src/hb-ot-shape-fallback.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-ot-shape-fallback-private.hh"

 static void
 zero_mark_advances (hb_buffer_t *buffer,
 		    unsigned int start,
 		    unsigned int end)
 {
   for (unsigned int i = start; i < end; i++)
     if (_hb_glyph_info_get_general_category (&buffer->info[i]) == HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK)
     {
       buffer->pos[i].x_advance = 0;
       buffer->pos[i].y_advance = 0;
     }
 }

 static unsigned int
 recategorize_combining_class (unsigned int modified_combining_class)
 {
   if (modified_combining_class >= 200)
     return modified_combining_class;

   /* This should be kept in sync with modified combining class mapping
    * from hb-unicode.cc. */
   switch (modified_combining_class)
   {

     /* Hebrew */

     case HB_MODIFIED_COMBINING_CLASS_CCC10: /* sheva */
     case HB_MODIFIED_COMBINING_CLASS_CCC11: /* hataf segol */
     case HB_MODIFIED_COMBINING_CLASS_CCC12: /* hataf patah */
     case HB_MODIFIED_COMBINING_CLASS_CCC13: /* hataf qamats */
     case HB_MODIFIED_COMBINING_CLASS_CCC14: /* hiriq */
     case HB_MODIFIED_COMBINING_CLASS_CCC15: /* tsere */
     case HB_MODIFIED_COMBINING_CLASS_CCC16: /* segol */
     case HB_MODIFIED_COMBINING_CLASS_CCC17: /* patah */
     case HB_MODIFIED_COMBINING_CLASS_CCC18: /* qamats */
     case HB_MODIFIED_COMBINING_CLASS_CCC20: /* qubuts */
     case HB_MODIFIED_COMBINING_CLASS_CCC22: /* meteg */
       return HB_UNICODE_COMBINING_CLASS_BELOW;

     case HB_MODIFIED_COMBINING_CLASS_CCC23: /* rafe */
       return HB_UNICODE_COMBINING_CLASS_ATTACHED_ABOVE;

     case HB_MODIFIED_COMBINING_CLASS_CCC24: /* shin dot */
       return HB_UNICODE_COMBINING_CLASS_ABOVE_RIGHT;

     case HB_MODIFIED_COMBINING_CLASS_CCC25: /* sin dot */
     case HB_MODIFIED_COMBINING_CLASS_CCC19: /* holam */
       return HB_UNICODE_COMBINING_CLASS_ABOVE_LEFT;

     case HB_MODIFIED_COMBINING_CLASS_CCC26: /* point varika */
       return HB_UNICODE_COMBINING_CLASS_ABOVE;

     case HB_MODIFIED_COMBINING_CLASS_CCC21: /* dagesh */
       break;


     /* Arabic and Syriac */

     case HB_MODIFIED_COMBINING_CLASS_CCC27: /* fathatan */
     case HB_MODIFIED_COMBINING_CLASS_CCC28: /* dammatan */
     case HB_MODIFIED_COMBINING_CLASS_CCC30: /* fatha */
     case HB_MODIFIED_COMBINING_CLASS_CCC31: /* damma */
     case HB_MODIFIED_COMBINING_CLASS_CCC33: /* shadda */
     case HB_MODIFIED_COMBINING_CLASS_CCC34: /* sukun */
     case HB_MODIFIED_COMBINING_CLASS_CCC35: /* superscript alef */
     case HB_MODIFIED_COMBINING_CLASS_CCC36: /* superscript alaph */
       return HB_UNICODE_COMBINING_CLASS_ABOVE;

     case HB_MODIFIED_COMBINING_CLASS_CCC29: /* kasratan */
     case HB_MODIFIED_COMBINING_CLASS_CCC32: /* kasra */
       return HB_UNICODE_COMBINING_CLASS_BELOW;


     /* Thai */

     /* Note: to be useful we also need to position U+0E3A that has ccc=9 (virama).
      * But viramas can be both above and below based on the codepoint / script. */

     case HB_MODIFIED_COMBINING_CLASS_CCC103: /* sara u / sara uu */
       return HB_UNICODE_COMBINING_CLASS_BELOW;

     case HB_MODIFIED_COMBINING_CLASS_CCC107: /* mai */
       return HB_UNICODE_COMBINING_CLASS_ABOVE;


     /* Lao */

     case HB_MODIFIED_COMBINING_CLASS_CCC118: /* sign u / sign uu */
       return HB_UNICODE_COMBINING_CLASS_BELOW;

     case HB_MODIFIED_COMBINING_CLASS_CCC122: /* mai */
       return HB_UNICODE_COMBINING_CLASS_ABOVE;


     /* Tibetan */

     case HB_MODIFIED_COMBINING_CLASS_CCC129: /* sign aa */
       return HB_UNICODE_COMBINING_CLASS_BELOW;

     case HB_MODIFIED_COMBINING_CLASS_CCC130: /* sign i*/
       return HB_UNICODE_COMBINING_CLASS_ABOVE;

     case HB_MODIFIED_COMBINING_CLASS_CCC132: /* sign u */
       return HB_UNICODE_COMBINING_CLASS_BELOW;

   }

   return modified_combining_class;
 }

 static inline void
 position_mark (const hb_ot_shape_plan_t *plan,
 	       hb_font_t *font,
 	       hb_buffer_t  *buffer,
 	       hb_glyph_extents_t &base_extents,
 	       unsigned int i,
 	       unsigned int combining_class)
 {
   hb_glyph_extents_t mark_extents;
   if (!font->get_glyph_extents (buffer->info[i].codepoint,
 				&mark_extents))
     return;

   hb_position_t y_gap = font->y_scale / 16;

   hb_glyph_position_t &pos = buffer->pos[i];
   pos.x_offset = pos.y_offset = 0;


   /* We dont position LEFT and RIGHT marks. */

   /* X positioning */
   switch (combining_class)
   {
     case HB_UNICODE_COMBINING_CLASS_DOUBLE_BELOW:
     case HB_UNICODE_COMBINING_CLASS_DOUBLE_ABOVE:
       if (buffer->props.direction == HB_DIRECTION_LTR) {
 	pos.x_offset += base_extents.x_bearing - mark_extents.width / 2 - mark_extents.x_bearing;
         break;
       } else if (buffer->props.direction == HB_DIRECTION_RTL) {
 	pos.x_offset += base_extents.x_bearing + base_extents.width - mark_extents.width / 2 - mark_extents.x_bearing;
         break;
       }
       /* Fall through */

     case HB_UNICODE_COMBINING_CLASS_ATTACHED_BELOW:
     case HB_UNICODE_COMBINING_CLASS_ATTACHED_ABOVE:
     case HB_UNICODE_COMBINING_CLASS_BELOW:
     case HB_UNICODE_COMBINING_CLASS_ABOVE:
       /* Center align. */
       pos.x_offset += base_extents.x_bearing + (base_extents.width - mark_extents.width) / 2 - mark_extents.x_bearing;
       break;

     case HB_UNICODE_COMBINING_CLASS_ATTACHED_BELOW_LEFT:
     case HB_UNICODE_COMBINING_CLASS_BELOW_LEFT:
     case HB_UNICODE_COMBINING_CLASS_ABOVE_LEFT:
       /* Left align. */
       pos.x_offset += base_extents.x_bearing - mark_extents.x_bearing;
       break;

     case HB_UNICODE_COMBINING_CLASS_ATTACHED_ABOVE_RIGHT:
     case HB_UNICODE_COMBINING_CLASS_BELOW_RIGHT:
     case HB_UNICODE_COMBINING_CLASS_ABOVE_RIGHT:
       /* Right align. */
       pos.x_offset += base_extents.x_bearing + base_extents.width - mark_extents.width - mark_extents.x_bearing;
       break;
   }

   /* Y positioning */
   switch (combining_class)
   {
     case HB_UNICODE_COMBINING_CLASS_DOUBLE_BELOW:
     case HB_UNICODE_COMBINING_CLASS_BELOW_LEFT:
     case HB_UNICODE_COMBINING_CLASS_BELOW:
     case HB_UNICODE_COMBINING_CLASS_BELOW_RIGHT:
       /* Add gap, fall-through. */
       base_extents.height -= y_gap;

     case HB_UNICODE_COMBINING_CLASS_ATTACHED_BELOW_LEFT:
     case HB_UNICODE_COMBINING_CLASS_ATTACHED_BELOW:
       pos.y_offset += base_extents.y_bearing + base_extents.height - mark_extents.y_bearing;
       base_extents.height += mark_extents.height;
       break;

     case HB_UNICODE_COMBINING_CLASS_DOUBLE_ABOVE:
     case HB_UNICODE_COMBINING_CLASS_ABOVE_LEFT:
     case HB_UNICODE_COMBINING_CLASS_ABOVE:
     case HB_UNICODE_COMBINING_CLASS_ABOVE_RIGHT:
       /* Add gap, fall-through. */
       base_extents.y_bearing += y_gap;
       base_extents.height -= y_gap;

     case HB_UNICODE_COMBINING_CLASS_ATTACHED_ABOVE:
     case HB_UNICODE_COMBINING_CLASS_ATTACHED_ABOVE_RIGHT:
       pos.y_offset += base_extents.y_bearing - (mark_extents.y_bearing + mark_extents.height);
       base_extents.y_bearing -= mark_extents.height;
       base_extents.height += mark_extents.height;
       break;
   }
 }

 static inline void
 position_around_base (const hb_ot_shape_plan_t *plan,
 		      hb_font_t *font,
 		      hb_buffer_t  *buffer,
 		      unsigned int base,
 		      unsigned int end)
 {
   hb_glyph_extents_t base_extents;
   if (!font->get_glyph_extents (buffer->info[base].codepoint,
 				&base_extents))
   {
     /* If extents don't work, zero marks and go home. */
     zero_mark_advances (buffer, base + 1, end);
     return;
   }
   base_extents.x_bearing += buffer->pos[base].x_offset;
   base_extents.y_bearing += buffer->pos[base].y_offset;

   /* XXX Handle ligature component positioning... */
   HB_UNUSED bool is_ligature = is_a_ligature (buffer->info[base]);

   hb_position_t x_offset = 0, y_offset = 0;
   if (HB_DIRECTION_IS_FORWARD (buffer->props.direction)) {
     x_offset -= buffer->pos[base].x_advance;
     y_offset -= buffer->pos[base].y_advance;
   }
   unsigned int last_combining_class = 255;
   hb_glyph_extents_t cluster_extents;
   for (unsigned int i = base + 1; i < end; i++)
     if (_hb_glyph_info_get_general_category (&buffer->info[i]) == HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK)
     {
       unsigned int this_combining_class = recategorize_combining_class (_hb_glyph_info_get_modified_combining_class (&buffer->info[i]));
       if (this_combining_class != last_combining_class)
         cluster_extents = base_extents;

       position_mark (plan, font, buffer, base_extents, i, this_combining_class);

       buffer->pos[i].x_advance = 0;
       buffer->pos[i].y_advance = 0;
       buffer->pos[i].x_offset += x_offset;
       buffer->pos[i].y_offset += y_offset;

       /* combine cluster extents. */

       last_combining_class = this_combining_class;
     } else {
       if (HB_DIRECTION_IS_FORWARD (buffer->props.direction)) {
 	x_offset -= buffer->pos[i].x_advance;
 	y_offset -= buffer->pos[i].y_advance;
       } else {
 	x_offset += buffer->pos[i].x_advance;
 	y_offset += buffer->pos[i].y_advance;
       }
     }


 }

 static inline void
 position_cluster (const hb_ot_shape_plan_t *plan,
 		  hb_font_t *font,
 		  hb_buffer_t  *buffer,
 		  unsigned int start,
 		  unsigned int end)
 {
   if (end - start < 2)
     return;

   /* Find the base glyph */
   for (unsigned int i = start; i < end; i++)
     if (is_a_ligature (buffer->info[i]) ||
         !(FLAG (_hb_glyph_info_get_general_category (&buffer->info[i])) &
 	  (FLAG (HB_UNICODE_GENERAL_CATEGORY_SPACING_MARK) |
 	   FLAG (HB_UNICODE_GENERAL_CATEGORY_ENCLOSING_MARK) |
 	   FLAG (HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK))))
     {
       position_around_base (plan, font, buffer, i, end);
       break;
     }
 }

 void
 _hb_ot_shape_fallback_position (const hb_ot_shape_plan_t *plan,
 				hb_font_t *font,
 				hb_buffer_t  *buffer)
 {
   unsigned int start = 0;
   unsigned int last_cluster = buffer->info[0].cluster;
   unsigned int count = buffer->len;
   for (unsigned int i = 1; i < count; i++)
     if (buffer->info[i].cluster != last_cluster) {
       position_cluster (plan, font, buffer, start, i);
       start = i;
       last_cluster = buffer->info[i].cluster;
     }
   position_cluster (plan, font, buffer, start, count);
 }
	/*
	* 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-ot-shape-fallback-private.hh"

	static void
	zero_mark_advances (hb_buffer_t *buffer,
	unsigned int start,
	unsigned int end)
	{
	for (unsigned int i = start; i < end; i++)
	if (_hb_glyph_info_get_general_category (&buffer->info[i]) == HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK)
	{
	buffer->pos[i].x_advance = 0;
	buffer->pos[i].y_advance = 0;
	}
	}

	static unsigned int
	recategorize_combining_class (unsigned int modified_combining_class)
	{
	if (modified_combining_class >= 200)
	return modified_combining_class;

	/* This should be kept in sync with modified combining class mapping
	* from hb-unicode.cc. */
	switch (modified_combining_class)
	{

	/* Hebrew */

	case HB_MODIFIED_COMBINING_CLASS_CCC10: /* sheva */
	case HB_MODIFIED_COMBINING_CLASS_CCC11: /* hataf segol */
	case HB_MODIFIED_COMBINING_CLASS_CCC12: /* hataf patah */
	case HB_MODIFIED_COMBINING_CLASS_CCC13: /* hataf qamats */
	case HB_MODIFIED_COMBINING_CLASS_CCC14: /* hiriq */
	case HB_MODIFIED_COMBINING_CLASS_CCC15: /* tsere */
	case HB_MODIFIED_COMBINING_CLASS_CCC16: /* segol */
	case HB_MODIFIED_COMBINING_CLASS_CCC17: /* patah */
	case HB_MODIFIED_COMBINING_CLASS_CCC18: /* qamats */
	case HB_MODIFIED_COMBINING_CLASS_CCC20: /* qubuts */
	case HB_MODIFIED_COMBINING_CLASS_CCC22: /* meteg */
	return HB_UNICODE_COMBINING_CLASS_BELOW;

	case HB_MODIFIED_COMBINING_CLASS_CCC23: /* rafe */
	return HB_UNICODE_COMBINING_CLASS_ATTACHED_ABOVE;

	case HB_MODIFIED_COMBINING_CLASS_CCC24: /* shin dot */
	return HB_UNICODE_COMBINING_CLASS_ABOVE_RIGHT;

	case HB_MODIFIED_COMBINING_CLASS_CCC25: /* sin dot */
	case HB_MODIFIED_COMBINING_CLASS_CCC19: /* holam */
	return HB_UNICODE_COMBINING_CLASS_ABOVE_LEFT;

	case HB_MODIFIED_COMBINING_CLASS_CCC26: /* point varika */
	return HB_UNICODE_COMBINING_CLASS_ABOVE;

	case HB_MODIFIED_COMBINING_CLASS_CCC21: /* dagesh */
	break;


	/* Arabic and Syriac */

	case HB_MODIFIED_COMBINING_CLASS_CCC27: /* fathatan */
	case HB_MODIFIED_COMBINING_CLASS_CCC28: /* dammatan */
	case HB_MODIFIED_COMBINING_CLASS_CCC30: /* fatha */
	case HB_MODIFIED_COMBINING_CLASS_CCC31: /* damma */
	case HB_MODIFIED_COMBINING_CLASS_CCC33: /* shadda */
	case HB_MODIFIED_COMBINING_CLASS_CCC34: /* sukun */
	case HB_MODIFIED_COMBINING_CLASS_CCC35: /* superscript alef */
	case HB_MODIFIED_COMBINING_CLASS_CCC36: /* superscript alaph */
	return HB_UNICODE_COMBINING_CLASS_ABOVE;

	case HB_MODIFIED_COMBINING_CLASS_CCC29: /* kasratan */
	case HB_MODIFIED_COMBINING_CLASS_CCC32: /* kasra */
	return HB_UNICODE_COMBINING_CLASS_BELOW;


	/* Thai */

	/* Note: to be useful we also need to position U+0E3A that has ccc=9 (virama).
	* But viramas can be both above and below based on the codepoint / script. */

	case HB_MODIFIED_COMBINING_CLASS_CCC103: /* sara u / sara uu */
	return HB_UNICODE_COMBINING_CLASS_BELOW;

	case HB_MODIFIED_COMBINING_CLASS_CCC107: /* mai */
	return HB_UNICODE_COMBINING_CLASS_ABOVE;


	/* Lao */

	case HB_MODIFIED_COMBINING_CLASS_CCC118: /* sign u / sign uu */
	return HB_UNICODE_COMBINING_CLASS_BELOW;

	case HB_MODIFIED_COMBINING_CLASS_CCC122: /* mai */
	return HB_UNICODE_COMBINING_CLASS_ABOVE;


	/* Tibetan */

	case HB_MODIFIED_COMBINING_CLASS_CCC129: /* sign aa */
	return HB_UNICODE_COMBINING_CLASS_BELOW;

	case HB_MODIFIED_COMBINING_CLASS_CCC130: /* sign i*/
	return HB_UNICODE_COMBINING_CLASS_ABOVE;

	case HB_MODIFIED_COMBINING_CLASS_CCC132: /* sign u */
	return HB_UNICODE_COMBINING_CLASS_BELOW;

	}

	return modified_combining_class;
	}

	static inline void
	position_mark (const hb_ot_shape_plan_t *plan,
	hb_font_t *font,
	hb_buffer_t *buffer,
	hb_glyph_extents_t &base_extents,
	unsigned int i,
	unsigned int combining_class)
	{
	hb_glyph_extents_t mark_extents;
	if (!font->get_glyph_extents (buffer->info[i].codepoint,
	&mark_extents))
	return;

	hb_position_t y_gap = font->y_scale / 16;

	hb_glyph_position_t &pos = buffer->pos[i];
	pos.x_offset = pos.y_offset = 0;


	/* We dont position LEFT and RIGHT marks. */

	/* X positioning */
	switch (combining_class)
	{
	case HB_UNICODE_COMBINING_CLASS_DOUBLE_BELOW:
	case HB_UNICODE_COMBINING_CLASS_DOUBLE_ABOVE:
	if (buffer->props.direction == HB_DIRECTION_LTR) {
	pos.x_offset += base_extents.x_bearing - mark_extents.width / 2 - mark_extents.x_bearing;
	break;
	} else if (buffer->props.direction == HB_DIRECTION_RTL) {
	pos.x_offset += base_extents.x_bearing + base_extents.width - mark_extents.width / 2 - mark_extents.x_bearing;
	break;
	}
	/* Fall through */

	case HB_UNICODE_COMBINING_CLASS_ATTACHED_BELOW:
	case HB_UNICODE_COMBINING_CLASS_ATTACHED_ABOVE:
	case HB_UNICODE_COMBINING_CLASS_BELOW:
	case HB_UNICODE_COMBINING_CLASS_ABOVE:
	/* Center align. */
	pos.x_offset += base_extents.x_bearing + (base_extents.width - mark_extents.width) / 2 - mark_extents.x_bearing;
	break;

	case HB_UNICODE_COMBINING_CLASS_ATTACHED_BELOW_LEFT:
	case HB_UNICODE_COMBINING_CLASS_BELOW_LEFT:
	case HB_UNICODE_COMBINING_CLASS_ABOVE_LEFT:
	/* Left align. */
	pos.x_offset += base_extents.x_bearing - mark_extents.x_bearing;
	break;

	case HB_UNICODE_COMBINING_CLASS_ATTACHED_ABOVE_RIGHT:
	case HB_UNICODE_COMBINING_CLASS_BELOW_RIGHT:
	case HB_UNICODE_COMBINING_CLASS_ABOVE_RIGHT:
	/* Right align. */
	pos.x_offset += base_extents.x_bearing + base_extents.width - mark_extents.width - mark_extents.x_bearing;
	break;
	}

	/* Y positioning */
	switch (combining_class)
	{
	case HB_UNICODE_COMBINING_CLASS_DOUBLE_BELOW:
	case HB_UNICODE_COMBINING_CLASS_BELOW_LEFT:
	case HB_UNICODE_COMBINING_CLASS_BELOW:
	case HB_UNICODE_COMBINING_CLASS_BELOW_RIGHT:
	/* Add gap, fall-through. */
	base_extents.height -= y_gap;

	case HB_UNICODE_COMBINING_CLASS_ATTACHED_BELOW_LEFT:
	case HB_UNICODE_COMBINING_CLASS_ATTACHED_BELOW:
	pos.y_offset += base_extents.y_bearing + base_extents.height - mark_extents.y_bearing;
	base_extents.height += mark_extents.height;
	break;

	case HB_UNICODE_COMBINING_CLASS_DOUBLE_ABOVE:
	case HB_UNICODE_COMBINING_CLASS_ABOVE_LEFT:
	case HB_UNICODE_COMBINING_CLASS_ABOVE:
	case HB_UNICODE_COMBINING_CLASS_ABOVE_RIGHT:
	/* Add gap, fall-through. */
	base_extents.y_bearing += y_gap;
	base_extents.height -= y_gap;

	case HB_UNICODE_COMBINING_CLASS_ATTACHED_ABOVE:
	case HB_UNICODE_COMBINING_CLASS_ATTACHED_ABOVE_RIGHT:
	pos.y_offset += base_extents.y_bearing - (mark_extents.y_bearing + mark_extents.height);
	base_extents.y_bearing -= mark_extents.height;
	base_extents.height += mark_extents.height;
	break;
	}
	}

	static inline void
	position_around_base (const hb_ot_shape_plan_t *plan,
	hb_font_t *font,
	hb_buffer_t *buffer,
	unsigned int base,
	unsigned int end)
	{
	hb_glyph_extents_t base_extents;
	if (!font->get_glyph_extents (buffer->info[base].codepoint,
	&base_extents))
	{
	/* If extents don't work, zero marks and go home. */
	zero_mark_advances (buffer, base + 1, end);
	return;
	}
	base_extents.x_bearing += buffer->pos[base].x_offset;
	base_extents.y_bearing += buffer->pos[base].y_offset;

	/* XXX Handle ligature component positioning... */
	HB_UNUSED bool is_ligature = is_a_ligature (buffer->info[base]);

	hb_position_t x_offset = 0, y_offset = 0;
	if (HB_DIRECTION_IS_FORWARD (buffer->props.direction)) {
	x_offset -= buffer->pos[base].x_advance;
	y_offset -= buffer->pos[base].y_advance;
	}
	unsigned int last_combining_class = 255;
	hb_glyph_extents_t cluster_extents;
	for (unsigned int i = base + 1; i < end; i++)
	if (_hb_glyph_info_get_general_category (&buffer->info[i]) == HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK)
	{
	unsigned int this_combining_class = recategorize_combining_class (_hb_glyph_info_get_modified_combining_class (&buffer->info[i]));
	if (this_combining_class != last_combining_class)
	cluster_extents = base_extents;

	position_mark (plan, font, buffer, base_extents, i, this_combining_class);

	buffer->pos[i].x_advance = 0;
	buffer->pos[i].y_advance = 0;
	buffer->pos[i].x_offset += x_offset;
	buffer->pos[i].y_offset += y_offset;

	/* combine cluster extents. */

	last_combining_class = this_combining_class;
	} else {
	if (HB_DIRECTION_IS_FORWARD (buffer->props.direction)) {
	x_offset -= buffer->pos[i].x_advance;
	y_offset -= buffer->pos[i].y_advance;
	} else {
	x_offset += buffer->pos[i].x_advance;
	y_offset += buffer->pos[i].y_advance;
	}
	}


	}

	static inline void
	position_cluster (const hb_ot_shape_plan_t *plan,
	hb_font_t *font,
	hb_buffer_t *buffer,
	unsigned int start,
	unsigned int end)
	{
	if (end - start < 2)
	return;

	/* Find the base glyph */
	for (unsigned int i = start; i < end; i++)
	if (is_a_ligature (buffer->info[i]) \|\|
	!(FLAG (_hb_glyph_info_get_general_category (&buffer->info[i])) &
	(FLAG (HB_UNICODE_GENERAL_CATEGORY_SPACING_MARK) \|
	FLAG (HB_UNICODE_GENERAL_CATEGORY_ENCLOSING_MARK) \|
	FLAG (HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK))))
	{
	position_around_base (plan, font, buffer, i, end);
	break;
	}
	}

	void
	_hb_ot_shape_fallback_position (const hb_ot_shape_plan_t *plan,
	hb_font_t *font,
	hb_buffer_t *buffer)
	{
	unsigned int start = 0;
	unsigned int last_cluster = buffer->info[0].cluster;
	unsigned int count = buffer->len;
	for (unsigned int i = 1; i < count; i++)
	if (buffer->info[i].cluster != last_cluster) {
	position_cluster (plan, font, buffer, start, i);
	start = i;
	last_cluster = buffer->info[i].cluster;
	}
	position_cluster (plan, font, buffer, start, count);
	}