[subset] Add subset plan to public API.

Add the ability to create a subset plan which an be used to gather info on things like glyph mappings in the final subset. The plan can then be passed on to perform the subsetting operation.

src/hb-subset-plan.cc

@@ -469,7 +469,7 @@ _nameid_closure (hb_face_t *face,
  * Return value: (transfer full): New subset plan. Destroy with
  * hb_subset_plan_destroy().
  *
- * Since: 1.7.5
+ * Since: REPLACEME
  **/
 hb_subset_plan_t *
 hb_subset_plan_create (hb_face_t	 *face,
@@ -542,7 +542,7 @@ hb_subset_plan_create (hb_face_t	 *face,
  * Decreases the reference count on @plan, and if it reaches zero, destroys
  * @plan, freeing all memory.
  *
- * Since: 1.7.5
+ * Since: REPLACEME
  **/
 void
 hb_subset_plan_destroy (hb_subset_plan_t *plan)
@@ -596,3 +596,48 @@ hb_subset_plan_destroy (hb_subset_plan_t *plan)
 
   hb_free (plan);
 }
+
+/**
+ * hb_subset_plan_old_to_new_glyph_mapping:
+ * @plan: a subsetting plan.
+ *
+ * Returns the mapping between glyphs in the original font to glyphs
+ * in the subset that will be produced by @plan.
+ *
+ * Since: REPLACEME
+ **/
+const hb_map_t*
+hb_subset_plan_old_to_new_glyph_mapping (const hb_subset_plan_t *plan)
+{
+  return plan->glyph_map;
+}
+
+/**
+ * hb_subset_plan_old_to_new_glyph_mapping:
+ * @plan: a subsetting plan.
+ *
+ * Returns the mapping between glyphs in the subset that will be produced by
+ * @plan and the glyph in the original font.
+ *
+ * Since: REPLACEME
+ **/
+const hb_map_t*
+hb_subset_plan_new_to_old_glyph_mapping (const hb_subset_plan_t *plan)
+{
+  return plan->reverse_glyph_map;
+}
+
+/**
+ * hb_subset_plan_old_to_new_glyph_mapping:
+ * @plan: a subsetting plan.
+ *
+ * Returns the mapping between codepoints in the original font and the
+ * associated glyph id in the original font.
+ *
+ * Since: REPLACEME
+ **/
+const hb_map_t*
+hb_subset_plan_codepoint_to_old_glyph_mapping (const hb_subset_plan_t *plan)
+{
+  return plan->codepoint_to_glyph;
+}

src/hb-subset-plan.hh

@@ -198,13 +198,4 @@ struct hb_subset_plan_t
   }
 };
 
-typedef struct hb_subset_plan_t hb_subset_plan_t;
-
-HB_INTERNAL hb_subset_plan_t *
-hb_subset_plan_create (hb_face_t           *face,
-		       const hb_subset_input_t   *input);
-
-HB_INTERNAL void
-hb_subset_plan_destroy (hb_subset_plan_t *plan);
-
 #endif /* HB_SUBSET_PLAN_HH */

src/hb-subset.cc

@@ -349,11 +349,33 @@ hb_subset_or_fail (hb_face_t *source, const hb_subset_input_t *input)
     return nullptr;
   }
 
+  hb_face_t * result = hb_subset_from_plan_or_fail (plan);
+  hb_subset_plan_destroy (plan);
+  return result;
+}
+
+
+/**
+ * hb_subset_from_plan_or_fail:
+ * @plan: a subsetting plan.
+ *
+ * Subsets a font according to provided plan. Returns nullptr
+ * if the subset operation fails.
+ *
+ * Since: REPLACEME
+ **/
+hb_face_t *
+hb_subset_from_plan_or_fail (hb_subset_plan_t *plan)
+{
+  if (unlikely (plan->in_error ())) {
+    return nullptr;
+  }
+
   hb_set_t tags_set;
   bool success = true;
   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))
+  while ((hb_face_get_table_tags (plan->source, offset, &num_tables, table_tags), num_tables))
   {
     for (unsigned i = 0; i < num_tables; ++i)
     {
@@ -367,8 +389,5 @@ hb_subset_or_fail (hb_face_t *source, const hb_subset_input_t *input)
   }
 end:
 
-  hb_face_t *result = success ? hb_face_reference (plan->dest) : nullptr;
-
-  hb_subset_plan_destroy (plan);
-  return result;
+  return success ? hb_face_reference (plan->dest) : nullptr;
 }

src/hb-subset.h

@@ -39,6 +39,15 @@ HB_BEGIN_DECLS
 
 typedef struct hb_subset_input_t hb_subset_input_t;
 
+/**
+ * hb_subset_plan_t:
+ *
+ * Contains information about how the subset operation will be executed.
+ * Such as mappings from the old glyph ids to the new ones in the subset.
+ */
+
+typedef struct hb_subset_plan_t hb_subset_plan_t;
+
 /**
  * hb_subset_flags_t:
  * @HB_SUBSET_FLAGS_DEFAULT: all flags at their default value of false.
@@ -145,6 +154,25 @@ hb_subset_input_set_flags (hb_subset_input_t *input,
 HB_EXTERN hb_face_t *
 hb_subset_or_fail (hb_face_t *source, const hb_subset_input_t *input);
 
+HB_EXTERN hb_face_t *
+hb_subset_from_plan_or_fail (hb_subset_plan_t *plan);
+
+HB_EXTERN hb_subset_plan_t *
+hb_subset_plan_create (hb_face_t           *face,
+		       const hb_subset_input_t   *input);
+
+HB_EXTERN void
+hb_subset_plan_destroy (hb_subset_plan_t *plan);
+
+HB_EXTERN const hb_map_t*
+hb_subset_plan_old_to_new_glyph_mapping (const hb_subset_plan_t *plan);
+
+HB_EXTERN const hb_map_t*
+hb_subset_plan_new_to_old_glyph_mapping (const hb_subset_plan_t *plan);
+
+HB_EXTERN const hb_map_t*
+hb_subset_plan_codepoint_to_old_glyph_mapping (const hb_subset_plan_t *plan);
+
 HB_END_DECLS
 
 #endif /* HB_SUBSET_H */

test/api/test-subset.c

@@ -155,6 +155,43 @@ test_subset_sets (void)
   hb_subset_input_destroy (input);
 }
 
+static void
+test_subset_plan (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_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_subset_plan_t* plan = hb_subset_plan_create (face_abc, input);
+
+  const hb_map_t* mapping = hb_subset_plan_old_to_new_glyph_mapping (plan);
+  g_assert (hb_map_get (mapping, 1) == 1);
+  g_assert (hb_map_get (mapping, 3) == 2);
+
+  mapping = hb_subset_plan_new_to_old_glyph_mapping (plan);
+  g_assert (hb_map_get (mapping, 1) == 1);
+  g_assert (hb_map_get (mapping, 2) == 3);
+
+  mapping = hb_subset_plan_codepoint_to_old_glyph_mapping (plan);
+  g_assert (hb_map_get (mapping, 0x63) == 3);
+
+  hb_face_t* face_abc_subset = hb_subset_from_plan_or_fail (plan);
+
+  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_input_destroy (input);
+  hb_subset_plan_destroy (plan);
+  hb_face_destroy (face_abc_subset);
+  hb_face_destroy (face_abc);
+  hb_face_destroy (face_ac);
+}
+
 int
 main (int argc, char **argv)
 {
@@ -165,6 +202,7 @@ main (int argc, char **argv)
   hb_test_add (test_subset_crash);
   hb_test_add (test_subset_set_flags);
   hb_test_add (test_subset_sets);
+  hb_test_add (test_subset_plan);
 
   return hb_test_run();
 }