path: root/gfx/ots/src/gsub.cc

// Copyright (c) 2011-2017 The OTS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "gsub.h"

#include <limits>
#include <vector>

#include "layout.h"
#include "maxp.h"

// GSUB - The Glyph Substitution Table
// http://www.microsoft.com/typography/otspec/gsub.htm

#define TABLE_NAME "GSUB"

namespace {

enum GSUB_TYPE {
  GSUB_TYPE_SINGLE = 1,
  GSUB_TYPE_MULTIPLE = 2,
  GSUB_TYPE_ALTERNATE = 3,
  GSUB_TYPE_LIGATURE = 4,
  GSUB_TYPE_CONTEXT = 5,
  GSUB_TYPE_CHANGING_CONTEXT = 6,
  GSUB_TYPE_EXTENSION_SUBSTITUTION = 7,
  GSUB_TYPE_REVERSE_CHAINING_CONTEXT_SINGLE = 8,
  GSUB_TYPE_RESERVED = 9
};

bool ParseSequenceTable(const ots::Font *font,
                        const uint8_t *data, const size_t length,
                        const uint16_t num_glyphs) {
  ots::Buffer subtable(data, length);

  uint16_t glyph_count = 0;
  if (!subtable.ReadU16(&glyph_count)) {
    return OTS_FAILURE_MSG("Failed to read glyph count in sequence table");
  }
  if (glyph_count > num_glyphs) {
    return OTS_FAILURE_MSG("bad glyph count %d > %d", glyph_count, num_glyphs);
  }
  for (unsigned i = 0; i < glyph_count; ++i) {
    uint16_t substitute = 0;
    if (!subtable.ReadU16(&substitute)) {
      return OTS_FAILURE_MSG("Failed to read substitution %d in sequence table", i);
    }
    if (substitute >= num_glyphs) {
      return OTS_FAILURE_MSG("Bad substitution (%d) %d > %d", i, substitute, num_glyphs);
    }
  }

  return true;
}

bool ParseAlternateSetTable(const ots::Font *font,
                            const uint8_t *data, const size_t length,
                            const uint16_t num_glyphs) {
  ots::Buffer subtable(data, length);

  uint16_t glyph_count = 0;
  if (!subtable.ReadU16(&glyph_count)) {
    return OTS_FAILURE_MSG("Failed to read alternate set header");
  }
  if (glyph_count > num_glyphs) {
    return OTS_FAILURE_MSG("Bad glyph count %d > %d in alternate set table", glyph_count, num_glyphs);
  }
  for (unsigned i = 0; i < glyph_count; ++i) {
    uint16_t alternate = 0;
    if (!subtable.ReadU16(&alternate)) {
      return OTS_FAILURE_MSG("Can't read alternate %d", i);
    }
    if (alternate >= num_glyphs) {
      return OTS_FAILURE_MSG("Too large alternate: %u", alternate);
    }
  }
  return true;
}

bool ParseLigatureTable(const ots::Font *font,
                        const uint8_t *data, const size_t length,
                        const uint16_t num_glyphs) {
  ots::Buffer subtable(data, length);

  uint16_t lig_glyph = 0;
  uint16_t comp_count = 0;

  if (!subtable.ReadU16(&lig_glyph) ||
      !subtable.ReadU16(&comp_count)) {
    return OTS_FAILURE_MSG("Failed to read ligature table header");
  }

  if (lig_glyph >= num_glyphs) {
    return OTS_FAILURE_MSG("too large lig_glyph: %u", lig_glyph);
  }
  if (comp_count == 0) {
    return OTS_FAILURE_MSG("Component count cannot be 0");
  }
  for (unsigned i = 0; i < comp_count - static_cast<unsigned>(1); ++i) {
    uint16_t component = 0;
    if (!subtable.ReadU16(&component)) {
      return OTS_FAILURE_MSG("Can't read ligature component %d", i);
    }
    if (component >= num_glyphs) {
      return OTS_FAILURE_MSG("Bad ligature component %d of %d", i, component);
    }
  }

  return true;
}

bool ParseLigatureSetTable(const ots::Font *font,
                           const uint8_t *data, const size_t length,
                           const uint16_t num_glyphs) {
  ots::Buffer subtable(data, length);

  uint16_t ligature_count = 0;

  if (!subtable.ReadU16(&ligature_count)) {
    return OTS_FAILURE_MSG("Can't read ligature count in ligature set");
  }

  const unsigned ligature_end = static_cast<unsigned>(2) + ligature_count * 2;
  if (ligature_end > std::numeric_limits<uint16_t>::max()) {
    return OTS_FAILURE_MSG("Bad end of ligature %d in ligature set", ligature_end);
  }
  for (unsigned i = 0; i < ligature_count; ++i) {
    uint16_t offset_ligature = 0;
    if (!subtable.ReadU16(&offset_ligature)) {
      return OTS_FAILURE_MSG("Failed to read ligature offset %d", i);
    }
    if (offset_ligature < ligature_end || offset_ligature >= length) {
      return OTS_FAILURE_MSG("Bad ligature offset %d for ligature %d", offset_ligature, i);
    }
    if (!ParseLigatureTable(font, data + offset_ligature, length - offset_ligature,
                            num_glyphs)) {
      return OTS_FAILURE_MSG("Failed to parse ligature %d", i);
    }
  }

  return true;
}

}  // namespace

namespace ots {

// Lookup Type 1:
// Single Substitution Subtable
bool OpenTypeGSUB::ParseSingleSubstitution(const uint8_t *data,
                                           const size_t length) {
  Font* font = GetFont();
  Buffer subtable(data, length);

  uint16_t format = 0;
  uint16_t offset_coverage = 0;

  if (!subtable.ReadU16(&format) ||
      !subtable.ReadU16(&offset_coverage)) {
    return Error("Failed to read single subst table header");
  }

  OpenTypeMAXP *maxp = static_cast<OpenTypeMAXP*>(
      font->GetTypedTable(OTS_TAG_MAXP));
  if (!maxp) {
    return Error("Required maxp table missing");
  }
  const uint16_t num_glyphs = maxp->num_glyphs;
  if (format == 1) {
    // Parse SingleSubstFormat1
    int16_t delta_glyph_id = 0;
    if (!subtable.ReadS16(&delta_glyph_id)) {
      return Error("Failed to read glyph shift from format 1 single subst table");
    }
    if (std::abs(delta_glyph_id) >= num_glyphs) {
      return Error("bad glyph shift of %d in format 1 single subst table", delta_glyph_id);
    }
  } else if (format == 2) {
    // Parse SingleSubstFormat2
    uint16_t glyph_count = 0;
    if (!subtable.ReadU16(&glyph_count)) {
      return Error("Failed to read glyph cound in format 2 single subst table");
    }
    if (glyph_count > num_glyphs) {
      return Error("Bad glyph count %d > %d in format 2 single subst table", glyph_count, num_glyphs);
    }
    for (unsigned i = 0; i < glyph_count; ++i) {
      uint16_t substitute = 0;
      if (!subtable.ReadU16(&substitute)) {
        return Error("Failed to read substitution %d in format 2 single subst table", i);
      }
      if (substitute >= num_glyphs) {
        return Error("too large substitute: %u", substitute);
      }
    }
  } else {
    return Error("Bad single subst table format %d", format);
  }

  if (offset_coverage < subtable.offset() || offset_coverage >= length) {
    return Error("Bad coverage offset %x", offset_coverage);
  }
  if (!ots::ParseCoverageTable(font, data + offset_coverage,
                               length - offset_coverage, num_glyphs)) {
    return Error("Failed to parse coverage table");
  }

  return true;
}

// Lookup Type 2:
// Multiple Substitution Subtable
bool OpenTypeGSUB::ParseMutipleSubstitution(const uint8_t *data,
                                            const size_t length) {
  Font* font = GetFont();
  Buffer subtable(data, length);

  uint16_t format = 0;
  uint16_t offset_coverage = 0;
  uint16_t sequence_count = 0;

  if (!subtable.ReadU16(&format) ||
      !subtable.ReadU16(&offset_coverage) ||
      !subtable.ReadU16(&sequence_count)) {
    return Error("Can't read header of multiple subst table");
  }

  if (format != 1) {
    return Error("Bad multiple subst table format %d", format);
  }

  OpenTypeMAXP *maxp = static_cast<OpenTypeMAXP*>(
      font->GetTypedTable(OTS_TAG_MAXP));
  if (!maxp) {
    return Error("Required maxp table missing");
  }
  const uint16_t num_glyphs = maxp->num_glyphs;
  const unsigned sequence_end = static_cast<unsigned>(6) +
      sequence_count * 2;
  if (sequence_end > std::numeric_limits<uint16_t>::max()) {
    return Error("Bad sequence end %d, in multiple subst", sequence_end);
  }
  for (unsigned i = 0; i < sequence_count; ++i) {
    uint16_t offset_sequence = 0;
    if (!subtable.ReadU16(&offset_sequence)) {
      return Error("Failed to read sequence offset for sequence %d", i);
    }
    if (offset_sequence < sequence_end || offset_sequence >= length) {
      return Error("Bad sequence offset %d for sequence %d", offset_sequence, i);
    }
    if (!ParseSequenceTable(font, data + offset_sequence, length - offset_sequence,
                            num_glyphs)) {
      return Error("Failed to parse sequence table %d", i);
    }
  }

  if (offset_coverage < sequence_end || offset_coverage >= length) {
    return Error("Bad coverage offset %d", offset_coverage);
  }
  if (!ots::ParseCoverageTable(font, data + offset_coverage,
                               length - offset_coverage, num_glyphs)) {
    return Error("Failed to parse coverage table");
  }

  return true;
}

// Lookup Type 3:
// Alternate Substitution Subtable
bool OpenTypeGSUB::ParseAlternateSubstitution(const uint8_t *data,
                                              const size_t length) {
  Font* font = GetFont();
  Buffer subtable(data, length);

  uint16_t format = 0;
  uint16_t offset_coverage = 0;
  uint16_t alternate_set_count = 0;

  if (!subtable.ReadU16(&format) ||
      !subtable.ReadU16(&offset_coverage) ||
      !subtable.ReadU16(&alternate_set_count)) {
    return Error("Can't read alternate subst header");
  }

  if (format != 1) {
    return Error("Bad alternate subst table format %d", format);
  }

  OpenTypeMAXP *maxp = static_cast<OpenTypeMAXP*>(
      font->GetTypedTable(OTS_TAG_MAXP));
  if (!maxp) {
    return Error("Required maxp table missing");
  }
  const uint16_t num_glyphs = maxp->num_glyphs;
  const unsigned alternate_set_end = static_cast<unsigned>(6) +
      alternate_set_count * 2;
  if (alternate_set_end > std::numeric_limits<uint16_t>::max()) {
    return Error("Bad end of alternate set %d", alternate_set_end);
  }
  for (unsigned i = 0; i < alternate_set_count; ++i) {
    uint16_t offset_alternate_set = 0;
    if (!subtable.ReadU16(&offset_alternate_set)) {
      return Error("Can't read alternate set offset for set %d", i);
    }
    if (offset_alternate_set < alternate_set_end ||
        offset_alternate_set >= length) {
      return Error("Bad alternate set offset %d for set %d", offset_alternate_set, i);
    }
    if (!ParseAlternateSetTable(font, data + offset_alternate_set,
                                length - offset_alternate_set,
                                num_glyphs)) {
      return Error("Failed to parse alternate set");
    }
  }

  if (offset_coverage < alternate_set_end || offset_coverage >= length) {
    return Error("Bad coverage offset %d", offset_coverage);
  }
  if (!ots::ParseCoverageTable(font, data + offset_coverage,
                               length - offset_coverage, num_glyphs)) {
    return Error("Failed to parse coverage table");
  }

  return true;
}

// Lookup Type 4:
// Ligature Substitution Subtable
bool OpenTypeGSUB::ParseLigatureSubstitution(const uint8_t *data,
                                             const size_t length) {
  Font* font = GetFont();
  Buffer subtable(data, length);

  uint16_t format = 0;
  uint16_t offset_coverage = 0;
  uint16_t lig_set_count = 0;

  if (!subtable.ReadU16(&format) ||
      !subtable.ReadU16(&offset_coverage) ||
      !subtable.ReadU16(&lig_set_count)) {
    return Error("Failed to read ligature substitution header");
  }

  if (format != 1) {
    return Error("Bad ligature substitution table format %d", format);
  }

  OpenTypeMAXP *maxp = static_cast<OpenTypeMAXP*>(
      font->GetTypedTable(OTS_TAG_MAXP));
  if (!maxp) {
    return Error("Required maxp table missing");
  }
  const uint16_t num_glyphs = maxp->num_glyphs;
  const unsigned ligature_set_end = static_cast<unsigned>(6) +
      lig_set_count * 2;
  if (ligature_set_end > std::numeric_limits<uint16_t>::max()) {
    return Error("Bad end of ligature set %d in ligature substitution table", ligature_set_end);
  }
  for (unsigned i = 0; i < lig_set_count; ++i) {
    uint16_t offset_ligature_set = 0;
    if (!subtable.ReadU16(&offset_ligature_set)) {
      return Error("Can't read ligature set offset %d", i);
    }
    if (offset_ligature_set < ligature_set_end ||
        offset_ligature_set >= length) {
      return Error("Bad ligature set offset %d for set %d", offset_ligature_set, i);
    }
    if (!ParseLigatureSetTable(font, data + offset_ligature_set,
                               length - offset_ligature_set, num_glyphs)) {
      return Error("Failed to parse ligature set %d", i);
    }
  }

  if (offset_coverage < ligature_set_end || offset_coverage >= length) {
    return Error("Bad coverage offset %d", offset_coverage);
  }
  if (!ots::ParseCoverageTable(font, data + offset_coverage,
                               length - offset_coverage, num_glyphs)) {
    return Error("Failed to parse coverage table");
  }

  return true;
}

// Lookup Type 5:
// Contextual Substitution Subtable
// OpenTypeLayoutTable::ParseContextSubtable()

// Lookup Type 6:
// Chaining Contextual Substitution Subtable
// OpenTypeLayoutTable::ParseChainingContextSubtable

// Lookup Type 7:
// Extension Substition
// OpenTypeLayoutTable::ParseExtensionSubtable

// Lookup Type 8:
// Reverse Chaining Contexual Single Substitution Subtable
bool OpenTypeGSUB::ParseReverseChainingContextSingleSubstitution(const uint8_t *data,
                                                                 const size_t length) {
  Font* font = GetFont();
  Buffer subtable(data, length);

  uint16_t format = 0;
  uint16_t offset_coverage = 0;

  if (!subtable.ReadU16(&format) ||
      !subtable.ReadU16(&offset_coverage)) {
    return Error("Failed to read reverse chaining header");
  }

  OpenTypeMAXP *maxp = static_cast<OpenTypeMAXP*>(
      font->GetTypedTable(OTS_TAG_MAXP));
  if (!maxp) {
    return Error("Required maxp table missing");
  }
  const uint16_t num_glyphs = maxp->num_glyphs;

  uint16_t backtrack_glyph_count = 0;
  if (!subtable.ReadU16(&backtrack_glyph_count)) {
    return Error("Failed to read backtrack glyph count in reverse chaining table");
  }
  std::vector<uint16_t> offsets_backtrack;
  offsets_backtrack.reserve(backtrack_glyph_count);
  for (unsigned i = 0; i < backtrack_glyph_count; ++i) {
    uint16_t offset = 0;
    if (!subtable.ReadU16(&offset)) {
      return Error("Failed to read backtrack offset %d", i);
    }
    offsets_backtrack.push_back(offset);
  }

  uint16_t lookahead_glyph_count = 0;
  if (!subtable.ReadU16(&lookahead_glyph_count)) {
    return Error("Failed to read look ahead glyph count");
  }
  std::vector<uint16_t> offsets_lookahead;
  offsets_lookahead.reserve(lookahead_glyph_count);
  for (unsigned i = 0; i < lookahead_glyph_count; ++i) {
    uint16_t offset = 0;
    if (!subtable.ReadU16(&offset)) {
      return Error("Can't read look ahead offset %d", i);
    }
    offsets_lookahead.push_back(offset);
  }

  uint16_t glyph_count = 0;
  if (!subtable.ReadU16(&glyph_count)) {
    return Error("Can't read glyph count in reverse chaining table");
  }
  for (unsigned i = 0; i < glyph_count; ++i) {
    uint16_t substitute = 0;
    if (!subtable.ReadU16(&substitute)) {
      return Error("Failed to read substitution %d reverse chaining table", i);
    }
    if (substitute >= num_glyphs) {
      return Error("Bad substitute glyph %d in reverse chaining table substitution %d", substitute, i);
    }
  }

  const unsigned substitute_end = static_cast<unsigned>(10) +
      (backtrack_glyph_count + lookahead_glyph_count + glyph_count) * 2;
  if (substitute_end > std::numeric_limits<uint16_t>::max()) {
    return Error("Bad substitute end offset in reverse chaining table");
  }

  if (offset_coverage < substitute_end || offset_coverage >= length) {
    return Error("Bad coverage offset %d in reverse chaining table", offset_coverage);
  }
  if (!ots::ParseCoverageTable(font, data + offset_coverage,
                               length - offset_coverage, num_glyphs)) {
    return Error("Failed to parse coverage table in reverse chaining table");
  }

  for (unsigned i = 0; i < backtrack_glyph_count; ++i) {
    if (offsets_backtrack[i] < substitute_end ||
        offsets_backtrack[i] >= length) {
      return Error("Bad backtrack offset %d for backtrack %d in reverse chaining table", offsets_backtrack[i], i);
    }
    if (!ots::ParseCoverageTable(font, data + offsets_backtrack[i],
                                 length - offsets_backtrack[i], num_glyphs)) {
      return Error("Failed to parse coverage table for backtrack %d in reverse chaining table", i);
    }
  }

  for (unsigned i = 0; i < lookahead_glyph_count; ++i) {
    if (offsets_lookahead[i] < substitute_end ||
        offsets_lookahead[i] >= length) {
      return Error("Bad lookahead offset %d for lookahead %d in reverse chaining table", offsets_lookahead[i], i);
    }
    if (!ots::ParseCoverageTable(font, data + offsets_lookahead[i],
                                 length - offsets_lookahead[i], num_glyphs)) {
      return Error("Failed to parse lookahead coverage table %d in reverse chaining table", i);
    }
  }

  return true;
}

bool OpenTypeGSUB::ValidLookupSubtableType(const uint16_t lookup_type,
                                           bool extension) const {
  if (extension && lookup_type == GSUB_TYPE_EXTENSION_SUBSTITUTION)
    return false;
  return lookup_type >= GSUB_TYPE_SINGLE && lookup_type < GSUB_TYPE_RESERVED;
}

bool OpenTypeGSUB::ParseLookupSubtable(const uint8_t *data, const size_t length,
                                       const uint16_t lookup_type) {
  switch (lookup_type) {
    case GSUB_TYPE_SINGLE:
      return ParseSingleSubstitution(data, length);
    case GSUB_TYPE_MULTIPLE:
      return ParseMutipleSubstitution(data, length);
    case GSUB_TYPE_ALTERNATE:
      return ParseAlternateSubstitution(data, length);
    case GSUB_TYPE_LIGATURE:
      return ParseLigatureSubstitution(data, length);
    case GSUB_TYPE_CONTEXT:
      return ParseContextSubtable(data, length);
    case GSUB_TYPE_CHANGING_CONTEXT:
      return ParseChainingContextSubtable(data, length);
    case GSUB_TYPE_EXTENSION_SUBSTITUTION:
      return ParseExtensionSubtable(data, length);
    case GSUB_TYPE_REVERSE_CHAINING_CONTEXT_SINGLE:
      return ParseReverseChainingContextSingleSubstitution(data, length);
  }
  return false;
}

}  // namespace ots

#undef TABLE_NAME