[subset] add a subset accelerator.

Can be optionally attached to the face during subsetting. Contains data which can accelerate future subsets.

src/hb-subset-accelerator.hh

@@ -0,0 +1,75 @@
+/*
+ * Copyright © 2022  Google, Inc.
+ *
+ *  This is part of HarfBuzz, a text shaping library.
+ *
+ * Permission is hereby granted, without written agreement and without
+ * license or royalty fees, to use, copy, modify, and distribute this
+ * software and its documentation for any purpose, provided that the
+ * above copyright notice and the following two paragraphs appear in
+ * all copies of this software.
+ *
+ * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
+ * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
+ * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
+ * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ *
+ * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
+ * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
+ * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
+ * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+ *
+ * Google Author(s): Garret Rieger
+ */
+
+#ifndef HB_SUBSET_ACCELERATOR_HH
+#define HB_SUBSET_ACCELERATOR_HH
+
+
+#include "hb.hh"
+
+#include "hb-map.hh"
+#include "hb-set.hh"
+
+struct hb_subset_accelerator_t
+{
+  static hb_user_data_key_t* user_data_key()
+  {
+    static hb_user_data_key_t key;
+    return &key;
+  }
+
+  static hb_subset_accelerator_t* create(const hb_map_t& unicode_to_gid_,
+                                         const hb_set_t& unicodes_) {
+    hb_subset_accelerator_t* accel =
+        (hb_subset_accelerator_t*) hb_malloc (sizeof(hb_subset_accelerator_t));
+    new (accel) hb_subset_accelerator_t (unicode_to_gid_, unicodes_);
+    return accel;
+  }
+
+  static void destroy(void* value) {
+    if (!value) return;
+
+    hb_subset_accelerator_t* accel = (hb_subset_accelerator_t*) value;
+    accel->~hb_subset_accelerator_t ();
+    hb_free (accel);
+  }
+
+  hb_subset_accelerator_t(const hb_map_t& unicode_to_gid_,
+                          const hb_set_t& unicodes_)
+      : unicode_to_gid(unicode_to_gid_), unicodes(unicodes_) {}
+
+  hb_map_t unicode_to_gid;
+  hb_set_t unicodes;
+  // TODO(garretrieger): cumulative glyf checksum map
+
+  bool in_error () const
+  {
+    return unicode_to_gid.in_error() || unicodes.in_error ();
+  }
+};
+
+
+#endif /* HB_SUBSET_ACCELERATOR_HH */

src/hb-subset.cc

@@ -56,6 +56,7 @@
 #include "hb-ot-math-table.hh"
 #include "hb-ot-stat-table.hh"
 #include "hb-repacker.hh"
+#include "hb-subset-accelerator.hh"
 
 using OT::Layout::GSUB;
 using OT::Layout::GPOS;
@@ -494,6 +495,27 @@ _subset_table (hb_subset_plan_t *plan,
   }
 }
 
+static void _attach_accelerator_data (const hb_subset_plan_t* plan,
+                                      hb_face_t* face /* IN/OUT */)
+{
+  hb_subset_accelerator_t* accel =
+      hb_subset_accelerator_t::create (*plan->codepoint_to_glyph,
+                                       *plan->unicodes);
+
+  if (accel->in_error ())
+  {
+    hb_subset_accelerator_t::destroy (accel);
+    return;
+  }
+
+  if (!hb_face_set_user_data(face,
+                             hb_subset_accelerator_t::user_data_key(),
+                             &accel,
+                             hb_subset_accelerator_t::destroy,
+                             true))
+    hb_subset_accelerator_t::destroy (accel);
+}
+
 /**
  * hb_subset_or_fail:
  * @source: font face data to be subset.
@@ -576,6 +598,10 @@ hb_subset_plan_execute_or_fail (hb_subset_plan_t *plan)
     offset += num_tables;
   }
 
+  if (success && plan->flags & HB_SUBSET_FLAGS_ADD_ACCELERATOR_DATA) {
+    _attach_accelerator_data (plan, plan->dest);
+  }
+
 end:
   return success ? hb_face_reference (plan->dest) : nullptr;
 }

src/meson.build

@@ -334,6 +334,7 @@ hb_subset_sources = files(
   'hb-ot-cff1-table.cc',
   'hb-ot-cff2-table.cc',
   'hb-static.cc',
+  'hb-subset-accelerator.hh',
   'hb-subset-cff-common.cc',
   'hb-subset-cff-common.hh',
   'hb-subset-cff1.cc',