hb-aat-layout-kerx-table.hh

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/*
 * Copyright © 2018  Ebrahim Byagowi
 * 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): Behdad Esfahbod
 */
 
#ifndef HB_AAT_LAYOUT_KERX_TABLE_HH
#define HB_AAT_LAYOUT_KERX_TABLE_HH
 
#include "hb-kern.hh"
#include "hb-aat-layout-ankr-table.hh"
 
/*
 * kerx -- Extended Kerning
 * https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6kerx.html
 */
#define HB_AAT_TAG_kerx HB_TAG('k','e','r','x')
 
 
namespace AAT {
 
using namespace OT;
 
 
static inline int
kerxTupleKern (int value,
           unsigned int tupleCount,
           const void *base,
           hb_aat_apply_context_t *c)
{
  if (likely (!tupleCount || !c)) return value;
 
  unsigned int offset = value;
  const FWORD *pv = &StructAtOffset<FWORD> (base, offset);
  if (unlikely (!c->sanitizer.check_array (pv, tupleCount))) return 0;
  return *pv;
}
 
 
struct hb_glyph_pair_t
{
  hb_codepoint_t left;
  hb_codepoint_t right;
};
 
struct KernPair
{
  int get_kerning () const { return value; }
 
  int cmp (const hb_glyph_pair_t &o) const
  {
    int ret = left.cmp (o.left);
    if (ret) return ret;
    return right.cmp (o.right);
  }
 
  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (c->check_struct (this));
  }
 
  protected:
  HBGlyphID16   left;
  HBGlyphID16   right;
  FWORD     value;
  public:
  DEFINE_SIZE_STATIC (6);
};
 
template <typename KernSubTableHeader>
struct KerxSubTableFormat0
{
  int get_kerning (hb_codepoint_t left, hb_codepoint_t right,
           hb_aat_apply_context_t *c = nullptr) const
  {
    hb_glyph_pair_t pair = {left, right};
    int v = pairs.bsearch (pair).get_kerning ();
    return kerxTupleKern (v, header.tuple_count (), this, c);
  }
 
  bool apply (hb_aat_apply_context_t *c) const
  {
    TRACE_APPLY (this);
 
    if (!c->plan->requested_kerning)
      return false;
 
    if (header.coverage & header.Backwards)
      return false;
 
    accelerator_t accel (*this, c);
    hb_kern_machine_t<accelerator_t> machine (accel, header.coverage & header.CrossStream);
    machine.kern (c->font, c->buffer, c->plan->kern_mask);
 
    return_trace (true);
  }
 
  struct accelerator_t
  {
    const KerxSubTableFormat0 &table;
    hb_aat_apply_context_t *c;
 
    accelerator_t (const KerxSubTableFormat0 &table_,
           hb_aat_apply_context_t *c_) :
             table (table_), c (c_) {}
 
    int get_kerning (hb_codepoint_t left, hb_codepoint_t right) const
    { return table.get_kerning (left, right, c); }
  };
 
 
  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (likely (pairs.sanitize (c)));
  }
 
  protected:
  KernSubTableHeader    header;
  BinSearchArrayOf<KernPair, typename KernSubTableHeader::Types::HBUINT>
            pairs;  /* Sorted kern records. */
  public:
  DEFINE_SIZE_ARRAY (KernSubTableHeader::static_size + 16, pairs);
};
 
 
template <bool extended>
struct Format1Entry;
 
template <>
struct Format1Entry<true>
{
  enum Flags
  {
    Push        = 0x8000,   /* If set, push this glyph on the kerning stack. */
    DontAdvance     = 0x4000,   /* If set, don't advance to the next glyph
                     * before going to the new state. */
    Reset       = 0x2000,   /* If set, reset the kerning data (clear the stack) */
    Reserved        = 0x1FFF,   /* Not used; set to 0. */
  };
 
  struct EntryData
  {
    HBUINT16    kernActionIndex;/* Index into the kerning value array. If
                 * this index is 0xFFFF, then no kerning
                 * is to be performed. */
    public:
    DEFINE_SIZE_STATIC (2);
  };
 
  static bool performAction (const Entry<EntryData> &entry)
  { return entry.data.kernActionIndex != 0xFFFF; }
 
  static unsigned int kernActionIndex (const Entry<EntryData> &entry)
  { return entry.data.kernActionIndex; }
};
template <>
struct Format1Entry<false>
{
  enum Flags
  {
    Push        = 0x8000,   /* If set, push this glyph on the kerning stack. */
    DontAdvance     = 0x4000,   /* If set, don't advance to the next glyph
                     * before going to the new state. */
    Offset      = 0x3FFF,   /* Byte offset from beginning of subtable to the
                     * value table for the glyphs on the kerning stack. */
 
    Reset       = 0x0000,   /* Not supported? */
  };
 
  typedef void EntryData;
 
  static bool performAction (const Entry<EntryData> &entry)
  { return entry.flags & Offset; }
 
  static unsigned int kernActionIndex (const Entry<EntryData> &entry)
  { return entry.flags & Offset; }
};
 
template <typename KernSubTableHeader>
struct KerxSubTableFormat1
{
  typedef typename KernSubTableHeader::Types Types;
  typedef typename Types::HBUINT HBUINT;
 
  typedef Format1Entry<Types::extended> Format1EntryT;
  typedef typename Format1EntryT::EntryData EntryData;
 
  struct driver_context_t
  {
    static constexpr bool in_place = true;
    enum
    {
      DontAdvance   = Format1EntryT::DontAdvance,
    };
 
    driver_context_t (const KerxSubTableFormat1 *table_,
              hb_aat_apply_context_t *c_) :
    c (c_),
    table (table_),
    /* Apparently the offset kernAction is from the beginning of the state-machine,
     * similar to offsets in morx table, NOT from beginning of this table, like
     * other subtables in kerx.  Discovered via testing. */
    kernAction (&table->machine + table->kernAction),
    depth (0),
    crossStream (table->header.coverage & table->header.CrossStream) {}
 
    bool is_actionable (StateTableDriver<Types, EntryData> *driver HB_UNUSED,
            const Entry<EntryData> &entry)
    { return Format1EntryT::performAction (entry); }
    void transition (StateTableDriver<Types, EntryData> *driver,
             const Entry<EntryData> &entry)
    {
      hb_buffer_t *buffer = driver->buffer;
      unsigned int flags = entry.flags;
 
      if (flags & Format1EntryT::Reset)
    depth = 0;
 
      if (flags & Format1EntryT::Push)
      {
    if (likely (depth < ARRAY_LENGTH (stack)))
      stack[depth++] = buffer->idx;
    else
      depth = 0; /* Probably not what CoreText does, but better? */
      }
 
      if (Format1EntryT::performAction (entry) && depth)
      {
    unsigned int tuple_count = hb_max (1u, table->header.tuple_count ());
 
    unsigned int kern_idx = Format1EntryT::kernActionIndex (entry);
    kern_idx = Types::byteOffsetToIndex (kern_idx, &table->machine, kernAction.arrayZ);
    const FWORD *actions = &kernAction[kern_idx];
    if (!c->sanitizer.check_array (actions, depth, tuple_count))
    {
      depth = 0;
      return;
    }
 
    hb_mask_t kern_mask = c->plan->kern_mask;
 
    /* From Apple 'kern' spec:
     * "Each pops one glyph from the kerning stack and applies the kerning value to it.
     * The end of the list is marked by an odd value... */
    bool last = false;
    while (!last && depth)
    {
      unsigned int idx = stack[--depth];
      int v = *actions;
      actions += tuple_count;
      if (idx >= buffer->len) continue;
 
      /* "The end of the list is marked by an odd value..." */
      last = v & 1;
      v &= ~1;
 
      hb_glyph_position_t &o = buffer->pos[idx];
 
      if (HB_DIRECTION_IS_HORIZONTAL (buffer->props.direction))
      {
        if (crossStream)
        {
          /* The following flag is undocumented in the spec, but described
           * in the 'kern' table example. */
          if (v == -0x8000)
          {
        o.attach_type() = ATTACH_TYPE_NONE;
        o.attach_chain() = 0;
        o.y_offset = 0;
          }
          else if (o.attach_type())
          {
        o.y_offset += c->font->em_scale_y (v);
        buffer->scratch_flags |= HB_BUFFER_SCRATCH_FLAG_HAS_GPOS_ATTACHMENT;
          }
        }
        else if (buffer->info[idx].mask & kern_mask)
        {
          o.x_advance += c->font->em_scale_x (v);
          o.x_offset += c->font->em_scale_x (v);
        }
      }
      else
      {
        if (crossStream)
        {
          /* CoreText doesn't do crossStream kerning in vertical.  We do. */
          if (v == -0x8000)
          {
        o.attach_type() = ATTACH_TYPE_NONE;
        o.attach_chain() = 0;
        o.x_offset = 0;
          }
          else if (o.attach_type())
          {
        o.x_offset += c->font->em_scale_x (v);
        buffer->scratch_flags |= HB_BUFFER_SCRATCH_FLAG_HAS_GPOS_ATTACHMENT;
          }
        }
        else if (buffer->info[idx].mask & kern_mask)
        {
          o.y_advance += c->font->em_scale_y (v);
          o.y_offset += c->font->em_scale_y (v);
        }
      }
    }
      }
    }
 
    private:
    hb_aat_apply_context_t *c;
    const KerxSubTableFormat1 *table;
    const UnsizedArrayOf<FWORD> &kernAction;
    unsigned int stack[8];
    unsigned int depth;
    bool crossStream;
  };
 
  bool apply (hb_aat_apply_context_t *c) const
  {
    TRACE_APPLY (this);
 
    if (!c->plan->requested_kerning &&
    !(header.coverage & header.CrossStream))
      return false;
 
    driver_context_t dc (this, c);
 
    StateTableDriver<Types, EntryData> driver (machine, c->buffer, c->font->face);
    driver.drive (&dc);
 
    return_trace (true);
  }
 
  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    /* The rest of array sanitizations are done at run-time. */
    return_trace (likely (c->check_struct (this) &&
              machine.sanitize (c)));
  }
 
  protected:
  KernSubTableHeader                header;
  StateTable<Types, EntryData>          machine;
  NNOffsetTo<UnsizedArrayOf<FWORD>, HBUINT> kernAction;
  public:
  DEFINE_SIZE_STATIC (KernSubTableHeader::static_size + 5 * sizeof (HBUINT));
};
 
template <typename KernSubTableHeader>
struct KerxSubTableFormat2
{
  typedef typename KernSubTableHeader::Types Types;
  typedef typename Types::HBUINT HBUINT;
 
  int get_kerning (hb_codepoint_t left, hb_codepoint_t right,
           hb_aat_apply_context_t *c) const
  {
    unsigned int num_glyphs = c->sanitizer.get_num_glyphs ();
    unsigned int l = (this+leftClassTable).get_class (left, num_glyphs, 0);
    unsigned int r = (this+rightClassTable).get_class (right, num_glyphs, 0);
 
    const UnsizedArrayOf<FWORD> &arrayZ = this+array;
    unsigned int kern_idx = l + r;
    kern_idx = Types::offsetToIndex (kern_idx, this, arrayZ.arrayZ);
    const FWORD *v = &arrayZ[kern_idx];
    if (unlikely (!v->sanitize (&c->sanitizer))) return 0;
 
    return kerxTupleKern (*v, header.tuple_count (), this, c);
  }
 
  bool apply (hb_aat_apply_context_t *c) const
  {
    TRACE_APPLY (this);
 
    if (!c->plan->requested_kerning)
      return false;
 
    if (header.coverage & header.Backwards)
      return false;
 
    accelerator_t accel (*this, c);
    hb_kern_machine_t<accelerator_t> machine (accel, header.coverage & header.CrossStream);
    machine.kern (c->font, c->buffer, c->plan->kern_mask);
 
    return_trace (true);
  }
 
  struct accelerator_t
  {
    const KerxSubTableFormat2 &table;
    hb_aat_apply_context_t *c;
 
    accelerator_t (const KerxSubTableFormat2 &table_,
           hb_aat_apply_context_t *c_) :
             table (table_), c (c_) {}
 
    int get_kerning (hb_codepoint_t left, hb_codepoint_t right) const
    { return table.get_kerning (left, right, c); }
  };
 
  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (likely (c->check_struct (this) &&
              leftClassTable.sanitize (c, this) &&
              rightClassTable.sanitize (c, this) &&
              c->check_range (this, array)));
  }
 
  protected:
  KernSubTableHeader    header;
  HBUINT        rowWidth;   /* The width, in bytes, of a row in the table. */
  NNOffsetTo<typename Types::ClassTypeWide, HBUINT>
            leftClassTable; /* Offset from beginning of this subtable to
                     * left-hand class table. */
  NNOffsetTo<typename Types::ClassTypeWide, HBUINT>
            rightClassTable;/* Offset from beginning of this subtable to
                     * right-hand class table. */
  NNOffsetTo<UnsizedArrayOf<FWORD>, HBUINT>
             array;     /* Offset from beginning of this subtable to
                     * the start of the kerning array. */
  public:
  DEFINE_SIZE_STATIC (KernSubTableHeader::static_size + 4 * sizeof (HBUINT));
};
 
template <typename KernSubTableHeader>
struct KerxSubTableFormat4
{
  typedef ExtendedTypes Types;
 
  struct EntryData
  {
    HBUINT16    ankrActionIndex;/* Either 0xFFFF (for no action) or the index of
                 * the action to perform. */
    public:
    DEFINE_SIZE_STATIC (2);
  };
 
  struct driver_context_t
  {
    static constexpr bool in_place = true;
    enum Flags
    {
      Mark      = 0x8000,   /* If set, remember this glyph as the marked glyph. */
      DontAdvance   = 0x4000,   /* If set, don't advance to the next glyph before
                     * going to the new state. */
      Reserved      = 0x3FFF,   /* Not used; set to 0. */
    };
 
    enum SubTableFlags
    {
      ActionType    = 0xC0000000,   /* A two-bit field containing the action type. */
      Unused        = 0x3F000000,   /* Unused - must be zero. */
      Offset        = 0x00FFFFFF,   /* Masks the offset in bytes from the beginning
                     * of the subtable to the beginning of the control
                     * point table. */
    };
 
    driver_context_t (const KerxSubTableFormat4 *table,
              hb_aat_apply_context_t *c_) :
    c (c_),
    action_type ((table->flags & ActionType) >> 30),
    ankrData ((HBUINT16 *) ((const char *) &table->machine + (table->flags & Offset))),
    mark_set (false),
    mark (0) {}
 
    bool is_actionable (StateTableDriver<Types, EntryData> *driver HB_UNUSED,
            const Entry<EntryData> &entry)
    { return entry.data.ankrActionIndex != 0xFFFF; }
    void transition (StateTableDriver<Types, EntryData> *driver,
             const Entry<EntryData> &entry)
    {
      hb_buffer_t *buffer = driver->buffer;
 
      if (mark_set && entry.data.ankrActionIndex != 0xFFFF && buffer->idx < buffer->len)
      {
    hb_glyph_position_t &o = buffer->cur_pos();
    switch (action_type)
    {
      case 0: /* Control Point Actions.*/
      {
        /* Indexed into glyph outline. */
        /* Each action (record in ankrData) contains two 16-bit fields, so we must
           double the ankrActionIndex to get the correct offset here. */
        const HBUINT16 *data = &ankrData[entry.data.ankrActionIndex * 2];
        if (!c->sanitizer.check_array (data, 2)) return;
        unsigned int markControlPoint = *data++;
        unsigned int currControlPoint = *data++;
        hb_position_t markX = 0;
        hb_position_t markY = 0;
        hb_position_t currX = 0;
        hb_position_t currY = 0;
        if (!c->font->get_glyph_contour_point_for_origin (c->buffer->info[mark].codepoint,
                                  markControlPoint,
                                  HB_DIRECTION_LTR /*XXX*/,
                                  &markX, &markY) ||
        !c->font->get_glyph_contour_point_for_origin (c->buffer->cur ().codepoint,
                                  currControlPoint,
                                  HB_DIRECTION_LTR /*XXX*/,
                                  &currX, &currY))
          return;
 
        o.x_offset = markX - currX;
        o.y_offset = markY - currY;
      }
      break;
 
      case 1: /* Anchor Point Actions. */
      {
        /* Indexed into 'ankr' table. */
        /* Each action (record in ankrData) contains two 16-bit fields, so we must
           double the ankrActionIndex to get the correct offset here. */
        const HBUINT16 *data = &ankrData[entry.data.ankrActionIndex * 2];
        if (!c->sanitizer.check_array (data, 2)) return;
        unsigned int markAnchorPoint = *data++;
        unsigned int currAnchorPoint = *data++;
        const Anchor &markAnchor = c->ankr_table->get_anchor (c->buffer->info[mark].codepoint,
                                  markAnchorPoint,
                                  c->sanitizer.get_num_glyphs ());
        const Anchor &currAnchor = c->ankr_table->get_anchor (c->buffer->cur ().codepoint,
                                  currAnchorPoint,
                                  c->sanitizer.get_num_glyphs ());
 
        o.x_offset = c->font->em_scale_x (markAnchor.xCoordinate) - c->font->em_scale_x (currAnchor.xCoordinate);
        o.y_offset = c->font->em_scale_y (markAnchor.yCoordinate) - c->font->em_scale_y (currAnchor.yCoordinate);
      }
      break;
 
      case 2: /* Control Point Coordinate Actions. */
      {
        /* Each action contains four 16-bit fields, so we multiply the ankrActionIndex
           by 4 to get the correct offset for the given action. */
        const FWORD *data = (const FWORD *) &ankrData[entry.data.ankrActionIndex * 4];
        if (!c->sanitizer.check_array (data, 4)) return;
        int markX = *data++;
        int markY = *data++;
        int currX = *data++;
        int currY = *data++;
 
        o.x_offset = c->font->em_scale_x (markX) - c->font->em_scale_x (currX);
        o.y_offset = c->font->em_scale_y (markY) - c->font->em_scale_y (currY);
      }
      break;
    }
    o.attach_type() = ATTACH_TYPE_MARK;
    o.attach_chain() = (int) mark - (int) buffer->idx;
    buffer->scratch_flags |= HB_BUFFER_SCRATCH_FLAG_HAS_GPOS_ATTACHMENT;
      }
 
      if (entry.flags & Mark)
      {
    mark_set = true;
    mark = buffer->idx;
      }
    }
 
    private:
    hb_aat_apply_context_t *c;
    unsigned int action_type;
    const HBUINT16 *ankrData;
    bool mark_set;
    unsigned int mark;
  };
 
  bool apply (hb_aat_apply_context_t *c) const
  {
    TRACE_APPLY (this);
 
    driver_context_t dc (this, c);
 
    StateTableDriver<Types, EntryData> driver (machine, c->buffer, c->font->face);
    driver.drive (&dc);
 
    return_trace (true);
  }
 
  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    /* The rest of array sanitizations are done at run-time. */
    return_trace (likely (c->check_struct (this) &&
              machine.sanitize (c)));
  }
 
  protected:
  KernSubTableHeader        header;
  StateTable<Types, EntryData>  machine;
  HBUINT32          flags;
  public:
  DEFINE_SIZE_STATIC (KernSubTableHeader::static_size + 20);
};
 
template <typename KernSubTableHeader>
struct KerxSubTableFormat6
{
  enum Flags
  {
    ValuesAreLong   = 0x00000001,
  };
 
  bool is_long () const { return flags & ValuesAreLong; }
 
  int get_kerning (hb_codepoint_t left, hb_codepoint_t right,
           hb_aat_apply_context_t *c) const
  {
    unsigned int num_glyphs = c->sanitizer.get_num_glyphs ();
    if (is_long ())
    {
      const typename U::Long &t = u.l;
      unsigned int l = (this+t.rowIndexTable).get_value_or_null (left, num_glyphs);
      unsigned int r = (this+t.columnIndexTable).get_value_or_null (right, num_glyphs);
      unsigned int offset = l + r;
      if (unlikely (offset < l)) return 0; /* Addition overflow. */
      if (unlikely (hb_unsigned_mul_overflows (offset, sizeof (FWORD32)))) return 0;
      const FWORD32 *v = &StructAtOffset<FWORD32> (&(this+t.array), offset * sizeof (FWORD32));
      if (unlikely (!v->sanitize (&c->sanitizer))) return 0;
      return kerxTupleKern (*v, header.tuple_count (), &(this+vector), c);
    }
    else
    {
      const typename U::Short &t = u.s;
      unsigned int l = (this+t.rowIndexTable).get_value_or_null (left, num_glyphs);
      unsigned int r = (this+t.columnIndexTable).get_value_or_null (right, num_glyphs);
      unsigned int offset = l + r;
      const FWORD *v = &StructAtOffset<FWORD> (&(this+t.array), offset * sizeof (FWORD));
      if (unlikely (!v->sanitize (&c->sanitizer))) return 0;
      return kerxTupleKern (*v, header.tuple_count (), &(this+vector), c);
    }
  }
 
  bool apply (hb_aat_apply_context_t *c) const
  {
    TRACE_APPLY (this);
 
    if (!c->plan->requested_kerning)
      return false;
 
    if (header.coverage & header.Backwards)
      return false;
 
    accelerator_t accel (*this, c);
    hb_kern_machine_t<accelerator_t> machine (accel, header.coverage & header.CrossStream);
    machine.kern (c->font, c->buffer, c->plan->kern_mask);
 
    return_trace (true);
  }
 
  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (likely (c->check_struct (this) &&
              (is_long () ?
               (
                 u.l.rowIndexTable.sanitize (c, this) &&
                 u.l.columnIndexTable.sanitize (c, this) &&
                 c->check_range (this, u.l.array)
               ) : (
                 u.s.rowIndexTable.sanitize (c, this) &&
                 u.s.columnIndexTable.sanitize (c, this) &&
                 c->check_range (this, u.s.array)
               )) &&
              (header.tuple_count () == 0 ||
               c->check_range (this, vector))));
  }
 
  struct accelerator_t
  {
    const KerxSubTableFormat6 &table;
    hb_aat_apply_context_t *c;
 
    accelerator_t (const KerxSubTableFormat6 &table_,
           hb_aat_apply_context_t *c_) :
             table (table_), c (c_) {}
 
    int get_kerning (hb_codepoint_t left, hb_codepoint_t right) const
    { return table.get_kerning (left, right, c); }
  };
 
  protected:
  KernSubTableHeader        header;
  HBUINT32          flags;
  HBUINT16          rowCount;
  HBUINT16          columnCount;
  union U
  {
    struct Long
    {
      NNOffset32To<Lookup<HBUINT32>>        rowIndexTable;
      NNOffset32To<Lookup<HBUINT32>>        columnIndexTable;
      NNOffset32To<UnsizedArrayOf<FWORD32>> array;
    } l;
    struct Short
    {
      NNOffset32To<Lookup<HBUINT16>>        rowIndexTable;
      NNOffset32To<Lookup<HBUINT16>>        columnIndexTable;
      NNOffset32To<UnsizedArrayOf<FWORD>>   array;
    } s;
  } u;
  NNOffset32To<UnsizedArrayOf<FWORD>>   vector;
  public:
  DEFINE_SIZE_STATIC (KernSubTableHeader::static_size + 24);
};
 
 
struct KerxSubTableHeader
{
  typedef ExtendedTypes Types;
 
  unsigned   tuple_count () const { return tupleCount; }
  bool     is_horizontal () const { return !(coverage & Vertical); }
 
  enum Coverage
  {
    Vertical    = 0x80000000u,  /* Set if table has vertical kerning values. */
    CrossStream = 0x40000000u,  /* Set if table has cross-stream kerning values. */
    Variation   = 0x20000000u,  /* Set if table has variation kerning values. */
    Backwards   = 0x10000000u,  /* If clear, process the glyphs forwards, that
                 * is, from first to last in the glyph stream.
                 * If we, process them from last to first.
                 * This flag only applies to state-table based
                 * 'kerx' subtables (types 1 and 4). */
    Reserved    = 0x0FFFFF00u,  /* Reserved, set to zero. */
    SubtableType= 0x000000FFu,  /* Subtable type. */
  };
 
  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (likely (c->check_struct (this)));
  }
 
  public:
  HBUINT32  length;
  HBUINT32  coverage;
  HBUINT32  tupleCount;
  public:
  DEFINE_SIZE_STATIC (12);
};
 
struct KerxSubTable
{
  friend struct kerx;
 
  unsigned int get_size () const { return u.header.length; }
  unsigned int get_type () const { return u.header.coverage & u.header.SubtableType; }
 
  template <typename context_t, typename ...Ts>
  typename context_t::return_t dispatch (context_t *c, Ts&&... ds) const
  {
    unsigned int subtable_type = get_type ();
    TRACE_DISPATCH (this, subtable_type);
    switch (subtable_type) {
    case 0: return_trace (c->dispatch (u.format0, std::forward<Ts> (ds)...));
    case 1: return_trace (c->dispatch (u.format1, std::forward<Ts> (ds)...));
    case 2: return_trace (c->dispatch (u.format2, std::forward<Ts> (ds)...));
    case 4: return_trace (c->dispatch (u.format4, std::forward<Ts> (ds)...));
    case 6: return_trace (c->dispatch (u.format6, std::forward<Ts> (ds)...));
    default:    return_trace (c->default_return_value ());
    }
  }
 
  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    if (!u.header.sanitize (c) ||
    u.header.length <= u.header.static_size ||
    !c->check_range (this, u.header.length))
      return_trace (false);
 
    return_trace (dispatch (c));
  }
 
  public:
  union {
  KerxSubTableHeader                header;
  KerxSubTableFormat0<KerxSubTableHeader>   format0;
  KerxSubTableFormat1<KerxSubTableHeader>   format1;
  KerxSubTableFormat2<KerxSubTableHeader>   format2;
  KerxSubTableFormat4<KerxSubTableHeader>   format4;
  KerxSubTableFormat6<KerxSubTableHeader>   format6;
  } u;
  public:
  DEFINE_SIZE_MIN (12);
};
 
 
/*
 * The 'kerx' Table
 */
 
template <typename T>
struct KerxTable
{
  /* https://en.wikipedia.org/wiki/Curiously_recurring_template_pattern */
  const T* thiz () const { return static_cast<const T *> (this); }
 
  bool has_state_machine () const
  {
    typedef typename T::SubTable SubTable;
 
    const SubTable *st = &thiz()->firstSubTable;
    unsigned int count = thiz()->tableCount;
    for (unsigned int i = 0; i < count; i++)
    {
      if (st->get_type () == 1)
    return true;
      st = &StructAfter<SubTable> (*st);
    }
    return false;
  }
 
  bool has_cross_stream () const
  {
    typedef typename T::SubTable SubTable;
 
    const SubTable *st = &thiz()->firstSubTable;
    unsigned int count = thiz()->tableCount;
    for (unsigned int i = 0; i < count; i++)
    {
      if (st->u.header.coverage & st->u.header.CrossStream)
    return true;
      st = &StructAfter<SubTable> (*st);
    }
    return false;
  }
 
  int get_h_kerning (hb_codepoint_t left, hb_codepoint_t right) const
  {
    typedef typename T::SubTable SubTable;
 
    int v = 0;
    const SubTable *st = &thiz()->firstSubTable;
    unsigned int count = thiz()->tableCount;
    for (unsigned int i = 0; i < count; i++)
    {
      if ((st->u.header.coverage & (st->u.header.Variation | st->u.header.CrossStream)) ||
      !st->u.header.is_horizontal ())
    continue;
      v += st->get_kerning (left, right);
      st = &StructAfter<SubTable> (*st);
    }
    return v;
  }
 
  bool apply (AAT::hb_aat_apply_context_t *c) const
  {
    typedef typename T::SubTable SubTable;
 
    bool ret = false;
    bool seenCrossStream = false;
    c->set_lookup_index (0);
    const SubTable *st = &thiz()->firstSubTable;
    unsigned int count = thiz()->tableCount;
    for (unsigned int i = 0; i < count; i++)
    {
      bool reverse;
 
      if (!T::Types::extended && (st->u.header.coverage & st->u.header.Variation))
    goto skip;
 
      if (HB_DIRECTION_IS_HORIZONTAL (c->buffer->props.direction) != st->u.header.is_horizontal ())
    goto skip;
 
      reverse = bool (st->u.header.coverage & st->u.header.Backwards) !=
        HB_DIRECTION_IS_BACKWARD (c->buffer->props.direction);
 
      if (!c->buffer->message (c->font, "start subtable %d", c->lookup_index))
    goto skip;
 
      if (!seenCrossStream &&
      (st->u.header.coverage & st->u.header.CrossStream))
      {
    /* Attach all glyphs into a chain. */
    seenCrossStream = true;
    hb_glyph_position_t *pos = c->buffer->pos;
    unsigned int count = c->buffer->len;
    for (unsigned int i = 0; i < count; i++)
    {
      pos[i].attach_type() = ATTACH_TYPE_CURSIVE;
      pos[i].attach_chain() = HB_DIRECTION_IS_FORWARD (c->buffer->props.direction) ? -1 : +1;
      /* We intentionally don't set HB_BUFFER_SCRATCH_FLAG_HAS_GPOS_ATTACHMENT,
       * since there needs to be a non-zero attachment for post-positioning to
       * be needed. */
    }
      }
 
      if (reverse)
    c->buffer->reverse ();
 
      {
    /* See comment in sanitize() for conditional here. */
    hb_sanitize_with_object_t with (&c->sanitizer, i < count - 1 ? st : (const SubTable *) nullptr);
    ret |= st->dispatch (c);
      }
 
      if (reverse)
    c->buffer->reverse ();
 
      (void) c->buffer->message (c->font, "end subtable %d", c->lookup_index);
 
    skip:
      st = &StructAfter<SubTable> (*st);
      c->set_lookup_index (c->lookup_index + 1);
    }
 
    return ret;
  }
 
  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    if (unlikely (!thiz()->version.sanitize (c) ||
          (unsigned) thiz()->version < (unsigned) T::minVersion ||
          !thiz()->tableCount.sanitize (c)))
      return_trace (false);
 
    typedef typename T::SubTable SubTable;
 
    const SubTable *st = &thiz()->firstSubTable;
    unsigned int count = thiz()->tableCount;
    for (unsigned int i = 0; i < count; i++)
    {
      if (unlikely (!st->u.header.sanitize (c)))
    return_trace (false);
      /* OpenType kern table has 2-byte subtable lengths.  That's limiting.
       * MS implementation also only supports one subtable, of format 0,
       * anyway.  Certain versions of some fonts, like Calibry, contain
       * kern subtable that exceeds 64kb.  Looks like, the subtable length
       * is simply ignored.  Which makes sense.  It's only needed if you
       * have multiple subtables.  To handle such fonts, we just ignore
       * the length for the last subtable. */
      hb_sanitize_with_object_t with (c, i < count - 1 ? st : (const SubTable *) nullptr);
 
      if (unlikely (!st->sanitize (c)))
    return_trace (false);
 
      st = &StructAfter<SubTable> (*st);
    }
 
    return_trace (true);
  }
};
 
struct kerx : KerxTable<kerx>
{
  friend struct KerxTable<kerx>;
 
  static constexpr hb_tag_t tableTag = HB_AAT_TAG_kerx;
  static constexpr unsigned minVersion = 2u;
 
  typedef KerxSubTableHeader SubTableHeader;
  typedef SubTableHeader::Types Types;
  typedef KerxSubTable SubTable;
 
  bool has_data () const { return version; }
 
  protected:
  HBUINT16  version;    /* The version number of the extended kerning table
                 * (currently 2, 3, or 4). */
  HBUINT16  unused;     /* Set to 0. */
  HBUINT32  tableCount; /* The number of subtables included in the extended kerning
                 * table. */
  SubTable  firstSubTable;  /* Subtables. */
/*subtableGlyphCoverageArray*/  /* Only if version >= 3. We don't use. */
 
  public:
  DEFINE_SIZE_MIN (8);
};
 
 
} /* namespace AAT */
 
 
#endif /* HB_AAT_LAYOUT_KERX_TABLE_HH */