hb-ot-shape.cc

/*
 * Copyright © 2009,2010  Red Hat, Inc.
 * Copyright © 2010,2011,2012  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
 */

#define HB_SHAPER ot
#define hb_ot_shape_plan_data_t hb_ot_shape_plan_t
#include "hb-shaper-impl.hh"

#include "hb-ot-shape.hh"
#include "hb-ot-shape-complex.hh"
#include "hb-ot-shape-fallback.hh"
#include "hb-ot-shape-normalize.hh"

#include "hb-ot-face.hh"
#include "hb-ot-layout.hh"
#include "hb-unicode.hh"
#include "hb-set.hh"

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

static hb_tag_t common_features[] = {
  HB_TAG('c','c','m','p'),
  HB_TAG('l','o','c','l'),
  HB_TAG('m','a','r','k'),
  HB_TAG('m','k','m','k'),
  HB_TAG('r','l','i','g'),
  HB_TAG('r','a','n','d'),
};


static hb_tag_t horizontal_features[] = {
  HB_TAG('c','a','l','t'),
  HB_TAG('c','l','i','g'),
  HB_TAG('c','u','r','s'),
  HB_TAG('k','e','r','n'),
  HB_TAG('l','i','g','a'),
  HB_TAG('r','c','l','t'),
};



static void
hb_ot_shape_collect_features (hb_ot_shape_planner_t          *planner,
			      const hb_segment_properties_t  *props,
			      const hb_feature_t             *user_features,
			      unsigned int                    num_user_features)
{
  hb_ot_map_builder_t *map = &planner->map;

  map->add_global_bool_feature (HB_TAG('r','v','r','n'));
  map->add_gsub_pause (nullptr);

  switch (props->direction) {
    case HB_DIRECTION_LTR:
      map->add_global_bool_feature (HB_TAG ('l','t','r','a'));
      map->add_global_bool_feature (HB_TAG ('l','t','r','m'));
      break;
    case HB_DIRECTION_RTL:
      map->add_global_bool_feature (HB_TAG ('r','t','l','a'));
      map->add_feature (HB_TAG ('r','t','l','m'), 1, F_NONE);
      break;
    case HB_DIRECTION_TTB:
    case HB_DIRECTION_BTT:
    case HB_DIRECTION_INVALID:
    default:
      break;
  }

  map->add_feature (HB_TAG ('f','r','a','c'), 1, F_NONE);
  map->add_feature (HB_TAG ('n','u','m','r'), 1, F_NONE);
  map->add_feature (HB_TAG ('d','n','o','m'), 1, F_NONE);

  if (planner->shaper->collect_features)
    planner->shaper->collect_features (planner);

  for (unsigned int i = 0; i < ARRAY_LENGTH (common_features); i++)
    map->add_global_bool_feature (common_features[i]);

  if (HB_DIRECTION_IS_HORIZONTAL (props->direction))
    for (unsigned int i = 0; i < ARRAY_LENGTH (horizontal_features); i++)
      map->add_feature (horizontal_features[i], 1, F_GLOBAL |
			(horizontal_features[i] == HB_TAG('k','e','r','n') ?
			 F_HAS_FALLBACK : F_NONE));
  else
  {
    /* We really want to find a 'vert' feature if there's any in the font, no
     * matter which script/langsys it is listed (or not) under.
     * See various bugs referenced from:
     * https://github.com/harfbuzz/harfbuzz/issues/63 */
    map->add_feature (HB_TAG ('v','e','r','t'), 1, F_GLOBAL | F_GLOBAL_SEARCH);
  }

  if (planner->shaper->override_features)
    planner->shaper->override_features (planner);

  for (unsigned int i = 0; i < num_user_features; i++) {
    const hb_feature_t *feature = &user_features[i];
    map->add_feature (feature->tag, feature->value,
		      (feature->start == 0 && feature->end == (unsigned int) -1) ?
		       F_GLOBAL : F_NONE);
  }
}


/*
 * shaper face data
 */

HB_SHAPER_DATA_ENSURE_DEFINE(ot, face)

hb_ot_face_data_t *
_hb_ot_shaper_face_data_create (hb_face_t *face)
{
  return _hb_ot_face_data_create (face);
}

void
_hb_ot_shaper_face_data_destroy (hb_ot_face_data_t *data)
{
  _hb_ot_face_data_destroy (data);
}


/*
 * shaper font data
 */

HB_SHAPER_DATA_ENSURE_DEFINE(ot, font)

struct hb_ot_font_data_t {};

hb_ot_font_data_t *
_hb_ot_shaper_font_data_create (hb_font_t *font HB_UNUSED)
{
  return (hb_ot_font_data_t *) HB_SHAPER_DATA_SUCCEEDED;
}

void
_hb_ot_shaper_font_data_destroy (hb_ot_font_data_t *data)
{
}


/*
 * shaper shape_plan data
 */

hb_ot_shape_plan_data_t *
_hb_ot_shaper_shape_plan_data_create (hb_shape_plan_t    *shape_plan,
				      const hb_feature_t *user_features,
				      unsigned int        num_user_features,
				      const int          *coords,
				      unsigned int        num_coords)
{
  hb_ot_shape_plan_t *plan = (hb_ot_shape_plan_t *) calloc (1, sizeof (hb_ot_shape_plan_t));
  if (unlikely (!plan))
    return nullptr;

  plan->init ();

  hb_ot_shape_planner_t planner (shape_plan);

  planner.shaper = hb_ot_shape_complex_categorize (&planner);

  hb_ot_shape_collect_features (&planner, &shape_plan->props,
				user_features, num_user_features);

  planner.compile (*plan, coords, num_coords);

  if (plan->shaper->data_create) {
    plan->data = plan->shaper->data_create (plan);
    if (unlikely (!plan->data))
    {
      free (plan);
      return nullptr;
    }
  }

  return plan;
}

void
_hb_ot_shaper_shape_plan_data_destroy (hb_ot_shape_plan_data_t *plan)
{
  if (plan->shaper->data_destroy)
    plan->shaper->data_destroy (const_cast<void *> (plan->data));

  plan->fini ();

  free (plan);
}


/*
 * shaper
 */

struct hb_ot_shape_context_t
{
  hb_ot_shape_plan_t *plan;
  hb_font_t *font;
  hb_face_t *face;
  hb_buffer_t  *buffer;
  const hb_feature_t *user_features;
  unsigned int        num_user_features;

  /* Transient stuff */
  bool fallback_positioning;
  bool fallback_glyph_classes;
  hb_direction_t target_direction;
};



/* Main shaper */


/* Prepare */

static void
hb_set_unicode_props (hb_buffer_t *buffer)
{
  unsigned int count = buffer->len;
  hb_glyph_info_t *info = buffer->info;
  for (unsigned int i = 0; i < count; i++)
    _hb_glyph_info_set_unicode_props (&info[i], buffer);
}

static void
hb_insert_dotted_circle (hb_buffer_t *buffer, hb_font_t *font)
{
  if (!(buffer->flags & HB_BUFFER_FLAG_BOT) ||
      buffer->context_len[0] ||
      _hb_glyph_info_get_general_category (&buffer->info[0]) !=
      HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK)
    return;

  if (!font->has_glyph (0x25CCu))
    return;

  hb_glyph_info_t dottedcircle = {0};
  dottedcircle.codepoint = 0x25CCu;
  _hb_glyph_info_set_unicode_props (&dottedcircle, buffer);

  buffer->clear_output ();

  buffer->idx = 0;
  hb_glyph_info_t info = dottedcircle;
  info.cluster = buffer->cur().cluster;
  info.mask = buffer->cur().mask;
  buffer->output_info (info);
  while (buffer->idx < buffer->len && buffer->successful)
    buffer->next_glyph ();

  buffer->swap_buffers ();
}

static void
hb_form_clusters (hb_buffer_t *buffer)
{
  if (!(buffer->scratch_flags & HB_BUFFER_SCRATCH_FLAG_HAS_NON_ASCII))
    return;

  /* Loop duplicated in hb_ensure_native_direction(), and in _hb-coretext.cc */
  unsigned int base = 0;
  unsigned int count = buffer->len;
  hb_glyph_info_t *info = buffer->info;
  for (unsigned int i = 1; i < count; i++)
  {
    if (likely (!HB_UNICODE_GENERAL_CATEGORY_IS_MARK (_hb_glyph_info_get_general_category (&info[i])) &&
		!_hb_glyph_info_is_joiner (&info[i])))
    {
      if (buffer->cluster_level == HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES)
	buffer->merge_clusters (base, i);
      else
	buffer->unsafe_to_break (base, i);
      base = i;
    }
  }
  if (buffer->cluster_level == HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES)
    buffer->merge_clusters (base, count);
  else
    buffer->unsafe_to_break (base, count);
}

static void
hb_ensure_native_direction (hb_buffer_t *buffer)
{
  hb_direction_t direction = buffer->props.direction;
  hb_direction_t horiz_dir = hb_script_get_horizontal_direction (buffer->props.script);

  /* TODO vertical:
   * The only BTT vertical script is Ogham, but it's not clear to me whether OpenType
   * Ogham fonts are supposed to be implemented BTT or not.  Need to research that
   * first. */
  if ((HB_DIRECTION_IS_HORIZONTAL (direction) &&
       direction != horiz_dir && horiz_dir != HB_DIRECTION_INVALID) ||
      (HB_DIRECTION_IS_VERTICAL   (direction) &&
       direction != HB_DIRECTION_TTB))
  {
    /* Same loop as hb_form_clusters().
     * Since form_clusters() merged clusters already, we don't merge. */
    unsigned int base = 0;
    unsigned int count = buffer->len;
    hb_glyph_info_t *info = buffer->info;
    for (unsigned int i = 1; i < count; i++)
    {
      if (likely (!HB_UNICODE_GENERAL_CATEGORY_IS_MARK (_hb_glyph_info_get_general_category (&info[i]))))
      {
	if (buffer->cluster_level == HB_BUFFER_CLUSTER_LEVEL_MONOTONE_CHARACTERS)
	  buffer->merge_clusters (base, i);
	buffer->reverse_range (base, i);

	base = i;
      }
    }
    if (buffer->cluster_level == HB_BUFFER_CLUSTER_LEVEL_MONOTONE_CHARACTERS)
      buffer->merge_clusters (base, count);
    buffer->reverse_range (base, count);

    buffer->reverse ();

    buffer->props.direction = HB_DIRECTION_REVERSE (buffer->props.direction);
  }
}


/* Substitute */

static inline void
hb_ot_mirror_chars (hb_ot_shape_context_t *c)
{
  if (HB_DIRECTION_IS_FORWARD (c->target_direction))
    return;

  hb_buffer_t *buffer = c->buffer;
  hb_unicode_funcs_t *unicode = buffer->unicode;
  hb_mask_t rtlm_mask = c->plan->rtlm_mask;

  unsigned int count = buffer->len;
  hb_glyph_info_t *info = buffer->info;
  for (unsigned int i = 0; i < count; i++) {
    hb_codepoint_t codepoint = unicode->mirroring (info[i].codepoint);
    if (likely (codepoint == info[i].codepoint || !c->font->has_glyph (codepoint)))
      info[i].mask |= rtlm_mask;
    else
      info[i].codepoint = codepoint;
  }
}

static inline void
hb_ot_shape_setup_masks_fraction (hb_ot_shape_context_t *c)
{
  if (!(c->buffer->scratch_flags & HB_BUFFER_SCRATCH_FLAG_HAS_NON_ASCII) ||
      !c->plan->has_frac)
    return;

  hb_buffer_t *buffer = c->buffer;

  hb_mask_t pre_mask, post_mask;
  if (HB_DIRECTION_IS_FORWARD (buffer->props.direction))
  {
    pre_mask = c->plan->numr_mask | c->plan->frac_mask;
    post_mask = c->plan->frac_mask | c->plan->dnom_mask;
  }
  else
  {
    pre_mask = c->plan->frac_mask | c->plan->dnom_mask;
    post_mask = c->plan->numr_mask | c->plan->frac_mask;
  }

  unsigned int count = buffer->len;
  hb_glyph_info_t *info = buffer->info;
  for (unsigned int i = 0; i < count; i++)
  {
    if (info[i].codepoint == 0x2044u) /* FRACTION SLASH */
    {
      unsigned int start = i, end = i + 1;
      while (start &&
	     _hb_glyph_info_get_general_category (&info[start - 1]) ==
	     HB_UNICODE_GENERAL_CATEGORY_DECIMAL_NUMBER)
        start--;
      while (end < count &&
	     _hb_glyph_info_get_general_category (&info[end]) ==
	     HB_UNICODE_GENERAL_CATEGORY_DECIMAL_NUMBER)
        end++;

      buffer->unsafe_to_break (start, end);

      for (unsigned int j = start; j < i; j++)
        info[j].mask |= pre_mask;
      info[i].mask |= c->plan->frac_mask;
      for (unsigned int j = i + 1; j < end; j++)
        info[j].mask |= post_mask;

      i = end - 1;
    }
  }
}

static inline void
hb_ot_shape_initialize_masks (hb_ot_shape_context_t *c)
{
  hb_ot_map_t *map = &c->plan->map;
  hb_buffer_t *buffer = c->buffer;

  hb_mask_t global_mask = map->get_global_mask ();
  buffer->reset_masks (global_mask);
}

static inline void
hb_ot_shape_setup_masks (hb_ot_shape_context_t *c)
{
  hb_ot_map_t *map = &c->plan->map;
  hb_buffer_t *buffer = c->buffer;

  hb_ot_shape_setup_masks_fraction (c);

  if (c->plan->shaper->setup_masks)
    c->plan->shaper->setup_masks (c->plan, buffer, c->font);

  for (unsigned int i = 0; i < c->num_user_features; i++)
  {
    const hb_feature_t *feature = &c->user_features[i];
    if (!(feature->start == 0 && feature->end == (unsigned int)-1)) {
      unsigned int shift;
      hb_mask_t mask = map->get_mask (feature->tag, &shift);
      buffer->set_masks (feature->value << shift, mask, feature->start, feature->end);
    }
  }
}

static void
hb_ot_zero_width_default_ignorables (hb_ot_shape_context_t *c)
{
  hb_buffer_t *buffer = c->buffer;

  if (!(buffer->scratch_flags & HB_BUFFER_SCRATCH_FLAG_HAS_DEFAULT_IGNORABLES) ||
      (buffer->flags & HB_BUFFER_FLAG_PRESERVE_DEFAULT_IGNORABLES) ||
      (buffer->flags & HB_BUFFER_FLAG_REMOVE_DEFAULT_IGNORABLES))
    return;

  unsigned int count = buffer->len;
  hb_glyph_info_t *info = buffer->info;
  hb_glyph_position_t *pos = buffer->pos;
  unsigned int i = 0;
  for (i = 0; i < count; i++)
    if (unlikely (_hb_glyph_info_is_default_ignorable (&info[i])))
      pos[i].x_advance = pos[i].y_advance = pos[i].x_offset = pos[i].y_offset = 0;
}

static void
hb_ot_hide_default_ignorables (hb_ot_shape_context_t *c)
{
  hb_buffer_t *buffer = c->buffer;

  if (!(buffer->scratch_flags & HB_BUFFER_SCRATCH_FLAG_HAS_DEFAULT_IGNORABLES) ||
      (buffer->flags & HB_BUFFER_FLAG_PRESERVE_DEFAULT_IGNORABLES))
    return;

  unsigned int count = buffer->len;
  hb_glyph_info_t *info = buffer->info;
  hb_glyph_position_t *pos = buffer->pos;
  unsigned int i = 0;
  for (i = 0; i < count; i++)
  {
    if (unlikely (_hb_glyph_info_is_default_ignorable (&info[i])))
      break;
  }

  /* No default-ignorables found; return. */
  if (i == count)
    return;

  hb_codepoint_t space;
  if (!(buffer->flags & HB_BUFFER_FLAG_REMOVE_DEFAULT_IGNORABLES) &&
      c->font->get_nominal_glyph (' ', &space))
  {
    /* Replace default-ignorables with a zero-advance space glyph. */
    for (/*continue*/; i < count; i++)
    {
      if (_hb_glyph_info_is_default_ignorable (&info[i]))
	info[i].codepoint = space;
    }
  }
  else
  {
    /* Merge clusters and delete default-ignorables.
     * NOTE! We can't use out-buffer as we have positioning data. */
    unsigned int j = i;
    for (; i < count; i++)
    {
      if (_hb_glyph_info_is_default_ignorable (&info[i]))
      {
	/* Merge clusters.
	 * Same logic as buffer->delete_glyph(), but for in-place removal. */

	unsigned int cluster = info[i].cluster;
	if (i + 1 < count && cluster == info[i + 1].cluster)
	  continue; /* Cluster survives; do nothing. */

	if (j)
	{
	  /* Merge cluster backward. */
	  if (cluster < info[j - 1].cluster)
	  {
	    unsigned int mask = info[i].mask;
	    unsigned int old_cluster = info[j - 1].cluster;
	    for (unsigned k = j; k && info[k - 1].cluster == old_cluster; k--)
	      buffer->set_cluster (info[k - 1], cluster, mask);
	  }
	  continue;
	}

	if (i + 1 < count)
	  buffer->merge_clusters (i, i + 2); /* Merge cluster forward. */

	continue;
      }

      if (j != i)
      {
	info[j] = info[i];
	pos[j] = pos[i];
      }
      j++;
    }
    buffer->len = j;
  }
}


static inline void
hb_ot_map_glyphs_fast (hb_buffer_t  *buffer)
{
  /* Normalization process sets up glyph_index(), we just copy it. */
  unsigned int count = buffer->len;
  hb_glyph_info_t *info = buffer->info;
  for (unsigned int i = 0; i < count; i++)
    info[i].codepoint = info[i].glyph_index();

  buffer->content_type = HB_BUFFER_CONTENT_TYPE_GLYPHS;
}

static inline void
hb_synthesize_glyph_classes (hb_ot_shape_context_t *c)
{
  unsigned int count = c->buffer->len;
  hb_glyph_info_t *info = c->buffer->info;
  for (unsigned int i = 0; i < count; i++)
  {
    hb_ot_layout_glyph_props_flags_t klass;

    /* Never mark default-ignorables as marks.
     * They won't get in the way of lookups anyway,
     * but having them as mark will cause them to be skipped
     * over if the lookup-flag says so, but at least for the
     * Mongolian variation selectors, looks like Uniscribe
     * marks them as non-mark.  Some Mongolian fonts without
     * GDEF rely on this.  Another notable character that
     * this applies to is COMBINING GRAPHEME JOINER. */
    klass = (_hb_glyph_info_get_general_category (&info[i]) !=
	     HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK ||
	     _hb_glyph_info_is_default_ignorable (&info[i])) ?
	    HB_OT_LAYOUT_GLYPH_PROPS_BASE_GLYPH :
	    HB_OT_LAYOUT_GLYPH_PROPS_MARK;
    _hb_glyph_info_set_glyph_props (&info[i], klass);
  }
}

static inline void
hb_ot_substitute_default (hb_ot_shape_context_t *c)
{
  hb_buffer_t *buffer = c->buffer;

  hb_ot_mirror_chars (c);

  HB_BUFFER_ALLOCATE_VAR (buffer, glyph_index);

  _hb_ot_shape_normalize (c->plan, buffer, c->font);

  hb_ot_shape_setup_masks (c);

  /* This is unfortunate to go here, but necessary... */
  if (c->fallback_positioning)
    _hb_ot_shape_fallback_position_recategorize_marks (c->plan, c->font, buffer);

  hb_ot_map_glyphs_fast (buffer);

  HB_BUFFER_DEALLOCATE_VAR (buffer, glyph_index);
}

static inline void
hb_ot_substitute_complex (hb_ot_shape_context_t *c)
{
  hb_buffer_t *buffer = c->buffer;

  hb_ot_layout_substitute_start (c->font, buffer);

  if (!hb_ot_layout_has_glyph_classes (c->face))
    hb_synthesize_glyph_classes (c);

  c->plan->substitute (c->font, buffer);

  if (0) /* XXX Call morx instead. */
    hb_aat_layout_substitute (c->font, c->buffer);
}

static inline void
hb_ot_substitute (hb_ot_shape_context_t *c)
{
  hb_ot_substitute_default (c);

  _hb_buffer_allocate_gsubgpos_vars (c->buffer);

  hb_ot_substitute_complex (c);
}

/* Position */

static inline void
adjust_mark_offsets (hb_glyph_position_t *pos)
{
  pos->x_offset -= pos->x_advance;
  pos->y_offset -= pos->y_advance;
}

static inline void
zero_mark_width (hb_glyph_position_t *pos)
{
  pos->x_advance = 0;
  pos->y_advance = 0;
}

static inline void
zero_mark_widths_by_gdef (hb_buffer_t *buffer, bool adjust_offsets)
{
  unsigned int count = buffer->len;
  hb_glyph_info_t *info = buffer->info;
  for (unsigned int i = 0; i < count; i++)
    if (_hb_glyph_info_is_mark (&info[i]))
    {
      if (adjust_offsets)
        adjust_mark_offsets (&buffer->pos[i]);
      zero_mark_width (&buffer->pos[i]);
    }
}

static inline void
hb_ot_position_default (hb_ot_shape_context_t *c)
{
  hb_direction_t direction = c->buffer->props.direction;
  unsigned int count = c->buffer->len;
  hb_glyph_info_t *info = c->buffer->info;
  hb_glyph_position_t *pos = c->buffer->pos;

  if (HB_DIRECTION_IS_HORIZONTAL (direction))
  {
    c->font->get_glyph_h_advances (count, &info[0].codepoint, sizeof(info[0]),
                                   &pos[0].x_advance, sizeof(pos[0]));
    /* The nil glyph_h_origin() func returns 0, so no need to apply it. */
    if (c->font->has_glyph_h_origin_func ())
      for (unsigned int i = 0; i < count; i++)
	c->font->subtract_glyph_h_origin (info[i].codepoint,
					  &pos[i].x_offset,
					  &pos[i].y_offset);
  }
  else
  {
    c->font->get_glyph_v_advances (count, &info[0].codepoint, sizeof(info[0]),
                                   &pos[0].y_advance, sizeof(pos[0]));
    for (unsigned int i = 0; i < count; i++)
    {
      c->font->subtract_glyph_v_origin (info[i].codepoint,
					&pos[i].x_offset,
					&pos[i].y_offset);
    }
  }
  if (c->buffer->scratch_flags & HB_BUFFER_SCRATCH_FLAG_HAS_SPACE_FALLBACK)
    _hb_ot_shape_fallback_spaces (c->plan, c->font, c->buffer);
}

static inline void
hb_ot_position_complex (hb_ot_shape_context_t *c)
{
  unsigned int count = c->buffer->len;
  hb_glyph_info_t *info = c->buffer->info;
  hb_glyph_position_t *pos = c->buffer->pos;

  /* If the font has no GPOS, AND, no fallback positioning will
   * happen, AND, direction is forward, then when zeroing mark
   * widths, we shift the mark with it, such that the mark
   * is positioned hanging over the previous glyph.  When
   * direction is backward we don't shift and it will end up
   * hanging over the next glyph after the final reordering.
   * If fallback positinoing happens or GPOS is present, we don't
   * care.
   */
  bool adjust_offsets_when_zeroing = c->fallback_positioning &&
				     !c->plan->shaper->fallback_position &&
				     HB_DIRECTION_IS_FORWARD (c->buffer->props.direction);

  /* We change glyph origin to what GPOS expects (horizontal), apply GPOS, change it back. */

  /* The nil glyph_h_origin() func returns 0, so no need to apply it. */
  if (c->font->has_glyph_h_origin_func ())
    for (unsigned int i = 0; i < count; i++)
      c->font->add_glyph_h_origin (info[i].codepoint,
				   &pos[i].x_offset,
				   &pos[i].y_offset);

  hb_ot_layout_position_start (c->font, c->buffer);

  switch (c->plan->shaper->zero_width_marks)
  {
    case HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_EARLY:
      zero_mark_widths_by_gdef (c->buffer, adjust_offsets_when_zeroing);
      break;

    default:
    case HB_OT_SHAPE_ZERO_WIDTH_MARKS_NONE:
    case HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_LATE:
      break;
  }

  if (likely (!c->fallback_positioning))
    c->plan->position (c->font, c->buffer);

  switch (c->plan->shaper->zero_width_marks)
  {
    case HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_LATE:
      zero_mark_widths_by_gdef (c->buffer, adjust_offsets_when_zeroing);
      break;

    default:
    case HB_OT_SHAPE_ZERO_WIDTH_MARKS_NONE:
    case HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_EARLY:
      break;
  }

  /* Finishing off GPOS has to follow a certain order. */
  hb_ot_layout_position_finish_advances (c->font, c->buffer);
  hb_ot_zero_width_default_ignorables (c);
  hb_ot_layout_position_finish_offsets (c->font, c->buffer);

  /* The nil glyph_h_origin() func returns 0, so no need to apply it. */
  if (c->font->has_glyph_h_origin_func ())
    for (unsigned int i = 0; i < count; i++)
      c->font->subtract_glyph_h_origin (info[i].codepoint,
					&pos[i].x_offset,
					&pos[i].y_offset);
}

static inline void
hb_ot_position (hb_ot_shape_context_t *c)
{
  c->buffer->clear_positions ();

  hb_ot_position_default (c);

  hb_ot_position_complex (c);

  if (c->fallback_positioning && c->plan->shaper->fallback_position)
    _hb_ot_shape_fallback_position (c->plan, c->font, c->buffer);

  if (HB_DIRECTION_IS_BACKWARD (c->buffer->props.direction))
    hb_buffer_reverse (c->buffer);

  /* Visual fallback goes here. */

  if (c->fallback_positioning)
    _hb_ot_shape_fallback_kern (c->plan, c->font, c->buffer);

  _hb_buffer_deallocate_gsubgpos_vars (c->buffer);

  //hb_aat_layout_position (c->font, c->buffer);
}

static inline void
hb_propagate_flags (hb_buffer_t *buffer)
{
  /* Propagate cluster-level glyph flags to be the same on all cluster glyphs.
   * Simplifies using them. */

  if (!(buffer->scratch_flags & HB_BUFFER_SCRATCH_FLAG_HAS_UNSAFE_TO_BREAK))
    return;

  hb_glyph_info_t *info = buffer->info;

  foreach_cluster (buffer, start, end)
  {
    unsigned int mask = 0;
    for (unsigned int i = start; i < end; i++)
      if (info[i].mask & HB_GLYPH_FLAG_UNSAFE_TO_BREAK)
      {
	 mask = HB_GLYPH_FLAG_UNSAFE_TO_BREAK;
	 break;
      }
    if (mask)
      for (unsigned int i = start; i < end; i++)
	info[i].mask |= mask;
  }
}

/* Pull it all together! */

static void
hb_ot_shape_internal (hb_ot_shape_context_t *c)
{
  c->buffer->deallocate_var_all ();
  c->buffer->scratch_flags = HB_BUFFER_SCRATCH_FLAG_DEFAULT;
  if (likely (!hb_unsigned_mul_overflows (c->buffer->len, HB_BUFFER_MAX_LEN_FACTOR)))
  {
    c->buffer->max_len = MAX (c->buffer->len * HB_BUFFER_MAX_LEN_FACTOR,
			      (unsigned) HB_BUFFER_MAX_LEN_MIN);
  }
  if (likely (!hb_unsigned_mul_overflows (c->buffer->len, HB_BUFFER_MAX_OPS_FACTOR)))
  {
    c->buffer->max_ops = MAX (c->buffer->len * HB_BUFFER_MAX_OPS_FACTOR,
			      (unsigned) HB_BUFFER_MAX_OPS_MIN);
  }

  bool disable_otl = c->plan->shaper->disable_otl && c->plan->shaper->disable_otl (c->plan);
  //c->fallback_substitute     = disable_otl || !hb_ot_layout_has_substitution (c->face);
  c->fallback_positioning    = disable_otl || !hb_ot_layout_has_positioning (c->face);
  c->fallback_glyph_classes  = disable_otl || !hb_ot_layout_has_glyph_classes (c->face);

  /* Save the original direction, we use it later. */
  c->target_direction = c->buffer->props.direction;

  _hb_buffer_allocate_unicode_vars (c->buffer);

  c->buffer->clear_output ();

  hb_ot_shape_initialize_masks (c);
  hb_set_unicode_props (c->buffer);
  hb_insert_dotted_circle (c->buffer, c->font);

  hb_form_clusters (c->buffer);

  hb_ensure_native_direction (c->buffer);

  if (c->plan->shaper->preprocess_text)
    c->plan->shaper->preprocess_text (c->plan, c->buffer, c->font);

  hb_ot_substitute (c);
  hb_ot_position (c);

  hb_ot_hide_default_ignorables (c);

  if (c->plan->shaper->postprocess_glyphs)
    c->plan->shaper->postprocess_glyphs (c->plan, c->buffer, c->font);

  hb_propagate_flags (c->buffer);

  _hb_buffer_deallocate_unicode_vars (c->buffer);

  c->buffer->props.direction = c->target_direction;

  c->buffer->max_len = HB_BUFFER_MAX_LEN_DEFAULT;
  c->buffer->max_ops = HB_BUFFER_MAX_OPS_DEFAULT;
  c->buffer->deallocate_var_all ();
}


hb_bool_t
_hb_ot_shape (hb_shape_plan_t    *shape_plan,
	      hb_font_t          *font,
	      hb_buffer_t        *buffer,
	      const hb_feature_t *features,
	      unsigned int        num_features)
{
  hb_ot_shape_context_t c = {HB_SHAPER_DATA_GET (shape_plan), font, font->face, buffer, features, num_features};
  hb_ot_shape_internal (&c);

  return true;
}


/**
 * hb_ot_shape_plan_collect_lookups:
 *
 * Since: 0.9.7
 **/
void
hb_ot_shape_plan_collect_lookups (hb_shape_plan_t *shape_plan,
				  hb_tag_t         table_tag,
				  hb_set_t        *lookup_indexes /* OUT */)
{
  /* XXX Does the first part always succeed? */
  HB_SHAPER_DATA_GET (shape_plan)->collect_lookups (table_tag, lookup_indexes);
}


/* TODO Move this to hb-ot-shape-normalize, make it do decompose, and make it public. */
static void
add_char (hb_font_t          *font,
	  hb_unicode_funcs_t *unicode,
	  hb_bool_t           mirror,
	  hb_codepoint_t      u,
	  hb_set_t           *glyphs)
{
  hb_codepoint_t glyph;
  if (font->get_nominal_glyph (u, &glyph))
    glyphs->add (glyph);
  if (mirror)
  {
    hb_codepoint_t m = unicode->mirroring (u);
    if (m != u && font->get_nominal_glyph (m, &glyph))
      glyphs->add (glyph);
  }
}


/**
 * hb_ot_shape_glyphs_closure:
 *
 * Since: 0.9.2
 **/
void
hb_ot_shape_glyphs_closure (hb_font_t          *font,
			    hb_buffer_t        *buffer,
			    const hb_feature_t *features,
			    unsigned int        num_features,
			    hb_set_t           *glyphs)
{
  const char *shapers[] = {"ot", nullptr};
  hb_shape_plan_t *shape_plan = hb_shape_plan_create_cached (font->face, &buffer->props,
							     features, num_features, shapers);

  bool mirror = hb_script_get_horizontal_direction (buffer->props.script) == HB_DIRECTION_RTL;

  unsigned int count = buffer->len;
  hb_glyph_info_t *info = buffer->info;
  for (unsigned int i = 0; i < count; i++)
    add_char (font, buffer->unicode, mirror, info[i].codepoint, glyphs);

  hb_set_t *lookups = hb_set_create ();
  hb_ot_shape_plan_collect_lookups (shape_plan, HB_OT_TAG_GSUB, lookups);
  hb_ot_layout_lookups_substitute_closure (font->face, lookups, glyphs);

  hb_set_destroy (lookups);

  hb_shape_plan_destroy (shape_plan);
}