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

 /*
  * Copyright © 2011,2012  Google, Inc.
  *
  *  This is part of HarfBuzz, a text shaping library.
  *
  * Permission is hereby granted, without written agreement and without
  * license or royalty fees, to use, copy, modify, and distribute this
  * software and its documentation for any purpose, provided that the
  * above copyright notice and the following two paragraphs appear in
  * all copies of this software.
  *
  * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
  * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
  * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
  * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
  * DAMAGE.
  *
  * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
  * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
  * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
  * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
  * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
  *
  * Google Author(s): Behdad Esfahbod
  */

 #include "hb.hh"

 #ifndef HB_NO_OT_SHAPE

 #include "hb-ot-shape-complex-khmer.hh"
 #include "hb-ot-shape-complex-khmer-machine.hh"
 #include "hb-ot-layout.hh"


 /*
  * Khmer shaper.
  */

 static const hb_ot_map_feature_t
 khmer_features[] =
 {
   /*
    * Basic features.
    * These features are applied all at once, before reordering, constrained
    * to the syllable.
    */
   {HB_TAG('p','r','e','f'), F_MANUAL_JOINERS},
   {HB_TAG('b','l','w','f'), F_MANUAL_JOINERS},
   {HB_TAG('a','b','v','f'), F_MANUAL_JOINERS},
   {HB_TAG('p','s','t','f'), F_MANUAL_JOINERS},
   {HB_TAG('c','f','a','r'), F_MANUAL_JOINERS},
   /*
    * Other features.
    * These features are applied all at once after clearing syllables.
    */
   {HB_TAG('p','r','e','s'), F_GLOBAL_MANUAL_JOINERS},
   {HB_TAG('a','b','v','s'), F_GLOBAL_MANUAL_JOINERS},
   {HB_TAG('b','l','w','s'), F_GLOBAL_MANUAL_JOINERS},
   {HB_TAG('p','s','t','s'), F_GLOBAL_MANUAL_JOINERS},
 };

 /*
  * Must be in the same order as the khmer_features array.
  */
 enum {
   KHMER_PREF,
   KHMER_BLWF,
   KHMER_ABVF,
   KHMER_PSTF,
   KHMER_CFAR,

   _KHMER_PRES,
   _KHMER_ABVS,
   _KHMER_BLWS,
   _KHMER_PSTS,

   KHMER_NUM_FEATURES,
   KHMER_BASIC_FEATURES = _KHMER_PRES, /* Don't forget to update this! */
 };

 static void
 setup_syllables_khmer (const hb_ot_shape_plan_t *plan,
 		       hb_font_t *font,
 		       hb_buffer_t *buffer);
 static void
 reorder_khmer (const hb_ot_shape_plan_t *plan,
 	       hb_font_t *font,
 	       hb_buffer_t *buffer);

 static void
 collect_features_khmer (hb_ot_shape_planner_t *plan)
 {
   hb_ot_map_builder_t *map = &plan->map;

   /* Do this before any lookups have been applied. */
   map->add_gsub_pause (setup_syllables_khmer);
   map->add_gsub_pause (reorder_khmer);

   /* Testing suggests that Uniscribe does NOT pause between basic
    * features.  Test with KhmerUI.ttf and the following three
    * sequences:
    *
    *   U+1789,U+17BC
    *   U+1789,U+17D2,U+1789
    *   U+1789,U+17D2,U+1789,U+17BC
    *
    * https://github.com/harfbuzz/harfbuzz/issues/974
    */
   map->enable_feature (HB_TAG('l','o','c','l'));
   map->enable_feature (HB_TAG('c','c','m','p'));

   unsigned int i = 0;
   for (; i < KHMER_BASIC_FEATURES; i++)
     map->add_feature (khmer_features[i]);

   map->add_gsub_pause (_hb_clear_syllables);

   for (; i < KHMER_NUM_FEATURES; i++)
     map->add_feature (khmer_features[i]);
 }

 static void
 override_features_khmer (hb_ot_shape_planner_t *plan)
 {
   hb_ot_map_builder_t *map = &plan->map;

   /* Khmer spec has 'clig' as part of required shaping features:
    * "Apply feature 'clig' to form ligatures that are desired for
    * typographical correctness.", hence in overrides... */
   map->enable_feature (HB_TAG('c','l','i','g'));

   /* Uniscribe does not apply 'kern' in Khmer. */
   if (hb_options ().uniscribe_bug_compatible)
   {
     map->disable_feature (HB_TAG('k','e','r','n'));
   }

   map->disable_feature (HB_TAG('l','i','g','a'));
 }


 struct khmer_shape_plan_t
 {
   hb_mask_t mask_array[KHMER_NUM_FEATURES];
 };

 static void *
 data_create_khmer (const hb_ot_shape_plan_t *plan)
 {
   khmer_shape_plan_t *khmer_plan = (khmer_shape_plan_t *) hb_calloc (1, sizeof (khmer_shape_plan_t));
   if (unlikely (!khmer_plan))
     return nullptr;

   for (unsigned int i = 0; i < ARRAY_LENGTH (khmer_plan->mask_array); i++)
     khmer_plan->mask_array[i] = (khmer_features[i].flags & F_GLOBAL) ?
 				 0 : plan->map.get_1_mask (khmer_features[i].tag);

   return khmer_plan;
 }

 static void
 data_destroy_khmer (void *data)
 {
   hb_free (data);
 }

 static void
 setup_masks_khmer (const hb_ot_shape_plan_t *plan HB_UNUSED,
 		   hb_buffer_t              *buffer,
 		   hb_font_t                *font HB_UNUSED)
 {
   HB_BUFFER_ALLOCATE_VAR (buffer, khmer_category);

   /* We cannot setup masks here.  We save information about characters
    * and setup masks later on in a pause-callback. */

   unsigned int count = buffer->len;
   hb_glyph_info_t *info = buffer->info;
   for (unsigned int i = 0; i < count; i++)
     set_khmer_properties (info[i]);
 }

 static void
 setup_syllables_khmer (const hb_ot_shape_plan_t *plan HB_UNUSED,
 		       hb_font_t *font HB_UNUSED,
 		       hb_buffer_t *buffer)
 {
   find_syllables_khmer (buffer);
   foreach_syllable (buffer, start, end)
     buffer->unsafe_to_break (start, end);
 }


 /* Rules from:
  * https://docs.microsoft.com/en-us/typography/script-development/devanagari */

 static void
 reorder_consonant_syllable (const hb_ot_shape_plan_t *plan,
 			    hb_face_t *face HB_UNUSED,
 			    hb_buffer_t *buffer,
 			    unsigned int start, unsigned int end)
 {
   const khmer_shape_plan_t *khmer_plan = (const khmer_shape_plan_t *) plan->data;
   hb_glyph_info_t *info = buffer->info;

   /* Setup masks. */
   {
     /* Post-base */
     hb_mask_t mask = khmer_plan->mask_array[KHMER_BLWF] |
 		     khmer_plan->mask_array[KHMER_ABVF] |
 		     khmer_plan->mask_array[KHMER_PSTF];
     for (unsigned int i = start + 1; i < end; i++)
       info[i].mask  |= mask;
   }

   unsigned int num_coengs = 0;
   for (unsigned int i = start + 1; i < end; i++)
   {
     /* """
      * When a COENG + (Cons | IndV) combination are found (and subscript count
      * is less than two) the character combination is handled according to the
      * subscript type of the character following the COENG.
      *
      * ...
      *
      * Subscript Type 2 - The COENG + RO characters are reordered to immediately
      * before the base glyph. Then the COENG + RO characters are assigned to have
      * the 'pref' OpenType feature applied to them.
      * """
      */
     if (info[i].khmer_category() == OT_Coeng && num_coengs <= 2 && i + 1 < end)
     {
       num_coengs++;

       if (info[i + 1].khmer_category() == OT_Ra)
       {
 	for (unsigned int j = 0; j < 2; j++)
 	  info[i + j].mask |= khmer_plan->mask_array[KHMER_PREF];

 	/* Move the Coeng,Ro sequence to the start. */
 	buffer->merge_clusters (start, i + 2);
 	hb_glyph_info_t t0 = info[i];
 	hb_glyph_info_t t1 = info[i + 1];
 	memmove (&info[start + 2], &info[start], (i - start) * sizeof (info[0]));
 	info[start] = t0;
 	info[start + 1] = t1;

 	/* Mark the subsequent stuff with 'cfar'.  Used in Khmer.
 	 * Read the feature spec.
 	 * This allows distinguishing the following cases with MS Khmer fonts:
 	 * U+1784,U+17D2,U+179A,U+17D2,U+1782
 	 * U+1784,U+17D2,U+1782,U+17D2,U+179A
 	 */
 	if (khmer_plan->mask_array[KHMER_CFAR])
 	  for (unsigned int j = i + 2; j < end; j++)
 	    info[j].mask |= khmer_plan->mask_array[KHMER_CFAR];

 	num_coengs = 2; /* Done. */
       }
     }

     /* Reorder left matra piece. */
     else if (info[i].khmer_category() == OT_VPre)
     {
       /* Move to the start. */
       buffer->merge_clusters (start, i + 1);
       hb_glyph_info_t t = info[i];
       memmove (&info[start + 1], &info[start], (i - start) * sizeof (info[0]));
       info[start] = t;
     }
   }
 }

 static void
 reorder_syllable_khmer (const hb_ot_shape_plan_t *plan,
 			hb_face_t *face,
 			hb_buffer_t *buffer,
 			unsigned int start, unsigned int end)
 {
   khmer_syllable_type_t syllable_type = (khmer_syllable_type_t) (buffer->info[start].syllable() & 0x0F);
   switch (syllable_type)
   {
     case khmer_broken_cluster: /* We already inserted dotted-circles, so just call the consonant_syllable. */
     case khmer_consonant_syllable:
      reorder_consonant_syllable (plan, face, buffer, start, end);
      break;

     case khmer_non_khmer_cluster:
       break;
   }
 }

 static void
 reorder_khmer (const hb_ot_shape_plan_t *plan,
 	       hb_font_t *font,
 	       hb_buffer_t *buffer)
 {
   if (buffer->message (font, "start reordering khmer"))
   {
     hb_syllabic_insert_dotted_circles (font, buffer,
 				       khmer_broken_cluster,
 				       OT_DOTTEDCIRCLE,
 				       OT_Repha);

     foreach_syllable (buffer, start, end)
       reorder_syllable_khmer (plan, font->face, buffer, start, end);
     (void) buffer->message (font, "end reordering khmer");
   }
   HB_BUFFER_DEALLOCATE_VAR (buffer, khmer_category);
 }


 static bool
 decompose_khmer (const hb_ot_shape_normalize_context_t *c,
 		 hb_codepoint_t  ab,
 		 hb_codepoint_t *a,
 		 hb_codepoint_t *b)
 {
   switch (ab)
   {
     /*
      * Decompose split matras that don't have Unicode decompositions.
      */

     /* Khmer */
     case 0x17BEu  : *a = 0x17C1u; *b= 0x17BEu; return true;
     case 0x17BFu  : *a = 0x17C1u; *b= 0x17BFu; return true;
     case 0x17C0u  : *a = 0x17C1u; *b= 0x17C0u; return true;
     case 0x17C4u  : *a = 0x17C1u; *b= 0x17C4u; return true;
     case 0x17C5u  : *a = 0x17C1u; *b= 0x17C5u; return true;
   }

   return (bool) c->unicode->decompose (ab, a, b);
 }

 static bool
 compose_khmer (const hb_ot_shape_normalize_context_t *c,
 	       hb_codepoint_t  a,
 	       hb_codepoint_t  b,
 	       hb_codepoint_t *ab)
 {
   /* Avoid recomposing split matras. */
   if (HB_UNICODE_GENERAL_CATEGORY_IS_MARK (c->unicode->general_category (a)))
     return false;

   return (bool) c->unicode->compose (a, b, ab);
 }


 const hb_ot_complex_shaper_t _hb_ot_complex_shaper_khmer =
 {
   collect_features_khmer,
   override_features_khmer,
   data_create_khmer,
   data_destroy_khmer,
   nullptr, /* preprocess_text */
   nullptr, /* postprocess_glyphs */
   HB_OT_SHAPE_NORMALIZATION_MODE_COMPOSED_DIACRITICS_NO_SHORT_CIRCUIT,
   decompose_khmer,
   compose_khmer,
   setup_masks_khmer,
   HB_TAG_NONE, /* gpos_tag */
   nullptr, /* reorder_marks */
   HB_OT_SHAPE_ZERO_WIDTH_MARKS_NONE,
   false, /* fallback_position */
 };


 #endif
	/*
	* Copyright © 2011,2012 Google, Inc.
	*
	* This is part of HarfBuzz, a text shaping library.
	*
	* Permission is hereby granted, without written agreement and without
	* license or royalty fees, to use, copy, modify, and distribute this
	* software and its documentation for any purpose, provided that the
	* above copyright notice and the following two paragraphs appear in
	* all copies of this software.
	*
	* IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
	* DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
	* ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
	* IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
	* DAMAGE.
	*
	* THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
	* BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
	* FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
	* ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
	* PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
	*
	* Google Author(s): Behdad Esfahbod
	*/

	#include "hb.hh"

	#ifndef HB_NO_OT_SHAPE

	#include "hb-ot-shape-complex-khmer.hh"
	#include "hb-ot-shape-complex-khmer-machine.hh"
	#include "hb-ot-layout.hh"


	/*
	* Khmer shaper.
	*/

	static const hb_ot_map_feature_t
	khmer_features[] =
	{
	/*
	* Basic features.
	* These features are applied all at once, before reordering, constrained
	* to the syllable.
	*/
	{HB_TAG('p','r','e','f'), F_MANUAL_JOINERS},
	{HB_TAG('b','l','w','f'), F_MANUAL_JOINERS},
	{HB_TAG('a','b','v','f'), F_MANUAL_JOINERS},
	{HB_TAG('p','s','t','f'), F_MANUAL_JOINERS},
	{HB_TAG('c','f','a','r'), F_MANUAL_JOINERS},
	/*
	* Other features.
	* These features are applied all at once after clearing syllables.
	*/
	{HB_TAG('p','r','e','s'), F_GLOBAL_MANUAL_JOINERS},
	{HB_TAG('a','b','v','s'), F_GLOBAL_MANUAL_JOINERS},
	{HB_TAG('b','l','w','s'), F_GLOBAL_MANUAL_JOINERS},
	{HB_TAG('p','s','t','s'), F_GLOBAL_MANUAL_JOINERS},
	};

	/*
	* Must be in the same order as the khmer_features array.
	*/
	enum {
	KHMER_PREF,
	KHMER_BLWF,
	KHMER_ABVF,
	KHMER_PSTF,
	KHMER_CFAR,

	_KHMER_PRES,
	_KHMER_ABVS,
	_KHMER_BLWS,
	_KHMER_PSTS,

	KHMER_NUM_FEATURES,
	KHMER_BASIC_FEATURES = _KHMER_PRES, /* Don't forget to update this! */
	};

	static void
	setup_syllables_khmer (const hb_ot_shape_plan_t *plan,
	hb_font_t *font,
	hb_buffer_t *buffer);
	static void
	reorder_khmer (const hb_ot_shape_plan_t *plan,
	hb_font_t *font,
	hb_buffer_t *buffer);

	static void
	collect_features_khmer (hb_ot_shape_planner_t *plan)
	{
	hb_ot_map_builder_t *map = &plan->map;

	/* Do this before any lookups have been applied. */
	map->add_gsub_pause (setup_syllables_khmer);
	map->add_gsub_pause (reorder_khmer);

	/* Testing suggests that Uniscribe does NOT pause between basic
	* features. Test with KhmerUI.ttf and the following three
	* sequences:
	*
	* U+1789,U+17BC
	* U+1789,U+17D2,U+1789
	* U+1789,U+17D2,U+1789,U+17BC
	*
	* https://github.com/harfbuzz/harfbuzz/issues/974
	*/
	map->enable_feature (HB_TAG('l','o','c','l'));
	map->enable_feature (HB_TAG('c','c','m','p'));

	unsigned int i = 0;
	for (; i < KHMER_BASIC_FEATURES; i++)
	map->add_feature (khmer_features[i]);

	map->add_gsub_pause (_hb_clear_syllables);

	for (; i < KHMER_NUM_FEATURES; i++)
	map->add_feature (khmer_features[i]);
	}

	static void
	override_features_khmer (hb_ot_shape_planner_t *plan)
	{
	hb_ot_map_builder_t *map = &plan->map;

	/* Khmer spec has 'clig' as part of required shaping features:
	* "Apply feature 'clig' to form ligatures that are desired for
	* typographical correctness.", hence in overrides... */
	map->enable_feature (HB_TAG('c','l','i','g'));

	/* Uniscribe does not apply 'kern' in Khmer. */
	if (hb_options ().uniscribe_bug_compatible)
	{
	map->disable_feature (HB_TAG('k','e','r','n'));
	}

	map->disable_feature (HB_TAG('l','i','g','a'));
	}


	struct khmer_shape_plan_t
	{
	hb_mask_t mask_array[KHMER_NUM_FEATURES];
	};

	static void *
	data_create_khmer (const hb_ot_shape_plan_t *plan)
	{
	khmer_shape_plan_t khmer_plan = (khmer_shape_plan_t ) hb_calloc (1, sizeof (khmer_shape_plan_t));
	if (unlikely (!khmer_plan))
	return nullptr;

	for (unsigned int i = 0; i < ARRAY_LENGTH (khmer_plan->mask_array); i++)
	khmer_plan->mask_array[i] = (khmer_features[i].flags & F_GLOBAL) ?
	0 : plan->map.get_1_mask (khmer_features[i].tag);

	return khmer_plan;
	}

	static void
	data_destroy_khmer (void *data)
	{
	hb_free (data);
	}

	static void
	setup_masks_khmer (const hb_ot_shape_plan_t *plan HB_UNUSED,
	hb_buffer_t *buffer,
	hb_font_t *font HB_UNUSED)
	{
	HB_BUFFER_ALLOCATE_VAR (buffer, khmer_category);

	/* We cannot setup masks here. We save information about characters
	* and setup masks later on in a pause-callback. */

	unsigned int count = buffer->len;
	hb_glyph_info_t *info = buffer->info;
	for (unsigned int i = 0; i < count; i++)
	set_khmer_properties (info[i]);
	}

	static void
	setup_syllables_khmer (const hb_ot_shape_plan_t *plan HB_UNUSED,
	hb_font_t *font HB_UNUSED,
	hb_buffer_t *buffer)
	{
	find_syllables_khmer (buffer);
	foreach_syllable (buffer, start, end)
	buffer->unsafe_to_break (start, end);
	}


	/* Rules from:
	* https://docs.microsoft.com/en-us/typography/script-development/devanagari */

	static void
	reorder_consonant_syllable (const hb_ot_shape_plan_t *plan,
	hb_face_t *face HB_UNUSED,
	hb_buffer_t *buffer,
	unsigned int start, unsigned int end)
	{
	const khmer_shape_plan_t khmer_plan = (const khmer_shape_plan_t ) plan->data;
	hb_glyph_info_t *info = buffer->info;

	/* Setup masks. */
	{
	/* Post-base */
	hb_mask_t mask = khmer_plan->mask_array[KHMER_BLWF] \|
	khmer_plan->mask_array[KHMER_ABVF] \|
	khmer_plan->mask_array[KHMER_PSTF];
	for (unsigned int i = start + 1; i < end; i++)
	info[i].mask \|= mask;
	}

	unsigned int num_coengs = 0;
	for (unsigned int i = start + 1; i < end; i++)
	{
	/* """
	* When a COENG + (Cons \| IndV) combination are found (and subscript count
	* is less than two) the character combination is handled according to the
	* subscript type of the character following the COENG.
	*
	* ...
	*
	* Subscript Type 2 - The COENG + RO characters are reordered to immediately
	* before the base glyph. Then the COENG + RO characters are assigned to have
	* the 'pref' OpenType feature applied to them.
	* """
	*/
	if (info[i].khmer_category() == OT_Coeng && num_coengs <= 2 && i + 1 < end)
	{
	num_coengs++;

	if (info[i + 1].khmer_category() == OT_Ra)
	{
	for (unsigned int j = 0; j < 2; j++)
	info[i + j].mask \|= khmer_plan->mask_array[KHMER_PREF];

	/* Move the Coeng,Ro sequence to the start. */
	buffer->merge_clusters (start, i + 2);
	hb_glyph_info_t t0 = info[i];
	hb_glyph_info_t t1 = info[i + 1];
	memmove (&info[start + 2], &info[start], (i - start) * sizeof (info[0]));
	info[start] = t0;
	info[start + 1] = t1;

	/* Mark the subsequent stuff with 'cfar'. Used in Khmer.
	* Read the feature spec.
	* This allows distinguishing the following cases with MS Khmer fonts:
	* U+1784,U+17D2,U+179A,U+17D2,U+1782
	* U+1784,U+17D2,U+1782,U+17D2,U+179A
	*/
	if (khmer_plan->mask_array[KHMER_CFAR])
	for (unsigned int j = i + 2; j < end; j++)
	info[j].mask \|= khmer_plan->mask_array[KHMER_CFAR];

	num_coengs = 2; /* Done. */
	}
	}

	/* Reorder left matra piece. */
	else if (info[i].khmer_category() == OT_VPre)
	{
	/* Move to the start. */
	buffer->merge_clusters (start, i + 1);
	hb_glyph_info_t t = info[i];
	memmove (&info[start + 1], &info[start], (i - start) * sizeof (info[0]));
	info[start] = t;
	}
	}
	}

	static void
	reorder_syllable_khmer (const hb_ot_shape_plan_t *plan,
	hb_face_t *face,
	hb_buffer_t *buffer,
	unsigned int start, unsigned int end)
	{
	khmer_syllable_type_t syllable_type = (khmer_syllable_type_t) (buffer->info[start].syllable() & 0x0F);
	switch (syllable_type)
	{
	case khmer_broken_cluster: /* We already inserted dotted-circles, so just call the consonant_syllable. */
	case khmer_consonant_syllable:
	reorder_consonant_syllable (plan, face, buffer, start, end);
	break;

	case khmer_non_khmer_cluster:
	break;
	}
	}

	static void
	reorder_khmer (const hb_ot_shape_plan_t *plan,
	hb_font_t *font,
	hb_buffer_t *buffer)
	{
	if (buffer->message (font, "start reordering khmer"))
	{
	hb_syllabic_insert_dotted_circles (font, buffer,
	khmer_broken_cluster,
	OT_DOTTEDCIRCLE,
	OT_Repha);

	foreach_syllable (buffer, start, end)
	reorder_syllable_khmer (plan, font->face, buffer, start, end);
	(void) buffer->message (font, "end reordering khmer");
	}
	HB_BUFFER_DEALLOCATE_VAR (buffer, khmer_category);
	}


	static bool
	decompose_khmer (const hb_ot_shape_normalize_context_t *c,
	hb_codepoint_t ab,
	hb_codepoint_t *a,
	hb_codepoint_t *b)
	{
	switch (ab)
	{
	/*
	* Decompose split matras that don't have Unicode decompositions.
	*/

	/* Khmer */
	case 0x17BEu : a = 0x17C1u; b= 0x17BEu; return true;
	case 0x17BFu : a = 0x17C1u; b= 0x17BFu; return true;
	case 0x17C0u : a = 0x17C1u; b= 0x17C0u; return true;
	case 0x17C4u : a = 0x17C1u; b= 0x17C4u; return true;
	case 0x17C5u : a = 0x17C1u; b= 0x17C5u; return true;
	}

	return (bool) c->unicode->decompose (ab, a, b);
	}

	static bool
	compose_khmer (const hb_ot_shape_normalize_context_t *c,
	hb_codepoint_t a,
	hb_codepoint_t b,
	hb_codepoint_t *ab)
	{
	/* Avoid recomposing split matras. */
	if (HB_UNICODE_GENERAL_CATEGORY_IS_MARK (c->unicode->general_category (a)))
	return false;

	return (bool) c->unicode->compose (a, b, ab);
	}


	const hb_ot_complex_shaper_t _hb_ot_complex_shaper_khmer =
	{
	collect_features_khmer,
	override_features_khmer,
	data_create_khmer,
	data_destroy_khmer,
	nullptr, /* preprocess_text */
	nullptr, /* postprocess_glyphs */
	HB_OT_SHAPE_NORMALIZATION_MODE_COMPOSED_DIACRITICS_NO_SHORT_CIRCUIT,
	decompose_khmer,
	compose_khmer,
	setup_masks_khmer,
	HB_TAG_NONE, /* gpos_tag */
	nullptr, /* reorder_marks */
	HB_OT_SHAPE_ZERO_WIDTH_MARKS_NONE,
	false, /* fallback_position */
	};


	#endif