hb_subset_test_check (face_ac, face_abc_subset, HB_TAG ('l','o','c', 'a'));
+  hb_subset_test_check (face_ac, face_abc_subset, HB_TAG ('g','l','y','f'));
+  hb_subset_test_check (face_ac, face_abc_subset, HB_TAG ('g','a','s','p'));
+
+  hb_subset_input_destroy (input);
+  hb_face_destroy (face_abc_subset);
+  hb_face_destroy (face_create_for_tables);
+  hb_face_destroy (face_abc);
+  hb_face_destroy (face_ac);
+}
+
 int
 main (int argc, char **argv)
 {
@@ -204,6 +240,7 @@ main (int argc, char **argv)
   hb_test_add (test_subset_set_flags);
   hb_test_add (test_subset_sets);
   hb_test_add (test_subset_plan);
+  hb_test_add (test_subset_create_for_tables_face);
 
   return hb_test_run();
 }