src/hb-ot-shape.cc - third_party/harfbuzz - Git at Google

 /*
  * Copyright (C) 2009  Red Hat, 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
  */

 #include "hb-ot-shape.h"

 #include "hb-buffer-private.hh"

 #include "hb-ot-layout.h"

 /* XXX vertical */
 hb_tag_t default_features[] = {
   HB_TAG('c','a','l','t'),
   HB_TAG('c','c','m','p'),
   HB_TAG('c','l','i','g'),
   HB_TAG('c','s','w','h'),
   HB_TAG('c','u','r','s'),
   HB_TAG('k','e','r','n'),
   HB_TAG('l','i','g','a'),
   HB_TAG('l','o','c','l'),
   HB_TAG('m','a','r','k'),
   HB_TAG('m','k','m','k'),
   HB_TAG('r','l','i','g')
 };

 enum {
   MASK_ALWAYS_ON = 1 << 0,
   MASK_RTLM      = 1 << 1
 };
 #define MASK_BITS_USED 2

 struct lookup_map {
   unsigned int index;
   hb_mask_t mask;
 };


 static void
 add_feature (hb_face_t    *face,
 	     hb_tag_t      table_tag,
 	     unsigned int  feature_index,
 	     hb_mask_t     mask,
 	     lookup_map   *lookups,
 	     unsigned int *num_lookups,
 	     unsigned int  room_lookups)
 {
   unsigned int i = room_lookups - *num_lookups;
   lookups += *num_lookups;

   unsigned int *lookup_indices = (unsigned int *) lookups;

   hb_ot_layout_feature_get_lookup_indexes (face, table_tag, feature_index, 0,
 					   &i,
 					   lookup_indices);

   *num_lookups += i;

   while (i--) {
     lookups[i].mask = mask;
     lookups[i].index = lookup_indices[i];
   }
 }

 static hb_bool_t
 maybe_add_feature (hb_face_t    *face,
 		   hb_tag_t      table_tag,
 		   unsigned int  script_index,
 		   unsigned int  language_index,
 		   hb_tag_t      feature_tag,
 		   hb_mask_t     mask,
 		   lookup_map   *lookups,
 		   unsigned int *num_lookups,
 		   unsigned int  room_lookups)
 {
   unsigned int feature_index;
   if (hb_ot_layout_language_find_feature (face, table_tag, script_index, language_index,
 					  feature_tag,
 					  &feature_index))
   {
     add_feature (face, table_tag, feature_index, mask, lookups, num_lookups, room_lookups);
     return TRUE;
   }
   return FALSE;
 }

 static int
 cmp_lookups (const void *p1, const void *p2)
 {
   const lookup_map *a = (const lookup_map *) p1;
   const lookup_map *b = (const lookup_map *) p2;

   return a->index - b->index;
 }

 static void
 setup_lookups (hb_face_t    *face,
 	       hb_buffer_t  *buffer,
 	       hb_feature_t *features,
 	       unsigned int  num_features,
 	       hb_tag_t      table_tag,
 	       lookup_map   *lookups,
 	       unsigned int *num_lookups,
 	       hb_direction_t original_direction)
 {
   unsigned int i, j, script_index, language_index, feature_index, room_lookups;

   room_lookups = *num_lookups;
   *num_lookups = 0;

   hb_ot_layout_table_choose_script (face, table_tag,
 				    hb_ot_tags_from_script (buffer->script),
 				    &script_index);
   hb_ot_layout_script_find_language (face, table_tag, script_index,
 				     hb_ot_tag_from_language (buffer->language),
 				     &language_index);

   if (hb_ot_layout_language_get_required_feature_index (face, table_tag, script_index, language_index,
 							&feature_index))
     add_feature (face, table_tag, feature_index, 1, lookups, num_lookups, room_lookups);

   for (i = 0; i < ARRAY_LENGTH (default_features); i++)
     maybe_add_feature (face, table_tag, script_index, language_index, default_features[i], 1, lookups, num_lookups, room_lookups);

   switch (original_direction) {
     case HB_DIRECTION_LTR:
       maybe_add_feature (face, table_tag, script_index, language_index, HB_TAG ('l','t','r','a'), 1, lookups, num_lookups, room_lookups);
       maybe_add_feature (face, table_tag, script_index, language_index, HB_TAG ('l','t','r','m'), 1, lookups, num_lookups, room_lookups);
       break;
     case HB_DIRECTION_RTL:
       maybe_add_feature (face, table_tag, script_index, language_index, HB_TAG ('r','t','l','a'), 1, lookups, num_lookups, room_lookups);
       break;
     case HB_DIRECTION_TTB:
     case HB_DIRECTION_BTT:
     default:
       break;
   }

   unsigned int next_bit = MASK_BITS_USED;
   hb_mask_t global_mask = 0;
   for (i = 0; i < num_features; i++)
   {
     hb_feature_t *feature = &features[i];
     if (!hb_ot_layout_language_find_feature (face, table_tag, script_index, language_index,
 					     feature->tag,
 					     &feature_index))
       continue;

     if (feature->value == 1 && feature->start == 0 && feature->end == (unsigned int) -1) {
       add_feature (face, table_tag, feature_index, 1, lookups, num_lookups, room_lookups);
       continue;
     }

     /* Allocate bits for the features */

     unsigned int bits_needed = _hb_bit_storage (feature->value);
     if (!bits_needed)
       continue; /* Feature disabled */

     if (next_bit + bits_needed > 8 * sizeof (hb_mask_t))
       continue; /* Oh well... */

     unsigned int mask = (1 << (next_bit + bits_needed)) - (1 << next_bit);
     unsigned int value = feature->value << next_bit;
     next_bit += bits_needed;

     add_feature (face, table_tag, feature_index, mask, lookups, num_lookups, room_lookups);

     if (feature->start == 0 && feature->end == (unsigned int) -1)
       global_mask |= value;
     else
       buffer->or_masks (mask, feature->start, feature->end);
   }

   if (global_mask)
     buffer->or_masks (global_mask, 0, (unsigned int) -1);

   qsort (lookups, *num_lookups, sizeof (lookups[0]), cmp_lookups);

   if (*num_lookups)
   {
     for (i = 1, j = 0; i < *num_lookups; i++)
       if (lookups[i].index != lookups[j].index)
 	lookups[++j] = lookups[i];
       else
         lookups[j].mask |= lookups[i].mask;
     j++;
     *num_lookups = j;
   }
 }


 static hb_bool_t
 hb_ot_substitute_complex (hb_font_t    *font HB_UNUSED,
 			  hb_face_t    *face,
 			  hb_buffer_t  *buffer,
 			  hb_feature_t *features,
 			  unsigned int  num_features,
 			  hb_direction_t original_direction)
 {
   lookup_map lookups[1000];
   unsigned int num_lookups = ARRAY_LENGTH (lookups);
   unsigned int i;

   if (!hb_ot_layout_has_substitution (face))
     return FALSE;

   setup_lookups (face, buffer, features, num_features,
 		 HB_OT_TAG_GSUB,
 		 lookups, &num_lookups,
 		 original_direction);

   for (i = 0; i < num_lookups; i++)
     hb_ot_layout_substitute_lookup (face, buffer, lookups[i].index, lookups[i].mask);

   return TRUE;
 }

 static hb_bool_t
 hb_ot_position_complex (hb_font_t    *font,
 			hb_face_t    *face,
 			hb_buffer_t  *buffer,
 			hb_feature_t *features,
 			unsigned int  num_features,
 			hb_direction_t original_direction)
 {
   lookup_map lookups[1000];
   unsigned int num_lookups = ARRAY_LENGTH (lookups);
   unsigned int i;

   if (!hb_ot_layout_has_positioning (face))
     return FALSE;

   setup_lookups (face, buffer, features, num_features,
 		 HB_OT_TAG_GPOS,
 		 lookups, &num_lookups,
 		 original_direction);

   for (i = 0; i < num_lookups; i++)
     hb_ot_layout_position_lookup (font, face, buffer, lookups[i].index, lookups[i].mask);

   hb_ot_layout_position_finish (font, face, buffer);

   return TRUE;
 }


 /* Main shaper */

 /* Prepare */

 static inline hb_bool_t
 is_variation_selector (hb_codepoint_t unicode)
 {
   return unlikely ((unicode >=  0x180B && unicode <=  0x180D) || /* MONGOLIAN FREE VARIATION SELECTOR ONE..THREE */
 		   (unicode >=  0xFE00 && unicode <=  0xFE0F) || /* VARIATION SELECTOR-1..16 */
 		   (unicode >= 0xE0100 && unicode <= 0xE01EF));  /* VARIATION SELECTOR-17..256 */
 }

 static void
 hb_form_clusters (hb_buffer_t *buffer)
 {
   unsigned int count = buffer->len;
   for (unsigned int i = 1; i < count; i++)
     if (buffer->unicode->v.get_general_category (buffer->info[i].codepoint) == HB_CATEGORY_NON_SPACING_MARK)
       buffer->info[i].cluster = buffer->info[i - 1].cluster;
 }

 static hb_direction_t
 hb_ensure_native_direction (hb_buffer_t *buffer)
 {
   hb_direction_t original_direction = buffer->direction;

   /* TODO vertical */
   if (HB_DIRECTION_IS_HORIZONTAL (original_direction) &&
       original_direction != _hb_script_get_horizontal_direction (buffer->script))
   {
     hb_buffer_reverse_clusters (buffer);
     buffer->direction = HB_DIRECTION_REVERSE (buffer->direction);
   }

   return original_direction;
 }


 /* Substitute */

 static void
 hb_mirror_chars (hb_buffer_t *buffer)
 {
   hb_unicode_get_mirroring_func_t get_mirroring = buffer->unicode->v.get_mirroring;

   if (HB_DIRECTION_IS_FORWARD (buffer->direction))
     return;

   unsigned int count = buffer->len;
   for (unsigned int i = 0; i < count; i++) {
     hb_codepoint_t codepoint = get_mirroring (buffer->info[i].codepoint);
     if (likely (codepoint == buffer->info[i].codepoint))
       buffer->info[i].mask |= MASK_RTLM;
     else
       buffer->info[i].codepoint = codepoint;
   }
 }

 static void
 hb_map_glyphs (hb_font_t    *font,
 	       hb_face_t    *face,
 	       hb_buffer_t  *buffer)
 {
   if (unlikely (!buffer->len))
     return;

   unsigned int count = buffer->len - 1;
   for (unsigned int i = 0; i < count; i++) {
     if (unlikely (is_variation_selector (buffer->info[i + 1].codepoint))) {
       buffer->info[i].codepoint = hb_font_get_glyph (font, face, buffer->info[i].codepoint, buffer->info[i + 1].codepoint);
       i++;
     } else {
       buffer->info[i].codepoint = hb_font_get_glyph (font, face, buffer->info[i].codepoint, 0);
     }
   }
   buffer->info[count].codepoint = hb_font_get_glyph (font, face, buffer->info[count].codepoint, 0);
 }

 static void
 hb_substitute_default (hb_font_t    *font,
 		       hb_face_t    *face,
 		       hb_buffer_t  *buffer,
 		       hb_feature_t *features HB_UNUSED,
 		       unsigned int  num_features HB_UNUSED)
 {
   hb_map_glyphs (font, face, buffer);
 }

 static void
 hb_substitute_complex_fallback (hb_font_t    *font HB_UNUSED,
 				hb_face_t    *face HB_UNUSED,
 				hb_buffer_t  *buffer HB_UNUSED,
 				hb_feature_t *features HB_UNUSED,
 				unsigned int  num_features HB_UNUSED)
 {
   /* TODO Arabic */
 }


 /* Position */

 static void
 hb_position_default (hb_font_t    *font,
 		     hb_face_t    *face,
 		     hb_buffer_t  *buffer,
 		     hb_feature_t *features HB_UNUSED,
 		     unsigned int  num_features HB_UNUSED)
 {
   hb_buffer_clear_positions (buffer);

   unsigned int count = buffer->len;
   for (unsigned int i = 0; i < count; i++) {
     hb_glyph_metrics_t metrics;
     hb_font_get_glyph_metrics (font, face, buffer->info[i].codepoint, &metrics);
     buffer->pos[i].x_advance = metrics.x_advance;
     buffer->pos[i].y_advance = metrics.y_advance;
   }
 }

 static void
 hb_position_complex_fallback (hb_font_t    *font HB_UNUSED,
 			      hb_face_t    *face HB_UNUSED,
 			      hb_buffer_t  *buffer HB_UNUSED,
 			      hb_feature_t *features HB_UNUSED,
 			      unsigned int  num_features HB_UNUSED)
 {
   /* TODO Mark pos */
 }

 static void
 hb_truetype_kern (hb_font_t    *font,
 		  hb_face_t    *face,
 		  hb_buffer_t  *buffer,
 		  hb_feature_t *features HB_UNUSED,
 		  unsigned int  num_features HB_UNUSED)
 {
   /* TODO Check for kern=0 */
   unsigned int count = buffer->len;
   for (unsigned int i = 1; i < count; i++) {
     hb_position_t kern, kern1, kern2;
     kern = hb_font_get_kerning (font, face, buffer->info[i - 1].codepoint, buffer->info[i].codepoint);
     kern1 = kern >> 1;
     kern2 = kern - kern1;
     buffer->pos[i - 1].x_advance += kern1;
     buffer->pos[i].x_advance += kern2;
     buffer->pos[i].x_offset += kern2;
   }
 }

 static void
 hb_position_complex_fallback_visual (hb_font_t    *font,
 				     hb_face_t    *face,
 				     hb_buffer_t  *buffer,
 				     hb_feature_t *features,
 				     unsigned int  num_features)
 {
   hb_truetype_kern (font, face, buffer, features, num_features);
 }


 /* Do it! */

 void
 hb_ot_shape (hb_font_t    *font,
 	     hb_face_t    *face,
 	     hb_buffer_t  *buffer,
 	     hb_feature_t *features,
 	     unsigned int  num_features)
 {
   hb_direction_t original_direction;
   hb_bool_t substitute_fallback, position_fallback;

   hb_form_clusters (buffer);

   /* SUBSTITUTE */

   buffer->clear_masks ();

   /* Mirroring needs to see the original direction */
   hb_mirror_chars (buffer);

   original_direction = hb_ensure_native_direction (buffer);

   hb_substitute_default (font, face, buffer, features, num_features);

   substitute_fallback = !hb_ot_substitute_complex (font, face, buffer, features, num_features, original_direction);

   if (substitute_fallback)
     hb_substitute_complex_fallback (font, face, buffer, features, num_features);


   /* POSITION */

   buffer->clear_masks ();

   hb_position_default (font, face, buffer, features, num_features);

   position_fallback = !hb_ot_position_complex (font, face, buffer, features, num_features, original_direction);

   if (position_fallback)
     hb_position_complex_fallback (font, face, buffer, features, num_features);

   if (HB_DIRECTION_IS_BACKWARD (buffer->direction))
     hb_buffer_reverse (buffer);

   if (position_fallback)
     hb_position_complex_fallback_visual (font, face, buffer, features, num_features);

   buffer->direction = original_direction;
 }
	/*
	* Copyright (C) 2009 Red Hat, 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
	*/

	#include "hb-ot-shape.h"

	#include "hb-buffer-private.hh"

	#include "hb-ot-layout.h"

	/* XXX vertical */
	hb_tag_t default_features[] = {
	HB_TAG('c','a','l','t'),
	HB_TAG('c','c','m','p'),
	HB_TAG('c','l','i','g'),
	HB_TAG('c','s','w','h'),
	HB_TAG('c','u','r','s'),
	HB_TAG('k','e','r','n'),
	HB_TAG('l','i','g','a'),
	HB_TAG('l','o','c','l'),
	HB_TAG('m','a','r','k'),
	HB_TAG('m','k','m','k'),
	HB_TAG('r','l','i','g')
	};

	enum {
	MASK_ALWAYS_ON = 1 << 0,
	MASK_RTLM = 1 << 1
	};
	#define MASK_BITS_USED 2

	struct lookup_map {
	unsigned int index;
	hb_mask_t mask;
	};


	static void
	add_feature (hb_face_t *face,
	hb_tag_t table_tag,
	unsigned int feature_index,
	hb_mask_t mask,
	lookup_map *lookups,
	unsigned int *num_lookups,
	unsigned int room_lookups)
	{
	unsigned int i = room_lookups - *num_lookups;
	lookups += *num_lookups;

	unsigned int lookup_indices = (unsigned int ) lookups;

	hb_ot_layout_feature_get_lookup_indexes (face, table_tag, feature_index, 0,
	&i,
	lookup_indices);

	*num_lookups += i;

	while (i--) {
	lookups[i].mask = mask;
	lookups[i].index = lookup_indices[i];
	}
	}

	static hb_bool_t
	maybe_add_feature (hb_face_t *face,
	hb_tag_t table_tag,
	unsigned int script_index,
	unsigned int language_index,
	hb_tag_t feature_tag,
	hb_mask_t mask,
	lookup_map *lookups,
	unsigned int *num_lookups,
	unsigned int room_lookups)
	{
	unsigned int feature_index;
	if (hb_ot_layout_language_find_feature (face, table_tag, script_index, language_index,
	feature_tag,
	&feature_index))
	{
	add_feature (face, table_tag, feature_index, mask, lookups, num_lookups, room_lookups);
	return TRUE;
	}
	return FALSE;
	}

	static int
	cmp_lookups (const void p1, const void p2)
	{
	const lookup_map a = (const lookup_map ) p1;
	const lookup_map b = (const lookup_map ) p2;

	return a->index - b->index;
	}

	static void
	setup_lookups (hb_face_t *face,
	hb_buffer_t *buffer,
	hb_feature_t *features,
	unsigned int num_features,
	hb_tag_t table_tag,
	lookup_map *lookups,
	unsigned int *num_lookups,
	hb_direction_t original_direction)
	{
	unsigned int i, j, script_index, language_index, feature_index, room_lookups;

	room_lookups = *num_lookups;
	*num_lookups = 0;

	hb_ot_layout_table_choose_script (face, table_tag,
	hb_ot_tags_from_script (buffer->script),
	&script_index);
	hb_ot_layout_script_find_language (face, table_tag, script_index,
	hb_ot_tag_from_language (buffer->language),
	&language_index);

	if (hb_ot_layout_language_get_required_feature_index (face, table_tag, script_index, language_index,
	&feature_index))
	add_feature (face, table_tag, feature_index, 1, lookups, num_lookups, room_lookups);

	for (i = 0; i < ARRAY_LENGTH (default_features); i++)
	maybe_add_feature (face, table_tag, script_index, language_index, default_features[i], 1, lookups, num_lookups, room_lookups);

	switch (original_direction) {
	case HB_DIRECTION_LTR:
	maybe_add_feature (face, table_tag, script_index, language_index, HB_TAG ('l','t','r','a'), 1, lookups, num_lookups, room_lookups);
	maybe_add_feature (face, table_tag, script_index, language_index, HB_TAG ('l','t','r','m'), 1, lookups, num_lookups, room_lookups);
	break;
	case HB_DIRECTION_RTL:
	maybe_add_feature (face, table_tag, script_index, language_index, HB_TAG ('r','t','l','a'), 1, lookups, num_lookups, room_lookups);
	break;
	case HB_DIRECTION_TTB:
	case HB_DIRECTION_BTT:
	default:
	break;
	}

	unsigned int next_bit = MASK_BITS_USED;
	hb_mask_t global_mask = 0;
	for (i = 0; i < num_features; i++)
	{
	hb_feature_t *feature = &features[i];
	if (!hb_ot_layout_language_find_feature (face, table_tag, script_index, language_index,
	feature->tag,
	&feature_index))
	continue;

	if (feature->value == 1 && feature->start == 0 && feature->end == (unsigned int) -1) {
	add_feature (face, table_tag, feature_index, 1, lookups, num_lookups, room_lookups);
	continue;
	}

	/* Allocate bits for the features */

	unsigned int bits_needed = _hb_bit_storage (feature->value);
	if (!bits_needed)
	continue; /* Feature disabled */

	if (next_bit + bits_needed > 8 * sizeof (hb_mask_t))
	continue; /* Oh well... */

	unsigned int mask = (1 << (next_bit + bits_needed)) - (1 << next_bit);
	unsigned int value = feature->value << next_bit;
	next_bit += bits_needed;

	add_feature (face, table_tag, feature_index, mask, lookups, num_lookups, room_lookups);

	if (feature->start == 0 && feature->end == (unsigned int) -1)
	global_mask \|= value;
	else
	buffer->or_masks (mask, feature->start, feature->end);
	}

	if (global_mask)
	buffer->or_masks (global_mask, 0, (unsigned int) -1);

	qsort (lookups, *num_lookups, sizeof (lookups[0]), cmp_lookups);

	if (*num_lookups)
	{
	for (i = 1, j = 0; i < *num_lookups; i++)
	if (lookups[i].index != lookups[j].index)
	lookups[++j] = lookups[i];
	else
	lookups[j].mask \|= lookups[i].mask;
	j++;
	*num_lookups = j;
	}
	}


	static hb_bool_t
	hb_ot_substitute_complex (hb_font_t *font HB_UNUSED,
	hb_face_t *face,
	hb_buffer_t *buffer,
	hb_feature_t *features,
	unsigned int num_features,
	hb_direction_t original_direction)
	{
	lookup_map lookups[1000];
	unsigned int num_lookups = ARRAY_LENGTH (lookups);
	unsigned int i;

	if (!hb_ot_layout_has_substitution (face))
	return FALSE;

	setup_lookups (face, buffer, features, num_features,
	HB_OT_TAG_GSUB,
	lookups, &num_lookups,
	original_direction);

	for (i = 0; i < num_lookups; i++)
	hb_ot_layout_substitute_lookup (face, buffer, lookups[i].index, lookups[i].mask);

	return TRUE;
	}

	static hb_bool_t
	hb_ot_position_complex (hb_font_t *font,
	hb_face_t *face,
	hb_buffer_t *buffer,
	hb_feature_t *features,
	unsigned int num_features,
	hb_direction_t original_direction)
	{
	lookup_map lookups[1000];
	unsigned int num_lookups = ARRAY_LENGTH (lookups);
	unsigned int i;

	if (!hb_ot_layout_has_positioning (face))
	return FALSE;

	setup_lookups (face, buffer, features, num_features,
	HB_OT_TAG_GPOS,
	lookups, &num_lookups,
	original_direction);

	for (i = 0; i < num_lookups; i++)
	hb_ot_layout_position_lookup (font, face, buffer, lookups[i].index, lookups[i].mask);

	hb_ot_layout_position_finish (font, face, buffer);

	return TRUE;
	}


	/* Main shaper */

	/* Prepare */

	static inline hb_bool_t
	is_variation_selector (hb_codepoint_t unicode)
	{
	return unlikely ((unicode >= 0x180B && unicode <= 0x180D) \|\| /* MONGOLIAN FREE VARIATION SELECTOR ONE..THREE */
	(unicode >= 0xFE00 && unicode <= 0xFE0F) \|\| /* VARIATION SELECTOR-1..16 */
	(unicode >= 0xE0100 && unicode <= 0xE01EF)); /* VARIATION SELECTOR-17..256 */
	}

	static void
	hb_form_clusters (hb_buffer_t *buffer)
	{
	unsigned int count = buffer->len;
	for (unsigned int i = 1; i < count; i++)
	if (buffer->unicode->v.get_general_category (buffer->info[i].codepoint) == HB_CATEGORY_NON_SPACING_MARK)
	buffer->info[i].cluster = buffer->info[i - 1].cluster;
	}

	static hb_direction_t
	hb_ensure_native_direction (hb_buffer_t *buffer)
	{
	hb_direction_t original_direction = buffer->direction;

	/* TODO vertical */
	if (HB_DIRECTION_IS_HORIZONTAL (original_direction) &&
	original_direction != _hb_script_get_horizontal_direction (buffer->script))
	{
	hb_buffer_reverse_clusters (buffer);
	buffer->direction = HB_DIRECTION_REVERSE (buffer->direction);
	}

	return original_direction;
	}


	/* Substitute */

	static void
	hb_mirror_chars (hb_buffer_t *buffer)
	{
	hb_unicode_get_mirroring_func_t get_mirroring = buffer->unicode->v.get_mirroring;

	if (HB_DIRECTION_IS_FORWARD (buffer->direction))
	return;

	unsigned int count = buffer->len;
	for (unsigned int i = 0; i < count; i++) {
	hb_codepoint_t codepoint = get_mirroring (buffer->info[i].codepoint);
	if (likely (codepoint == buffer->info[i].codepoint))
	buffer->info[i].mask \|= MASK_RTLM;
	else
	buffer->info[i].codepoint = codepoint;
	}
	}

	static void
	hb_map_glyphs (hb_font_t *font,
	hb_face_t *face,
	hb_buffer_t *buffer)
	{
	if (unlikely (!buffer->len))
	return;

	unsigned int count = buffer->len - 1;
	for (unsigned int i = 0; i < count; i++) {
	if (unlikely (is_variation_selector (buffer->info[i + 1].codepoint))) {
	buffer->info[i].codepoint = hb_font_get_glyph (font, face, buffer->info[i].codepoint, buffer->info[i + 1].codepoint);
	i++;
	} else {
	buffer->info[i].codepoint = hb_font_get_glyph (font, face, buffer->info[i].codepoint, 0);
	}
	}
	buffer->info[count].codepoint = hb_font_get_glyph (font, face, buffer->info[count].codepoint, 0);
	}

	static void
	hb_substitute_default (hb_font_t *font,
	hb_face_t *face,
	hb_buffer_t *buffer,
	hb_feature_t *features HB_UNUSED,
	unsigned int num_features HB_UNUSED)
	{
	hb_map_glyphs (font, face, buffer);
	}

	static void
	hb_substitute_complex_fallback (hb_font_t *font HB_UNUSED,
	hb_face_t *face HB_UNUSED,
	hb_buffer_t *buffer HB_UNUSED,
	hb_feature_t *features HB_UNUSED,
	unsigned int num_features HB_UNUSED)
	{
	/* TODO Arabic */
	}


	/* Position */

	static void
	hb_position_default (hb_font_t *font,
	hb_face_t *face,
	hb_buffer_t *buffer,
	hb_feature_t *features HB_UNUSED,
	unsigned int num_features HB_UNUSED)
	{
	hb_buffer_clear_positions (buffer);

	unsigned int count = buffer->len;
	for (unsigned int i = 0; i < count; i++) {
	hb_glyph_metrics_t metrics;
	hb_font_get_glyph_metrics (font, face, buffer->info[i].codepoint, &metrics);
	buffer->pos[i].x_advance = metrics.x_advance;
	buffer->pos[i].y_advance = metrics.y_advance;
	}
	}

	static void
	hb_position_complex_fallback (hb_font_t *font HB_UNUSED,
	hb_face_t *face HB_UNUSED,
	hb_buffer_t *buffer HB_UNUSED,
	hb_feature_t *features HB_UNUSED,
	unsigned int num_features HB_UNUSED)
	{
	/* TODO Mark pos */
	}

	static void
	hb_truetype_kern (hb_font_t *font,
	hb_face_t *face,
	hb_buffer_t *buffer,
	hb_feature_t *features HB_UNUSED,
	unsigned int num_features HB_UNUSED)
	{
	/* TODO Check for kern=0 */
	unsigned int count = buffer->len;
	for (unsigned int i = 1; i < count; i++) {
	hb_position_t kern, kern1, kern2;
	kern = hb_font_get_kerning (font, face, buffer->info[i - 1].codepoint, buffer->info[i].codepoint);
	kern1 = kern >> 1;
	kern2 = kern - kern1;
	buffer->pos[i - 1].x_advance += kern1;
	buffer->pos[i].x_advance += kern2;
	buffer->pos[i].x_offset += kern2;
	}
	}

	static void
	hb_position_complex_fallback_visual (hb_font_t *font,
	hb_face_t *face,
	hb_buffer_t *buffer,
	hb_feature_t *features,
	unsigned int num_features)
	{
	hb_truetype_kern (font, face, buffer, features, num_features);
	}


	/* Do it! */

	void
	hb_ot_shape (hb_font_t *font,
	hb_face_t *face,
	hb_buffer_t *buffer,
	hb_feature_t *features,
	unsigned int num_features)
	{
	hb_direction_t original_direction;
	hb_bool_t substitute_fallback, position_fallback;

	hb_form_clusters (buffer);

	/* SUBSTITUTE */

	buffer->clear_masks ();

	/* Mirroring needs to see the original direction */
	hb_mirror_chars (buffer);

	original_direction = hb_ensure_native_direction (buffer);

	hb_substitute_default (font, face, buffer, features, num_features);

	substitute_fallback = !hb_ot_substitute_complex (font, face, buffer, features, num_features, original_direction);

	if (substitute_fallback)
	hb_substitute_complex_fallback (font, face, buffer, features, num_features);


	/* POSITION */

	buffer->clear_masks ();

	hb_position_default (font, face, buffer, features, num_features);

	position_fallback = !hb_ot_position_complex (font, face, buffer, features, num_features, original_direction);

	if (position_fallback)
	hb_position_complex_fallback (font, face, buffer, features, num_features);

	if (HB_DIRECTION_IS_BACKWARD (buffer->direction))
	hb_buffer_reverse (buffer);

	if (position_fallback)
	hb_position_complex_fallback_visual (font, face, buffer, features, num_features);

	buffer->direction = original_direction;
	}