xref: /dports/mail/thunderbird/thunderbird-91.8.0/gfx/harfbuzz/src/hb-ot-layout-gpos-table.hh

/*
 * Copyright © 2007,2008,2009,2010  Red Hat, Inc.
 * Copyright © 2010,2012,2013  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.
 *
 * Red Hat Author(s): Behdad Esfahbod
 * Google Author(s): Behdad Esfahbod
 */

#ifndef HB_OT_LAYOUT_GPOS_TABLE_HH
#define HB_OT_LAYOUT_GPOS_TABLE_HH

#include "hb-ot-layout-gsubgpos.hh"


namespace OT {

struct MarkArray;
static void Markclass_closure_and_remap_indexes (const Coverage  &mark_coverage,
						 const MarkArray &mark_array,
						 const hb_set_t  &glyphset,
						 hb_map_t*        klass_mapping /* INOUT */);

/* buffer **position** var allocations */
#define attach_chain() var.i16[0] /* glyph to which this attaches to, relative to current glyphs; negative for going back, positive for forward. */
#define attach_type() var.u8[2] /* attachment type */
/* Note! if attach_chain() is zero, the value of attach_type() is irrelevant. */

enum attach_type_t {
  ATTACH_TYPE_NONE	= 0X00,

  /* Each attachment should be either a mark or a cursive; can't be both. */
  ATTACH_TYPE_MARK	= 0X01,
  ATTACH_TYPE_CURSIVE	= 0X02,
};


/* Shared Tables: ValueRecord, Anchor Table, and MarkArray */

typedef HBUINT16 Value;

typedef UnsizedArrayOf<Value> ValueRecord;

struct ValueFormat : HBUINT16
{
  enum Flags {
    xPlacement	= 0x0001u,	/* Includes horizontal adjustment for placement */
    yPlacement	= 0x0002u,	/* Includes vertical adjustment for placement */
    xAdvance	= 0x0004u,	/* Includes horizontal adjustment for advance */
    yAdvance	= 0x0008u,	/* Includes vertical adjustment for advance */
    xPlaDevice	= 0x0010u,	/* Includes horizontal Device table for placement */
    yPlaDevice	= 0x0020u,	/* Includes vertical Device table for placement */
    xAdvDevice	= 0x0040u,	/* Includes horizontal Device table for advance */
    yAdvDevice	= 0x0080u,	/* Includes vertical Device table for advance */
    ignored	= 0x0F00u,	/* Was used in TrueType Open for MM fonts */
    reserved	= 0xF000u,	/* For future use */

    devices	= 0x00F0u	/* Mask for having any Device table */
  };

/* All fields are options.  Only those available advance the value pointer. */
#if 0
  HBINT16		xPlacement;	/* Horizontal adjustment for
					 * placement--in design units */
  HBINT16		yPlacement;	/* Vertical adjustment for
					 * placement--in design units */
  HBINT16		xAdvance;	/* Horizontal adjustment for
					 * advance--in design units (only used
					 * for horizontal writing) */
  HBINT16		yAdvance;	/* Vertical adjustment for advance--in
					 * design units (only used for vertical
					 * writing) */
  Offset16To<Device>	xPlaDevice;	/* Offset to Device table for
					 * horizontal placement--measured from
					 * beginning of PosTable (may be NULL) */
  Offset16To<Device>	yPlaDevice;	/* Offset to Device table for vertical
					 * placement--measured from beginning
					 * of PosTable (may be NULL) */
  Offset16To<Device>	xAdvDevice;	/* Offset to Device table for
					 * horizontal advance--measured from
					 * beginning of PosTable (may be NULL) */
  Offset16To<Device>	yAdvDevice;	/* Offset to Device table for vertical
					 * advance--measured from beginning of
					 * PosTable (may be NULL) */
#endif

  IntType& operator = (uint16_t i) { v = i; return *this; }

  unsigned int get_len () const  { return hb_popcount ((unsigned int) *this); }
  unsigned int get_size () const { return get_len () * Value::static_size; }

  bool apply_value (hb_ot_apply_context_t *c,
		    const void            *base,
		    const Value           *values,
		    hb_glyph_position_t   &glyph_pos) const
  {
    bool ret = false;
    unsigned int format = *this;
    if (!format) return ret;

    hb_font_t *font = c->font;
    bool horizontal = HB_DIRECTION_IS_HORIZONTAL (c->direction);

    if (format & xPlacement) glyph_pos.x_offset  += font->em_scale_x (get_short (values++, &ret));
    if (format & yPlacement) glyph_pos.y_offset  += font->em_scale_y (get_short (values++, &ret));
    if (format & xAdvance) {
      if (likely (horizontal)) glyph_pos.x_advance += font->em_scale_x (get_short (values, &ret));
      values++;
    }
    /* y_advance values grow downward but font-space grows upward, hence negation */
    if (format & yAdvance) {
      if (unlikely (!horizontal)) glyph_pos.y_advance -= font->em_scale_y (get_short (values, &ret));
      values++;
    }

    if (!has_device ()) return ret;

    bool use_x_device = font->x_ppem || font->num_coords;
    bool use_y_device = font->y_ppem || font->num_coords;

    if (!use_x_device && !use_y_device) return ret;

    const VariationStore &store = c->var_store;

    /* pixel -> fractional pixel */
    if (format & xPlaDevice) {
      if (use_x_device) glyph_pos.x_offset  += (base + get_device (values, &ret)).get_x_delta (font, store);
      values++;
    }
    if (format & yPlaDevice) {
      if (use_y_device) glyph_pos.y_offset  += (base + get_device (values, &ret)).get_y_delta (font, store);
      values++;
    }
    if (format & xAdvDevice) {
      if (horizontal && use_x_device) glyph_pos.x_advance += (base + get_device (values, &ret)).get_x_delta (font, store);
      values++;
    }
    if (format & yAdvDevice) {
      /* y_advance values grow downward but font-space grows upward, hence negation */
      if (!horizontal && use_y_device) glyph_pos.y_advance -= (base + get_device (values, &ret)).get_y_delta (font, store);
      values++;
    }
    return ret;
  }

  unsigned int get_effective_format (const Value *values) const
  {
    unsigned int format = *this;
    for (unsigned flag = xPlacement; flag <= yAdvDevice; flag = flag << 1) {
      if (format & flag) should_drop (*values++, (Flags) flag, &format);
    }

    return format;
  }

  template<typename Iterator,
      hb_requires (hb_is_iterator (Iterator))>
  unsigned int get_effective_format (Iterator it) const {
    unsigned int new_format = 0;

    for (const hb_array_t<const Value>& values : it)
      new_format = new_format | get_effective_format (&values);

    return new_format;
  }

  void copy_values (hb_serialize_context_t *c,
                    unsigned int new_format,
                    const void *base,
                    const Value *values,
                    const hb_map_t *layout_variation_idx_map) const
  {
    unsigned int format = *this;
    if (!format) return;

    if (format & xPlacement) copy_value (c, new_format, xPlacement, *values++);
    if (format & yPlacement) copy_value (c, new_format, yPlacement, *values++);
    if (format & xAdvance)   copy_value (c, new_format, xAdvance, *values++);
    if (format & yAdvance)   copy_value (c, new_format, yAdvance, *values++);

    if (format & xPlaDevice) copy_device (c, base, values++, layout_variation_idx_map);
    if (format & yPlaDevice) copy_device (c, base, values++, layout_variation_idx_map);
    if (format & xAdvDevice) copy_device (c, base, values++, layout_variation_idx_map);
    if (format & yAdvDevice) copy_device (c, base, values++, layout_variation_idx_map);
  }

  void copy_value (hb_serialize_context_t *c,
                   unsigned int new_format,
                   Flags flag,
                   Value value) const
  {
    // Filter by new format.
    if (!(new_format & flag)) return;
    c->copy (value);
  }

  void collect_variation_indices (hb_collect_variation_indices_context_t *c,
				  const void *base,
				  const hb_array_t<const Value>& values) const
  {
    unsigned format = *this;
    unsigned i = 0;
    if (format & xPlacement) i++;
    if (format & yPlacement) i++;
    if (format & xAdvance) i++;
    if (format & yAdvance) i++;
    if (format & xPlaDevice)
    {
      (base + get_device (&(values[i]))).collect_variation_indices (c->layout_variation_indices);
      i++;
    }

    if (format & ValueFormat::yPlaDevice)
    {
      (base + get_device (&(values[i]))).collect_variation_indices (c->layout_variation_indices);
      i++;
    }

    if (format & ValueFormat::xAdvDevice)
    {

      (base + get_device (&(values[i]))).collect_variation_indices (c->layout_variation_indices);
      i++;
    }

    if (format & ValueFormat::yAdvDevice)
    {

      (base + get_device (&(values[i]))).collect_variation_indices (c->layout_variation_indices);
      i++;
    }
  }

  private:
  bool sanitize_value_devices (hb_sanitize_context_t *c, const void *base, const Value *values) const
  {
    unsigned int format = *this;

    if (format & xPlacement) values++;
    if (format & yPlacement) values++;
    if (format & xAdvance)   values++;
    if (format & yAdvance)   values++;

    if ((format & xPlaDevice) && !get_device (values++).sanitize (c, base)) return false;
    if ((format & yPlaDevice) && !get_device (values++).sanitize (c, base)) return false;
    if ((format & xAdvDevice) && !get_device (values++).sanitize (c, base)) return false;
    if ((format & yAdvDevice) && !get_device (values++).sanitize (c, base)) return false;

    return true;
  }

  static inline Offset16To<Device>& get_device (Value* value)
  {
    return *static_cast<Offset16To<Device> *> (value);
  }
  static inline const Offset16To<Device>& get_device (const Value* value, bool *worked=nullptr)
  {
    if (worked) *worked |= bool (*value);
    return *static_cast<const Offset16To<Device> *> (value);
  }

  bool copy_device (hb_serialize_context_t *c, const void *base,
		    const Value *src_value, const hb_map_t *layout_variation_idx_map) const
  {
    Value	*dst_value = c->copy (*src_value);

    if (!dst_value) return false;
    if (*dst_value == 0) return true;

    *dst_value = 0;
    c->push ();
    if ((base + get_device (src_value)).copy (c, layout_variation_idx_map))
    {
      c->add_link (*dst_value, c->pop_pack ());
      return true;
    }
    else
    {
      c->pop_discard ();
      return false;
    }
  }

  static inline const HBINT16& get_short (const Value* value, bool *worked=nullptr)
  {
    if (worked) *worked |= bool (*value);
    return *reinterpret_cast<const HBINT16 *> (value);
  }

  public:

  bool has_device () const
  {
    unsigned int format = *this;
    return (format & devices) != 0;
  }

  bool sanitize_value (hb_sanitize_context_t *c, const void *base, const Value *values) const
  {
    TRACE_SANITIZE (this);
    return_trace (c->check_range (values, get_size ()) && (!has_device () || sanitize_value_devices (c, base, values)));
  }

  bool sanitize_values (hb_sanitize_context_t *c, const void *base, const Value *values, unsigned int count) const
  {
    TRACE_SANITIZE (this);
    unsigned int len = get_len ();

    if (!c->check_range (values, count, get_size ())) return_trace (false);

    if (!has_device ()) return_trace (true);

    for (unsigned int i = 0; i < count; i++) {
      if (!sanitize_value_devices (c, base, values))
	return_trace (false);
      values += len;
    }

    return_trace (true);
  }

  /* Just sanitize referenced Device tables.  Doesn't check the values themselves. */
  bool sanitize_values_stride_unsafe (hb_sanitize_context_t *c, const void *base, const Value *values, unsigned int count, unsigned int stride) const
  {
    TRACE_SANITIZE (this);

    if (!has_device ()) return_trace (true);

    for (unsigned int i = 0; i < count; i++) {
      if (!sanitize_value_devices (c, base, values))
	return_trace (false);
      values += stride;
    }

    return_trace (true);
  }

 private:

  void should_drop (Value value, Flags flag, unsigned int* format) const
  {
    if (value) return;
    *format = *format & ~flag;
  }

};

template<typename Iterator, typename SrcLookup>
static void SinglePos_serialize (hb_serialize_context_t *c,
				 const SrcLookup *src,
				 Iterator it,
				 const hb_map_t *layout_variation_idx_map);


struct AnchorFormat1
{
  void get_anchor (hb_ot_apply_context_t *c, hb_codepoint_t glyph_id HB_UNUSED,
		   float *x, float *y) const
  {
    hb_font_t *font = c->font;
    *x = font->em_fscale_x (xCoordinate);
    *y = font->em_fscale_y (yCoordinate);
  }

  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (c->check_struct (this));
  }

  AnchorFormat1* copy (hb_serialize_context_t *c) const
  {
    TRACE_SERIALIZE (this);
    AnchorFormat1* out = c->embed<AnchorFormat1> (this);
    if (!out) return_trace (out);
    out->format = 1;
    return_trace (out);
  }

  protected:
  HBUINT16	format;			/* Format identifier--format = 1 */
  FWORD		xCoordinate;		/* Horizontal value--in design units */
  FWORD		yCoordinate;		/* Vertical value--in design units */
  public:
  DEFINE_SIZE_STATIC (6);
};

struct AnchorFormat2
{
  void get_anchor (hb_ot_apply_context_t *c, hb_codepoint_t glyph_id,
		   float *x, float *y) const
  {
    hb_font_t *font = c->font;

#ifdef HB_NO_HINTING
    *x = font->em_fscale_x (xCoordinate);
    *y = font->em_fscale_y (yCoordinate);
    return;
#endif

    unsigned int x_ppem = font->x_ppem;
    unsigned int y_ppem = font->y_ppem;
    hb_position_t cx = 0, cy = 0;
    bool ret;

    ret = (x_ppem || y_ppem) &&
	  font->get_glyph_contour_point_for_origin (glyph_id, anchorPoint, HB_DIRECTION_LTR, &cx, &cy);
    *x = ret && x_ppem ? cx : font->em_fscale_x (xCoordinate);
    *y = ret && y_ppem ? cy : font->em_fscale_y (yCoordinate);
  }

  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (c->check_struct (this));
  }

  AnchorFormat2* copy (hb_serialize_context_t *c) const
  {
    TRACE_SERIALIZE (this);
    return_trace (c->embed<AnchorFormat2> (this));
  }

  protected:
  HBUINT16	format;			/* Format identifier--format = 2 */
  FWORD		xCoordinate;		/* Horizontal value--in design units */
  FWORD		yCoordinate;		/* Vertical value--in design units */
  HBUINT16	anchorPoint;		/* Index to glyph contour point */
  public:
  DEFINE_SIZE_STATIC (8);
};

struct AnchorFormat3
{
  void get_anchor (hb_ot_apply_context_t *c, hb_codepoint_t glyph_id HB_UNUSED,
		   float *x, float *y) const
  {
    hb_font_t *font = c->font;
    *x = font->em_fscale_x (xCoordinate);
    *y = font->em_fscale_y (yCoordinate);

    if (font->x_ppem || font->num_coords)
      *x += (this+xDeviceTable).get_x_delta (font, c->var_store);
    if (font->y_ppem || font->num_coords)
      *y += (this+yDeviceTable).get_y_delta (font, c->var_store);
  }

  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (c->check_struct (this) && xDeviceTable.sanitize (c, this) && yDeviceTable.sanitize (c, this));
  }

  AnchorFormat3* copy (hb_serialize_context_t *c,
		       const hb_map_t *layout_variation_idx_map) const
  {
    TRACE_SERIALIZE (this);
    if (!layout_variation_idx_map) return_trace (nullptr);

    auto *out = c->embed<AnchorFormat3> (this);
    if (unlikely (!out)) return_trace (nullptr);

    out->xDeviceTable.serialize_copy (c, xDeviceTable, this, 0, hb_serialize_context_t::Head, layout_variation_idx_map);
    out->yDeviceTable.serialize_copy (c, yDeviceTable, this, 0, hb_serialize_context_t::Head, layout_variation_idx_map);
    return_trace (out);
  }

  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const
  {
    (this+xDeviceTable).collect_variation_indices (c->layout_variation_indices);
    (this+yDeviceTable).collect_variation_indices (c->layout_variation_indices);
  }

  protected:
  HBUINT16	format;			/* Format identifier--format = 3 */
  FWORD		xCoordinate;		/* Horizontal value--in design units */
  FWORD		yCoordinate;		/* Vertical value--in design units */
  Offset16To<Device>
		xDeviceTable;		/* Offset to Device table for X
					 * coordinate-- from beginning of
					 * Anchor table (may be NULL) */
  Offset16To<Device>
		yDeviceTable;		/* Offset to Device table for Y
					 * coordinate-- from beginning of
					 * Anchor table (may be NULL) */
  public:
  DEFINE_SIZE_STATIC (10);
};

struct Anchor
{
  void get_anchor (hb_ot_apply_context_t *c, hb_codepoint_t glyph_id,
		   float *x, float *y) const
  {
    *x = *y = 0;
    switch (u.format) {
    case 1: u.format1.get_anchor (c, glyph_id, x, y); return;
    case 2: u.format2.get_anchor (c, glyph_id, x, y); return;
    case 3: u.format3.get_anchor (c, glyph_id, x, y); return;
    default:					      return;
    }
  }

  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    if (!u.format.sanitize (c)) return_trace (false);
    switch (u.format) {
    case 1: return_trace (u.format1.sanitize (c));
    case 2: return_trace (u.format2.sanitize (c));
    case 3: return_trace (u.format3.sanitize (c));
    default:return_trace (true);
    }
  }

  bool subset (hb_subset_context_t *c) const
  {
    TRACE_SUBSET (this);
    switch (u.format) {
    case 1: return_trace (bool (reinterpret_cast<Anchor *> (u.format1.copy (c->serializer))));
    case 2:
      if (c->plan->drop_hints)
      {
        // AnchorFormat 2 just containins extra hinting information, so
        // if hints are being dropped convert to format 1.
        return_trace (bool (reinterpret_cast<Anchor *> (u.format1.copy (c->serializer))));
      }
      return_trace (bool (reinterpret_cast<Anchor *> (u.format2.copy (c->serializer))));
    case 3: return_trace (bool (reinterpret_cast<Anchor *> (u.format3.copy (c->serializer,
                                                                            c->plan->layout_variation_idx_map))));
    default:return_trace (false);
    }
  }

  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const
  {
    switch (u.format) {
    case 1: case 2:
      return;
    case 3:
      u.format3.collect_variation_indices (c);
      return;
    default: return;
    }
  }

  protected:
  union {
  HBUINT16		format;		/* Format identifier */
  AnchorFormat1		format1;
  AnchorFormat2		format2;
  AnchorFormat3		format3;
  } u;
  public:
  DEFINE_SIZE_UNION (2, format);
};


struct AnchorMatrix
{
  const Anchor& get_anchor (unsigned int row, unsigned int col,
			    unsigned int cols, bool *found) const
  {
    *found = false;
    if (unlikely (row >= rows || col >= cols)) return Null (Anchor);
    *found = !matrixZ[row * cols + col].is_null ();
    return this+matrixZ[row * cols + col];
  }

  template <typename Iterator,
	    hb_requires (hb_is_iterator (Iterator))>
  void collect_variation_indices (hb_collect_variation_indices_context_t *c,
				  Iterator index_iter) const
  {
    for (unsigned i : index_iter)
      (this+matrixZ[i]).collect_variation_indices (c);
  }

  template <typename Iterator,
      hb_requires (hb_is_iterator (Iterator))>
  bool subset (hb_subset_context_t *c,
               unsigned             num_rows,
               Iterator             index_iter) const
  {
    TRACE_SUBSET (this);

    auto *out = c->serializer->start_embed (this);

    if (!index_iter) return_trace (false);
    if (unlikely (!c->serializer->extend_min (out)))  return_trace (false);

    out->rows = num_rows;
    for (const unsigned i : index_iter)
    {
      auto *offset = c->serializer->embed (matrixZ[i]);
      if (!offset) return_trace (false);
      offset->serialize_subset (c, matrixZ[i], this);
    }

    return_trace (true);
  }

  bool sanitize (hb_sanitize_context_t *c, unsigned int cols) const
  {
    TRACE_SANITIZE (this);
    if (!c->check_struct (this)) return_trace (false);
    if (unlikely (hb_unsigned_mul_overflows (rows, cols))) return_trace (false);
    unsigned int count = rows * cols;
    if (!c->check_array (matrixZ.arrayZ, count)) return_trace (false);
    for (unsigned int i = 0; i < count; i++)
      if (!matrixZ[i].sanitize (c, this)) return_trace (false);
    return_trace (true);
  }

  HBUINT16	rows;			/* Number of rows */
  UnsizedArrayOf<Offset16To<Anchor>>
		matrixZ;		/* Matrix of offsets to Anchor tables--
					 * from beginning of AnchorMatrix table */
  public:
  DEFINE_SIZE_ARRAY (2, matrixZ);
};


struct MarkRecord
{
  friend struct MarkArray;

  unsigned get_class () const { return (unsigned) klass; }
  bool sanitize (hb_sanitize_context_t *c, const void *base) const
  {
    TRACE_SANITIZE (this);
    return_trace (c->check_struct (this) && markAnchor.sanitize (c, base));
  }

  MarkRecord *subset (hb_subset_context_t    *c,
                      const void             *src_base,
                      const hb_map_t         *klass_mapping) const
  {
    TRACE_SUBSET (this);
    auto *out = c->serializer->embed (this);
    if (unlikely (!out)) return_trace (nullptr);

    out->klass = klass_mapping->get (klass);
    out->markAnchor.serialize_subset (c, markAnchor, src_base);
    return_trace (out);
  }

  void collect_variation_indices (hb_collect_variation_indices_context_t *c,
				  const void *src_base) const
  {
    (src_base+markAnchor).collect_variation_indices (c);
  }

  protected:
  HBUINT16	klass;			/* Class defined for this mark */
  Offset16To<Anchor>
		markAnchor;		/* Offset to Anchor table--from
					 * beginning of MarkArray table */
  public:
  DEFINE_SIZE_STATIC (4);
};

struct MarkArray : Array16Of<MarkRecord>	/* Array of MarkRecords--in Coverage order */
{
  bool apply (hb_ot_apply_context_t *c,
	      unsigned int mark_index, unsigned int glyph_index,
	      const AnchorMatrix &anchors, unsigned int class_count,
	      unsigned int glyph_pos) const
  {
    TRACE_APPLY (this);
    hb_buffer_t *buffer = c->buffer;
    const MarkRecord &record = Array16Of<MarkRecord>::operator[](mark_index);
    unsigned int mark_class = record.klass;

    const Anchor& mark_anchor = this + record.markAnchor;
    bool found;
    const Anchor& glyph_anchor = anchors.get_anchor (glyph_index, mark_class, class_count, &found);
    /* If this subtable doesn't have an anchor for this base and this class,
     * return false such that the subsequent subtables have a chance at it. */
    if (unlikely (!found)) return_trace (false);

    float mark_x, mark_y, base_x, base_y;

    buffer->unsafe_to_break (glyph_pos, buffer->idx);
    mark_anchor.get_anchor (c, buffer->cur().codepoint, &mark_x, &mark_y);
    glyph_anchor.get_anchor (c, buffer->info[glyph_pos].codepoint, &base_x, &base_y);

    hb_glyph_position_t &o = buffer->cur_pos();
    o.x_offset = roundf (base_x - mark_x);
    o.y_offset = roundf (base_y - mark_y);
    o.attach_type() = ATTACH_TYPE_MARK;
    o.attach_chain() = (int) glyph_pos - (int) buffer->idx;
    buffer->scratch_flags |= HB_BUFFER_SCRATCH_FLAG_HAS_GPOS_ATTACHMENT;

    buffer->idx++;
    return_trace (true);
  }

  template <typename Iterator,
      hb_requires (hb_is_iterator (Iterator))>
  bool subset (hb_subset_context_t *c,
               Iterator		    coverage,
               const hb_map_t      *klass_mapping) const
  {
    TRACE_SUBSET (this);
    const hb_set_t &glyphset = *c->plan->glyphset_gsub ();

    auto* out = c->serializer->start_embed (this);
    if (unlikely (!c->serializer->extend_min (out))) return_trace (false);

    auto mark_iter =
    + hb_zip (coverage, this->iter ())
    | hb_filter (glyphset, hb_first)
    | hb_map (hb_second)
    ;

    unsigned new_length = 0;
    for (const auto& mark_record : mark_iter) {
      if (unlikely (!mark_record.subset (c, this, klass_mapping)))
        return_trace (false);
      new_length++;
    }

    if (unlikely (!c->serializer->check_assign (out->len, new_length,
                                                HB_SERIALIZE_ERROR_ARRAY_OVERFLOW)))
      return_trace (false);

    return_trace (true);
  }

  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (Array16Of<MarkRecord>::sanitize (c, this));
  }
};


/* Lookups */

struct SinglePosFormat1
{
  bool intersects (const hb_set_t *glyphs) const
  { return (this+coverage).intersects (glyphs); }

  void closure_lookups (hb_closure_lookups_context_t *c) const {}
  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const
  {
    if (!valueFormat.has_device ()) return;

    auto it =
    + hb_iter (this+coverage)
    | hb_filter (c->glyph_set)
    ;

    if (!it) return;
    valueFormat.collect_variation_indices (c, this, values.as_array (valueFormat.get_len ()));
  }

  void collect_glyphs (hb_collect_glyphs_context_t *c) const
  { if (unlikely (!(this+coverage).collect_coverage (c->input))) return; }

  const Coverage &get_coverage () const { return this+coverage; }

  ValueFormat get_value_format () const { return valueFormat; }

  bool apply (hb_ot_apply_context_t *c) const
  {
    TRACE_APPLY (this);
    hb_buffer_t *buffer = c->buffer;
    unsigned int index = (this+coverage).get_coverage  (buffer->cur().codepoint);
    if (likely (index == NOT_COVERED)) return_trace (false);

    valueFormat.apply_value (c, this, values, buffer->cur_pos());

    buffer->idx++;
    return_trace (true);
  }

  template<typename Iterator,
      typename SrcLookup,
      hb_requires (hb_is_iterator (Iterator))>
  void serialize (hb_serialize_context_t *c,
		  const SrcLookup *src,
		  Iterator it,
		  ValueFormat newFormat,
		  const hb_map_t *layout_variation_idx_map)
  {
    if (unlikely (!c->extend_min (*this))) return;
    if (unlikely (!c->check_assign (valueFormat,
                                    newFormat,
                                    HB_SERIALIZE_ERROR_INT_OVERFLOW))) return;

    for (const hb_array_t<const Value>& _ : + it | hb_map (hb_second))
    {
      src->get_value_format ().copy_values (c, newFormat, src,  &_, layout_variation_idx_map);
      // Only serialize the first entry in the iterator, the rest are assumed to
      // be the same.
      break;
    }

    auto glyphs =
    + it
    | hb_map_retains_sorting (hb_first)
    ;

    // TODO(garretrieger): serialize_subset this.
    coverage.serialize (c, this).serialize (c, glyphs);
  }

  bool subset (hb_subset_context_t *c) const
  {
    TRACE_SUBSET (this);
    const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
    const hb_map_t &glyph_map = *c->plan->glyph_map;

    auto it =
    + hb_iter (this+coverage)
    | hb_filter (glyphset)
    | hb_map_retains_sorting (glyph_map)
    | hb_zip (hb_repeat (values.as_array (valueFormat.get_len ())))
    ;

    bool ret = bool (it);
    SinglePos_serialize (c->serializer, this, it, c->plan->layout_variation_idx_map);
    return_trace (ret);
  }

  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (c->check_struct (this) &&
		  coverage.sanitize (c, this) &&
		  valueFormat.sanitize_value (c, this, values));
  }

  protected:
  HBUINT16	format;			/* Format identifier--format = 1 */
  Offset16To<Coverage>
		coverage;		/* Offset to Coverage table--from
					 * beginning of subtable */
  ValueFormat	valueFormat;		/* Defines the types of data in the
					 * ValueRecord */
  ValueRecord	values;			/* Defines positioning
					 * value(s)--applied to all glyphs in
					 * the Coverage table */
  public:
  DEFINE_SIZE_ARRAY (6, values);
};

struct SinglePosFormat2
{
  bool intersects (const hb_set_t *glyphs) const
  { return (this+coverage).intersects (glyphs); }

  void closure_lookups (hb_closure_lookups_context_t *c) const {}
  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const
  {
    if (!valueFormat.has_device ()) return;

    auto it =
    + hb_zip (this+coverage, hb_range ((unsigned) valueCount))
    | hb_filter (c->glyph_set, hb_first)
    ;

    if (!it) return;

    unsigned sub_length = valueFormat.get_len ();
    const hb_array_t<const Value> values_array = values.as_array (valueCount * sub_length);

    for (unsigned i : + it
		      | hb_map (hb_second))
      valueFormat.collect_variation_indices (c, this, values_array.sub_array (i * sub_length, sub_length));

  }

  void collect_glyphs (hb_collect_glyphs_context_t *c) const
  { if (unlikely (!(this+coverage).collect_coverage (c->input))) return; }

  const Coverage &get_coverage () const { return this+coverage; }

  ValueFormat get_value_format () const { return valueFormat; }

  bool apply (hb_ot_apply_context_t *c) const
  {
    TRACE_APPLY (this);
    hb_buffer_t *buffer = c->buffer;
    unsigned int index = (this+coverage).get_coverage  (buffer->cur().codepoint);
    if (likely (index == NOT_COVERED)) return_trace (false);

    if (likely (index >= valueCount)) return_trace (false);

    valueFormat.apply_value (c, this,
			     &values[index * valueFormat.get_len ()],
			     buffer->cur_pos());

    buffer->idx++;
    return_trace (true);
  }

  template<typename Iterator,
      typename SrcLookup,
      hb_requires (hb_is_iterator (Iterator))>
  void serialize (hb_serialize_context_t *c,
		  const SrcLookup *src,
		  Iterator it,
		  ValueFormat newFormat,
		  const hb_map_t *layout_variation_idx_map)
  {
    auto out = c->extend_min (*this);
    if (unlikely (!out)) return;
    if (unlikely (!c->check_assign (valueFormat, newFormat, HB_SERIALIZE_ERROR_INT_OVERFLOW))) return;
    if (unlikely (!c->check_assign (valueCount, it.len (), HB_SERIALIZE_ERROR_ARRAY_OVERFLOW))) return;

    + it
    | hb_map (hb_second)
    | hb_apply ([&] (hb_array_t<const Value> _)
    { src->get_value_format ().copy_values (c, newFormat, src, &_, layout_variation_idx_map); })
    ;

    auto glyphs =
    + it
    | hb_map_retains_sorting (hb_first)
    ;

    coverage.serialize (c, this).serialize (c, glyphs);
  }

  bool subset (hb_subset_context_t *c) const
  {
    TRACE_SUBSET (this);
    const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
    const hb_map_t &glyph_map = *c->plan->glyph_map;

    unsigned sub_length = valueFormat.get_len ();
    auto values_array = values.as_array (valueCount * sub_length);

    auto it =
    + hb_zip (this+coverage, hb_range ((unsigned) valueCount))
    | hb_filter (glyphset, hb_first)
    | hb_map_retains_sorting ([&] (const hb_pair_t<hb_codepoint_t, unsigned>& _)
			      {
				return hb_pair (glyph_map[_.first],
						values_array.sub_array (_.second * sub_length,
									sub_length));
			      })
    ;

    bool ret = bool (it);
    SinglePos_serialize (c->serializer, this, it, c->plan->layout_variation_idx_map);
    return_trace (ret);
  }

  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (c->check_struct (this) &&
		  coverage.sanitize (c, this) &&
		  valueFormat.sanitize_values (c, this, values, valueCount));
  }

  protected:
  HBUINT16	format;			/* Format identifier--format = 2 */
  Offset16To<Coverage>
		coverage;		/* Offset to Coverage table--from
					 * beginning of subtable */
  ValueFormat	valueFormat;		/* Defines the types of data in the
					 * ValueRecord */
  HBUINT16	valueCount;		/* Number of ValueRecords */
  ValueRecord	values;			/* Array of ValueRecords--positioning
					 * values applied to glyphs */
  public:
  DEFINE_SIZE_ARRAY (8, values);
};

struct SinglePos
{
  template<typename Iterator,
	   hb_requires (hb_is_iterator (Iterator))>
  unsigned get_format (Iterator glyph_val_iter_pairs)
  {
    hb_array_t<const Value> first_val_iter = hb_second (*glyph_val_iter_pairs);

    for (const auto iter : glyph_val_iter_pairs)
      for (const auto _ : hb_zip (iter.second, first_val_iter))
	if (_.first != _.second)
	  return 2;

    return 1;
  }


  template<typename Iterator,
      typename SrcLookup,
      hb_requires (hb_is_iterator (Iterator))>
  void serialize (hb_serialize_context_t *c,
		  const SrcLookup* src,
		  Iterator glyph_val_iter_pairs,
		  const hb_map_t *layout_variation_idx_map)
  {
    if (unlikely (!c->extend_min (u.format))) return;
    unsigned format = 2;
    ValueFormat new_format = src->get_value_format ();

    if (glyph_val_iter_pairs)
    {
      format = get_format (glyph_val_iter_pairs);
      new_format = src->get_value_format ().get_effective_format (+ glyph_val_iter_pairs | hb_map (hb_second));
    }

    u.format = format;
    switch (u.format) {
    case 1: u.format1.serialize (c,
                                 src,
                                 glyph_val_iter_pairs,
                                 new_format,
                                 layout_variation_idx_map);
      return;
    case 2: u.format2.serialize (c,
                                 src,
                                 glyph_val_iter_pairs,
                                 new_format,
                                 layout_variation_idx_map);
      return;
    default:return;
    }
  }

  template <typename context_t, typename ...Ts>
  typename context_t::return_t dispatch (context_t *c, Ts&&... ds) const
  {
    TRACE_DISPATCH (this, u.format);
    if (unlikely (!c->may_dispatch (this, &u.format))) return_trace (c->no_dispatch_return_value ());
    switch (u.format) {
    case 1: return_trace (c->dispatch (u.format1, hb_forward<Ts> (ds)...));
    case 2: return_trace (c->dispatch (u.format2, hb_forward<Ts> (ds)...));
    default:return_trace (c->default_return_value ());
    }
  }

  protected:
  union {
  HBUINT16		format;		/* Format identifier */
  SinglePosFormat1	format1;
  SinglePosFormat2	format2;
  } u;
};

template<typename Iterator, typename SrcLookup>
static void
SinglePos_serialize (hb_serialize_context_t *c,
		     const SrcLookup *src,
		     Iterator it,
		     const hb_map_t *layout_variation_idx_map)
{ c->start_embed<SinglePos> ()->serialize (c, src, it, layout_variation_idx_map); }


struct PairValueRecord
{
  friend struct PairSet;

  int cmp (hb_codepoint_t k) const
  { return secondGlyph.cmp (k); }

  struct context_t
  {
    const void 		*base;
    const ValueFormat	*valueFormats;
    const ValueFormat	*newFormats;
    unsigned		len1; /* valueFormats[0].get_len() */
    const hb_map_t 	*glyph_map;
    const hb_map_t      *layout_variation_idx_map;
  };

  bool subset (hb_subset_context_t *c,
               context_t *closure) const
  {
    TRACE_SERIALIZE (this);
    auto *s = c->serializer;
    auto *out = s->start_embed (*this);
    if (unlikely (!s->extend_min (out))) return_trace (false);

    out->secondGlyph = (*closure->glyph_map)[secondGlyph];

    closure->valueFormats[0].copy_values (s,
                                          closure->newFormats[0],
                                          closure->base, &values[0],
                                          closure->layout_variation_idx_map);
    closure->valueFormats[1].copy_values (s,
                                          closure->newFormats[1],
                                          closure->base,
                                          &values[closure->len1],
                                          closure->layout_variation_idx_map);

    return_trace (true);
  }

  void collect_variation_indices (hb_collect_variation_indices_context_t *c,
				  const ValueFormat *valueFormats,
				  const void *base) const
  {
    unsigned record1_len = valueFormats[0].get_len ();
    unsigned record2_len = valueFormats[1].get_len ();
    const hb_array_t<const Value> values_array = values.as_array (record1_len + record2_len);

    if (valueFormats[0].has_device ())
      valueFormats[0].collect_variation_indices (c, base, values_array.sub_array (0, record1_len));

    if (valueFormats[1].has_device ())
      valueFormats[1].collect_variation_indices (c, base, values_array.sub_array (record1_len, record2_len));
  }

  bool intersects (const hb_set_t& glyphset) const
  {
    return glyphset.has(secondGlyph);
  }

  const Value* get_values_1 () const
  {
    return &values[0];
  }

  const Value* get_values_2 (ValueFormat format1) const
  {
    return &values[format1.get_len ()];
  }

  protected:
  HBGlyphID	secondGlyph;		/* GlyphID of second glyph in the
					 * pair--first glyph is listed in the
					 * Coverage table */
  ValueRecord	values;			/* Positioning data for the first glyph
					 * followed by for second glyph */
  public:
  DEFINE_SIZE_ARRAY (2, values);
};

struct PairSet
{
  friend struct PairPosFormat1;

  bool intersects (const hb_set_t *glyphs,
		   const ValueFormat *valueFormats) const
  {
    unsigned int len1 = valueFormats[0].get_len ();
    unsigned int len2 = valueFormats[1].get_len ();
    unsigned int record_size = HBUINT16::static_size * (1 + len1 + len2);

    const PairValueRecord *record = &firstPairValueRecord;
    unsigned int count = len;
    for (unsigned int i = 0; i < count; i++)
    {
      if (glyphs->has (record->secondGlyph))
	return true;
      record = &StructAtOffset<const PairValueRecord> (record, record_size);
    }
    return false;
  }

  void collect_glyphs (hb_collect_glyphs_context_t *c,
		       const ValueFormat *valueFormats) const
  {
    unsigned int len1 = valueFormats[0].get_len ();
    unsigned int len2 = valueFormats[1].get_len ();
    unsigned int record_size = HBUINT16::static_size * (1 + len1 + len2);

    const PairValueRecord *record = &firstPairValueRecord;
    c->input->add_array (&record->secondGlyph, len, record_size);
  }

  void collect_variation_indices (hb_collect_variation_indices_context_t *c,
				  const ValueFormat *valueFormats) const
  {
    unsigned len1 = valueFormats[0].get_len ();
    unsigned len2 = valueFormats[1].get_len ();
    unsigned record_size = HBUINT16::static_size * (1 + len1 + len2);

    const PairValueRecord *record = &firstPairValueRecord;
    unsigned count = len;
    for (unsigned i = 0; i < count; i++)
    {
      if (c->glyph_set->has (record->secondGlyph))
      { record->collect_variation_indices (c, valueFormats, this); }

      record = &StructAtOffset<const PairValueRecord> (record, record_size);
    }
  }

  bool apply (hb_ot_apply_context_t *c,
	      const ValueFormat *valueFormats,
	      unsigned int pos) const
  {
    TRACE_APPLY (this);
    hb_buffer_t *buffer = c->buffer;
    unsigned int len1 = valueFormats[0].get_len ();
    unsigned int len2 = valueFormats[1].get_len ();
    unsigned int record_size = HBUINT16::static_size * (1 + len1 + len2);

    const PairValueRecord *record = hb_bsearch (buffer->info[pos].codepoint,
						&firstPairValueRecord,
						len,
						record_size);
    if (record)
    {
      /* Note the intentional use of "|" instead of short-circuit "||". */
      if (valueFormats[0].apply_value (c, this, &record->values[0], buffer->cur_pos()) |
	  valueFormats[1].apply_value (c, this, &record->values[len1], buffer->pos[pos]))
	buffer->unsafe_to_break (buffer->idx, pos + 1);
      if (len2)
	pos++;
      buffer->idx = pos;
      return_trace (true);
    }
    return_trace (false);
  }

  bool subset (hb_subset_context_t *c,
	       const ValueFormat valueFormats[2],
               const ValueFormat newFormats[2]) const
  {
    TRACE_SUBSET (this);
    auto snap = c->serializer->snapshot ();

    auto *out = c->serializer->start_embed (*this);
    if (unlikely (!c->serializer->extend_min (out))) return_trace (false);
    out->len = 0;

    const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
    const hb_map_t &glyph_map = *c->plan->glyph_map;

    unsigned len1 = valueFormats[0].get_len ();
    unsigned len2 = valueFormats[1].get_len ();
    unsigned record_size = HBUINT16::static_size + Value::static_size * (len1 + len2);

    PairValueRecord::context_t context =
    {
      this,
      valueFormats,
      newFormats,
      len1,
      &glyph_map,
      c->plan->layout_variation_idx_map
    };

    const PairValueRecord *record = &firstPairValueRecord;
    unsigned count = len, num = 0;
    for (unsigned i = 0; i < count; i++)
    {
      if (glyphset.has (record->secondGlyph)
	 && record->subset (c, &context)) num++;
      record = &StructAtOffset<const PairValueRecord> (record, record_size);
    }

    out->len = num;
    if (!num) c->serializer->revert (snap);
    return_trace (num);
  }

  struct sanitize_closure_t
  {
    const ValueFormat *valueFormats;
    unsigned int len1; /* valueFormats[0].get_len() */
    unsigned int stride; /* 1 + len1 + len2 */
  };

  bool sanitize (hb_sanitize_context_t *c, const sanitize_closure_t *closure) const
  {
    TRACE_SANITIZE (this);
    if (!(c->check_struct (this)
       && c->check_range (&firstPairValueRecord,
			  len,
			  HBUINT16::static_size,
			  closure->stride))) return_trace (false);

    unsigned int count = len;
    const PairValueRecord *record = &firstPairValueRecord;
    return_trace (closure->valueFormats[0].sanitize_values_stride_unsafe (c, this, &record->values[0], count, closure->stride) &&
		  closure->valueFormats[1].sanitize_values_stride_unsafe (c, this, &record->values[closure->len1], count, closure->stride));
  }

  protected:
  HBUINT16		len;	/* Number of PairValueRecords */
  PairValueRecord	firstPairValueRecord;
				/* Array of PairValueRecords--ordered
				 * by GlyphID of the second glyph */
  public:
  DEFINE_SIZE_MIN (2);
};

struct PairPosFormat1
{
  bool intersects (const hb_set_t *glyphs) const
  {
    return
    + hb_zip (this+coverage, pairSet)
    | hb_filter (*glyphs, hb_first)
    | hb_map (hb_second)
    | hb_map ([glyphs, this] (const Offset16To<PairSet> &_)
	      { return (this+_).intersects (glyphs, valueFormat); })
    | hb_any
    ;
  }

  void closure_lookups (hb_closure_lookups_context_t *c) const {}
  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const
  {
    if ((!valueFormat[0].has_device ()) && (!valueFormat[1].has_device ())) return;

    auto it =
    + hb_zip (this+coverage, pairSet)
    | hb_filter (c->glyph_set, hb_first)
    | hb_map (hb_second)
    ;

    if (!it) return;
    + it
    | hb_map (hb_add (this))
    | hb_apply ([&] (const PairSet& _) { _.collect_variation_indices (c, valueFormat); })
    ;
  }

  void collect_glyphs (hb_collect_glyphs_context_t *c) const
  {
    if (unlikely (!(this+coverage).collect_coverage (c->input))) return;
    unsigned int count = pairSet.len;
    for (unsigned int i = 0; i < count; i++)
      (this+pairSet[i]).collect_glyphs (c, valueFormat);
  }

  const Coverage &get_coverage () const { return this+coverage; }

  bool apply (hb_ot_apply_context_t *c) const
  {
    TRACE_APPLY (this);
    hb_buffer_t *buffer = c->buffer;
    unsigned int index = (this+coverage).get_coverage  (buffer->cur().codepoint);
    if (likely (index == NOT_COVERED)) return_trace (false);

    hb_ot_apply_context_t::skipping_iterator_t &skippy_iter = c->iter_input;
    skippy_iter.reset (buffer->idx, 1);
    if (!skippy_iter.next ()) return_trace (false);

    return_trace ((this+pairSet[index]).apply (c, valueFormat, skippy_iter.idx));
  }

  bool subset (hb_subset_context_t *c) const
  {
    TRACE_SUBSET (this);

    const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
    const hb_map_t &glyph_map = *c->plan->glyph_map;

    auto *out = c->serializer->start_embed (*this);
    if (unlikely (!c->serializer->extend_min (out))) return_trace (false);
    out->format = format;
    out->valueFormat[0] = valueFormat[0];
    out->valueFormat[1] = valueFormat[1];
    if (c->plan->drop_hints)
    {
      hb_pair_t<unsigned, unsigned> newFormats = compute_effective_value_formats (glyphset);
      out->valueFormat[0] = newFormats.first;
      out->valueFormat[1] = newFormats.second;
    }

    hb_sorted_vector_t<hb_codepoint_t> new_coverage;

    + hb_zip (this+coverage, pairSet)
    | hb_filter (glyphset, hb_first)
    | hb_filter ([this, c, out] (const Offset16To<PairSet>& _)
		 {
		   auto *o = out->pairSet.serialize_append (c->serializer);
		   if (unlikely (!o)) return false;
		   auto snap = c->serializer->snapshot ();
		   bool ret = o->serialize_subset (c, _, this, valueFormat, out->valueFormat);
		   if (!ret)
		   {
		     out->pairSet.pop ();
		     c->serializer->revert (snap);
		   }
		   return ret;
		 },
		 hb_second)
    | hb_map (hb_first)
    | hb_map (glyph_map)
    | hb_sink (new_coverage)
    ;

    out->coverage.serialize (c->serializer, out)
		 .serialize (c->serializer, new_coverage.iter ());

    return_trace (bool (new_coverage));
  }


  hb_pair_t<unsigned, unsigned> compute_effective_value_formats (const hb_set_t& glyphset) const
  {
    unsigned len1 = valueFormat[0].get_len ();
    unsigned len2 = valueFormat[1].get_len ();
    unsigned record_size = HBUINT16::static_size + Value::static_size * (len1 + len2);

    unsigned format1 = 0;
    unsigned format2 = 0;
    for (const Offset16To<PairSet>& _ :
             + hb_zip (this+coverage, pairSet) | hb_filter (glyphset, hb_first) | hb_map (hb_second))
    {
      const PairSet& set = (this + _);
      const PairValueRecord *record = &set.firstPairValueRecord;

      for (unsigned i = 0; i < set.len; i++)
      {
        if (record->intersects (glyphset))
        {
          format1 = format1 | valueFormat[0].get_effective_format (record->get_values_1 ());
          format2 = format2 | valueFormat[1].get_effective_format (record->get_values_2 (valueFormat[0]));
        }
        record = &StructAtOffset<const PairValueRecord> (record, record_size);
      }
    }

    return hb_pair (format1, format2);
  }


  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);

    if (!c->check_struct (this)) return_trace (false);

    unsigned int len1 = valueFormat[0].get_len ();
    unsigned int len2 = valueFormat[1].get_len ();
    PairSet::sanitize_closure_t closure =
    {
      valueFormat,
      len1,
      1 + len1 + len2
    };

    return_trace (coverage.sanitize (c, this) && pairSet.sanitize (c, this, &closure));
  }

  protected:
  HBUINT16	format;			/* Format identifier--format = 1 */
  Offset16To<Coverage>
		coverage;		/* Offset to Coverage table--from
					 * beginning of subtable */
  ValueFormat	valueFormat[2];		/* [0] Defines the types of data in
					 * ValueRecord1--for the first glyph
					 * in the pair--may be zero (0) */
					/* [1] Defines the types of data in
					 * ValueRecord2--for the second glyph
					 * in the pair--may be zero (0) */
  Array16OfOffset16To<PairSet>
		pairSet;		/* Array of PairSet tables
					 * ordered by Coverage Index */
  public:
  DEFINE_SIZE_ARRAY (10, pairSet);
};

struct PairPosFormat2
{
  bool intersects (const hb_set_t *glyphs) const
  {
    return (this+coverage).intersects (glyphs) &&
	   (this+classDef2).intersects (glyphs);
  }

  void closure_lookups (hb_closure_lookups_context_t *c) const {}
  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const
  {
    if (!intersects (c->glyph_set)) return;
    if ((!valueFormat1.has_device ()) && (!valueFormat2.has_device ())) return;

    hb_set_t klass1_glyphs, klass2_glyphs;
    if (!(this+classDef1).collect_coverage (&klass1_glyphs)) return;
    if (!(this+classDef2).collect_coverage (&klass2_glyphs)) return;

    hb_set_t class1_set, class2_set;
    for (const unsigned cp : + c->glyph_set->iter () | hb_filter (this + coverage))
    {
      if (!klass1_glyphs.has (cp)) class1_set.add (0);
      else
      {
        unsigned klass1 = (this+classDef1).get (cp);
        class1_set.add (klass1);
      }
    }

    class2_set.add (0);
    for (const unsigned cp : + c->glyph_set->iter () | hb_filter (klass2_glyphs))
    {
      unsigned klass2 = (this+classDef2).get (cp);
      class2_set.add (klass2);
    }

    if (class1_set.is_empty ()
        || class2_set.is_empty ()
        || (class2_set.get_population() == 1 && class2_set.has(0)))
      return;

    unsigned len1 = valueFormat1.get_len ();
    unsigned len2 = valueFormat2.get_len ();
    const hb_array_t<const Value> values_array = values.as_array ((unsigned)class1Count * (unsigned) class2Count * (len1 + len2));
    for (const unsigned class1_idx : class1_set.iter ())
    {
      for (const unsigned class2_idx : class2_set.iter ())
      {
	unsigned start_offset = (class1_idx * (unsigned) class2Count + class2_idx) * (len1 + len2);
	if (valueFormat1.has_device ())
	  valueFormat1.collect_variation_indices (c, this, values_array.sub_array (start_offset, len1));

	if (valueFormat2.has_device ())
	  valueFormat2.collect_variation_indices (c, this, values_array.sub_array (start_offset+len1, len2));
      }
    }
  }

  void collect_glyphs (hb_collect_glyphs_context_t *c) const
  {
    if (unlikely (!(this+coverage).collect_coverage (c->input))) return;
    if (unlikely (!(this+classDef2).collect_coverage (c->input))) return;
  }

  const Coverage &get_coverage () const { return this+coverage; }

  bool apply (hb_ot_apply_context_t *c) const
  {
    TRACE_APPLY (this);
    hb_buffer_t *buffer = c->buffer;
    unsigned int index = (this+coverage).get_coverage  (buffer->cur().codepoint);
    if (likely (index == NOT_COVERED)) return_trace (false);

    hb_ot_apply_context_t::skipping_iterator_t &skippy_iter = c->iter_input;
    skippy_iter.reset (buffer->idx, 1);
    if (!skippy_iter.next ()) return_trace (false);

    unsigned int len1 = valueFormat1.get_len ();
    unsigned int len2 = valueFormat2.get_len ();
    unsigned int record_len = len1 + len2;

    unsigned int klass1 = (this+classDef1).get_class (buffer->cur().codepoint);
    unsigned int klass2 = (this+classDef2).get_class (buffer->info[skippy_iter.idx].codepoint);
    if (unlikely (klass1 >= class1Count || klass2 >= class2Count)) return_trace (false);

    const Value *v = &values[record_len * (klass1 * class2Count + klass2)];
    /* Note the intentional use of "|" instead of short-circuit "||". */
    if (valueFormat1.apply_value (c, this, v, buffer->cur_pos()) |
	valueFormat2.apply_value (c, this, v + len1, buffer->pos[skippy_iter.idx]))
      buffer->unsafe_to_break (buffer->idx, skippy_iter.idx + 1);

    buffer->idx = skippy_iter.idx;
    if (len2)
      buffer->idx++;

    return_trace (true);
  }

  bool subset (hb_subset_context_t *c) const
  {
    TRACE_SUBSET (this);
    auto *out = c->serializer->start_embed (*this);
    if (unlikely (!c->serializer->extend_min (out))) return_trace (false);
    out->format = format;

    hb_map_t klass1_map;
    out->classDef1.serialize_subset (c, classDef1, this, &klass1_map, true, true, &(this + coverage));
    out->class1Count = klass1_map.get_population ();

    hb_map_t klass2_map;
    out->classDef2.serialize_subset (c, classDef2, this, &klass2_map, true, false);
    out->class2Count = klass2_map.get_population ();

    unsigned len1 = valueFormat1.get_len ();
    unsigned len2 = valueFormat2.get_len ();

    hb_pair_t<unsigned, unsigned> newFormats = hb_pair (valueFormat1, valueFormat2);
    if (c->plan->drop_hints)
      newFormats = compute_effective_value_formats (klass1_map, klass2_map);

    out->valueFormat1 = newFormats.first;
    out->valueFormat2 = newFormats.second;

    for (unsigned class1_idx : + hb_range ((unsigned) class1Count) | hb_filter (klass1_map))
    {
      for (unsigned class2_idx : + hb_range ((unsigned) class2Count) | hb_filter (klass2_map))
      {
        unsigned idx = (class1_idx * (unsigned) class2Count + class2_idx) * (len1 + len2);
        valueFormat1.copy_values (c->serializer, newFormats.first, this, &values[idx], c->plan->layout_variation_idx_map);
        valueFormat2.copy_values (c->serializer, newFormats.second, this, &values[idx + len1], c->plan->layout_variation_idx_map);
      }
    }

    const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
    const hb_map_t &glyph_map = *c->plan->glyph_map;

    auto it =
    + hb_iter (this+coverage)
    | hb_filter (glyphset)
    | hb_map_retains_sorting (glyph_map)
    ;

    out->coverage.serialize (c->serializer, out).serialize (c->serializer, it);
    return_trace (out->class1Count && out->class2Count && bool (it));
  }


  hb_pair_t<unsigned, unsigned> compute_effective_value_formats (const hb_map_t& klass1_map,
                                                                 const hb_map_t& klass2_map) const
  {
    unsigned len1 = valueFormat1.get_len ();
    unsigned len2 = valueFormat2.get_len ();

    unsigned format1 = 0;
    unsigned format2 = 0;

    for (unsigned class1_idx : + hb_range ((unsigned) class1Count) | hb_filter (klass1_map))
    {
      for (unsigned class2_idx : + hb_range ((unsigned) class2Count) | hb_filter (klass2_map))
      {
        unsigned idx = (class1_idx * (unsigned) class2Count + class2_idx) * (len1 + len2);
        format1 = format1 | valueFormat1.get_effective_format (&values[idx]);
        format2 = format2 | valueFormat2.get_effective_format (&values[idx + len1]);
      }
    }

    return hb_pair (format1, format2);
  }


  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    if (!(c->check_struct (this)
       && coverage.sanitize (c, this)
       && classDef1.sanitize (c, this)
       && classDef2.sanitize (c, this))) return_trace (false);

    unsigned int len1 = valueFormat1.get_len ();
    unsigned int len2 = valueFormat2.get_len ();
    unsigned int stride = len1 + len2;
    unsigned int record_size = valueFormat1.get_size () + valueFormat2.get_size ();
    unsigned int count = (unsigned int) class1Count * (unsigned int) class2Count;
    return_trace (c->check_range ((const void *) values,
				  count,
				  record_size) &&
		  valueFormat1.sanitize_values_stride_unsafe (c, this, &values[0], count, stride) &&
		  valueFormat2.sanitize_values_stride_unsafe (c, this, &values[len1], count, stride));
  }

  protected:
  HBUINT16	format;			/* Format identifier--format = 2 */
  Offset16To<Coverage>
		coverage;		/* Offset to Coverage table--from
					 * beginning of subtable */
  ValueFormat	valueFormat1;		/* ValueRecord definition--for the
					 * first glyph of the pair--may be zero
					 * (0) */
  ValueFormat	valueFormat2;		/* ValueRecord definition--for the
					 * second glyph of the pair--may be
					 * zero (0) */
  Offset16To<ClassDef>
		classDef1;		/* Offset to ClassDef table--from
					 * beginning of PairPos subtable--for
					 * the first glyph of the pair */
  Offset16To<ClassDef>
		classDef2;		/* Offset to ClassDef table--from
					 * beginning of PairPos subtable--for
					 * the second glyph of the pair */
  HBUINT16	class1Count;		/* Number of classes in ClassDef1
					 * table--includes Class0 */
  HBUINT16	class2Count;		/* Number of classes in ClassDef2
					 * table--includes Class0 */
  ValueRecord	values;			/* Matrix of value pairs:
					 * class1-major, class2-minor,
					 * Each entry has value1 and value2 */
  public:
  DEFINE_SIZE_ARRAY (16, values);
};

struct PairPos
{
  template <typename context_t, typename ...Ts>
  typename context_t::return_t dispatch (context_t *c, Ts&&... ds) const
  {
    TRACE_DISPATCH (this, u.format);
    if (unlikely (!c->may_dispatch (this, &u.format))) return_trace (c->no_dispatch_return_value ());
    switch (u.format) {
    case 1: return_trace (c->dispatch (u.format1, hb_forward<Ts> (ds)...));
    case 2: return_trace (c->dispatch (u.format2, hb_forward<Ts> (ds)...));
    default:return_trace (c->default_return_value ());
    }
  }

  protected:
  union {
  HBUINT16		format;		/* Format identifier */
  PairPosFormat1	format1;
  PairPosFormat2	format2;
  } u;
};


struct EntryExitRecord
{
  friend struct CursivePosFormat1;

  bool sanitize (hb_sanitize_context_t *c, const void *base) const
  {
    TRACE_SANITIZE (this);
    return_trace (entryAnchor.sanitize (c, base) && exitAnchor.sanitize (c, base));
  }

  void collect_variation_indices (hb_collect_variation_indices_context_t *c,
				  const void *src_base) const
  {
    (src_base+entryAnchor).collect_variation_indices (c);
    (src_base+exitAnchor).collect_variation_indices (c);
  }

  EntryExitRecord* subset (hb_subset_context_t *c,
                           const void *src_base) const
  {
    TRACE_SERIALIZE (this);
    auto *out = c->serializer->embed (this);
    if (unlikely (!out)) return_trace (nullptr);

    out->entryAnchor.serialize_subset (c, entryAnchor, src_base);
    out->exitAnchor.serialize_subset (c, exitAnchor, src_base);
    return_trace (out);
  }

  protected:
  Offset16To<Anchor>
		entryAnchor;		/* Offset to EntryAnchor table--from
					 * beginning of CursivePos
					 * subtable--may be NULL */
  Offset16To<Anchor>
		exitAnchor;		/* Offset to ExitAnchor table--from
					 * beginning of CursivePos
					 * subtable--may be NULL */
  public:
  DEFINE_SIZE_STATIC (4);
};

static void
reverse_cursive_minor_offset (hb_glyph_position_t *pos, unsigned int i, hb_direction_t direction, unsigned int new_parent);

struct CursivePosFormat1
{
  bool intersects (const hb_set_t *glyphs) const
  { return (this+coverage).intersects (glyphs); }

  void closure_lookups (hb_closure_lookups_context_t *c) const {}

  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const
  {
    + hb_zip (this+coverage, entryExitRecord)
    | hb_filter (c->glyph_set, hb_first)
    | hb_map (hb_second)
    | hb_apply ([&] (const EntryExitRecord& record) { record.collect_variation_indices (c, this); })
    ;
  }

  void collect_glyphs (hb_collect_glyphs_context_t *c) const
  { if (unlikely (!(this+coverage).collect_coverage (c->input))) return; }

  const Coverage &get_coverage () const { return this+coverage; }

  bool apply (hb_ot_apply_context_t *c) const
  {
    TRACE_APPLY (this);
    hb_buffer_t *buffer = c->buffer;

    const EntryExitRecord &this_record = entryExitRecord[(this+coverage).get_coverage  (buffer->cur().codepoint)];
    if (!this_record.entryAnchor) return_trace (false);

    hb_ot_apply_context_t::skipping_iterator_t &skippy_iter = c->iter_input;
    skippy_iter.reset (buffer->idx, 1);
    if (!skippy_iter.prev ()) return_trace (false);

    const EntryExitRecord &prev_record = entryExitRecord[(this+coverage).get_coverage  (buffer->info[skippy_iter.idx].codepoint)];
    if (!prev_record.exitAnchor) return_trace (false);

    unsigned int i = skippy_iter.idx;
    unsigned int j = buffer->idx;

    buffer->unsafe_to_break (i, j);
    float entry_x, entry_y, exit_x, exit_y;
    (this+prev_record.exitAnchor).get_anchor (c, buffer->info[i].codepoint, &exit_x, &exit_y);
    (this+this_record.entryAnchor).get_anchor (c, buffer->info[j].codepoint, &entry_x, &entry_y);

    hb_glyph_position_t *pos = buffer->pos;

    hb_position_t d;
    /* Main-direction adjustment */
    switch (c->direction) {
      case HB_DIRECTION_LTR:
	pos[i].x_advance  = roundf (exit_x) + pos[i].x_offset;

	d = roundf (entry_x) + pos[j].x_offset;
	pos[j].x_advance -= d;
	pos[j].x_offset  -= d;
	break;
      case HB_DIRECTION_RTL:
	d = roundf (exit_x) + pos[i].x_offset;
	pos[i].x_advance -= d;
	pos[i].x_offset  -= d;

	pos[j].x_advance  = roundf (entry_x) + pos[j].x_offset;
	break;
      case HB_DIRECTION_TTB:
	pos[i].y_advance  = roundf (exit_y) + pos[i].y_offset;

	d = roundf (entry_y) + pos[j].y_offset;
	pos[j].y_advance -= d;
	pos[j].y_offset  -= d;
	break;
      case HB_DIRECTION_BTT:
	d = roundf (exit_y) + pos[i].y_offset;
	pos[i].y_advance -= d;
	pos[i].y_offset  -= d;

	pos[j].y_advance  = roundf (entry_y);
	break;
      case HB_DIRECTION_INVALID:
      default:
	break;
    }

    /* Cross-direction adjustment */

    /* We attach child to parent (think graph theory and rooted trees whereas
     * the root stays on baseline and each node aligns itself against its
     * parent.
     *
     * Optimize things for the case of RightToLeft, as that's most common in
     * Arabic. */
    unsigned int child  = i;
    unsigned int parent = j;
    hb_position_t x_offset = entry_x - exit_x;
    hb_position_t y_offset = entry_y - exit_y;
    if  (!(c->lookup_props & LookupFlag::RightToLeft))
    {
      unsigned int k = child;
      child = parent;
      parent = k;
      x_offset = -x_offset;
      y_offset = -y_offset;
    }

    /* If child was already connected to someone else, walk through its old
     * chain and reverse the link direction, such that the whole tree of its
     * previous connection now attaches to new parent.  Watch out for case
     * where new parent is on the path from old chain...
     */
    reverse_cursive_minor_offset (pos, child, c->direction, parent);

    pos[child].attach_type() = ATTACH_TYPE_CURSIVE;
    pos[child].attach_chain() = (int) parent - (int) child;
    buffer->scratch_flags |= HB_BUFFER_SCRATCH_FLAG_HAS_GPOS_ATTACHMENT;
    if (likely (HB_DIRECTION_IS_HORIZONTAL (c->direction)))
      pos[child].y_offset = y_offset;
    else
      pos[child].x_offset = x_offset;

    /* If parent was attached to child, break them free.
     * https://github.com/harfbuzz/harfbuzz/issues/2469
     */
    if (unlikely (pos[parent].attach_chain() == -pos[child].attach_chain()))
      pos[parent].attach_chain() = 0;

    buffer->idx++;
    return_trace (true);
  }

  template <typename Iterator,
	    hb_requires (hb_is_iterator (Iterator))>
  void serialize (hb_subset_context_t *c,
		  Iterator it,
		  const void *src_base)
  {
    if (unlikely (!c->serializer->extend_min ((*this)))) return;
    this->format = 1;
    this->entryExitRecord.len = it.len ();

    for (const EntryExitRecord& entry_record : + it
					       | hb_map (hb_second))
      entry_record.subset (c, src_base);

    auto glyphs =
    + it
    | hb_map_retains_sorting (hb_first)
    ;

    coverage.serialize (c->serializer, this).serialize (c->serializer, glyphs);
  }

  bool subset (hb_subset_context_t *c) const
  {
    TRACE_SUBSET (this);
    const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
    const hb_map_t &glyph_map = *c->plan->glyph_map;

    auto *out = c->serializer->start_embed (*this);
    if (unlikely (!out)) return_trace (false);

    auto it =
    + hb_zip (this+coverage, entryExitRecord)
    | hb_filter (glyphset, hb_first)
    | hb_map_retains_sorting ([&] (hb_pair_t<hb_codepoint_t, const EntryExitRecord&> p) -> hb_pair_t<hb_codepoint_t, const EntryExitRecord&>
			      { return hb_pair (glyph_map[p.first], p.second);})
    ;

    bool ret = bool (it);
    out->serialize (c, it, this);
    return_trace (ret);
  }

  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (coverage.sanitize (c, this) && entryExitRecord.sanitize (c, this));
  }

  protected:
  HBUINT16	format;			/* Format identifier--format = 1 */
  Offset16To<Coverage>
		coverage;		/* Offset to Coverage table--from
					 * beginning of subtable */
  Array16Of<EntryExitRecord>
		entryExitRecord;	/* Array of EntryExit records--in
					 * Coverage Index order */
  public:
  DEFINE_SIZE_ARRAY (6, entryExitRecord);
};

struct CursivePos
{
  template <typename context_t, typename ...Ts>
  typename context_t::return_t dispatch (context_t *c, Ts&&... ds) const
  {
    TRACE_DISPATCH (this, u.format);
    if (unlikely (!c->may_dispatch (this, &u.format))) return_trace (c->no_dispatch_return_value ());
    switch (u.format) {
    case 1: return_trace (c->dispatch (u.format1, hb_forward<Ts> (ds)...));
    default:return_trace (c->default_return_value ());
    }
  }

  protected:
  union {
  HBUINT16		format;		/* Format identifier */
  CursivePosFormat1	format1;
  } u;
};


typedef AnchorMatrix BaseArray;		/* base-major--
					 * in order of BaseCoverage Index--,
					 * mark-minor--
					 * ordered by class--zero-based. */

static void Markclass_closure_and_remap_indexes (const Coverage  &mark_coverage,
						 const MarkArray &mark_array,
						 const hb_set_t  &glyphset,
						 hb_map_t*        klass_mapping /* INOUT */)
{
  hb_set_t orig_classes;

  + hb_zip (mark_coverage, mark_array)
  | hb_filter (glyphset, hb_first)
  | hb_map (hb_second)
  | hb_map (&MarkRecord::get_class)
  | hb_sink (orig_classes)
  ;

  unsigned idx = 0;
  for (auto klass : orig_classes.iter ())
  {
    if (klass_mapping->has (klass)) continue;
    klass_mapping->set (klass, idx);
    idx++;
  }
}

struct MarkBasePosFormat1
{
  bool intersects (const hb_set_t *glyphs) const
  {
    return (this+markCoverage).intersects (glyphs) &&
	   (this+baseCoverage).intersects (glyphs);
  }

  void closure_lookups (hb_closure_lookups_context_t *c) const {}

  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const
  {
    + hb_zip (this+markCoverage, this+markArray)
    | hb_filter (c->glyph_set, hb_first)
    | hb_map (hb_second)
    | hb_apply ([&] (const MarkRecord& record) { record.collect_variation_indices (c, &(this+markArray)); })
    ;

    hb_map_t klass_mapping;
    Markclass_closure_and_remap_indexes (this+markCoverage, this+markArray, *c->glyph_set, &klass_mapping);

    unsigned basecount = (this+baseArray).rows;
    auto base_iter =
    + hb_zip (this+baseCoverage, hb_range (basecount))
    | hb_filter (c->glyph_set, hb_first)
    | hb_map (hb_second)
    ;

    hb_sorted_vector_t<unsigned> base_indexes;
    for (const unsigned row : base_iter)
    {
      + hb_range ((unsigned) classCount)
      | hb_filter (klass_mapping)
      | hb_map ([&] (const unsigned col) { return row * (unsigned) classCount + col; })
      | hb_sink (base_indexes)
      ;
    }
    (this+baseArray).collect_variation_indices (c, base_indexes.iter ());
  }

  void collect_glyphs (hb_collect_glyphs_context_t *c) const
  {
    if (unlikely (!(this+markCoverage).collect_coverage (c->input))) return;
    if (unlikely (!(this+baseCoverage).collect_coverage (c->input))) return;
  }

  const Coverage &get_coverage () const { return this+markCoverage; }

  bool apply (hb_ot_apply_context_t *c) const
  {
    TRACE_APPLY (this);
    hb_buffer_t *buffer = c->buffer;
    unsigned int mark_index = (this+markCoverage).get_coverage  (buffer->cur().codepoint);
    if (likely (mark_index == NOT_COVERED)) return_trace (false);

    /* Now we search backwards for a non-mark glyph */
    hb_ot_apply_context_t::skipping_iterator_t &skippy_iter = c->iter_input;
    skippy_iter.reset (buffer->idx, 1);
    skippy_iter.set_lookup_props (LookupFlag::IgnoreMarks);
    do {
      if (!skippy_iter.prev ()) return_trace (false);
      /* We only want to attach to the first of a MultipleSubst sequence.
       * https://github.com/harfbuzz/harfbuzz/issues/740
       * Reject others...
       * ...but stop if we find a mark in the MultipleSubst sequence:
       * https://github.com/harfbuzz/harfbuzz/issues/1020 */
      if (!_hb_glyph_info_multiplied (&buffer->info[skippy_iter.idx]) ||
	  0 == _hb_glyph_info_get_lig_comp (&buffer->info[skippy_iter.idx]) ||
	  (skippy_iter.idx == 0 ||
	   _hb_glyph_info_is_mark (&buffer->info[skippy_iter.idx - 1]) ||
	   _hb_glyph_info_get_lig_id (&buffer->info[skippy_iter.idx]) !=
	   _hb_glyph_info_get_lig_id (&buffer->info[skippy_iter.idx - 1]) ||
	   _hb_glyph_info_get_lig_comp (&buffer->info[skippy_iter.idx]) !=
	   _hb_glyph_info_get_lig_comp (&buffer->info[skippy_iter.idx - 1]) + 1
	   ))
	break;
      skippy_iter.reject ();
    } while (true);

    /* Checking that matched glyph is actually a base glyph by GDEF is too strong; disabled */
    //if (!_hb_glyph_info_is_base_glyph (&buffer->info[skippy_iter.idx])) { return_trace (false); }

    unsigned int base_index = (this+baseCoverage).get_coverage  (buffer->info[skippy_iter.idx].codepoint);
    if (base_index == NOT_COVERED) return_trace (false);

    return_trace ((this+markArray).apply (c, mark_index, base_index, this+baseArray, classCount, skippy_iter.idx));
  }

  bool subset (hb_subset_context_t *c) const
  {
    TRACE_SUBSET (this);
    const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
    const hb_map_t &glyph_map = *c->plan->glyph_map;

    auto *out = c->serializer->start_embed (*this);
    if (unlikely (!c->serializer->extend_min (out))) return_trace (false);
    out->format = format;

    hb_map_t klass_mapping;
    Markclass_closure_and_remap_indexes (this+markCoverage, this+markArray, glyphset, &klass_mapping);

    if (!klass_mapping.get_population ()) return_trace (false);
    out->classCount = klass_mapping.get_population ();

    auto mark_iter =
    + hb_zip (this+markCoverage, this+markArray)
    | hb_filter (glyphset, hb_first)
    ;

    hb_sorted_vector_t<hb_codepoint_t> new_coverage;
    + mark_iter
    | hb_map (hb_first)
    | hb_map (glyph_map)
    | hb_sink (new_coverage)
    ;

    if (!out->markCoverage.serialize (c->serializer, out)
			  .serialize (c->serializer, new_coverage.iter ()))
      return_trace (false);

    out->markArray.serialize_subset (c, markArray, this,
                                     (this+markCoverage).iter (),
                                     &klass_mapping);

    unsigned basecount = (this+baseArray).rows;
    auto base_iter =
    + hb_zip (this+baseCoverage, hb_range (basecount))
    | hb_filter (glyphset, hb_first)
    ;

    new_coverage.reset ();
    + base_iter
    | hb_map (hb_first)
    | hb_map (glyph_map)
    | hb_sink (new_coverage)
    ;

    if (!out->baseCoverage.serialize (c->serializer, out)
			  .serialize (c->serializer, new_coverage.iter ()))
      return_trace (false);

    hb_sorted_vector_t<unsigned> base_indexes;
    for (const unsigned row : + base_iter
			      | hb_map (hb_second))
    {
      + hb_range ((unsigned) classCount)
      | hb_filter (klass_mapping)
      | hb_map ([&] (const unsigned col) { return row * (unsigned) classCount + col; })
      | hb_sink (base_indexes)
      ;
    }

    out->baseArray.serialize_subset (c, baseArray, this,
                                     base_iter.len (),
                                     base_indexes.iter ());

    return_trace (true);
  }

  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (c->check_struct (this) &&
		  markCoverage.sanitize (c, this) &&
		  baseCoverage.sanitize (c, this) &&
		  markArray.sanitize (c, this) &&
		  baseArray.sanitize (c, this, (unsigned int) classCount));
  }

  protected:
  HBUINT16	format;			/* Format identifier--format = 1 */
  Offset16To<Coverage>
		markCoverage;		/* Offset to MarkCoverage table--from
					 * beginning of MarkBasePos subtable */
  Offset16To<Coverage>
		baseCoverage;		/* Offset to BaseCoverage table--from
					 * beginning of MarkBasePos subtable */
  HBUINT16	classCount;		/* Number of classes defined for marks */
  Offset16To<MarkArray>
		markArray;		/* Offset to MarkArray table--from
					 * beginning of MarkBasePos subtable */
  Offset16To<BaseArray>
		baseArray;		/* Offset to BaseArray table--from
					 * beginning of MarkBasePos subtable */
  public:
  DEFINE_SIZE_STATIC (12);
};

struct MarkBasePos
{
  template <typename context_t, typename ...Ts>
  typename context_t::return_t dispatch (context_t *c, Ts&&... ds) const
  {
    TRACE_DISPATCH (this, u.format);
    if (unlikely (!c->may_dispatch (this, &u.format))) return_trace (c->no_dispatch_return_value ());
    switch (u.format) {
    case 1: return_trace (c->dispatch (u.format1, hb_forward<Ts> (ds)...));
    default:return_trace (c->default_return_value ());
    }
  }

  protected:
  union {
  HBUINT16		format;		/* Format identifier */
  MarkBasePosFormat1	format1;
  } u;
};


typedef AnchorMatrix LigatureAttach;	/* component-major--
					 * in order of writing direction--,
					 * mark-minor--
					 * ordered by class--zero-based. */

/* Array of LigatureAttach tables ordered by LigatureCoverage Index */
struct LigatureArray : List16OfOffset16To<LigatureAttach>
{
  template <typename Iterator,
	    hb_requires (hb_is_iterator (Iterator))>
  bool subset (hb_subset_context_t *c,
               Iterator		    coverage,
	       unsigned		    class_count,
	       const hb_map_t	   *klass_mapping) const
  {
    TRACE_SUBSET (this);
    const hb_set_t &glyphset = *c->plan->glyphset_gsub ();

    auto *out = c->serializer->start_embed (this);
    if (unlikely (!c->serializer->extend_min (out)))  return_trace (false);

    for (const auto _ : + hb_zip (coverage, *this)
		  | hb_filter (glyphset, hb_first))
    {
      auto *matrix = out->serialize_append (c->serializer);
      if (unlikely (!matrix)) return_trace (false);

      const LigatureAttach& src = (this + _.second);
      auto indexes =
          + hb_range (src.rows * class_count)
          | hb_filter ([=] (unsigned index) { return klass_mapping->has (index % class_count); })
          ;
      matrix->serialize_subset (c,
				_.second,
				this,
                                src.rows,
                                indexes);
    }
    return_trace (this->len);
  }
};

struct MarkLigPosFormat1
{
  bool intersects (const hb_set_t *glyphs) const
  {
    return (this+markCoverage).intersects (glyphs) &&
	   (this+ligatureCoverage).intersects (glyphs);
  }

  void closure_lookups (hb_closure_lookups_context_t *c) const {}

  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const
  {
    + hb_zip (this+markCoverage, this+markArray)
    | hb_filter (c->glyph_set, hb_first)
    | hb_map (hb_second)
    | hb_apply ([&] (const MarkRecord& record) { record.collect_variation_indices (c, &(this+markArray)); })
    ;

    hb_map_t klass_mapping;
    Markclass_closure_and_remap_indexes (this+markCoverage, this+markArray, *c->glyph_set, &klass_mapping);

    unsigned ligcount = (this+ligatureArray).len;
    auto lig_iter =
    + hb_zip (this+ligatureCoverage, hb_range (ligcount))
    | hb_filter (c->glyph_set, hb_first)
    | hb_map (hb_second)
    ;

    const LigatureArray& lig_array = this+ligatureArray;
    for (const unsigned i : lig_iter)
    {
      hb_sorted_vector_t<unsigned> lig_indexes;
      unsigned row_count = lig_array[i].rows;
      for (unsigned row : + hb_range (row_count))
      {
	+ hb_range ((unsigned) classCount)
	| hb_filter (klass_mapping)
	| hb_map ([&] (const unsigned col) { return row * (unsigned) classCount + col; })
	| hb_sink (lig_indexes)
	;
      }

      lig_array[i].collect_variation_indices (c, lig_indexes.iter ());
    }
  }

  void collect_glyphs (hb_collect_glyphs_context_t *c) const
  {
    if (unlikely (!(this+markCoverage).collect_coverage (c->input))) return;
    if (unlikely (!(this+ligatureCoverage).collect_coverage (c->input))) return;
  }

  const Coverage &get_coverage () const { return this+markCoverage; }

  bool apply (hb_ot_apply_context_t *c) const
  {
    TRACE_APPLY (this);
    hb_buffer_t *buffer = c->buffer;
    unsigned int mark_index = (this+markCoverage).get_coverage  (buffer->cur().codepoint);
    if (likely (mark_index == NOT_COVERED)) return_trace (false);

    /* Now we search backwards for a non-mark glyph */
    hb_ot_apply_context_t::skipping_iterator_t &skippy_iter = c->iter_input;
    skippy_iter.reset (buffer->idx, 1);
    skippy_iter.set_lookup_props (LookupFlag::IgnoreMarks);
    if (!skippy_iter.prev ()) return_trace (false);

    /* Checking that matched glyph is actually a ligature by GDEF is too strong; disabled */
    //if (!_hb_glyph_info_is_ligature (&buffer->info[skippy_iter.idx])) { return_trace (false); }

    unsigned int j = skippy_iter.idx;
    unsigned int lig_index = (this+ligatureCoverage).get_coverage  (buffer->info[j].codepoint);
    if (lig_index == NOT_COVERED) return_trace (false);

    const LigatureArray& lig_array = this+ligatureArray;
    const LigatureAttach& lig_attach = lig_array[lig_index];

    /* Find component to attach to */
    unsigned int comp_count = lig_attach.rows;
    if (unlikely (!comp_count)) return_trace (false);

    /* We must now check whether the ligature ID of the current mark glyph
     * is identical to the ligature ID of the found ligature.  If yes, we
     * can directly use the component index.  If not, we attach the mark
     * glyph to the last component of the ligature. */
    unsigned int comp_index;
    unsigned int lig_id = _hb_glyph_info_get_lig_id (&buffer->info[j]);
    unsigned int mark_id = _hb_glyph_info_get_lig_id (&buffer->cur());
    unsigned int mark_comp = _hb_glyph_info_get_lig_comp (&buffer->cur());
    if (lig_id && lig_id == mark_id && mark_comp > 0)
      comp_index = hb_min (comp_count, _hb_glyph_info_get_lig_comp (&buffer->cur())) - 1;
    else
      comp_index = comp_count - 1;

    return_trace ((this+markArray).apply (c, mark_index, comp_index, lig_attach, classCount, j));
  }

  bool subset (hb_subset_context_t *c) const
  {
    TRACE_SUBSET (this);
    const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
    const hb_map_t &glyph_map = *c->plan->glyph_map;

    auto *out = c->serializer->start_embed (*this);
    if (unlikely (!c->serializer->extend_min (out))) return_trace (false);
    out->format = format;

    hb_map_t klass_mapping;
    Markclass_closure_and_remap_indexes (this+markCoverage, this+markArray, glyphset, &klass_mapping);

    if (!klass_mapping.get_population ()) return_trace (false);
    out->classCount = klass_mapping.get_population ();

    auto mark_iter =
    + hb_zip (this+markCoverage, this+markArray)
    | hb_filter (glyphset, hb_first)
    ;

    auto new_mark_coverage =
    + mark_iter
    | hb_map_retains_sorting (hb_first)
    | hb_map_retains_sorting (glyph_map)
    ;

    if (!out->markCoverage.serialize (c->serializer, out)
			  .serialize (c->serializer, new_mark_coverage))
      return_trace (false);

    out->markArray.serialize_subset (c, markArray, this,
                                     (this+markCoverage).iter (),
                                     &klass_mapping);

    auto new_ligature_coverage =
    + hb_iter (this + ligatureCoverage)
    | hb_filter (glyphset)
    | hb_map_retains_sorting (glyph_map)
    ;

    if (!out->ligatureCoverage.serialize (c->serializer, out)
			      .serialize (c->serializer, new_ligature_coverage))
      return_trace (false);

    out->ligatureArray.serialize_subset (c, ligatureArray, this,
                                         hb_iter (this+ligatureCoverage), classCount, &klass_mapping);

    return_trace (true);
  }

  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (c->check_struct (this) &&
		  markCoverage.sanitize (c, this) &&
		  ligatureCoverage.sanitize (c, this) &&
		  markArray.sanitize (c, this) &&
		  ligatureArray.sanitize (c, this, (unsigned int) classCount));
  }

  protected:
  HBUINT16	format;			/* Format identifier--format = 1 */
  Offset16To<Coverage>
		markCoverage;		/* Offset to Mark Coverage table--from
					 * beginning of MarkLigPos subtable */
  Offset16To<Coverage>
		ligatureCoverage;	/* Offset to Ligature Coverage
					 * table--from beginning of MarkLigPos
					 * subtable */
  HBUINT16	classCount;		/* Number of defined mark classes */
  Offset16To<MarkArray>
		markArray;		/* Offset to MarkArray table--from
					 * beginning of MarkLigPos subtable */
  Offset16To<LigatureArray>
		ligatureArray;		/* Offset to LigatureArray table--from
					 * beginning of MarkLigPos subtable */
  public:
  DEFINE_SIZE_STATIC (12);
};


struct MarkLigPos
{
  template <typename context_t, typename ...Ts>
  typename context_t::return_t dispatch (context_t *c, Ts&&... ds) const
  {
    TRACE_DISPATCH (this, u.format);
    if (unlikely (!c->may_dispatch (this, &u.format))) return_trace (c->no_dispatch_return_value ());
    switch (u.format) {
    case 1: return_trace (c->dispatch (u.format1, hb_forward<Ts> (ds)...));
    default:return_trace (c->default_return_value ());
    }
  }

  protected:
  union {
  HBUINT16		format;		/* Format identifier */
  MarkLigPosFormat1	format1;
  } u;
};


typedef AnchorMatrix Mark2Array;	/* mark2-major--
					 * in order of Mark2Coverage Index--,
					 * mark1-minor--
					 * ordered by class--zero-based. */

struct MarkMarkPosFormat1
{
  bool intersects (const hb_set_t *glyphs) const
  {
    return (this+mark1Coverage).intersects (glyphs) &&
	   (this+mark2Coverage).intersects (glyphs);
  }

  void closure_lookups (hb_closure_lookups_context_t *c) const {}

  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const
  {
    + hb_zip (this+mark1Coverage, this+mark1Array)
    | hb_filter (c->glyph_set, hb_first)
    | hb_map (hb_second)
    | hb_apply ([&] (const MarkRecord& record) { record.collect_variation_indices (c, &(this+mark1Array)); })
    ;

    hb_map_t klass_mapping;
    Markclass_closure_and_remap_indexes (this+mark1Coverage, this+mark1Array, *c->glyph_set, &klass_mapping);

    unsigned mark2_count = (this+mark2Array).rows;
    auto mark2_iter =
    + hb_zip (this+mark2Coverage, hb_range (mark2_count))
    | hb_filter (c->glyph_set, hb_first)
    | hb_map (hb_second)
    ;

    hb_sorted_vector_t<unsigned> mark2_indexes;
    for (const unsigned row : mark2_iter)
    {
      + hb_range ((unsigned) classCount)
      | hb_filter (klass_mapping)
      | hb_map ([&] (const unsigned col) { return row * (unsigned) classCount + col; })
      | hb_sink (mark2_indexes)
      ;
    }
    (this+mark2Array).collect_variation_indices (c, mark2_indexes.iter ());
  }

  void collect_glyphs (hb_collect_glyphs_context_t *c) const
  {
    if (unlikely (!(this+mark1Coverage).collect_coverage (c->input))) return;
    if (unlikely (!(this+mark2Coverage).collect_coverage (c->input))) return;
  }

  const Coverage &get_coverage () const { return this+mark1Coverage; }

  bool apply (hb_ot_apply_context_t *c) const
  {
    TRACE_APPLY (this);
    hb_buffer_t *buffer = c->buffer;
    unsigned int mark1_index = (this+mark1Coverage).get_coverage  (buffer->cur().codepoint);
    if (likely (mark1_index == NOT_COVERED)) return_trace (false);

    /* now we search backwards for a suitable mark glyph until a non-mark glyph */
    hb_ot_apply_context_t::skipping_iterator_t &skippy_iter = c->iter_input;
    skippy_iter.reset (buffer->idx, 1);
    skippy_iter.set_lookup_props (c->lookup_props & ~LookupFlag::IgnoreFlags);
    if (!skippy_iter.prev ()) return_trace (false);

    if (!_hb_glyph_info_is_mark (&buffer->info[skippy_iter.idx])) { return_trace (false); }

    unsigned int j = skippy_iter.idx;

    unsigned int id1 = _hb_glyph_info_get_lig_id (&buffer->cur());
    unsigned int id2 = _hb_glyph_info_get_lig_id (&buffer->info[j]);
    unsigned int comp1 = _hb_glyph_info_get_lig_comp (&buffer->cur());
    unsigned int comp2 = _hb_glyph_info_get_lig_comp (&buffer->info[j]);

    if (likely (id1 == id2))
    {
      if (id1 == 0) /* Marks belonging to the same base. */
	goto good;
      else if (comp1 == comp2) /* Marks belonging to the same ligature component. */
	goto good;
    }
    else
    {
      /* If ligature ids don't match, it may be the case that one of the marks
       * itself is a ligature.  In which case match. */
      if ((id1 > 0 && !comp1) || (id2 > 0 && !comp2))
	goto good;
    }

    /* Didn't match. */
    return_trace (false);

    good:
    unsigned int mark2_index = (this+mark2Coverage).get_coverage  (buffer->info[j].codepoint);
    if (mark2_index == NOT_COVERED) return_trace (false);

    return_trace ((this+mark1Array).apply (c, mark1_index, mark2_index, this+mark2Array, classCount, j));
  }

  bool subset (hb_subset_context_t *c) const
  {
    TRACE_SUBSET (this);
    const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
    const hb_map_t &glyph_map = *c->plan->glyph_map;

    auto *out = c->serializer->start_embed (*this);
    if (unlikely (!c->serializer->extend_min (out))) return_trace (false);
    out->format = format;

    hb_map_t klass_mapping;
    Markclass_closure_and_remap_indexes (this+mark1Coverage, this+mark1Array, glyphset, &klass_mapping);

    if (!klass_mapping.get_population ()) return_trace (false);
    out->classCount = klass_mapping.get_population ();

    auto mark1_iter =
    + hb_zip (this+mark1Coverage, this+mark1Array)
    | hb_filter (glyphset, hb_first)
    ;

    hb_sorted_vector_t<hb_codepoint_t> new_coverage;
    + mark1_iter
    | hb_map (hb_first)
    | hb_map (glyph_map)
    | hb_sink (new_coverage)
    ;

    if (!out->mark1Coverage.serialize (c->serializer, out)
			   .serialize (c->serializer, new_coverage.iter ()))
      return_trace (false);

    out->mark1Array.serialize_subset (c, mark1Array, this,
                                      (this+mark1Coverage).iter (),
                                      &klass_mapping);

    unsigned mark2count = (this+mark2Array).rows;
    auto mark2_iter =
    + hb_zip (this+mark2Coverage, hb_range (mark2count))
    | hb_filter (glyphset, hb_first)
    ;

    new_coverage.reset ();
    + mark2_iter
    | hb_map (hb_first)
    | hb_map (glyph_map)
    | hb_sink (new_coverage)
    ;

    if (!out->mark2Coverage.serialize (c->serializer, out)
			   .serialize (c->serializer, new_coverage.iter ()))
      return_trace (false);

    hb_sorted_vector_t<unsigned> mark2_indexes;
    for (const unsigned row : + mark2_iter
			      | hb_map (hb_second))
    {
      + hb_range ((unsigned) classCount)
      | hb_filter (klass_mapping)
      | hb_map ([&] (const unsigned col) { return row * (unsigned) classCount + col; })
      | hb_sink (mark2_indexes)
      ;
    }

    out->mark2Array.serialize_subset (c, mark2Array, this, mark2_iter.len (), mark2_indexes.iter ());

    return_trace (true);
  }

  bool sanitize (hb_sanitize_context_t *c) const
  {
    TRACE_SANITIZE (this);
    return_trace (c->check_struct (this) &&
		  mark1Coverage.sanitize (c, this) &&
		  mark2Coverage.sanitize (c, this) &&
		  mark1Array.sanitize (c, this) &&
		  mark2Array.sanitize (c, this, (unsigned int) classCount));
  }

  protected:
  HBUINT16	format;			/* Format identifier--format = 1 */
  Offset16To<Coverage>
		mark1Coverage;		/* Offset to Combining Mark1 Coverage
					 * table--from beginning of MarkMarkPos
					 * subtable */
  Offset16To<Coverage>
		mark2Coverage;		/* Offset to Combining Mark2 Coverage
					 * table--from beginning of MarkMarkPos
					 * subtable */
  HBUINT16	classCount;		/* Number of defined mark classes */
  Offset16To<MarkArray>
		mark1Array;		/* Offset to Mark1Array table--from
					 * beginning of MarkMarkPos subtable */
  Offset16To<Mark2Array>
		mark2Array;		/* Offset to Mark2Array table--from
					 * beginning of MarkMarkPos subtable */
  public:
  DEFINE_SIZE_STATIC (12);
};

struct MarkMarkPos
{
  template <typename context_t, typename ...Ts>
  typename context_t::return_t dispatch (context_t *c, Ts&&... ds) const
  {
    TRACE_DISPATCH (this, u.format);
    if (unlikely (!c->may_dispatch (this, &u.format))) return_trace (c->no_dispatch_return_value ());
    switch (u.format) {
    case 1: return_trace (c->dispatch (u.format1, hb_forward<Ts> (ds)...));
    default:return_trace (c->default_return_value ());
    }
  }

  protected:
  union {
  HBUINT16		format;		/* Format identifier */
  MarkMarkPosFormat1	format1;
  } u;
};


struct ContextPos : Context {};

struct ChainContextPos : ChainContext {};

struct ExtensionPos : Extension<ExtensionPos>
{
  typedef struct PosLookupSubTable SubTable;
};



/*
 * PosLookup
 */


struct PosLookupSubTable
{
  friend struct Lookup;
  friend struct PosLookup;

  enum Type {
    Single		= 1,
    Pair		= 2,
    Cursive		= 3,
    MarkBase		= 4,
    MarkLig		= 5,
    MarkMark		= 6,
    Context		= 7,
    ChainContext	= 8,
    Extension		= 9
  };

  template <typename context_t, typename ...Ts>
  typename context_t::return_t dispatch (context_t *c, unsigned int lookup_type, Ts&&... ds) const
  {
    TRACE_DISPATCH (this, lookup_type);
    switch (lookup_type) {
    case Single:		return_trace (u.single.dispatch (c, hb_forward<Ts> (ds)...));
    case Pair:			return_trace (u.pair.dispatch (c, hb_forward<Ts> (ds)...));
    case Cursive:		return_trace (u.cursive.dispatch (c, hb_forward<Ts> (ds)...));
    case MarkBase:		return_trace (u.markBase.dispatch (c, hb_forward<Ts> (ds)...));
    case MarkLig:		return_trace (u.markLig.dispatch (c, hb_forward<Ts> (ds)...));
    case MarkMark:		return_trace (u.markMark.dispatch (c, hb_forward<Ts> (ds)...));
    case Context:		return_trace (u.context.dispatch (c, hb_forward<Ts> (ds)...));
    case ChainContext:		return_trace (u.chainContext.dispatch (c, hb_forward<Ts> (ds)...));
    case Extension:		return_trace (u.extension.dispatch (c, hb_forward<Ts> (ds)...));
    default:			return_trace (c->default_return_value ());
    }
  }

  bool intersects (const hb_set_t *glyphs, unsigned int lookup_type) const
  {
    hb_intersects_context_t c (glyphs);
    return dispatch (&c, lookup_type);
  }

  protected:
  union {
  SinglePos		single;
  PairPos		pair;
  CursivePos		cursive;
  MarkBasePos		markBase;
  MarkLigPos		markLig;
  MarkMarkPos		markMark;
  ContextPos		context;
  ChainContextPos	chainContext;
  ExtensionPos		extension;
  } u;
  public:
  DEFINE_SIZE_MIN (0);
};


struct PosLookup : Lookup
{
  typedef struct PosLookupSubTable SubTable;

  const SubTable& get_subtable (unsigned int i) const
  { return Lookup::get_subtable<SubTable> (i); }

  bool is_reverse () const
  {
    return false;
  }

  bool apply (hb_ot_apply_context_t *c) const
  {
    TRACE_APPLY (this);
    return_trace (dispatch (c));
  }

  bool intersects (const hb_set_t *glyphs) const
  {
    hb_intersects_context_t c (glyphs);
    return dispatch (&c);
  }

  hb_collect_glyphs_context_t::return_t collect_glyphs (hb_collect_glyphs_context_t *c) const
  { return dispatch (c); }

  hb_closure_lookups_context_t::return_t closure_lookups (hb_closure_lookups_context_t *c, unsigned this_index) const
  {
    if (c->is_lookup_visited (this_index))
      return hb_closure_lookups_context_t::default_return_value ();

    c->set_lookup_visited (this_index);
    if (!intersects (c->glyphs))
    {
      c->set_lookup_inactive (this_index);
      return hb_closure_lookups_context_t::default_return_value ();
    }
    c->set_recurse_func (dispatch_closure_lookups_recurse_func);

    hb_closure_lookups_context_t::return_t ret = dispatch (c);
    return ret;
  }

  template <typename set_t>
  void collect_coverage (set_t *glyphs) const
  {
    hb_collect_coverage_context_t<set_t> c (glyphs);
    dispatch (&c);
  }

  static inline bool apply_recurse_func (hb_ot_apply_context_t *c, unsigned int lookup_index);

  template <typename context_t>
  static typename context_t::return_t dispatch_recurse_func (context_t *c, unsigned int lookup_index);

  HB_INTERNAL static hb_closure_lookups_context_t::return_t dispatch_closure_lookups_recurse_func (hb_closure_lookups_context_t *c, unsigned this_index);

  template <typename context_t, typename ...Ts>
  typename context_t::return_t dispatch (context_t *c, Ts&&... ds) const
  { return Lookup::dispatch<SubTable> (c, hb_forward<Ts> (ds)...); }

  bool subset (hb_subset_context_t *c) const
  { return Lookup::subset<SubTable> (c); }

  bool sanitize (hb_sanitize_context_t *c) const
  { return Lookup::sanitize<SubTable> (c); }
};

/*
 * GPOS -- Glyph Positioning
 * https://docs.microsoft.com/en-us/typography/opentype/spec/gpos
 */

struct GPOS : GSUBGPOS
{
  static constexpr hb_tag_t tableTag = HB_OT_TAG_GPOS;

  const PosLookup& get_lookup (unsigned int i) const
  { return static_cast<const PosLookup &> (GSUBGPOS::get_lookup (i)); }

  static inline void position_start (hb_font_t *font, hb_buffer_t *buffer);
  static inline void position_finish_advances (hb_font_t *font, hb_buffer_t *buffer);
  static inline void position_finish_offsets (hb_font_t *font, hb_buffer_t *buffer);

  bool subset (hb_subset_context_t *c) const
  {
    hb_subset_layout_context_t l (c, tableTag, c->plan->gpos_lookups, c->plan->gpos_langsys, c->plan->gpos_features);
    return GSUBGPOS::subset<PosLookup> (&l);
  }

  bool sanitize (hb_sanitize_context_t *c) const
  { return GSUBGPOS::sanitize<PosLookup> (c); }

  HB_INTERNAL bool is_blocklisted (hb_blob_t *blob,
				   hb_face_t *face) const;

  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const
  {
    for (unsigned i = 0; i < GSUBGPOS::get_lookup_count (); i++)
    {
      if (!c->gpos_lookups->has (i)) continue;
      const PosLookup &l = get_lookup (i);
      l.dispatch (c);
    }
  }

  void closure_lookups (hb_face_t      *face,
			const hb_set_t *glyphs,
			hb_set_t       *lookup_indexes /* IN/OUT */) const
  { GSUBGPOS::closure_lookups<PosLookup> (face, glyphs, lookup_indexes); }

  typedef GSUBGPOS::accelerator_t<GPOS> accelerator_t;
};


static void
reverse_cursive_minor_offset (hb_glyph_position_t *pos, unsigned int i, hb_direction_t direction, unsigned int new_parent)
{
  int chain = pos[i].attach_chain(), type = pos[i].attach_type();
  if (likely (!chain || 0 == (type & ATTACH_TYPE_CURSIVE)))
    return;

  pos[i].attach_chain() = 0;

  unsigned int j = (int) i + chain;

  /* Stop if we see new parent in the chain. */
  if (j == new_parent)
    return;

  reverse_cursive_minor_offset (pos, j, direction, new_parent);

  if (HB_DIRECTION_IS_HORIZONTAL (direction))
    pos[j].y_offset = -pos[i].y_offset;
  else
    pos[j].x_offset = -pos[i].x_offset;

  pos[j].attach_chain() = -chain;
  pos[j].attach_type() = type;
}
static void
propagate_attachment_offsets (hb_glyph_position_t *pos,
			      unsigned int len,
			      unsigned int i,
			      hb_direction_t direction)
{
  /* Adjusts offsets of attached glyphs (both cursive and mark) to accumulate
   * offset of glyph they are attached to. */
  int chain = pos[i].attach_chain(), type = pos[i].attach_type();
  if (likely (!chain))
    return;

  pos[i].attach_chain() = 0;

  unsigned int j = (int) i + chain;

  if (unlikely (j >= len))
    return;

  propagate_attachment_offsets (pos, len, j, direction);

  assert (!!(type & ATTACH_TYPE_MARK) ^ !!(type & ATTACH_TYPE_CURSIVE));

  if (type & ATTACH_TYPE_CURSIVE)
  {
    if (HB_DIRECTION_IS_HORIZONTAL (direction))
      pos[i].y_offset += pos[j].y_offset;
    else
      pos[i].x_offset += pos[j].x_offset;
  }
  else /*if (type & ATTACH_TYPE_MARK)*/
  {
    pos[i].x_offset += pos[j].x_offset;
    pos[i].y_offset += pos[j].y_offset;

    assert (j < i);
    if (HB_DIRECTION_IS_FORWARD (direction))
      for (unsigned int k = j; k < i; k++) {
	pos[i].x_offset -= pos[k].x_advance;
	pos[i].y_offset -= pos[k].y_advance;
      }
    else
      for (unsigned int k = j + 1; k < i + 1; k++) {
	pos[i].x_offset += pos[k].x_advance;
	pos[i].y_offset += pos[k].y_advance;
      }
  }
}

void
GPOS::position_start (hb_font_t *font HB_UNUSED, hb_buffer_t *buffer)
{
  unsigned int count = buffer->len;
  for (unsigned int i = 0; i < count; i++)
    buffer->pos[i].attach_chain() = buffer->pos[i].attach_type() = 0;
}

void
GPOS::position_finish_advances (hb_font_t *font HB_UNUSED, hb_buffer_t *buffer HB_UNUSED)
{
  //_hb_buffer_assert_gsubgpos_vars (buffer);
}

void
GPOS::position_finish_offsets (hb_font_t *font HB_UNUSED, hb_buffer_t *buffer)
{
  _hb_buffer_assert_gsubgpos_vars (buffer);

  unsigned int len;
  hb_glyph_position_t *pos = hb_buffer_get_glyph_positions (buffer, &len);
  hb_direction_t direction = buffer->props.direction;

  /* Handle attachments */
  if (buffer->scratch_flags & HB_BUFFER_SCRATCH_FLAG_HAS_GPOS_ATTACHMENT)
    for (unsigned int i = 0; i < len; i++)
      propagate_attachment_offsets (pos, len, i, direction);
}


struct GPOS_accelerator_t : GPOS::accelerator_t {};


/* Out-of-class implementation for methods recursing */

#ifndef HB_NO_OT_LAYOUT
template <typename context_t>
/*static*/ typename context_t::return_t PosLookup::dispatch_recurse_func (context_t *c, unsigned int lookup_index)
{
  const PosLookup &l = c->face->table.GPOS.get_relaxed ()->table->get_lookup (lookup_index);
  return l.dispatch (c);
}

/*static*/ inline hb_closure_lookups_context_t::return_t PosLookup::dispatch_closure_lookups_recurse_func (hb_closure_lookups_context_t *c, unsigned this_index)
{
  const PosLookup &l = c->face->table.GPOS.get_relaxed ()->table->get_lookup (this_index);
  return l.closure_lookups (c, this_index);
}

/*static*/ bool PosLookup::apply_recurse_func (hb_ot_apply_context_t *c, unsigned int lookup_index)
{
  const PosLookup &l = c->face->table.GPOS.get_relaxed ()->table->get_lookup (lookup_index);
  unsigned int saved_lookup_props = c->lookup_props;
  unsigned int saved_lookup_index = c->lookup_index;
  c->set_lookup_index (lookup_index);
  c->set_lookup_props (l.get_props ());
  bool ret = l.dispatch (c);
  c->set_lookup_index (saved_lookup_index);
  c->set_lookup_props (saved_lookup_props);
  return ret;
}
#endif


} /* namespace OT */


#endif /* HB_OT_LAYOUT_GPOS_TABLE_HH */