Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2481 insertions, 0 deletions

diff --git a/gfx/harfbuzz/src/hb-ot-layout.cc b/gfx/harfbuzz/src/hb-ot-layout.cc
new file mode 100644
index 0000000000..c66ee8cfd0
--- /dev/null
+++ b/gfx/harfbuzz/src/hb-ot-layout.cc
@@ -0,0 +1,2481 @@
+/*
+ * 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->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->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->has_cross_stream ();
+}
+
+void
+hb_ot_layout_kern (const hb_ot_shape_plan_t *plan,
+		   hb_font_t *font,
+		   hb_buffer_t  *buffer)
+{
+  hb_blob_t *blob = font->face->table.kern.get_blob ();
+  const AAT::kern& kern = *blob->as<AAT::kern> ();
+
+  AAT::hb_aat_apply_context_t c (plan, font, buffer, blob);
+
+  if (!buffer->message (font, "start table kern")) return;
+  kern.apply (&c);
+  (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):
+      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) (optional): 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) (optional): 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) (optional): 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) (optional): The index of the requested script
+ * @chosen_script: (out) (optional): #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) (optional): 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) (optional): 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) (optional): 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) (optional): 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) (optional): 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 array 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_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 (hb_codepoint_t feature_index = HB_SET_VALUE_INVALID;
+       hb_set_next (&feature_indexes, &feature_index);)
+    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): Array of glyphs preceding the substitution range
+ * @glyphs_input: (out): Array of input glyphs that would be substituted by the lookup
+ * @glyphs_after: (out): Array of glyphs following the substitution range
+ * @glyphs_output: (out): 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);
+
+  return g.find_variations_index (coords, num_coords, variations_index);
+}
+
+
+/**
+ * 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) (optional): 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 (hb_codepoint_t lookup_index = HB_SET_VALUE_INVALID; hb_set_next (lookups, &lookup_index);)
+	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) (optional): The ‘name’ table name ID that specifies a string
+ *            for a user-interface label for this feature. (May be NULL.)
+ * @tooltip_id: (out) (optional): The ‘name’ table name ID that specifies a string
+ *              that an application can use for tooltip text for this
+ *              feature. (May be NULL.)
+ * @sample_id: (out) (optional): The ‘name’ table name ID that specifies sample text
+ *             that illustrates the effect of this feature. (May be NULL.)
+ * @num_named_parameters: (out) (optional):  Number of named parameters. (May be zero.)
+ * @first_param_id: (out) (optional): 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) (optional): 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,
+	       unsigned subtable_count)
+{
+  bool use_cache = accel.cache_enter (c);
+
+  bool ret = false;
+  hb_buffer_t *buffer = c->buffer;
+  while (buffer->idx < buffer->len && buffer->successful)
+  {
+    bool applied = false;
+    if (accel.digest.may_have (buffer->cur().codepoint) &&
+	(buffer->cur().mask & c->lookup_mask) &&
+	c->check_glyph_property (&buffer->cur(), c->lookup_props))
+     {
+       applied = accel.apply (c, subtable_count, use_cache);
+     }
+
+    if (applied)
+      ret = true;
+    else
+      (void) buffer->next_glyph ();
+  }
+
+  if (use_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,
+	       unsigned subtable_count)
+{
+  bool ret = false;
+  hb_buffer_t *buffer = c->buffer;
+  do
+  {
+    if (accel.digest.may_have (buffer->cur().codepoint) &&
+	(buffer->cur().mask & c->lookup_mask) &&
+	c->check_glyph_property (&buffer->cur(), c->lookup_props))
+      ret |= accel.apply (c, subtable_count, 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;
+  unsigned subtable_count = lookup.get_subtable_count ();
+
+  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, subtable_count);
+
+    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, subtable_count);
+  }
+
+  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;
+  OT::hb_ot_apply_context_t c (table_index, font, buffer);
+  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;
+
+      /* c.digest is a digest of all the current glyphs in the buffer
+       * (plus some past glyphs).
+       *
+       * Only try applying the lookup if there is any overlap. */
+      if (accel->digest.may_have (c.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. */
+	c.digest = buffer->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")) return;
+  apply (proxy, plan, font, buffer);
+  if (buffer->messaging ())
+    (void) buffer->message (font, "end table GSUB");
+}
+
+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")) return;
+  apply (proxy, plan, font, buffer);
+  if (buffer->messaging ())
+    (void) buffer->message (font, "end table GPOS");
+}
+
+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
+/**
+ * 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_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;
+  }
+}
+
+#endif
+
+
+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)...) )
+};
+
+#ifndef HB_NO_LAYOUT_RARELY_USED
+/**
+ * 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) (optional): 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.
+ *
+ * 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_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_glyph_position_t pos = {0};
+  hb_position_single_dispatch_t c;
+  lookup.dispatch (&c, font, 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