tor-browser

hb-ot-layout.cc (93143B)

---

/*
* Copyright © 1998-2004  David Turner and Werner Lemberg
* Copyright © 2006  Behdad Esfahbod
* Copyright © 2007,2008,2009  Red Hat, Inc.
* Copyright © 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
*/

#include "hb.hh"

#ifndef HB_NO_OT_LAYOUT

#ifdef HB_NO_OT_TAG
#error "Cannot compile hb-ot-layout.cc with HB_NO_OT_TAG."
#endif

#include "hb-open-type.hh"
#include "hb-ot-layout.hh"
#include "hb-ot-face.hh"
#include "hb-ot-map.hh"
#include "hb-map.hh"

#include "hb-ot-kern-table.hh"
#include "hb-ot-layout-gdef-table.hh"
#include "hb-ot-layout-gsub-table.hh"
#include "hb-ot-layout-gpos-table.hh"
#include "hb-ot-layout-base-table.hh"
#include "hb-ot-layout-jstf-table.hh" // Just so we compile it; unused otherwise.
#include "hb-ot-name-table.hh"
#include "hb-ot-os2-table.hh"

#include "hb-aat-layout-morx-table.hh"
#include "hb-aat-layout-opbd-table.hh" // Just so we compile it; unused otherwise.

using OT::Layout::GSUB;
using OT::Layout::GPOS;

/**
* SECTION:hb-ot-layout
* @title: hb-ot-layout
* @short_description: OpenType Layout
* @include: hb-ot.h
*
* Functions for querying OpenType Layout features in the font face.
* See the [OpenType specification](http://www.microsoft.com/typography/otspec/)
* for details.
**/


/*
* kern
*/

#ifndef HB_NO_OT_KERN
/**
* hb_ot_layout_has_kerning:
* @face: The #hb_face_t to work on
*
* Tests whether a face includes any kerning data in the 'kern' table.
* Does NOT test for kerning lookups in the GPOS table.
*
* Return value: `true` if data found, `false` otherwise
*
**/
bool
hb_ot_layout_has_kerning (hb_face_t *face)
{
 return face->table.kern->table->has_data ();
}

/**
* hb_ot_layout_has_machine_kerning:
* @face: The #hb_face_t to work on
*
* Tests whether a face includes any state-machine kerning in the 'kern' table.
* Does NOT examine the GPOS table.
*
* Return value: `true` if data found, `false` otherwise
*
**/
bool
hb_ot_layout_has_machine_kerning (hb_face_t *face)
{
 return face->table.kern->table->has_state_machine ();
}

/**
* hb_ot_layout_has_cross_kerning:
* @face: The #hb_face_t to work on
*
* Tests whether a face has any cross-stream kerning (i.e., kerns
* that make adjustments perpendicular to the direction of the text
* flow: Y adjustments in horizontal text or X adjustments in
* vertical text) in the 'kern' table.
*
* Does NOT examine the GPOS table.
*
* Return value: `true` is data found, `false` otherwise
*
**/
bool
hb_ot_layout_has_cross_kerning (hb_face_t *face)
{
 return face->table.kern->table->has_cross_stream ();
}

void
hb_ot_layout_kern (const hb_ot_shape_plan_t *plan,
	   hb_font_t *font,
	   hb_buffer_t  *buffer)
{
 auto &accel = *font->face->table.kern;
 hb_blob_t *blob = accel.get_blob ();

 AAT::hb_aat_apply_context_t c (plan, font, buffer, blob);

 if (!buffer->message (font, "start table kern")) return;
 c.buffer_glyph_set = accel.scratch.create_buffer_glyph_set ();
 accel.apply (&c);
 accel.scratch.destroy_buffer_glyph_set (c.buffer_glyph_set);
 (void) buffer->message (font, "end table kern");
}
#endif


/*
* GDEF
*/

bool
OT::GDEF::is_blocklisted (hb_blob_t *blob,
		  hb_face_t *face) const
{
#ifdef HB_NO_OT_LAYOUT_BLOCKLIST
 return false;
#endif
 /* The ugly business of blocklisting individual fonts' tables happen here!
  * See this thread for why we finally had to bend in and do this:
  * https://lists.freedesktop.org/archives/harfbuzz/2016-February/005489.html
  *
  * In certain versions of Times New Roman Italic and Bold Italic,
  * ASCII double quotation mark U+0022 has wrong glyph class 3 (mark)
  * in GDEF.  Many versions of Tahoma have bad GDEF tables that
  * incorrectly classify some spacing marks such as certain IPA
  * symbols as glyph class 3. So do older versions of Microsoft
  * Himalaya, and the version of Cantarell shipped by Ubuntu 16.04.
  *
  * Nuke the GDEF tables of to avoid unwanted width-zeroing.
  *
  * See https://bugzilla.mozilla.org/show_bug.cgi?id=1279925
  *     https://bugzilla.mozilla.org/show_bug.cgi?id=1279693
  *     https://bugzilla.mozilla.org/show_bug.cgi?id=1279875
  */
 switch HB_CODEPOINT_ENCODE3(blob->length,
		      face->table.GSUB->table.get_length (),
		      face->table.GPOS->table.get_length ())
 {
   /* sha1sum:c5ee92f0bca4bfb7d06c4d03e8cf9f9cf75d2e8a Windows 7? timesi.ttf */
   case HB_CODEPOINT_ENCODE3 (442, 2874, 42038):
   /* sha1sum:37fc8c16a0894ab7b749e35579856c73c840867b Windows 7? timesbi.ttf */
   case HB_CODEPOINT_ENCODE3 (430, 2874, 40662):
   /* sha1sum:19fc45110ea6cd3cdd0a5faca256a3797a069a80 Windows 7 timesi.ttf */
   case HB_CODEPOINT_ENCODE3 (442, 2874, 39116):
   /* sha1sum:6d2d3c9ed5b7de87bc84eae0df95ee5232ecde26 Windows 7 timesbi.ttf */
   case HB_CODEPOINT_ENCODE3 (430, 2874, 39374):
   /* sha1sum:8583225a8b49667c077b3525333f84af08c6bcd8 OS X 10.11.3 Times New Roman Italic.ttf */
   case HB_CODEPOINT_ENCODE3 (490, 3046, 41638):
   /* sha1sum:ec0f5a8751845355b7c3271d11f9918a966cb8c9 OS X 10.11.3 Times New Roman Bold Italic.ttf */
   case HB_CODEPOINT_ENCODE3 (478, 3046, 41902):
   /* sha1sum:96eda93f7d33e79962451c6c39a6b51ee893ce8c  tahoma.ttf from Windows 8 */
   case HB_CODEPOINT_ENCODE3 (898, 12554, 46470):
   /* sha1sum:20928dc06014e0cd120b6fc942d0c3b1a46ac2bc  tahomabd.ttf from Windows 8 */
   case HB_CODEPOINT_ENCODE3 (910, 12566, 47732):
   /* sha1sum:4f95b7e4878f60fa3a39ca269618dfde9721a79e  tahoma.ttf from Windows 8.1 */
   case HB_CODEPOINT_ENCODE3 (928, 23298, 59332):
   /* sha1sum:6d400781948517c3c0441ba42acb309584b73033  tahomabd.ttf from Windows 8.1 */
   case HB_CODEPOINT_ENCODE3 (940, 23310, 60732):
   /* tahoma.ttf v6.04 from Windows 8.1 x64, see https://bugzilla.mozilla.org/show_bug.cgi?id=1279925 */
   case HB_CODEPOINT_ENCODE3 (964, 23836, 60072):
   /* tahomabd.ttf v6.04 from Windows 8.1 x64, see https://bugzilla.mozilla.org/show_bug.cgi?id=1279925 */
   case HB_CODEPOINT_ENCODE3 (976, 23832, 61456):
   /* sha1sum:e55fa2dfe957a9f7ec26be516a0e30b0c925f846  tahoma.ttf from Windows 10 */
   case HB_CODEPOINT_ENCODE3 (994, 24474, 60336):
   /* sha1sum:7199385abb4c2cc81c83a151a7599b6368e92343  tahomabd.ttf from Windows 10 */
   case HB_CODEPOINT_ENCODE3 (1006, 24470, 61740):
   /* tahoma.ttf v6.91 from Windows 10 x64, see https://bugzilla.mozilla.org/show_bug.cgi?id=1279925 */
   case HB_CODEPOINT_ENCODE3 (1006, 24576, 61346):
   /* tahomabd.ttf v6.91 from Windows 10 x64, see https://bugzilla.mozilla.org/show_bug.cgi?id=1279925 */
   case HB_CODEPOINT_ENCODE3 (1018, 24572, 62828):
   /* sha1sum:b9c84d820c49850d3d27ec498be93955b82772b5  tahoma.ttf from Windows 10 AU */
   case HB_CODEPOINT_ENCODE3 (1006, 24576, 61352):
   /* sha1sum:2bdfaab28174bdadd2f3d4200a30a7ae31db79d2  tahomabd.ttf from Windows 10 AU */
   case HB_CODEPOINT_ENCODE3 (1018, 24572, 62834):
   /* sha1sum:b0d36cf5a2fbe746a3dd277bffc6756a820807a7  Tahoma.ttf from Mac OS X 10.9 */
   case HB_CODEPOINT_ENCODE3 (832, 7324, 47162):
   /* sha1sum:12fc4538e84d461771b30c18b5eb6bd434e30fba  Tahoma Bold.ttf from Mac OS X 10.9 */
   case HB_CODEPOINT_ENCODE3 (844, 7302, 45474):
   /* sha1sum:eb8afadd28e9cf963e886b23a30b44ab4fd83acc  himalaya.ttf from Windows 7 */
   case HB_CODEPOINT_ENCODE3 (180, 13054, 7254):
   /* sha1sum:73da7f025b238a3f737aa1fde22577a6370f77b0  himalaya.ttf from Windows 8 */
   case HB_CODEPOINT_ENCODE3 (192, 12638, 7254):
   /* sha1sum:6e80fd1c0b059bbee49272401583160dc1e6a427  himalaya.ttf from Windows 8.1 */
   case HB_CODEPOINT_ENCODE3 (192, 12690, 7254):
   /* 8d9267aea9cd2c852ecfb9f12a6e834bfaeafe44  cantarell-fonts-0.0.21/otf/Cantarell-Regular.otf */
   /* 983988ff7b47439ab79aeaf9a45bd4a2c5b9d371  cantarell-fonts-0.0.21/otf/Cantarell-Oblique.otf */
   case HB_CODEPOINT_ENCODE3 (188, 248, 3852):
   /* 2c0c90c6f6087ffbfea76589c93113a9cbb0e75f  cantarell-fonts-0.0.21/otf/Cantarell-Bold.otf */
   /* 55461f5b853c6da88069ffcdf7f4dd3f8d7e3e6b  cantarell-fonts-0.0.21/otf/Cantarell-Bold-Oblique.otf */
   case HB_CODEPOINT_ENCODE3 (188, 264, 3426):
   /* d125afa82a77a6475ac0e74e7c207914af84b37a padauk-2.80/Padauk.ttf RHEL 7.2 */
   case HB_CODEPOINT_ENCODE3 (1058, 47032, 11818):
   /* 0f7b80437227b90a577cc078c0216160ae61b031 padauk-2.80/Padauk-Bold.ttf RHEL 7.2*/
   case HB_CODEPOINT_ENCODE3 (1046, 47030, 12600):
   /* d3dde9aa0a6b7f8f6a89ef1002e9aaa11b882290 padauk-2.80/Padauk.ttf Ubuntu 16.04 */
   case HB_CODEPOINT_ENCODE3 (1058, 71796, 16770):
   /* 5f3c98ccccae8a953be2d122c1b3a77fd805093f padauk-2.80/Padauk-Bold.ttf Ubuntu 16.04 */
   case HB_CODEPOINT_ENCODE3 (1046, 71790, 17862):
   /* 6c93b63b64e8b2c93f5e824e78caca555dc887c7 padauk-2.80/Padauk-book.ttf */
   case HB_CODEPOINT_ENCODE3 (1046, 71788, 17112):
   /* d89b1664058359b8ec82e35d3531931125991fb9 padauk-2.80/Padauk-bookbold.ttf */
   case HB_CODEPOINT_ENCODE3 (1058, 71794, 17514):
   /* 824cfd193aaf6234b2b4dc0cf3c6ef576c0d00ef padauk-3.0/Padauk-book.ttf */
   case HB_CODEPOINT_ENCODE3 (1330, 109904, 57938):
   /* 91fcc10cf15e012d27571e075b3b4dfe31754a8a padauk-3.0/Padauk-bookbold.ttf */
   case HB_CODEPOINT_ENCODE3 (1330, 109904, 58972):
   /* sha1sum: c26e41d567ed821bed997e937bc0c41435689e85  Padauk.ttf
    *  "Padauk Regular" "Version 2.5", see https://crbug.com/681813 */
   case HB_CODEPOINT_ENCODE3 (1004, 59092, 14836):
   /* 88d2006ca084f04af2df1954ed714a8c71e8400f  Courier New.ttf from macOS 15 */
   case HB_CODEPOINT_ENCODE3 (588, 5078, 14418):
   /* 608e3ebb6dd1aee521cff08eb07d500a2c59df68  Courier New Bold.ttf from macOS 15 */
   case HB_CODEPOINT_ENCODE3 (588, 5078, 14238):
   /* d13221044ff054efd78f1cd8631b853c3ce85676  cour.ttf from Windows 10 */
   case HB_CODEPOINT_ENCODE3 (894, 17162, 33960):
   /* 68ed4a22d8067fcf1622ac6f6e2f4d3a2e3ec394  courbd.ttf from Windows 10 */
   case HB_CODEPOINT_ENCODE3 (894, 17154, 34472):
   /* 4cdb0259c96b7fd7c103821bb8f08f7cc6b211d7  cour.ttf from Windows 8.1 */
   case HB_CODEPOINT_ENCODE3 (816, 7868, 17052):
   /* 920483d8a8ed37f7f0afdabbe7f679aece7c75d8  courbd.ttf from Windows 8.1 */
   case HB_CODEPOINT_ENCODE3 (816, 7868, 17138):
     return true;
 }
 return false;
}

static void
_hb_ot_layout_set_glyph_props (hb_font_t *font,
		       hb_buffer_t *buffer)
{
 _hb_buffer_assert_gsubgpos_vars (buffer);

 const auto &gdef = *font->face->table.GDEF;
 unsigned int count = buffer->len;
 hb_glyph_info_t *info = buffer->info;
 for (unsigned int i = 0; i < count; i++)
 {
   _hb_glyph_info_set_glyph_props (&info[i], gdef.get_glyph_props (info[i].codepoint));
   _hb_glyph_info_clear_lig_props (&info[i]);
 }
}

/* Public API */

/**
* hb_ot_layout_has_glyph_classes:
* @face: #hb_face_t to work upon
*
* Tests whether a face has any glyph classes defined in its GDEF table.
*
* Return value: `true` if data found, `false` otherwise
*
**/
hb_bool_t
hb_ot_layout_has_glyph_classes (hb_face_t *face)
{
 return face->table.GDEF->table->has_glyph_classes ();
}

/**
* hb_ot_layout_get_glyph_class:
* @face: The #hb_face_t to work on
* @glyph: The #hb_codepoint_t code point to query
*
* Fetches the GDEF class of the requested glyph in the specified face.
*
* Return value: The #hb_ot_layout_glyph_class_t glyph class of the given code
* point in the GDEF table of the face.
*
* Since: 0.9.7
**/
hb_ot_layout_glyph_class_t
hb_ot_layout_get_glyph_class (hb_face_t      *face,
		      hb_codepoint_t  glyph)
{
 return (hb_ot_layout_glyph_class_t) face->table.GDEF->table->get_glyph_class (glyph);
}

/**
* hb_ot_layout_get_glyphs_in_class:
* @face: The #hb_face_t to work on
* @klass: The #hb_ot_layout_glyph_class_t GDEF class to retrieve
* @glyphs: (out): The #hb_set_t set of all glyphs belonging to the requested
*          class.
*
* Retrieves the set of all glyphs from the face that belong to the requested
* glyph class in the face's GDEF table.
*
* Since: 0.9.7
**/
void
hb_ot_layout_get_glyphs_in_class (hb_face_t                  *face,
			  hb_ot_layout_glyph_class_t  klass,
			  hb_set_t                   *glyphs /* OUT */)
{
 return face->table.GDEF->table->get_glyphs_in_class (klass, glyphs);
}

#ifndef HB_NO_LAYOUT_UNUSED
/**
* hb_ot_layout_get_attach_points:
* @face: The #hb_face_t to work on
* @glyph: The #hb_codepoint_t code point to query
* @start_offset: offset of the first attachment point to retrieve
* @point_count: (inout) (nullable): Input = the maximum number of attachment points to return;
*               Output = the actual number of attachment points returned (may be zero)
* @point_array: (out) (array length=point_count): The array of attachment points found for the query
*
* Fetches a list of all attachment points for the specified glyph in the GDEF
* table of the face. The list returned will begin at the offset provided.
*
* Useful if the client program wishes to cache the list.
*
* Return value: Total number of attachment points for @glyph.
*
**/
unsigned int
hb_ot_layout_get_attach_points (hb_face_t      *face,
			hb_codepoint_t  glyph,
			unsigned int    start_offset,
			unsigned int   *point_count /* IN/OUT */,
			unsigned int   *point_array /* OUT */)
{
 return face->table.GDEF->table->get_attach_points (glyph,
					     start_offset,
					     point_count,
					     point_array);
}
/**
* hb_ot_layout_get_ligature_carets:
* @font: The #hb_font_t to work on
* @direction: The #hb_direction_t text direction to use
* @glyph: The #hb_codepoint_t code point to query
* @start_offset: offset of the first caret position to retrieve
* @caret_count: (inout) (nullable): Input = the maximum number of caret positions to return;
*               Output = the actual number of caret positions returned (may be zero)
* @caret_array: (out) (array length=caret_count): The array of caret positions found for the query
*
* Fetches a list of the caret positions defined for a ligature glyph in the GDEF
* table of the font. The list returned will begin at the offset provided.
*
* Note that a ligature that is formed from n characters will have n-1
* caret positions. The first character is not represented in the array,
* since its caret position is the glyph position.
*
* The positions returned by this function are 'unshaped', and will have to
* be fixed up for kerning that may be applied to the ligature glyph.
*
* Return value: Total number of ligature caret positions for @glyph.
*
**/
unsigned int
hb_ot_layout_get_ligature_carets (hb_font_t      *font,
			  hb_direction_t  direction,
			  hb_codepoint_t  glyph,
			  unsigned int    start_offset,
			  unsigned int   *caret_count /* IN/OUT */,
			  hb_position_t  *caret_array /* OUT */)
{
 return font->face->table.GDEF->table->get_lig_carets (font, direction, glyph, start_offset, caret_count, caret_array);
}
#endif


/*
* GSUB/GPOS
*/

bool
GSUB::is_blocklisted (hb_blob_t *blob HB_UNUSED,
		  hb_face_t *face) const
{
#ifdef HB_NO_OT_LAYOUT_BLOCKLIST
 return false;
#endif
 return false;
}

bool
GPOS::is_blocklisted (hb_blob_t *blob HB_UNUSED,
		  hb_face_t *face HB_UNUSED) const
{
#ifdef HB_NO_OT_LAYOUT_BLOCKLIST
 return false;
#endif
 return false;
}

static const OT::GSUBGPOS&
get_gsubgpos_table (hb_face_t *face,
	    hb_tag_t   table_tag)
{
 switch (table_tag) {
   case HB_OT_TAG_GSUB: return *face->table.GSUB->table;
   case HB_OT_TAG_GPOS: return *face->table.GPOS->table;
   default:             return Null (OT::GSUBGPOS);
 }
}


/**
* hb_ot_layout_table_get_script_tags:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
* @start_offset: offset of the first script tag to retrieve
* @script_count: (inout) (nullable): Input = the maximum number of script tags to return;
*                Output = the actual number of script tags returned (may be zero)
* @script_tags: (out) (array length=script_count): The array of #hb_tag_t script tags found for the query
*
* Fetches a list of all scripts enumerated in the specified face's GSUB table
* or GPOS table. The list returned will begin at the offset provided.
*
* Return value: Total number of script tags.
*
**/
unsigned int
hb_ot_layout_table_get_script_tags (hb_face_t    *face,
			    hb_tag_t      table_tag,
			    unsigned int  start_offset,
			    unsigned int *script_count /* IN/OUT */,
			    hb_tag_t     *script_tags  /* OUT */)
{
 const OT::GSUBGPOS &g = get_gsubgpos_table (face, table_tag);

 return g.get_script_tags (start_offset, script_count, script_tags);
}

#define HB_OT_TAG_LATIN_SCRIPT		HB_TAG ('l', 'a', 't', 'n')

/**
* hb_ot_layout_table_find_script:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
* @script_tag: #hb_tag_t of the script tag requested
* @script_index: (out): The index of the requested script tag
*
* Fetches the index if a given script tag in the specified face's GSUB table
* or GPOS table.
*
* Return value: `true` if the script is found, `false` otherwise
*
**/
hb_bool_t
hb_ot_layout_table_find_script (hb_face_t    *face,
			hb_tag_t      table_tag,
			hb_tag_t      script_tag,
			unsigned int *script_index /* OUT */)
{
 static_assert ((OT::Index::NOT_FOUND_INDEX == HB_OT_LAYOUT_NO_SCRIPT_INDEX), "");
 const OT::GSUBGPOS &g = get_gsubgpos_table (face, table_tag);

 if (g.find_script_index (script_tag, script_index))
   return true;

 /* try finding 'DFLT' */
 if (g.find_script_index (HB_OT_TAG_DEFAULT_SCRIPT, script_index))
   return false;

 /* try with 'dflt'; MS site has had typos and many fonts use it now :(.
  * including many versions of DejaVu Sans Mono! */
 if (g.find_script_index (HB_OT_TAG_DEFAULT_LANGUAGE, script_index))
   return false;

 /* try with 'latn'; some old fonts put their features there even though
    they're really trying to support Thai, for example :( */
 if (g.find_script_index (HB_OT_TAG_LATIN_SCRIPT, script_index))
   return false;

 if (script_index) *script_index = HB_OT_LAYOUT_NO_SCRIPT_INDEX;
 return false;
}

#ifndef HB_DISABLE_DEPRECATED
/**
* hb_ot_layout_table_choose_script:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
* @script_tags: Array of #hb_tag_t script tags
* @script_index: (out): The index of the chosen script
* @chosen_script: (out): #hb_tag_t of the chosen script
*
* Deprecated since 2.0.0
**/
hb_bool_t
hb_ot_layout_table_choose_script (hb_face_t      *face,
			  hb_tag_t        table_tag,
			  const hb_tag_t *script_tags,
			  unsigned int   *script_index  /* OUT */,
			  hb_tag_t       *chosen_script /* OUT */)
{
 const hb_tag_t *t;
 for (t = script_tags; *t; t++);
 return hb_ot_layout_table_select_script (face, table_tag, t - script_tags, script_tags, script_index, chosen_script);
}
#endif

/**
* hb_ot_layout_table_select_script:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
* @script_count: Number of script tags in the array
* @script_tags: Array of #hb_tag_t script tags
* @script_index: (out) (nullable): The index of the requested script
* @chosen_script: (out) (nullable): #hb_tag_t of the requested script
*
* Selects an OpenType script for @table_tag from the @script_tags array.
*
* If the table does not have any of the requested scripts, then `DFLT`,
* `dflt`, and `latn` tags are tried in that order. If the table still does not
* have any of these scripts, @script_index is set to
* #HB_OT_LAYOUT_NO_SCRIPT_INDEX and @chosen_script is set to #HB_TAG_NONE.
*
* Return value:
* `true` if one of the requested scripts is selected, `false` if a fallback
* script is selected or if no scripts are selected.
*
* Since: 2.0.0
**/
hb_bool_t
hb_ot_layout_table_select_script (hb_face_t      *face,
			  hb_tag_t        table_tag,
			  unsigned int    script_count,
			  const hb_tag_t *script_tags,
			  unsigned int   *script_index  /* OUT */,
			  hb_tag_t       *chosen_script /* OUT */)
{
 static_assert ((OT::Index::NOT_FOUND_INDEX == HB_OT_LAYOUT_NO_SCRIPT_INDEX), "");
 const OT::GSUBGPOS &g = get_gsubgpos_table (face, table_tag);
 unsigned int i;

 for (i = 0; i < script_count; i++)
 {
   if (g.find_script_index (script_tags[i], script_index))
   {
     if (chosen_script)
*chosen_script = script_tags[i];
     return true;
   }
 }

 /* try finding 'DFLT' */
 if (g.find_script_index (HB_OT_TAG_DEFAULT_SCRIPT, script_index)) {
   if (chosen_script)
     *chosen_script = HB_OT_TAG_DEFAULT_SCRIPT;
   return false;
 }

 /* try with 'dflt'; MS site has had typos and many fonts use it now :( */
 if (g.find_script_index (HB_OT_TAG_DEFAULT_LANGUAGE, script_index)) {
   if (chosen_script)
     *chosen_script = HB_OT_TAG_DEFAULT_LANGUAGE;
   return false;
 }

 /* try with 'latn'; some old fonts put their features there even though
    they're really trying to support Thai, for example :( */
 if (g.find_script_index (HB_OT_TAG_LATIN_SCRIPT, script_index)) {
   if (chosen_script)
     *chosen_script = HB_OT_TAG_LATIN_SCRIPT;
   return false;
 }

 if (script_index) *script_index = HB_OT_LAYOUT_NO_SCRIPT_INDEX;
 if (chosen_script)
   *chosen_script = HB_TAG_NONE;
 return false;
}


/**
* hb_ot_layout_table_get_feature_tags:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
* @start_offset: offset of the first feature tag to retrieve
* @feature_count: (inout) (nullable): Input = the maximum number of feature tags to return;
*                 Output = the actual number of feature tags returned (may be zero)
* @feature_tags: (out) (array length=feature_count): Array of feature tags found in the table
*
* Fetches a list of all feature tags in the given face's GSUB or GPOS table.
* Note that there might be duplicate feature tags, belonging to different
* script/language-system pairs of the table.
*
* Return value: Total number of feature tags.
*
* Since: 0.6.0
*
**/
unsigned int
hb_ot_layout_table_get_feature_tags (hb_face_t    *face,
			     hb_tag_t      table_tag,
			     unsigned int  start_offset,
			     unsigned int *feature_count /* IN/OUT */,
			     hb_tag_t     *feature_tags  /* OUT */)
{
 const OT::GSUBGPOS &g = get_gsubgpos_table (face, table_tag);

 return g.get_feature_tags (start_offset, feature_count, feature_tags);
}


/**
* hb_ot_layout_table_find_feature:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
* @feature_tag: The #hb_tag_t of the requested feature tag
* @feature_index: (out): The index of the requested feature
*
* Fetches the index for a given feature tag in the specified face's GSUB table
* or GPOS table.
*
* Return value: `true` if the feature is found, `false` otherwise
*
* Since: 0.6.0
*
**/
bool
hb_ot_layout_table_find_feature (hb_face_t    *face,
			 hb_tag_t      table_tag,
			 hb_tag_t      feature_tag,
			 unsigned int *feature_index /* OUT */)
{
 static_assert ((OT::Index::NOT_FOUND_INDEX == HB_OT_LAYOUT_NO_FEATURE_INDEX), "");
 const OT::GSUBGPOS &g = get_gsubgpos_table (face, table_tag);

 unsigned int num_features = g.get_feature_count ();
 for (unsigned int i = 0; i < num_features; i++)
 {
   if (feature_tag == g.get_feature_tag (i)) {
     if (feature_index) *feature_index = i;
     return true;
   }
 }

 if (feature_index) *feature_index = HB_OT_LAYOUT_NO_FEATURE_INDEX;
 return false;
}


/**
* hb_ot_layout_script_get_language_tags:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
* @script_index: The index of the requested script tag
* @start_offset: offset of the first language tag to retrieve
* @language_count: (inout) (nullable): Input = the maximum number of language tags to return;
*                  Output = the actual number of language tags returned (may be zero)
* @language_tags: (out) (array length=language_count): Array of language tags found in the table
*
* Fetches a list of language tags in the given face's GSUB or GPOS table, underneath
* the specified script index. The list returned will begin at the offset provided.
*
* Return value: Total number of language tags.
*
* Since: 0.6.0
*
**/
unsigned int
hb_ot_layout_script_get_language_tags (hb_face_t    *face,
			       hb_tag_t      table_tag,
			       unsigned int  script_index,
			       unsigned int  start_offset,
			       unsigned int *language_count /* IN/OUT */,
			       hb_tag_t     *language_tags  /* OUT */)
{
 const OT::Script &s = get_gsubgpos_table (face, table_tag).get_script (script_index);

 return s.get_lang_sys_tags (start_offset, language_count, language_tags);
}


#ifndef HB_DISABLE_DEPRECATED
/**
* hb_ot_layout_script_find_language:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
* @script_index: The index of the requested script tag
* @language_tag: The #hb_tag_t of the requested language
* @language_index: The index of the requested language
*
* Fetches the index of a given language tag in the specified face's GSUB table
* or GPOS table, underneath the specified script tag.
*
* Return value: `true` if the language tag is found, `false` otherwise
*
* Since: 0.6.0
* Deprecated: 2.0.0
**/
hb_bool_t
hb_ot_layout_script_find_language (hb_face_t    *face,
			   hb_tag_t      table_tag,
			   unsigned int  script_index,
			   hb_tag_t      language_tag,
			   unsigned int *language_index)
{
 return hb_ot_layout_script_select_language (face,
				      table_tag,
				      script_index,
				      1,
				      &language_tag,
				      language_index);
}
#endif


/**
* hb_ot_layout_script_select_language2:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
* @script_index: The index of the requested script tag
* @language_count: The number of languages in the specified script
* @language_tags: The array of language tags
* @language_index: (out): The index of the chosen language
* @chosen_language: (out): #hb_tag_t of the chosen language
*
* Fetches the index of the first language tag fom @language_tags that is present
* in the specified face's GSUB or GPOS table, underneath the specified script
* index.
*
* If none of the given language tags is found, `false` is returned and
* @language_index is set to #HB_OT_LAYOUT_DEFAULT_LANGUAGE_INDEX and
* @chosen_language is set to #HB_TAG_NONE.
*
* Return value: `true` if one of the given language tags is found, `false` otherwise
*
* Since: 7.0.0
**/
hb_bool_t
hb_ot_layout_script_select_language2 (hb_face_t      *face,
			     hb_tag_t        table_tag,
			     unsigned int    script_index,
			     unsigned int    language_count,
			     const hb_tag_t *language_tags,
			     unsigned int   *language_index /* OUT */,
			     hb_tag_t       *chosen_language /* OUT */)
{
 static_assert ((OT::Index::NOT_FOUND_INDEX == HB_OT_LAYOUT_DEFAULT_LANGUAGE_INDEX), "");
 const OT::Script &s = get_gsubgpos_table (face, table_tag).get_script (script_index);
 unsigned int i;

 for (i = 0; i < language_count; i++)
 {
   if (s.find_lang_sys_index (language_tags[i], language_index))
   {
     if (chosen_language)
       *chosen_language = language_tags[i];
     return true;
   }
 }

 /* try finding 'dflt' */
 if (s.find_lang_sys_index (HB_OT_TAG_DEFAULT_LANGUAGE, language_index))
 {
   if (chosen_language)
     *chosen_language = HB_OT_TAG_DEFAULT_LANGUAGE;
   return false;
 }

 if (language_index)
   *language_index = HB_OT_LAYOUT_DEFAULT_LANGUAGE_INDEX;
 if (chosen_language)
   *chosen_language = HB_TAG_NONE;
 return false;
}

/**
* hb_ot_layout_script_select_language:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
* @script_index: The index of the requested script tag
* @language_count: The number of languages in the specified script
* @language_tags: The array of language tags
* @language_index: (out): The index of the requested language
*
* Fetches the index of the first language tag fom @language_tags that is present
* in the specified face's GSUB or GPOS table, underneath the specified script
* index.
*
* If none of the given language tags is found, `false` is returned and
* @language_index is set to the default language index.
*
* Return value: `true` if one of the given language tags is found, `false` otherwise
*
* Since: 2.0.0
**/
hb_bool_t
hb_ot_layout_script_select_language (hb_face_t      *face,
			     hb_tag_t        table_tag,
			     unsigned int    script_index,
			     unsigned int    language_count,
			     const hb_tag_t *language_tags,
			     unsigned int   *language_index /* OUT */)
{
 return hb_ot_layout_script_select_language2 (face, table_tag,
				       script_index,
				       language_count, language_tags,
				       language_index, nullptr);
}

/**
* hb_ot_layout_language_get_required_feature_index:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
* @script_index: The index of the requested script tag
* @language_index: The index of the requested language tag
* @feature_index: (out): The index of the requested feature
*
* Fetches the index of a requested feature in the given face's GSUB or GPOS table,
* underneath the specified script and language.
*
* Return value: `true` if the feature is found, `false` otherwise
*
* Since: 0.6.0
*
**/
hb_bool_t
hb_ot_layout_language_get_required_feature_index (hb_face_t    *face,
					  hb_tag_t      table_tag,
					  unsigned int  script_index,
					  unsigned int  language_index,
					  unsigned int *feature_index /* OUT */)
{
 return hb_ot_layout_language_get_required_feature (face,
					     table_tag,
					     script_index,
					     language_index,
					     feature_index,
					     nullptr);
}


/**
* hb_ot_layout_language_get_required_feature:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
* @script_index: The index of the requested script tag
* @language_index: The index of the requested language tag
* @feature_index: (out): The index of the requested feature
* @feature_tag: (out): The #hb_tag_t of the requested feature
*
* Fetches the tag of a requested feature index in the given face's GSUB or GPOS table,
* underneath the specified script and language.
*
* Return value: `true` if the feature is found, `false` otherwise
*
* Since: 0.9.30
**/
hb_bool_t
hb_ot_layout_language_get_required_feature (hb_face_t    *face,
				    hb_tag_t      table_tag,
				    unsigned int  script_index,
				    unsigned int  language_index,
				    unsigned int *feature_index /* OUT */,
				    hb_tag_t     *feature_tag   /* OUT */)
{
 const OT::GSUBGPOS &g = get_gsubgpos_table (face, table_tag);
 const OT::LangSys &l = g.get_script (script_index).get_lang_sys (language_index);

 unsigned int index = l.get_required_feature_index ();
 if (feature_index) *feature_index = index;
 if (feature_tag) *feature_tag = g.get_feature_tag (index);

 return l.has_required_feature ();
}


/**
* hb_ot_layout_language_get_feature_indexes:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
* @script_index: The index of the requested script tag
* @language_index: The index of the requested language tag
* @start_offset: offset of the first feature tag to retrieve
* @feature_count: (inout) (nullable): Input = the maximum number of feature tags to return;
*                 Output: the actual number of feature tags returned (may be zero)
* @feature_indexes: (out) (array length=feature_count): The array of feature indexes found for the query
*
* Fetches a list of all features in the specified face's GSUB table
* or GPOS table, underneath the specified script and language. The list
* returned will begin at the offset provided.
*
* Return value: Total number of features.
*
* Since: 0.6.0
*
**/
unsigned int
hb_ot_layout_language_get_feature_indexes (hb_face_t    *face,
				   hb_tag_t      table_tag,
				   unsigned int  script_index,
				   unsigned int  language_index,
				   unsigned int  start_offset,
				   unsigned int *feature_count   /* IN/OUT */,
				   unsigned int *feature_indexes /* OUT */)
{
 const OT::GSUBGPOS &g = get_gsubgpos_table (face, table_tag);
 const OT::LangSys &l = g.get_script (script_index).get_lang_sys (language_index);

 return l.get_feature_indexes (start_offset, feature_count, feature_indexes);
}


/**
* hb_ot_layout_language_get_feature_tags:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
* @script_index: The index of the requested script tag
* @language_index: The index of the requested language tag
* @start_offset: offset of the first feature tag to retrieve
* @feature_count: (inout) (nullable): Input = the maximum number of feature tags to return;
*                 Output = the actual number of feature tags returned (may be zero)
* @feature_tags: (out) (array length=feature_count): The array of #hb_tag_t feature tags found for the query
*
* Fetches a list of all features in the specified face's GSUB table
* or GPOS table, underneath the specified script and language. The list
* returned will begin at the offset provided.
*
* Return value: Total number of feature tags.
*
* Since: 0.6.0
*
**/
unsigned int
hb_ot_layout_language_get_feature_tags (hb_face_t    *face,
				hb_tag_t      table_tag,
				unsigned int  script_index,
				unsigned int  language_index,
				unsigned int  start_offset,
				unsigned int *feature_count /* IN/OUT */,
				hb_tag_t     *feature_tags  /* OUT */)
{
 const OT::GSUBGPOS &g = get_gsubgpos_table (face, table_tag);
 const OT::LangSys &l = g.get_script (script_index).get_lang_sys (language_index);

 static_assert ((sizeof (unsigned int) == sizeof (hb_tag_t)), "");
 unsigned int ret = l.get_feature_indexes (start_offset, feature_count, (unsigned int *) feature_tags);

 if (feature_tags) {
   unsigned int count = *feature_count;
   for (unsigned int i = 0; i < count; i++)
     feature_tags[i] = g.get_feature_tag ((unsigned int) feature_tags[i]);
 }

 return ret;
}


/**
* hb_ot_layout_language_find_feature:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
* @script_index: The index of the requested script tag
* @language_index: The index of the requested language tag
* @feature_tag: #hb_tag_t of the feature tag requested
* @feature_index: (out): The index of the requested feature
*
* Fetches the index of a given feature tag in the specified face's GSUB table
* or GPOS table, underneath the specified script and language.
*
* Return value: `true` if the feature is found, `false` otherwise
*
* Since: 0.6.0
*
**/
hb_bool_t
hb_ot_layout_language_find_feature (hb_face_t    *face,
			    hb_tag_t      table_tag,
			    unsigned int  script_index,
			    unsigned int  language_index,
			    hb_tag_t      feature_tag,
			    unsigned int *feature_index /* OUT */)
{
 static_assert ((OT::Index::NOT_FOUND_INDEX == HB_OT_LAYOUT_NO_FEATURE_INDEX), "");
 const OT::GSUBGPOS &g = get_gsubgpos_table (face, table_tag);
 const OT::LangSys &l = g.get_script (script_index).get_lang_sys (language_index);

 unsigned int num_features = l.get_feature_count ();
 for (unsigned int i = 0; i < num_features; i++) {
   unsigned int f_index = l.get_feature_index (i);

   if (feature_tag == g.get_feature_tag (f_index)) {
     if (feature_index) *feature_index = f_index;
     return true;
   }
 }

 if (feature_index) *feature_index = HB_OT_LAYOUT_NO_FEATURE_INDEX;
 return false;
}


/**
* hb_ot_layout_feature_get_lookups:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
* @feature_index: The index of the requested feature
* @start_offset: offset of the first lookup to retrieve
* @lookup_count: (inout) (nullable): Input = the maximum number of lookups to return;
*                Output = the actual number of lookups returned (may be zero)
* @lookup_indexes: (out) (array length=lookup_count): The array of lookup indexes found for the query
*
* Fetches a list of all lookups enumerated for the specified feature, in
* the specified face's GSUB table or GPOS table. The list returned will
* begin at the offset provided.
*
* Return value: Total number of lookups.
*
* Since: 0.9.7
**/
unsigned int
hb_ot_layout_feature_get_lookups (hb_face_t    *face,
			  hb_tag_t      table_tag,
			  unsigned int  feature_index,
			  unsigned int  start_offset,
			  unsigned int *lookup_count   /* IN/OUT */,
			  unsigned int *lookup_indexes /* OUT */)
{
 return hb_ot_layout_feature_with_variations_get_lookups (face,
						   table_tag,
						   feature_index,
						   HB_OT_LAYOUT_NO_VARIATIONS_INDEX,
						   start_offset,
						   lookup_count,
						   lookup_indexes);
}


/**
* hb_ot_layout_table_get_lookup_count:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
*
* Fetches the total number of lookups enumerated in the specified
* face's GSUB table or GPOS table.
*
* Return value: Total number of lookups.
*
* Since: 0.9.22
**/
unsigned int
hb_ot_layout_table_get_lookup_count (hb_face_t    *face,
			     hb_tag_t      table_tag)
{
 return get_gsubgpos_table (face, table_tag).get_lookup_count ();
}


struct hb_collect_features_context_t
{
 hb_collect_features_context_t (hb_face_t *face,
			 hb_tag_t   table_tag,
			 hb_set_t  *feature_indices_,
			 const hb_tag_t *features)

   : g (get_gsubgpos_table (face, table_tag)),
     feature_indices (feature_indices_),
     has_feature_filter (false),
     script_count (0),langsys_count (0), feature_index_count (0)
 {
   compute_feature_filter (features);
 }

 void compute_feature_filter (const hb_tag_t *features)
 {
   if (features == nullptr)
   {
     has_feature_filter = false;
     return;
   }

   has_feature_filter = true;
   hb_set_t features_set;
   for (; *features; features++)
     features_set.add (*features);

   for (unsigned i = 0; i < g.get_feature_count (); i++)
   {
     hb_tag_t tag = g.get_feature_tag (i);
     if (features_set.has (tag))
feature_indices_filter.add(i);
   }
 }

 bool visited (const OT::Script &s)
 {
   /* We might have Null() object here.  Don't want to involve
    * that in the memoize.  So, detect empty objects and return. */
   if (unlikely (!s.has_default_lang_sys () &&
	  !s.get_lang_sys_count ()))
     return true;

   if (script_count++ > HB_MAX_SCRIPTS)
     return true;

   return visited (s, visited_script);
 }
 bool visited (const OT::LangSys &l)
 {
   /* We might have Null() object here.  Don't want to involve
    * that in the memoize.  So, detect empty objects and return. */
   if (unlikely (!l.has_required_feature () &&
	  !l.get_feature_count ()))
     return true;

   if (langsys_count++ > HB_MAX_LANGSYS)
     return true;

   return visited (l, visited_langsys);
 }

 bool visited_feature_indices (unsigned count)
 {
   feature_index_count += count;
   return feature_index_count > HB_MAX_FEATURE_INDICES;
 }

 private:
 template <typename T>
 bool visited (const T &p, hb_set_t &visited_set)
 {
   hb_codepoint_t delta = (hb_codepoint_t) ((uintptr_t) &p - (uintptr_t) &g);
    if (visited_set.has (delta))
     return true;

   visited_set.add (delta);
   return false;
 }

 public:
 const OT::GSUBGPOS &g;
 hb_set_t *feature_indices;
 hb_set_t  feature_indices_filter;
 bool has_feature_filter;

 private:
 hb_set_t visited_script;
 hb_set_t visited_langsys;
 unsigned int script_count;
 unsigned int langsys_count;
 unsigned int feature_index_count;
};

static void
langsys_collect_features (hb_collect_features_context_t *c,
		  const OT::LangSys  &l)
{
 if (c->visited (l)) return;

 if (!c->has_feature_filter)
 {
   /* All features. */
   if (l.has_required_feature () && !c->visited_feature_indices (1))
     c->feature_indices->add (l.get_required_feature_index ());

   // TODO(garretrieger): filter out indices >= feature count?
   if (!c->visited_feature_indices (l.featureIndex.len))
     l.add_feature_indexes_to (c->feature_indices);
 }
 else
 {
   if (c->feature_indices_filter.is_empty()) return;
   unsigned int num_features = l.get_feature_count ();
   for (unsigned int i = 0; i < num_features; i++)
   {
     unsigned int feature_index = l.get_feature_index (i);
     if (!c->feature_indices_filter.has (feature_index)) continue;

     c->feature_indices->add (feature_index);
     c->feature_indices_filter.del (feature_index);
   }
 }
}

static void
script_collect_features (hb_collect_features_context_t *c,
		 const OT::Script   &s,
		 const hb_tag_t *languages)
{
 if (c->visited (s)) return;

 if (!languages)
 {
   /* All languages. */
   if (s.has_default_lang_sys ())
     langsys_collect_features (c,
			s.get_default_lang_sys ());


   unsigned int count = s.get_lang_sys_count ();
   for (unsigned int language_index = 0; language_index < count; language_index++)
     langsys_collect_features (c,
			s.get_lang_sys (language_index));
 }
 else
 {
   for (; *languages; languages++)
   {
     unsigned int language_index;
     if (s.find_lang_sys_index (*languages, &language_index))
langsys_collect_features (c,
			  s.get_lang_sys (language_index));

   }
 }
}


/**
* hb_ot_layout_collect_features:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
* @scripts: (nullable) (array zero-terminated=1): The array of scripts to collect features for,
*   terminated by %HB_TAG_NONE
* @languages: (nullable) (array zero-terminated=1): The array of languages to collect features for,
*   terminated by %HB_TAG_NONE
* @features: (nullable) (array zero-terminated=1): The array of features to collect,
*   terminated by %HB_TAG_NONE
* @feature_indexes: (out): The set of feature indexes found for the query
*
* Fetches a list of all feature indexes in the specified face's GSUB table
* or GPOS table, underneath the specified scripts, languages, and features.
* If no list of scripts is provided, all scripts will be queried. If no list
* of languages is provided, all languages will be queried. If no list of
* features is provided, all features will be queried.
*
* Since: 1.8.5
**/
void
hb_ot_layout_collect_features (hb_face_t      *face,
		       hb_tag_t        table_tag,
		       const hb_tag_t *scripts,
		       const hb_tag_t *languages,
		       const hb_tag_t *features,
		       hb_set_t       *feature_indexes /* OUT */)
{
 hb_collect_features_context_t c (face, table_tag, feature_indexes, features);
 if (!scripts)
 {
   /* All scripts. */
   unsigned int count = c.g.get_script_count ();
   for (unsigned int script_index = 0; script_index < count; script_index++)
     script_collect_features (&c,
		       c.g.get_script (script_index),
		       languages);
 }
 else
 {
   for (; *scripts; scripts++)
   {
     unsigned int script_index;
     if (c.g.find_script_index (*scripts, &script_index))
script_collect_features (&c,
			 c.g.get_script (script_index),
			 languages);
   }
 }
}

/**
* hb_ot_layout_collect_features_map:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
* @script_index: The index of the requested script tag
* @language_index: The index of the requested language tag
* @feature_map: (out): The map of feature tag to feature index.
*
* Fetches the mapping from feature tags to feature indexes for
* the specified script and language.
*
* Since: 8.1.0
**/
void
hb_ot_layout_collect_features_map (hb_face_t      *face,
			   hb_tag_t        table_tag,
			   unsigned        script_index,
			   unsigned        language_index,
			   hb_map_t       *feature_map /* OUT */)
{
 const OT::GSUBGPOS &g = get_gsubgpos_table (face, table_tag);
 const OT::LangSys &l = g.get_script (script_index).get_lang_sys (language_index);

 unsigned int count = l.get_feature_indexes (0, nullptr, nullptr);
 feature_map->alloc (count);

 /* Loop in reverse, such that earlier entries win. That emulates
  * a linear search, which seems to be what other implementations do.
  * We found that with arialuni_t.ttf, the "ur" language system has
  * duplicate features, and the earlier ones work but not later ones.
  */
 for (unsigned int i = count; i; i--)
 {
   unsigned feature_index = 0;
   unsigned feature_count = 1;
   l.get_feature_indexes (i - 1, &feature_count, &feature_index);
   if (!feature_count)
     break;
   hb_tag_t feature_tag = g.get_feature_tag (feature_index);
   feature_map->set (feature_tag, feature_index);
 }
}


/**
* hb_ot_layout_collect_lookups:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
* @scripts: (nullable) (array zero-terminated=1): The array of scripts to collect lookups for,
*   terminated by %HB_TAG_NONE
* @languages: (nullable) (array zero-terminated=1): The array of languages to collect lookups for,
*   terminated by %HB_TAG_NONE
* @features: (nullable) (array zero-terminated=1): The array of features to collect lookups for,
*   terminated by %HB_TAG_NONE
* @lookup_indexes: (out): The array of lookup indexes found for the query
*
* Fetches a list of all feature-lookup indexes in the specified face's GSUB
* table or GPOS table, underneath the specified scripts, languages, and
* features. If no list of scripts is provided, all scripts will be queried.
* If no list of languages is provided, all languages will be queried. If no
* list of features is provided, all features will be queried.
*
* Since: 0.9.8
**/
void
hb_ot_layout_collect_lookups (hb_face_t      *face,
		      hb_tag_t        table_tag,
		      const hb_tag_t *scripts,
		      const hb_tag_t *languages,
		      const hb_tag_t *features,
		      hb_set_t       *lookup_indexes /* OUT */)
{
 const OT::GSUBGPOS &g = get_gsubgpos_table (face, table_tag);

 hb_set_t feature_indexes;
 hb_ot_layout_collect_features (face, table_tag, scripts, languages, features, &feature_indexes);

 for (auto feature_index : feature_indexes)
   g.get_feature (feature_index).add_lookup_indexes_to (lookup_indexes);

 g.feature_variation_collect_lookups (&feature_indexes, nullptr, lookup_indexes);
}


#ifndef HB_NO_LAYOUT_COLLECT_GLYPHS
/**
* hb_ot_layout_lookup_collect_glyphs:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
* @lookup_index: The index of the feature lookup to query
* @glyphs_before: (out) (nullable): Array of glyphs preceding the substitution range
* @glyphs_input: (out) (nullable): Array of input glyphs that would be substituted by the lookup
* @glyphs_after: (out) (nullable): Array of glyphs following the substitution range
* @glyphs_output: (out) (nullable): Array of glyphs that would be the substituted output of the lookup
*
* Fetches a list of all glyphs affected by the specified lookup in the
* specified face's GSUB table or GPOS table.
*
* Since: 0.9.7
**/
void
hb_ot_layout_lookup_collect_glyphs (hb_face_t    *face,
			    hb_tag_t      table_tag,
			    unsigned int  lookup_index,
			    hb_set_t     *glyphs_before, /* OUT.  May be NULL */
			    hb_set_t     *glyphs_input,  /* OUT.  May be NULL */
			    hb_set_t     *glyphs_after,  /* OUT.  May be NULL */
			    hb_set_t     *glyphs_output  /* OUT.  May be NULL */)
{
 OT::hb_collect_glyphs_context_t c (face,
			     glyphs_before,
			     glyphs_input,
			     glyphs_after,
			     glyphs_output);

 switch (table_tag)
 {
   case HB_OT_TAG_GSUB:
   {
     const OT::SubstLookup& l = face->table.GSUB->table->get_lookup (lookup_index);
     l.collect_glyphs (&c);
     return;
   }
   case HB_OT_TAG_GPOS:
   {
     const OT::PosLookup& l = face->table.GPOS->table->get_lookup (lookup_index);
     l.collect_glyphs (&c);
     return;
   }
 }
}
#endif


/* Variations support */


/**
* hb_ot_layout_table_find_feature_variations:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
* @coords: The variation coordinates to query
* @num_coords: The number of variation coordinates
* @variations_index: (out): The array of feature variations found for the query
*
* Fetches a list of feature variations in the specified face's GSUB table
* or GPOS table, at the specified variation coordinates.
*
* Return value: `true` if feature variations were found, `false` otherwise.
*
* Since: 1.4.0
*
**/
hb_bool_t
hb_ot_layout_table_find_feature_variations (hb_face_t    *face,
				    hb_tag_t      table_tag,
				    const int    *coords,
				    unsigned int  num_coords,
				    unsigned int *variations_index /* out */)
{
 const OT::GSUBGPOS &g = get_gsubgpos_table (face, table_tag);
 const OT::GDEF &gdef = *face->table.GDEF->table;

 auto instancer = OT::ItemVarStoreInstancer(&gdef.get_var_store(), nullptr,
				     hb_array (coords, num_coords));

 return g.find_variations_index (coords, num_coords, variations_index, &instancer);
}


/**
* hb_ot_layout_feature_with_variations_get_lookups:
* @face: #hb_face_t to work upon
* @table_tag: #HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
* @feature_index: The index of the feature to query
* @variations_index: The index of the feature variation to query
* @start_offset: offset of the first lookup to retrieve
* @lookup_count: (inout) (nullable): Input = the maximum number of lookups to return;
*                Output = the actual number of lookups returned (may be zero)
* @lookup_indexes: (out) (array length=lookup_count): The array of lookups found for the query
*
* Fetches a list of all lookups enumerated for the specified feature, in
* the specified face's GSUB table or GPOS table, enabled at the specified
* variations index. The list returned will begin at the offset provided.
*
* Return value: Total number of lookups.
*
* Since: 1.4.0
*
**/
unsigned int
hb_ot_layout_feature_with_variations_get_lookups (hb_face_t    *face,
					  hb_tag_t      table_tag,
					  unsigned int  feature_index,
					  unsigned int  variations_index,
					  unsigned int  start_offset,
					  unsigned int *lookup_count /* IN/OUT */,
					  unsigned int *lookup_indexes /* OUT */)
{
 static_assert ((OT::FeatureVariations::NOT_FOUND_INDEX == HB_OT_LAYOUT_NO_VARIATIONS_INDEX), "");
 const OT::GSUBGPOS &g = get_gsubgpos_table (face, table_tag);

 const OT::Feature &f = g.get_feature_variation (feature_index, variations_index);

 return f.get_lookup_indexes (start_offset, lookup_count, lookup_indexes);
}


/*
* OT::GSUB
*/


/**
* hb_ot_layout_has_substitution:
* @face: #hb_face_t to work upon
*
* Tests whether the specified face includes any GSUB substitutions.
*
* Return value: `true` if data found, `false` otherwise
*
* Since: 0.6.0
*
**/
hb_bool_t
hb_ot_layout_has_substitution (hb_face_t *face)
{
 return face->table.GSUB->table->has_data ();
}


/**
* hb_ot_layout_lookup_would_substitute:
* @face: #hb_face_t to work upon
* @lookup_index: The index of the lookup to query
* @glyphs: The sequence of glyphs to query for substitution
* @glyphs_length: The length of the glyph sequence
* @zero_context: #hb_bool_t indicating whether pre-/post-context are disallowed
* in substitutions
*
* Tests whether a specified lookup in the specified face would
* trigger a substitution on the given glyph sequence.
*
* Return value: `true` if a substitution would be triggered, `false` otherwise
*
* Since: 0.9.7
**/
hb_bool_t
hb_ot_layout_lookup_would_substitute (hb_face_t            *face,
			      unsigned int          lookup_index,
			      const hb_codepoint_t *glyphs,
			      unsigned int          glyphs_length,
			      hb_bool_t             zero_context)
{
 auto &gsub = face->table.GSUB;
 if (unlikely (lookup_index >= gsub->lookup_count)) return false;
 OT::hb_would_apply_context_t c (face, glyphs, glyphs_length, (bool) zero_context);

 const OT::SubstLookup& l = gsub->table->get_lookup (lookup_index);
 auto *accel = gsub->get_accel (lookup_index);
 return accel && l.would_apply (&c, accel);
}


/**
* hb_ot_layout_substitute_start:
* @font: #hb_font_t to use
* @buffer: #hb_buffer_t buffer to work upon
*
* Called before substitution lookups are performed, to ensure that glyph
* class and other properties are set on the glyphs in the buffer.
*
**/
void
hb_ot_layout_substitute_start (hb_font_t    *font,
		       hb_buffer_t  *buffer)
{
 _hb_ot_layout_set_glyph_props (font, buffer);
}

/**
* hb_ot_layout_lookup_substitute_closure:
* @face: #hb_face_t to work upon
* @lookup_index: index of the feature lookup to query
* @glyphs: (out): Array of glyphs comprising the transitive closure of the lookup
*
* Compute the transitive closure of glyphs needed for a
* specified lookup.
*
* Since: 0.9.7
**/
void
hb_ot_layout_lookup_substitute_closure (hb_face_t    *face,
				unsigned int  lookup_index,
				hb_set_t     *glyphs /* OUT */)
{
 hb_map_t done_lookups_glyph_count;
 hb_hashmap_t<unsigned, hb::unique_ptr<hb_set_t>> done_lookups_glyph_set;
 OT::hb_closure_context_t c (face, glyphs, &done_lookups_glyph_count, &done_lookups_glyph_set);

 const OT::SubstLookup& l = face->table.GSUB->table->get_lookup (lookup_index);

 l.closure (&c, lookup_index);
}

/**
* hb_ot_layout_lookups_substitute_closure:
* @face: #hb_face_t to work upon
* @lookups: The set of lookups to query
* @glyphs: (out): Array of glyphs comprising the transitive closure of the lookups
*
* Compute the transitive closure of glyphs needed for all of the
* provided lookups.
*
* Since: 1.8.1
**/
void
hb_ot_layout_lookups_substitute_closure (hb_face_t      *face,
				 const hb_set_t *lookups,
				 hb_set_t       *glyphs /* OUT */)
{
 hb_map_t done_lookups_glyph_count;
 hb_hashmap_t<unsigned, hb::unique_ptr<hb_set_t>> done_lookups_glyph_set;
 OT::hb_closure_context_t c (face, glyphs, &done_lookups_glyph_count, &done_lookups_glyph_set);
 const GSUB& gsub = *face->table.GSUB->table;

 unsigned int iteration_count = 0;
 unsigned int glyphs_length;
 do
 {
   c.reset_lookup_visit_count ();
   glyphs_length = glyphs->get_population ();
   if (lookups)
   {
     for (auto lookup_index : *lookups)
gsub.get_lookup (lookup_index).closure (&c, lookup_index);
   }
   else
   {
     for (unsigned int i = 0; i < gsub.get_lookup_count (); i++)
gsub.get_lookup (i).closure (&c, i);
   }
 } while (iteration_count++ <= HB_CLOSURE_MAX_STAGES &&
   glyphs_length != glyphs->get_population ());
}

/*
* GPOS
*/


/**
* hb_ot_layout_has_positioning:
* @face: #hb_face_t to work upon
*
* Tests whether the specified face includes any GPOS positioning.
*
* Return value: `true` if the face has GPOS data, `false` otherwise
*
**/
hb_bool_t
hb_ot_layout_has_positioning (hb_face_t *face)
{
 return face->table.GPOS->table->has_data ();
}

/**
* hb_ot_layout_position_start:
* @font: #hb_font_t to use
* @buffer: #hb_buffer_t buffer to work upon
*
* Called before positioning lookups are performed, to ensure that glyph
* attachment types and glyph-attachment chains are set for the glyphs in the buffer.
*
**/
void
hb_ot_layout_position_start (hb_font_t *font, hb_buffer_t *buffer)
{
 GPOS::position_start (font, buffer);
}


/**
* hb_ot_layout_position_finish_advances:
* @font: #hb_font_t to use
* @buffer: #hb_buffer_t buffer to work upon
*
* Called after positioning lookups are performed, to finish glyph advances.
*
**/
void
hb_ot_layout_position_finish_advances (hb_font_t *font, hb_buffer_t *buffer)
{
 GPOS::position_finish_advances (font, buffer);
}

/**
* hb_ot_layout_position_finish_offsets:
* @font: #hb_font_t to use
* @buffer: #hb_buffer_t buffer to work upon
*
* Called after positioning lookups are performed, to finish glyph offsets.
*
**/
void
hb_ot_layout_position_finish_offsets (hb_font_t *font, hb_buffer_t *buffer)
{
 GPOS::position_finish_offsets (font, buffer);
}


#ifndef HB_NO_LAYOUT_FEATURE_PARAMS
/**
* hb_ot_layout_get_size_params:
* @face: #hb_face_t to work upon
* @design_size: (out): The design size of the face
* @subfamily_id: (out): The identifier of the face within the font subfamily
* @subfamily_name_id: (out): The ‘name’ table name ID of the face within the font subfamily
* @range_start: (out): The minimum size of the recommended size range for the face
* @range_end: (out): The maximum size of the recommended size range for the face
*
* Fetches optical-size feature data (i.e., the `size` feature from GPOS). Note that
* the subfamily_id and the subfamily name string (accessible via the subfamily_name_id)
* as used here are defined as pertaining only to fonts within a font family that differ
* specifically in their respective size ranges; other ways to differentiate fonts within
* a subfamily are not covered by the `size` feature.
*
* For more information on this distinction, see the [`size` feature documentation](
* https://docs.microsoft.com/en-us/typography/opentype/spec/features_pt#tag-size).
*
* Return value: `true` if data found, `false` otherwise
*
* Since: 0.9.10
**/
hb_bool_t
hb_ot_layout_get_size_params (hb_face_t       *face,
		      unsigned int    *design_size,       /* OUT.  May be NULL */
		      unsigned int    *subfamily_id,      /* OUT.  May be NULL */
		      hb_ot_name_id_t *subfamily_name_id, /* OUT.  May be NULL */
		      unsigned int    *range_start,       /* OUT.  May be NULL */
		      unsigned int    *range_end          /* OUT.  May be NULL */)
{
 const GPOS &gpos = *face->table.GPOS->table;
 const hb_tag_t tag = HB_TAG ('s','i','z','e');

 unsigned int num_features = gpos.get_feature_count ();
 for (unsigned int i = 0; i < num_features; i++)
 {
   if (tag == gpos.get_feature_tag (i))
   {
     const OT::Feature &f = gpos.get_feature (i);
     const OT::FeatureParamsSize &params = f.get_feature_params ().get_size_params (tag);

     if (params.designSize)
     {
if (design_size) *design_size = params.designSize;
if (subfamily_id) *subfamily_id = params.subfamilyID;
if (subfamily_name_id) *subfamily_name_id = params.subfamilyNameID;
if (range_start) *range_start = params.rangeStart;
if (range_end) *range_end = params.rangeEnd;

return true;
     }
   }
 }

 if (design_size) *design_size = 0;
 if (subfamily_id) *subfamily_id = 0;
 if (subfamily_name_id) *subfamily_name_id = HB_OT_NAME_ID_INVALID;
 if (range_start) *range_start = 0;
 if (range_end) *range_end = 0;

 return false;
}


/**
* hb_ot_layout_feature_get_name_ids:
* @face: #hb_face_t to work upon
* @table_tag: table tag to query, "GSUB" or "GPOS".
* @feature_index: index of feature to query.
* @label_id: (out) (nullable): The ‘name’ table name ID that specifies a string
*            for a user-interface label for this feature.
* @tooltip_id: (out) (nullable): The ‘name’ table name ID that specifies a string
*              that an application can use for tooltip text for this
*              feature.
* @sample_id: (out) (nullable): The ‘name’ table name ID that specifies sample text
*             that illustrates the effect of this feature.
* @num_named_parameters: (out) (nullable):  Number of named parameters.
* @first_param_id: (out) (nullable): The first ‘name’ table name ID used to specify
*                  strings for user-interface labels for the feature
*                  parameters. (Must be zero if numParameters is zero.)
*
* Fetches name indices from feature parameters for "Stylistic Set" ('ssXX') or
* "Character Variant" ('cvXX') features.
*
* Return value: `true` if data found, `false` otherwise
*
* Since: 2.0.0
**/
hb_bool_t
hb_ot_layout_feature_get_name_ids (hb_face_t       *face,
			   hb_tag_t         table_tag,
			   unsigned int     feature_index,
			   hb_ot_name_id_t *label_id,             /* OUT.  May be NULL */
			   hb_ot_name_id_t *tooltip_id,           /* OUT.  May be NULL */
			   hb_ot_name_id_t *sample_id,            /* OUT.  May be NULL */
			   unsigned int    *num_named_parameters, /* OUT.  May be NULL */
			   hb_ot_name_id_t *first_param_id        /* OUT.  May be NULL */)
{
 const OT::GSUBGPOS &g = get_gsubgpos_table (face, table_tag);

 hb_tag_t feature_tag = g.get_feature_tag (feature_index);
 const OT::Feature &f = g.get_feature (feature_index);

 const OT::FeatureParams &feature_params = f.get_feature_params ();
 if (&feature_params != &Null (OT::FeatureParams))
 {
   const OT::FeatureParamsStylisticSet& ss_params =
     feature_params.get_stylistic_set_params (feature_tag);
   if (&ss_params != &Null (OT::FeatureParamsStylisticSet)) /* ssXX */
   {
     if (label_id) *label_id = ss_params.uiNameID;
     // ssXX features don't have the rest
     if (tooltip_id) *tooltip_id = HB_OT_NAME_ID_INVALID;
     if (sample_id) *sample_id = HB_OT_NAME_ID_INVALID;
     if (num_named_parameters) *num_named_parameters = 0;
     if (first_param_id) *first_param_id = HB_OT_NAME_ID_INVALID;
     return true;
   }
   const OT::FeatureParamsCharacterVariants& cv_params =
     feature_params.get_character_variants_params (feature_tag);
   if (&cv_params != &Null (OT::FeatureParamsCharacterVariants)) /* cvXX */
   {
     if (label_id) *label_id = cv_params.featUILableNameID;
     if (tooltip_id) *tooltip_id = cv_params.featUITooltipTextNameID;
     if (sample_id) *sample_id = cv_params.sampleTextNameID;
     if (num_named_parameters) *num_named_parameters = cv_params.numNamedParameters;
     if (first_param_id) *first_param_id = cv_params.firstParamUILabelNameID;
     return true;
   }
 }

 if (label_id) *label_id = HB_OT_NAME_ID_INVALID;
 if (tooltip_id) *tooltip_id = HB_OT_NAME_ID_INVALID;
 if (sample_id) *sample_id = HB_OT_NAME_ID_INVALID;
 if (num_named_parameters) *num_named_parameters = 0;
 if (first_param_id) *first_param_id = HB_OT_NAME_ID_INVALID;
 return false;
}
/**
* hb_ot_layout_feature_get_characters:
* @face: #hb_face_t to work upon
* @table_tag: table tag to query, "GSUB" or "GPOS".
* @feature_index: index of feature to query.
* @start_offset: offset of the first character to retrieve
* @char_count: (inout) (nullable): Input = the maximum number of characters to return;
*              Output = the actual number of characters returned (may be zero)
* @characters: (out caller-allocates) (array length=char_count): A buffer pointer.
*              The Unicode codepoints of the characters for which this feature provides
*               glyph variants.
*
* Fetches a list of the characters defined as having a variant under the specified
* "Character Variant" ("cvXX") feature tag.
*
* Return value: Number of total sample characters in the cvXX feature.
*
* Since: 2.0.0
**/
unsigned int
hb_ot_layout_feature_get_characters (hb_face_t      *face,
			     hb_tag_t        table_tag,
			     unsigned int    feature_index,
			     unsigned int    start_offset,
			     unsigned int   *char_count, /* IN/OUT.  May be NULL */
			     hb_codepoint_t *characters  /* OUT.     May be NULL */)
{
 const OT::GSUBGPOS &g = get_gsubgpos_table (face, table_tag);
 return g.get_feature (feature_index)
  .get_feature_params ()
  .get_character_variants_params(g.get_feature_tag (feature_index))
  .get_characters (start_offset, char_count, characters);
}
#endif


/*
* Parts of different types are implemented here such that they have direct
* access to GSUB/GPOS lookups.
*/


struct GSUBProxy
{
 static constexpr unsigned table_index = 0u;
 static constexpr bool always_inplace = false;
 typedef OT::SubstLookup Lookup;

 GSUBProxy (hb_face_t *face) :
   accel (*face->table.GSUB) {}

 const GSUB::accelerator_t &accel;
};

struct GPOSProxy
{
 static constexpr unsigned table_index = 1u;
 static constexpr bool always_inplace = true;
 typedef OT::PosLookup Lookup;

 GPOSProxy (hb_face_t *face) :
   accel (*face->table.GPOS) {}

 const GPOS::accelerator_t &accel;
};


static inline bool
apply_forward (OT::hb_ot_apply_context_t *c,
       const OT::hb_ot_layout_lookup_accelerator_t &accel)
{
 bool use_hot_subtable_cache = accel.cache_enter (c);

 bool ret = false;
 hb_buffer_t *buffer = c->buffer;
 while (buffer->successful)
 {
   hb_glyph_info_t *info = buffer->info;
   unsigned j = buffer->idx;
   while (j < buffer->len &&
   !(accel.digest.may_have (info[j].codepoint) &&
     (info[j].mask & c->lookup_mask) &&
     c->check_glyph_property (&info[j], c->lookup_props)))
     j++;
   if (unlikely (j > buffer->idx && !buffer->next_glyphs (j - buffer->idx)))
     break;
   if (buffer->idx >= buffer->len)
     break;

   if (accel.apply (c, use_hot_subtable_cache))
     ret = true;
   else
     (void) buffer->next_glyph ();
 }

 if (use_hot_subtable_cache)
   accel.cache_leave (c);

 return ret;
}

static inline bool
apply_backward (OT::hb_ot_apply_context_t *c,
       const OT::hb_ot_layout_lookup_accelerator_t &accel)
{
 bool ret = false;
 hb_buffer_t *buffer = c->buffer;
 do
 {
   auto &cur = buffer->cur();
   if (accel.digest.may_have (cur.codepoint) &&
(cur.mask & c->lookup_mask) &&
c->check_glyph_property (&cur, c->lookup_props))
     ret |= accel.apply (c, false);

   /* The reverse lookup doesn't "advance" cursor (for good reason). */
   buffer->idx--;
 }
 while ((int) buffer->idx >= 0);
 return ret;
}

template <typename Proxy>
static inline bool
apply_string (OT::hb_ot_apply_context_t *c,
      const typename Proxy::Lookup &lookup,
      const OT::hb_ot_layout_lookup_accelerator_t &accel)
{
 hb_buffer_t *buffer = c->buffer;

 if (unlikely (!buffer->len || !c->lookup_mask))
   return false;

 bool ret = false;

 c->set_lookup_props (lookup.get_props ());

 if (likely (!lookup.is_reverse ()))
 {
   /* in/out forward substitution/positioning */
   if (!Proxy::always_inplace)
     buffer->clear_output ();

   buffer->idx = 0;
   ret = apply_forward (c, accel);

   if (!Proxy::always_inplace)
     buffer->sync ();
 }
 else
 {
   /* in-place backward substitution/positioning */
   assert (!buffer->have_output);
   buffer->idx = buffer->len - 1;
   ret = apply_backward (c, accel);
 }

 return ret;
}

template <typename Proxy>
inline void hb_ot_map_t::apply (const Proxy &proxy,
			const hb_ot_shape_plan_t *plan,
			hb_font_t *font,
			hb_buffer_t *buffer) const
{
 const unsigned int table_index = proxy.table_index;
 unsigned int i = 0;

 auto *font_data = font->data.ot.get ();
 auto *var_store_cache = (OT::hb_scalar_cache_t *) font_data;

 OT::hb_ot_apply_context_t c (table_index, font, buffer, proxy.accel.get_blob (), var_store_cache);
 c.set_recurse_func (Proxy::Lookup::template dispatch_recurse_func<OT::hb_ot_apply_context_t>);

 for (unsigned int stage_index = 0; stage_index < stages[table_index].length; stage_index++)
 {
   const stage_map_t *stage = &stages[table_index][stage_index];
   for (; i < stage->last_lookup; i++)
   {
     auto &lookup = lookups[table_index][i];

     unsigned int lookup_index = lookup.index;

     auto *accel = proxy.accel.get_accel (lookup_index);
     if (unlikely (!accel)) continue;

     if (buffer->messaging () &&
  !buffer->message (font, "start lookup %u feature '%c%c%c%c'", lookup_index, HB_UNTAG (lookup.feature_tag))) continue;

     /* Only try applying the lookup if there is any overlap. */
     if (accel->digest.may_intersect (buffer->digest))
     {
c.set_lookup_index (lookup_index);
c.set_lookup_mask (lookup.mask, false);
c.set_auto_zwj (lookup.auto_zwj, false);
c.set_auto_zwnj (lookup.auto_zwnj, false);
c.set_random (lookup.random);
c.set_per_syllable (lookup.per_syllable, false);
/* apply_string's set_lookup_props initializes the iterators. */

apply_string<Proxy> (&c,
		     proxy.accel.table->get_lookup (lookup_index),
		     *accel);
     }
     else if (buffer->messaging ())
(void) buffer->message (font, "skipped lookup %u feature '%c%c%c%c' because no glyph matches", lookup_index, HB_UNTAG (lookup.feature_tag));

     if (buffer->messaging ())
(void) buffer->message (font, "end lookup %u feature '%c%c%c%c'", lookup_index, HB_UNTAG (lookup.feature_tag));
   }

   if (stage->pause_func)
   {
     if (stage->pause_func (plan, font, buffer))
     {
/* Refresh working buffer digest since buffer changed. */
buffer->update_digest ();
     }
   }
 }
}

void hb_ot_map_t::substitute (const hb_ot_shape_plan_t *plan, hb_font_t *font, hb_buffer_t *buffer) const
{
 GSUBProxy proxy (font->face);
 if (buffer->messaging () &&
     !buffer->message (font, "start table GSUB script tag '%c%c%c%c'", HB_UNTAG (chosen_script[0]))) return;
 apply (proxy, plan, font, buffer);
 if (buffer->messaging ())
   (void) buffer->message (font, "end table GSUB script tag '%c%c%c%c'", HB_UNTAG (chosen_script[0]));
}

void hb_ot_map_t::position (const hb_ot_shape_plan_t *plan, hb_font_t *font, hb_buffer_t *buffer) const
{
 GPOSProxy proxy (font->face);
 if (buffer->messaging () &&
     !buffer->message (font, "start table GPOS script tag '%c%c%c%c'", HB_UNTAG (chosen_script[1]))) return;
 apply (proxy, plan, font, buffer);
 if (buffer->messaging ())
   (void) buffer->message (font, "end table GPOS script tag '%c%c%c%c'", HB_UNTAG (chosen_script[1]));
}

void
hb_ot_layout_substitute_lookup (OT::hb_ot_apply_context_t *c,
			const OT::SubstLookup &lookup,
			const OT::hb_ot_layout_lookup_accelerator_t &accel)
{
 apply_string<GSUBProxy> (c, lookup, accel);
}

#ifndef HB_NO_BASE

static void
choose_base_tags (hb_script_t    script,
	  hb_language_t  language,
	  hb_tag_t      *script_tag,
	  hb_tag_t      *language_tag)
{
 hb_tag_t script_tags[HB_OT_MAX_TAGS_PER_SCRIPT];
 unsigned script_count = ARRAY_LENGTH (script_tags);

 hb_tag_t language_tags[HB_OT_MAX_TAGS_PER_LANGUAGE];
 unsigned language_count = ARRAY_LENGTH (language_tags);

 hb_ot_tags_from_script_and_language (script, language,
			       &script_count, script_tags,
			       &language_count, language_tags);

 *script_tag = script_count ? script_tags[script_count - 1] : HB_OT_TAG_DEFAULT_SCRIPT;
 *language_tag = language_count ? language_tags[language_count - 1] : HB_OT_TAG_DEFAULT_LANGUAGE;
}

/**
* hb_ot_layout_get_font_extents:
* @font: a font
* @direction: text direction.
* @script_tag:  script tag.
* @language_tag: language tag.
* @extents: (out) (nullable): font extents if found.
*
* Fetches script/language-specific font extents.  These values are
* looked up in the `BASE` table's `MinMax` records.
*
* If no such extents are found, the default extents for the font are
* fetched. As such, the return value of this function can for the
* most part be ignored.  Note that the per-script/language extents
* do not have a line-gap value, and the line-gap is set to zero in
* that case.
*
* Return value: `true` if found script/language-specific font extents.
*
* Since: 8.0.0
**/
hb_bool_t
hb_ot_layout_get_font_extents (hb_font_t         *font,
		       hb_direction_t     direction,
		       hb_tag_t           script_tag,
		       hb_tag_t           language_tag,
		       hb_font_extents_t *extents)
{
 hb_position_t min = 0, max = 0;
 if (font->face->table.BASE->get_min_max (font, direction, script_tag, language_tag, HB_TAG_NONE,
				   &min, &max))
 {
   if (extents)
   {
     extents->ascender  = max;
     extents->descender = min;
     extents->line_gap  = 0;
   }
   return true;
 }

 hb_font_get_extents_for_direction (font, direction, extents);
 return false;
}

/**
* hb_ot_layout_get_font_extents2:
* @font: a font
* @direction: text direction.
* @script:  script.
* @language: (nullable): language.
* @extents: (out) (nullable): font extents if found.
*
* Fetches script/language-specific font extents.  These values are
* looked up in the `BASE` table's `MinMax` records.
*
* If no such extents are found, the default extents for the font are
* fetched. As such, the return value of this function can for the
* most part be ignored.  Note that the per-script/language extents
* do not have a line-gap value, and the line-gap is set to zero in
* that case.
*
* This function is like hb_ot_layout_get_font_extents() but takes
* #hb_script_t and #hb_language_t instead of OpenType #hb_tag_t.
*
* Return value: `true` if found script/language-specific font extents.
*
* Since: 8.0.0
**/
hb_bool_t
hb_ot_layout_get_font_extents2 (hb_font_t         *font,
			hb_direction_t     direction,
			hb_script_t        script,
			hb_language_t      language,
			hb_font_extents_t *extents)
{
 hb_tag_t script_tag, language_tag;
 choose_base_tags (script, language, &script_tag, &language_tag);
 return hb_ot_layout_get_font_extents (font,
				direction,
				script_tag,
				language_tag,
				extents);
}

/**
* hb_ot_layout_get_horizontal_baseline_tag_for_script:
* @script: a script tag.
*
* Fetches the dominant horizontal baseline tag used by @script.
*
* Return value: dominant baseline tag for the @script.
*
* Since: 4.0.0
**/
hb_ot_layout_baseline_tag_t
hb_ot_layout_get_horizontal_baseline_tag_for_script (hb_script_t script)
{
 /* Keep in sync with hb_ot_layout_get_baseline_with_fallback */
 switch ((int) script)
 {
   /* Unicode-1.1 additions */
   case HB_SCRIPT_BENGALI:
   case HB_SCRIPT_DEVANAGARI:
   case HB_SCRIPT_GUJARATI:
   case HB_SCRIPT_GURMUKHI:
   /* Unicode-2.0 additions */
   case HB_SCRIPT_TIBETAN:
   /* Unicode-4.0 additions */
   case HB_SCRIPT_LIMBU:
   /* Unicode-4.1 additions */
   case HB_SCRIPT_SYLOTI_NAGRI:
   /* Unicode-5.0 additions */
   case HB_SCRIPT_PHAGS_PA:
   /* Unicode-5.2 additions */
   case HB_SCRIPT_MEETEI_MAYEK:
   /* Unicode-6.1 additions */
   case HB_SCRIPT_SHARADA:
   case HB_SCRIPT_TAKRI:
   /* Unicode-7.0 additions */
   case HB_SCRIPT_MODI:
   case HB_SCRIPT_SIDDHAM:
   case HB_SCRIPT_TIRHUTA:
   /* Unicode-9.0 additions */
   case HB_SCRIPT_MARCHEN:
   case HB_SCRIPT_NEWA:
   /* Unicode-10.0 additions */
   case HB_SCRIPT_SOYOMBO:
   case HB_SCRIPT_ZANABAZAR_SQUARE:
   /* Unicode-11.0 additions */
   case HB_SCRIPT_DOGRA:
   case HB_SCRIPT_GUNJALA_GONDI:
   /* Unicode-12.0 additions */
   case HB_SCRIPT_NANDINAGARI:
     return HB_OT_LAYOUT_BASELINE_TAG_HANGING;

   /* Unicode-1.1 additions */
   case HB_SCRIPT_HANGUL:
   case HB_SCRIPT_HAN:
   case HB_SCRIPT_HIRAGANA:
   case HB_SCRIPT_KATAKANA:
   /* Unicode-3.0 additions */
   case HB_SCRIPT_BOPOMOFO:
   /* Unicode-9.0 additions */
   case HB_SCRIPT_TANGUT:
   /* Unicode-10.0 additions */
   case HB_SCRIPT_NUSHU:
   /* Unicode-13.0 additions */
   case HB_SCRIPT_KHITAN_SMALL_SCRIPT:
     return HB_OT_LAYOUT_BASELINE_TAG_IDEO_FACE_BOTTOM_OR_LEFT;

   default:
     return HB_OT_LAYOUT_BASELINE_TAG_ROMAN;
 }
}

/**
* hb_ot_layout_get_baseline:
* @font: a font
* @baseline_tag: a baseline tag
* @direction: text direction.
* @script_tag:  script tag.
* @language_tag: language tag, currently unused.
* @coord: (out) (nullable): baseline value if found.
*
* Fetches a baseline value from the face.
*
* Return value: `true` if found baseline value in the font.
*
* Since: 2.6.0
**/
hb_bool_t
hb_ot_layout_get_baseline (hb_font_t                   *font,
		   hb_ot_layout_baseline_tag_t  baseline_tag,
		   hb_direction_t               direction,
		   hb_tag_t                     script_tag,
		   hb_tag_t                     language_tag,
		   hb_position_t               *coord        /* OUT.  May be NULL. */)
{
 return font->face->table.BASE->get_baseline (font, baseline_tag, direction, script_tag, language_tag, coord);
}

/**
* hb_ot_layout_get_baseline2:
* @font: a font
* @baseline_tag: a baseline tag
* @direction: text direction.
* @script:  script.
* @language: (nullable): language, currently unused.
* @coord: (out) (nullable): baseline value if found.
*
* Fetches a baseline value from the face.
*
* This function is like hb_ot_layout_get_baseline() but takes
* #hb_script_t and #hb_language_t instead of OpenType #hb_tag_t.
*
* Return value: `true` if found baseline value in the font.
*
* Since: 8.0.0
**/
hb_bool_t
hb_ot_layout_get_baseline2 (hb_font_t                   *font,
		    hb_ot_layout_baseline_tag_t  baseline_tag,
		    hb_direction_t               direction,
		    hb_script_t                  script,
		    hb_language_t                language,
		    hb_position_t               *coord        /* OUT.  May be NULL. */)
{
 hb_tag_t script_tag, language_tag;
 choose_base_tags (script, language, &script_tag, &language_tag);
 return hb_ot_layout_get_baseline (font,
			    baseline_tag,
			    direction,
			    script_tag,
			    language_tag,
			    coord);
}

/**
* hb_ot_layout_get_baseline_with_fallback:
* @font: a font
* @baseline_tag: a baseline tag
* @direction: text direction.
* @script_tag:  script tag.
* @language_tag: language tag, currently unused.
* @coord: (out): baseline value if found.
*
* Fetches a baseline value from the face, and synthesizes
* it if the font does not have it.
*
* Since: 4.0.0
**/
void
hb_ot_layout_get_baseline_with_fallback (hb_font_t                   *font,
				 hb_ot_layout_baseline_tag_t  baseline_tag,
				 hb_direction_t               direction,
				 hb_tag_t                     script_tag,
				 hb_tag_t                     language_tag,
				 hb_position_t               *coord /* OUT */)
{
 if (hb_ot_layout_get_baseline (font,
			 baseline_tag,
			 direction,
			 script_tag,
			 language_tag,
			 coord))
   return;

 /* Synthesize missing baselines.
  * See https://www.w3.org/TR/css-inline-3/#baseline-synthesis-fonts
  */
 switch (baseline_tag)
 {
 case HB_OT_LAYOUT_BASELINE_TAG_ROMAN:
   *coord = 0; // FIXME origin ?
   break;

 case HB_OT_LAYOUT_BASELINE_TAG_MATH:
   {
     hb_codepoint_t glyph;
     hb_glyph_extents_t extents;
     if (HB_DIRECTION_IS_HORIZONTAL (direction) &&
  (hb_font_get_nominal_glyph (font, 0x2212u, &glyph) ||
   hb_font_get_nominal_glyph (font, '-', &glyph)) &&
  hb_font_get_glyph_extents (font, glyph, &extents))
     {
*coord = extents.y_bearing + extents.height / 2;
     }
     else
     {
hb_position_t x_height = font->y_scale / 2;
#ifndef HB_NO_METRICS
hb_ot_metrics_get_position_with_fallback (font, HB_OT_METRICS_TAG_X_HEIGHT, &x_height);
#endif
*coord = x_height / 2;
     }
   }
   break;

 case HB_OT_LAYOUT_BASELINE_TAG_IDEO_FACE_TOP_OR_RIGHT:
 case HB_OT_LAYOUT_BASELINE_TAG_IDEO_FACE_BOTTOM_OR_LEFT:
   {
     hb_position_t embox_top, embox_bottom;

     hb_ot_layout_get_baseline_with_fallback (font,
				       HB_OT_LAYOUT_BASELINE_TAG_IDEO_EMBOX_TOP_OR_RIGHT,
				       direction,
				       script_tag,
				       language_tag,
				       &embox_top);
     hb_ot_layout_get_baseline_with_fallback (font,
				       HB_OT_LAYOUT_BASELINE_TAG_IDEO_EMBOX_BOTTOM_OR_LEFT,
				       direction,
				       script_tag,
				       language_tag,
				       &embox_bottom);

     if (baseline_tag == HB_OT_LAYOUT_BASELINE_TAG_IDEO_FACE_TOP_OR_RIGHT)
*coord = embox_top + (embox_bottom - embox_top) / 10;
     else
*coord = embox_bottom + (embox_top - embox_bottom) / 10;
   }
   break;

 case HB_OT_LAYOUT_BASELINE_TAG_IDEO_EMBOX_TOP_OR_RIGHT:
   if (hb_ot_layout_get_baseline (font,
			   HB_OT_LAYOUT_BASELINE_TAG_IDEO_EMBOX_BOTTOM_OR_LEFT,
			   direction,
			   script_tag,
			   language_tag,
			   coord))
     *coord += HB_DIRECTION_IS_HORIZONTAL (direction) ? font->y_scale : font->x_scale;
   else
   {
     hb_font_extents_t font_extents;
     hb_font_get_extents_for_direction (font, direction, &font_extents);
     *coord = font_extents.ascender;
   }
   break;

 case HB_OT_LAYOUT_BASELINE_TAG_IDEO_EMBOX_BOTTOM_OR_LEFT:
   if (hb_ot_layout_get_baseline (font,
			   HB_OT_LAYOUT_BASELINE_TAG_IDEO_EMBOX_TOP_OR_RIGHT,
			   direction,
			   script_tag,
			   language_tag,
			   coord))
     *coord -= HB_DIRECTION_IS_HORIZONTAL (direction) ? font->y_scale : font->x_scale;
   else
   {
     hb_font_extents_t font_extents;
     hb_font_get_extents_for_direction (font, direction, &font_extents);
     *coord = font_extents.descender;
   }
   break;

 case HB_OT_LAYOUT_BASELINE_TAG_HANGING:
   if (HB_DIRECTION_IS_HORIZONTAL (direction))
   {
     hb_codepoint_t ch;
     hb_codepoint_t glyph;
     hb_glyph_extents_t extents;

     /* Keep in sync with hb_ot_layout_get_horizontal_baseline_for_script */
     switch ((int) script_tag)
     {
     /* Unicode-1.1 additions */
     case HB_SCRIPT_BENGALI:          ch = 0x0995u; break;
     case HB_SCRIPT_DEVANAGARI:       ch = 0x0915u; break;
     case HB_SCRIPT_GUJARATI:         ch = 0x0a95u; break;
     case HB_SCRIPT_GURMUKHI:         ch = 0x0a15u; break;
     /* Unicode-2.0 additions */
     case HB_SCRIPT_TIBETAN:          ch = 0x0f40u; break;
     /* Unicode-4.0 additions */
     case HB_SCRIPT_LIMBU:            ch = 0x1901u; break;
     /* Unicode-4.1 additions */
     case HB_SCRIPT_SYLOTI_NAGRI:     ch = 0xa807u; break;
     /* Unicode-5.0 additions */
     case HB_SCRIPT_PHAGS_PA:         ch = 0xa840u; break;
     /* Unicode-5.2 additions */
     case HB_SCRIPT_MEETEI_MAYEK:     ch = 0xabc0u; break;
     /* Unicode-6.1 additions */
     case HB_SCRIPT_SHARADA:          ch = 0x11191u; break;
     case HB_SCRIPT_TAKRI:            ch = 0x1168cu; break;
     /* Unicode-7.0 additions */
     case HB_SCRIPT_MODI:             ch = 0x1160eu;break;
     case HB_SCRIPT_SIDDHAM:          ch = 0x11590u; break;
     case HB_SCRIPT_TIRHUTA:          ch = 0x1148fu; break;
     /* Unicode-9.0 additions */
     case HB_SCRIPT_MARCHEN:          ch = 0x11c72u; break;
     case HB_SCRIPT_NEWA:             ch = 0x1140eu; break;
     /* Unicode-10.0 additions */
     case HB_SCRIPT_SOYOMBO:          ch = 0x11a5cu; break;
     case HB_SCRIPT_ZANABAZAR_SQUARE: ch = 0x11a0bu; break;
     /* Unicode-11.0 additions */
     case HB_SCRIPT_DOGRA:            ch = 0x1180au; break;
     case HB_SCRIPT_GUNJALA_GONDI:    ch = 0x11d6cu; break;
     /* Unicode-12.0 additions */
     case HB_SCRIPT_NANDINAGARI:      ch = 0x119b0u; break;
     default:                         ch = 0;        break;
     }

     if (ch &&
  hb_font_get_nominal_glyph (font, ch, &glyph) &&
  hb_font_get_glyph_extents (font, glyph, &extents))
*coord = extents.y_bearing;
     else
*coord = font->y_scale * 6 / 10; // FIXME makes assumptions about origin
   }
   else
     *coord = font->x_scale * 6 / 10; // FIXME makes assumptions about origin
   break;

 case HB_OT_LAYOUT_BASELINE_TAG_IDEO_EMBOX_CENTRAL:
   {
     hb_position_t top, bottom;
     hb_ot_layout_get_baseline_with_fallback (font,
				       HB_OT_LAYOUT_BASELINE_TAG_IDEO_EMBOX_TOP_OR_RIGHT,
				       direction,
				       script_tag,
				       language_tag,
				       &top);
     hb_ot_layout_get_baseline_with_fallback (font,
				       HB_OT_LAYOUT_BASELINE_TAG_IDEO_EMBOX_BOTTOM_OR_LEFT,
				       direction,
				       script_tag,
				       language_tag,
				       &bottom);
     *coord = (top + bottom) / 2;

   }
   break;

 case HB_OT_LAYOUT_BASELINE_TAG_IDEO_FACE_CENTRAL:
   {
     hb_position_t top, bottom;
     hb_ot_layout_get_baseline_with_fallback (font,
				       HB_OT_LAYOUT_BASELINE_TAG_IDEO_FACE_TOP_OR_RIGHT,
				       direction,
				       script_tag,
				       language_tag,
				       &top);
     hb_ot_layout_get_baseline_with_fallback (font,
				       HB_OT_LAYOUT_BASELINE_TAG_IDEO_FACE_BOTTOM_OR_LEFT,
				       direction,
				       script_tag,
				       language_tag,
				       &bottom);
     *coord = (top + bottom) / 2;

   }
   break;

 case _HB_OT_LAYOUT_BASELINE_TAG_MAX_VALUE:
 default:
   *coord = 0;
   break;
 }
}

/**
* hb_ot_layout_get_baseline_with_fallback2:
* @font: a font
* @baseline_tag: a baseline tag
* @direction: text direction.
* @script:  script.
* @language: (nullable): language, currently unused.
* @coord: (out): baseline value if found.
*
* Fetches a baseline value from the face, and synthesizes
* it if the font does not have it.
*
* This function is like hb_ot_layout_get_baseline_with_fallback() but takes
* #hb_script_t and #hb_language_t instead of OpenType #hb_tag_t.
*
* Since: 8.0.0
**/
void
hb_ot_layout_get_baseline_with_fallback2 (hb_font_t                   *font,
				  hb_ot_layout_baseline_tag_t  baseline_tag,
				  hb_direction_t               direction,
				  hb_script_t                  script,
				  hb_language_t                language,
				  hb_position_t               *coord        /* OUT */)
{
 hb_tag_t script_tag, language_tag;
 choose_base_tags (script, language, &script_tag, &language_tag);
 hb_ot_layout_get_baseline_with_fallback (font,
				   baseline_tag,
				   direction,
				   script_tag,
				   language_tag,
				   coord);
}

#endif


#ifndef HB_NO_LAYOUT_RARELY_USED
struct hb_get_glyph_alternates_dispatch_t :
      hb_dispatch_context_t<hb_get_glyph_alternates_dispatch_t, unsigned>
{
 static return_t default_return_value () { return 0; }
 bool stop_sublookup_iteration (return_t r) const { return r; }

 private:
 template <typename T, typename ...Ts> auto
 _dispatch (const T &obj, hb_priority<1>, Ts&&... ds) HB_AUTO_RETURN
 ( obj.get_glyph_alternates (std::forward<Ts> (ds)...) )
 template <typename T, typename ...Ts> auto
 _dispatch (const T &obj, hb_priority<0>, Ts&&... ds) HB_AUTO_RETURN
 ( default_return_value () )
 public:
 template <typename T, typename ...Ts> auto
 dispatch (const T &obj, Ts&&... ds) HB_AUTO_RETURN
 ( _dispatch (obj, hb_prioritize, std::forward<Ts> (ds)...) )
};

/**
* hb_ot_layout_lookup_get_glyph_alternates:
* @face: a face.
* @lookup_index: index of the feature lookup to query.
* @glyph: a glyph id.
* @start_offset: starting offset.
* @alternate_count: (inout) (nullable): Input = the maximum number of alternate glyphs to return;
*                   Output = the actual number of alternate glyphs returned (may be zero).
* @alternate_glyphs: (out caller-allocates) (array length=alternate_count): A glyphs buffer.
*                    Alternate glyphs associated with the glyph id.
*
* Fetches alternates of a glyph from a given GSUB lookup index. Note that for one-to-one GSUB
* glyph substitutions, this function fetches the substituted glyph.
*
* Return value: Total number of alternates found in the specific lookup index for the given glyph id.
*
* Since: 2.6.8
**/
HB_EXTERN unsigned
hb_ot_layout_lookup_get_glyph_alternates (hb_face_t      *face,
				  unsigned        lookup_index,
				  hb_codepoint_t  glyph,
				  unsigned        start_offset,
				  unsigned       *alternate_count  /* IN/OUT.  May be NULL. */,
				  hb_codepoint_t *alternate_glyphs /* OUT.     May be NULL. */)
{
 hb_get_glyph_alternates_dispatch_t c;
 const OT::SubstLookup &lookup = face->table.GSUB->table->get_lookup (lookup_index);
 auto ret = lookup.dispatch (&c, glyph, start_offset, alternate_count, alternate_glyphs);
 if (!ret && alternate_count) *alternate_count = 0;
 return ret;
}

struct hb_collect_glyph_alternates_dispatch_t :
      hb_dispatch_context_t<hb_collect_glyph_alternates_dispatch_t, bool>
{
 static return_t default_return_value () { return false; }
 bool stop_sublookup_iteration (return_t r) const { return false; }

 private:
 template <typename T, typename ...Ts> auto
 _dispatch (const T &obj, hb_priority<1>, Ts&&... ds) HB_AUTO_RETURN
 ( (obj.collect_glyph_alternates (std::forward<Ts> (ds)...), true) )
 template <typename T, typename ...Ts> auto
 _dispatch (const T &obj, hb_priority<0>, Ts&&... ds) HB_AUTO_RETURN
 ( default_return_value () )
 public:
 template <typename T, typename ...Ts> auto
 dispatch (const T &obj, Ts&&... ds) HB_AUTO_RETURN
 ( _dispatch (obj, hb_prioritize, std::forward<Ts> (ds)...) )
};

/**
* hb_ot_layout_lookup_collect_glyph_alternates:
* @face: a face.
* @lookup_index: index of the feature lookup to query.
* @alternate_count: (inout): mapping from glyph index to number of alternates for that glyph.
* @alternate_glyphs: (inout): mapping from encoded glyph index and alternate index, to alternate glyph ids.
*
* Collects alternates of glyphs from a given GSUB lookup index.
*
* For one-to-one GSUB glyph substitutions, this function collects the
* substituted glyph.
*
* For lookups that assign multiple alternates to a glyph, all alternate glyphs are collected.
*
* For other lookup types, nothing is performed and `false` is returned.
*
* The `alternate_count` mapping will contain the number of alternates for each glyph id.
* Upon entry, this mapping should contain the glyph ids as keys, and the number of alternates
* currently known for each glyph id as values.
*
* The `alternate_glyphs` mapping will contain the alternate glyph ids for each glyph id.
* The mapping is encoded in the following way, upon entry and after processing:
* If G is the glyph id, and A0, A1, ..., A(n-1) are the alternate glyph ids,
* the mapping will contain the following entries: (G + (i << 24)) -> A(i)
* for i = 0, 1, ..., n-1 where n is the number of alternates for G as per `alternate_count`.
*
* Return value: `true` if alternates were collected, `false` otherwise.
* Since: 12.1.0
*/
HB_EXTERN hb_bool_t
hb_ot_layout_lookup_collect_glyph_alternates (hb_face_t *face,
				      unsigned   lookup_index,
				      hb_map_t  *alternate_count /* IN/OUT */,
				      hb_map_t  *alternate_glyphs /* IN/OUT */)
{
 hb_collect_glyph_alternates_dispatch_t c;
 const OT::SubstLookup &lookup = face->table.GSUB->table->get_lookup (lookup_index);
 return lookup.dispatch (&c, alternate_count, alternate_glyphs);
}

struct hb_position_single_dispatch_t :
      hb_dispatch_context_t<hb_position_single_dispatch_t, bool>
{
 static return_t default_return_value () { return false; }
 bool stop_sublookup_iteration (return_t r) const { return r; }

 private:
 template <typename T, typename ...Ts> auto
 _dispatch (const T &obj, hb_priority<1>, Ts&&... ds) HB_AUTO_RETURN
 ( obj.position_single (std::forward<Ts> (ds)...) )
 template <typename T, typename ...Ts> auto
 _dispatch (const T &obj, hb_priority<0>, Ts&&... ds) HB_AUTO_RETURN
 ( default_return_value () )
 public:
 template <typename T, typename ...Ts> auto
 dispatch (const T &obj, Ts&&... ds) HB_AUTO_RETURN
 ( _dispatch (obj, hb_prioritize, std::forward<Ts> (ds)...) )
};

/**
* hb_ot_layout_lookup_get_optical_bound:
* @font: a font.
* @lookup_index: index of the feature lookup to query.
* @direction: edge of the glyph to query.
* @glyph: a glyph id.
*
* Fetches the optical bound of a glyph positioned at the margin of text.
* The direction identifies which edge of the glyph to query.
*
* Return value: Adjustment value. Negative values mean the glyph will stick out of the margin.
*
* Since: 5.3.0
**/
hb_position_t
hb_ot_layout_lookup_get_optical_bound (hb_font_t      *font,
			       unsigned        lookup_index,
			       hb_direction_t  direction,
			       hb_codepoint_t  glyph)
{
 const OT::PosLookup &lookup = font->face->table.GPOS->table->get_lookup (lookup_index);
 hb_blob_t *blob = font->face->table.GPOS->get_blob ();
 hb_glyph_position_t pos = {0};
 hb_position_single_dispatch_t c;
 lookup.dispatch (&c, font, blob, direction, glyph, pos);
 hb_position_t ret = 0;
 switch (direction)
 {
   case HB_DIRECTION_LTR:
     ret = pos.x_offset;
     break;
   case HB_DIRECTION_RTL:
     ret = pos.x_advance - pos.x_offset;
     break;
   case HB_DIRECTION_TTB:
     ret = pos.y_offset;
     break;
   case HB_DIRECTION_BTT:
     ret = pos.y_advance - pos.y_offset;
     break;
   case HB_DIRECTION_INVALID:
   default:
     break;
 }
 return ret;
}
#endif


#endif