src/hb-subset.cc

/*
 * Copyright © 2018  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, Rod Sheeter, Behdad Esfahbod
 */

#include "hb.hh"
#include "hb-open-type.hh"

#include "hb-subset.hh"

#include "hb-open-file.hh"
#include "hb-ot-cmap-table.hh"
#include "hb-ot-glyf-table.hh"
#include "hb-ot-hdmx-table.hh"
#include "hb-ot-head-table.hh"
#include "hb-ot-hhea-table.hh"
#include "hb-ot-hmtx-table.hh"
#include "hb-ot-maxp-table.hh"
#include "hb-ot-color-sbix-table.hh"
#include "hb-ot-color-colr-table.hh"
#include "hb-ot-color-cpal-table.hh"
#include "hb-ot-os2-table.hh"
#include "hb-ot-post-table.hh"
#include "hb-ot-post-table-v2subset.hh"
#include "hb-ot-cff1-table.hh"
#include "hb-ot-cff2-table.hh"
#include "hb-ot-vorg-table.hh"
#include "hb-ot-name-table.hh"
#include "hb-ot-color-cbdt-table.hh"
#include "hb-ot-layout-gsub-table.hh"
#include "hb-ot-layout-gpos-table.hh"
#include "hb-ot-var-gvar-table.hh"
#include "hb-ot-var-hvar-table.hh"
#include "hb-ot-math-table.hh"
#include "hb-repacker.hh"

/**
 * SECTION:hb-subset
 * @title: hb-subset
 * @short_description: Subsets font files.
 * @include: hb-subset.h
 *
 * Subsetting reduces the codepoint coverage of font files and removes all data
 * that is no longer needed. A subset input describes the desired subset. The input is
 * provided along with a font to the subsetting operation. Output is a new font file
 * containing only the data specified in the input.
 *
 * Currently most outline and bitmap tables are supported: glyf, CFF, CFF2, sbix,
 * COLR, and CBDT/CBLC. This also includes fonts with variable outlines via OpenType
 * variations. Notably EBDT/EBLC and SVG are not supported. Layout subsetting is supported
 * only for OpenType Layout tables (GSUB, GPOS, GDEF). Notably subsetting of graphite or AAT tables
 * is not yet supported.
 *
 * Fonts with graphite or AAT tables may still be subsetted but will likely need to use the
 * retain glyph ids option and configure the subset to pass through the layout tables untouched.
 */

static unsigned
_plan_estimate_subset_table_size (hb_subset_plan_t *plan, unsigned table_len)
{
  unsigned src_glyphs = plan->source->get_num_glyphs ();
  unsigned dst_glyphs = plan->glyphset ()->get_population ();

  if (unlikely (!src_glyphs))
    return 512 + table_len;

  return 512 + (unsigned) (table_len * sqrt ((double) dst_glyphs / src_glyphs));
}

/*
 * Repack the serialization buffer if any offset overflows exist.
 */
static hb_blob_t*
_repack (hb_tag_t tag, const hb_serialize_context_t& c)
{
  if (tag != HB_OT_TAG_GPOS
      &&  tag != HB_OT_TAG_GSUB)
  {
    // Check for overflow in a non-handled table.
    return c.successful () ? c.copy_blob () : nullptr;
  }

  if (!c.offset_overflow ())
    return c.copy_blob ();

  hb_vector_t<char> buf;
  int buf_size = c.end - c.start;
  if (unlikely (!buf.alloc (buf_size)))
    return nullptr;

  hb_serialize_context_t repacked ((void *) buf, buf_size);
  hb_resolve_overflows (c.object_graph (), tag, &repacked);

  if (unlikely (repacked.in_error ()))
    // TODO(garretrieger): refactor so we can share the resize/retry logic with the subset
    //                     portion.
    return nullptr;

  return repacked.copy_blob ();
}

template<typename TableType>
static
bool
_try_subset (const TableType *table,
             hb_vector_t<char>* buf,
             unsigned buf_size,
             hb_subset_context_t* c /* OUT */)
{
  c->serializer->start_serialize<TableType> ();
  if (c->serializer->in_error ()) return false;

  bool needed = table->subset (c);
  if (!c->serializer->ran_out_of_room ())
  {
    c->serializer->end_serialize ();
    return needed;
  }

  buf_size += (buf_size >> 1) + 32;
  DEBUG_MSG (SUBSET, nullptr, "OT::%c%c%c%c ran out of room; reallocating to %u bytes.",
             HB_UNTAG (c->table_tag), buf_size);

  if (unlikely (!buf->alloc (buf_size)))
  {
    DEBUG_MSG (SUBSET, nullptr, "OT::%c%c%c%c failed to reallocate %u bytes.",
               HB_UNTAG (c->table_tag), buf_size);
    return needed;
  }

  c->serializer->reset (buf->arrayZ, buf_size);
  return _try_subset (table, buf, buf_size, c);
}

template<typename TableType>
static bool
_subset (hb_subset_plan_t *plan)
{
  hb_blob_t *source_blob = hb_sanitize_context_t ().reference_table<TableType> (plan->source);
  const TableType *table = source_blob->as<TableType> ();

  hb_tag_t tag = TableType::tableTag;
  if (!source_blob->data)
  {
    DEBUG_MSG (SUBSET, nullptr,
               "OT::%c%c%c%c::subset sanitize failed on source table.", HB_UNTAG (tag));
    hb_blob_destroy (source_blob);
    return false;
  }

  hb_vector_t<char> buf;
  /* TODO Not all tables are glyph-related.  'name' table size for example should not be
   * affected by number of glyphs.  Accommodate that. */
  unsigned buf_size = _plan_estimate_subset_table_size (plan, source_blob->length);
  DEBUG_MSG (SUBSET, nullptr,
             "OT::%c%c%c%c initial estimated table size: %u bytes.", HB_UNTAG (tag), buf_size);
  if (unlikely (!buf.alloc (buf_size)))
  {
    DEBUG_MSG (SUBSET, nullptr, "OT::%c%c%c%c failed to allocate %u bytes.", HB_UNTAG (tag), buf_size);
    hb_blob_destroy (source_blob);
    return false;
  }

  bool needed = false;
  hb_serialize_context_t serializer (buf.arrayZ, buf_size);
  {
    hb_subset_context_t c (source_blob, plan, &serializer, tag);
    needed = _try_subset (table, &buf, buf_size, &c);
  }
  hb_blob_destroy (source_blob);

  if (serializer.in_error () && !serializer.only_offset_overflow ())
  {
    DEBUG_MSG (SUBSET, nullptr, "OT::%c%c%c%c::subset FAILED!", HB_UNTAG (tag));
    return false;
  }

  if (!needed)
  {
    DEBUG_MSG (SUBSET, nullptr, "OT::%c%c%c%c::subset table subsetted to empty.", HB_UNTAG (tag));
    return true;
  }

  bool result = false;
  hb_blob_t *dest_blob = _repack (tag, serializer);
  if (dest_blob)
  {
    DEBUG_MSG (SUBSET, nullptr,
               "OT::%c%c%c%c final subset table size: %u bytes.",
               HB_UNTAG (tag), dest_blob->length);
    result = plan->add_table (tag, dest_blob);
    hb_blob_destroy (dest_blob);
  }

  DEBUG_MSG (SUBSET, nullptr, "OT::%c%c%c%c::subset %s",
             HB_UNTAG (tag), result ? "success" : "FAILED!");
  return result;
}

static bool
_is_table_present (hb_face_t *source, hb_tag_t 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))
  {
    for (unsigned i = 0; i < num_tables; ++i)
      if (table_tags[i] == tag)
	return true;
    offset += num_tables;
  }
  return false;
}

static bool
_should_drop_table (hb_subset_plan_t *plan, hb_tag_t tag)
{
  if (plan->drop_tables->has (tag))
    return true;

  switch (tag)
  {
  case HB_TAG ('c','v','a','r'): /* hint table, fallthrough */
  case HB_TAG ('c','v','t',' '): /* hint table, fallthrough */
  case HB_TAG ('f','p','g','m'): /* hint table, fallthrough */
  case HB_TAG ('p','r','e','p'): /* hint table, fallthrough */
  case HB_TAG ('h','d','m','x'): /* hint table, fallthrough */
  case HB_TAG ('V','D','M','X'): /* hint table, fallthrough */
    return plan->flags & HB_SUBSET_FLAGS_NO_HINTING;

#ifdef HB_NO_SUBSET_LAYOUT
    // Drop Layout Tables if requested.
  case HB_OT_TAG_GDEF:
  case HB_OT_TAG_GPOS:
  case HB_OT_TAG_GSUB:
  case HB_TAG ('m','o','r','x'):
  case HB_TAG ('m','o','r','t'):
  case HB_TAG ('k','e','r','x'):
  case HB_TAG ('k','e','r','n'):
    return true;
#endif

  default:
    return false;
  }
}

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)
  {
  case HB_OT_TAG_glyf: return _subset<const OT::glyf> (plan);
  case HB_OT_TAG_hdmx: return _subset<const OT::hdmx> (plan);
  case HB_OT_TAG_name: return _subset<const OT::name> (plan);
  case HB_OT_TAG_head:
    if (_is_table_present (plan->source, HB_OT_TAG_glyf) && !_should_drop_table (plan, HB_OT_TAG_glyf))
      return true; /* skip head, handled by glyf */
    return _subset<const OT::head> (plan);
  case HB_OT_TAG_hhea: return true; /* skip hhea, handled by hmtx */
  case HB_OT_TAG_hmtx: return _subset<const OT::hmtx> (plan);
  case HB_OT_TAG_vhea: return true; /* skip vhea, handled by vmtx */
  case HB_OT_TAG_vmtx: return _subset<const OT::vmtx> (plan);
  case HB_OT_TAG_maxp: return _subset<const OT::maxp> (plan);
  case HB_OT_TAG_sbix: return _subset<const OT::sbix> (plan);
  case HB_OT_TAG_loca: return true; /* skip loca, handled by glyf */
  case HB_OT_TAG_cmap: return _subset<const OT::cmap> (plan);
  case HB_OT_TAG_OS2 : return _subset<const OT::OS2 > (plan);
  case HB_OT_TAG_post: return _subset<const OT::post> (plan);
  case HB_OT_TAG_COLR: return _subset<const OT::COLR> (plan);
  case HB_OT_TAG_CPAL: return _subset<const OT::CPAL> (plan);
  case HB_OT_TAG_CBLC: return _subset<const OT::CBLC> (plan);
  case HB_OT_TAG_CBDT: return true; /* skip CBDT, handled by CBLC */
  case HB_OT_TAG_MATH: return _subset<const OT::MATH> (plan);

#ifndef HB_NO_SUBSET_CFF
  case HB_OT_TAG_cff1: return _subset<const OT::cff1> (plan);
  case HB_OT_TAG_cff2: return _subset<const OT::cff2> (plan);
  case HB_OT_TAG_VORG: return _subset<const OT::VORG> (plan);
#endif

#ifndef HB_NO_SUBSET_LAYOUT
  case HB_OT_TAG_GDEF: return _subset<const OT::GDEF> (plan);
  case HB_OT_TAG_GSUB: return _subset<const OT::GSUB> (plan);
  case HB_OT_TAG_GPOS: return _subset<const OT::GPOS> (plan);
  case HB_OT_TAG_gvar: return _subset<const OT::gvar> (plan);
  case HB_OT_TAG_HVAR: return _subset<const OT::HVAR> (plan);
  case HB_OT_TAG_VVAR: return _subset<const OT::VVAR> (plan);
#endif

  default:
    if (plan->flags & HB_SUBSET_FLAGS_PASSTHROUGH_UNRECOGNIZED)
      return _passthrough (plan, tag);

    // Drop table
    return true;
  }
}

/**
 * hb_subset_or_fail:
 * @source: font face data to be subset.
 * @input: input to use for the subsetting.
 *
 * Subsets a font according to provided input. Returns nullptr
 * if the subset operation fails.
 *
 * Since: 2.9.0
 **/
hb_face_t *
hb_subset_or_fail (hb_face_t *source, const hb_subset_input_t *input)
{
  if (unlikely (!input || !source)) return hb_face_get_empty ();

  hb_subset_plan_t *plan = hb_subset_plan_create (source, input);
  if (unlikely (plan->in_error ())) {
    hb_subset_plan_destroy (plan);
    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))
  {
    for (unsigned i = 0; i < num_tables; ++i)
    {
      hb_tag_t tag = table_tags[i];
      if (_should_drop_table (plan, tag) && !tags_set.has (tag)) continue;
      tags_set.add (tag);
      success = _subset_table (plan, tag);
      if (unlikely (!success)) goto end;
    }
    offset += num_tables;
  }
end:

  hb_face_t *result = success ? hb_face_reference (plan->dest) : nullptr;

  hb_subset_plan_destroy (plan);
  return result;
}