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      1 /*
      2  * Copyright  2010,2012  Google, Inc.
      3  *
      4  *  This is part of HarfBuzz, a text shaping library.
      5  *
      6  * Permission is hereby granted, without written agreement and without
      7  * license or royalty fees, to use, copy, modify, and distribute this
      8  * software and its documentation for any purpose, provided that the
      9  * above copyright notice and the following two paragraphs appear in
     10  * all copies of this software.
     11  *
     12  * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
     13  * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
     14  * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
     15  * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
     16  * DAMAGE.
     17  *
     18  * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
     19  * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
     20  * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
     21  * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
     22  * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
     23  *
     24  * Google Author(s): Behdad Esfahbod
     25  */
     26 
     27 #include "hb-ot-shape-complex-arabic-private.hh"
     28 #include "hb-ot-shape-private.hh"
     29 
     30 
     31 #ifndef HB_DEBUG_ARABIC
     32 #define HB_DEBUG_ARABIC (HB_DEBUG+0)
     33 #endif
     34 
     35 
     36 /* buffer var allocations */
     37 #define arabic_shaping_action() complex_var_u8_0() /* arabic shaping action */
     38 
     39 #define HB_BUFFER_SCRATCH_FLAG_ARABIC_HAS_STCH HB_BUFFER_SCRATCH_FLAG_COMPLEX0
     40 
     41 /* See:
     42  * https://github.com/behdad/harfbuzz/commit/6e6f82b6f3dde0fc6c3c7d991d9ec6cfff57823d#commitcomment-14248516 */
     43 #define HB_ARABIC_GENERAL_CATEGORY_IS_WORD(gen_cat) \
     44 	(FLAG_SAFE (gen_cat) & \
     45 	 (FLAG (HB_UNICODE_GENERAL_CATEGORY_UNASSIGNED) | \
     46 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_PRIVATE_USE) | \
     47 	  /*FLAG (HB_UNICODE_GENERAL_CATEGORY_LOWERCASE_LETTER) |*/ \
     48 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_MODIFIER_LETTER) | \
     49 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_OTHER_LETTER) | \
     50 	  /*FLAG (HB_UNICODE_GENERAL_CATEGORY_TITLECASE_LETTER) |*/ \
     51 	  /*FLAG (HB_UNICODE_GENERAL_CATEGORY_UPPERCASE_LETTER) |*/ \
     52 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_SPACING_MARK) | \
     53 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_ENCLOSING_MARK) | \
     54 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK) | \
     55 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_DECIMAL_NUMBER) | \
     56 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_LETTER_NUMBER) | \
     57 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_OTHER_NUMBER) | \
     58 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_CURRENCY_SYMBOL) | \
     59 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_MODIFIER_SYMBOL) | \
     60 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_MATH_SYMBOL) | \
     61 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_OTHER_SYMBOL)))
     62 
     63 
     64 /*
     65  * Joining types:
     66  */
     67 
     68 /*
     69  * Bits used in the joining tables
     70  */
     71 enum hb_arabic_joining_type_t {
     72   JOINING_TYPE_U		= 0,
     73   JOINING_TYPE_L		= 1,
     74   JOINING_TYPE_R		= 2,
     75   JOINING_TYPE_D		= 3,
     76   JOINING_TYPE_C		= JOINING_TYPE_D,
     77   JOINING_GROUP_ALAPH		= 4,
     78   JOINING_GROUP_DALATH_RISH	= 5,
     79   NUM_STATE_MACHINE_COLS	= 6,
     80 
     81   JOINING_TYPE_T = 7,
     82   JOINING_TYPE_X = 8  /* means: use general-category to choose between U or T. */
     83 };
     84 
     85 #include "hb-ot-shape-complex-arabic-table.hh"
     86 
     87 static unsigned int get_joining_type (hb_codepoint_t u, hb_unicode_general_category_t gen_cat)
     88 {
     89   unsigned int j_type = joining_type(u);
     90   if (likely (j_type != JOINING_TYPE_X))
     91     return j_type;
     92 
     93   return (FLAG_SAFE(gen_cat) &
     94 	  (FLAG(HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK) |
     95 	   FLAG(HB_UNICODE_GENERAL_CATEGORY_ENCLOSING_MARK) |
     96 	   FLAG(HB_UNICODE_GENERAL_CATEGORY_FORMAT))
     97 	 ) ?  JOINING_TYPE_T : JOINING_TYPE_U;
     98 }
     99 
    100 #define FEATURE_IS_SYRIAC(tag) hb_in_range<unsigned char> ((unsigned char) (tag), '2', '3')
    101 
    102 static const hb_tag_t arabic_features[] =
    103 {
    104   HB_TAG('i','s','o','l'),
    105   HB_TAG('f','i','n','a'),
    106   HB_TAG('f','i','n','2'),
    107   HB_TAG('f','i','n','3'),
    108   HB_TAG('m','e','d','i'),
    109   HB_TAG('m','e','d','2'),
    110   HB_TAG('i','n','i','t'),
    111   HB_TAG_NONE
    112 };
    113 
    114 
    115 /* Same order as the feature array */
    116 enum arabic_action_t {
    117   ISOL,
    118   FINA,
    119   FIN2,
    120   FIN3,
    121   MEDI,
    122   MED2,
    123   INIT,
    124 
    125   NONE,
    126 
    127   ARABIC_NUM_FEATURES = NONE,
    128 
    129   /* We abuse the same byte for other things... */
    130   STCH_FIXED,
    131   STCH_REPEATING,
    132 };
    133 
    134 static const struct arabic_state_table_entry {
    135 	uint8_t prev_action;
    136 	uint8_t curr_action;
    137 	uint16_t next_state;
    138 } arabic_state_table[][NUM_STATE_MACHINE_COLS] =
    139 {
    140   /*   jt_U,          jt_L,          jt_R,          jt_D,          jg_ALAPH,      jg_DALATH_RISH */
    141 
    142   /* State 0: prev was U, not willing to join. */
    143   { {NONE,NONE,0}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,6}, },
    144 
    145   /* State 1: prev was R or ISOL/ALAPH, not willing to join. */
    146   { {NONE,NONE,0}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,2}, {NONE,FIN2,5}, {NONE,ISOL,6}, },
    147 
    148   /* State 2: prev was D/L in ISOL form, willing to join. */
    149   { {NONE,NONE,0}, {NONE,ISOL,2}, {INIT,FINA,1}, {INIT,FINA,3}, {INIT,FINA,4}, {INIT,FINA,6}, },
    150 
    151   /* State 3: prev was D in FINA form, willing to join. */
    152   { {NONE,NONE,0}, {NONE,ISOL,2}, {MEDI,FINA,1}, {MEDI,FINA,3}, {MEDI,FINA,4}, {MEDI,FINA,6}, },
    153 
    154   /* State 4: prev was FINA ALAPH, not willing to join. */
    155   { {NONE,NONE,0}, {NONE,ISOL,2}, {MED2,ISOL,1}, {MED2,ISOL,2}, {MED2,FIN2,5}, {MED2,ISOL,6}, },
    156 
    157   /* State 5: prev was FIN2/FIN3 ALAPH, not willing to join. */
    158   { {NONE,NONE,0}, {NONE,ISOL,2}, {ISOL,ISOL,1}, {ISOL,ISOL,2}, {ISOL,FIN2,5}, {ISOL,ISOL,6}, },
    159 
    160   /* State 6: prev was DALATH/RISH, not willing to join. */
    161   { {NONE,NONE,0}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,2}, {NONE,FIN3,5}, {NONE,ISOL,6}, }
    162 };
    163 
    164 
    165 static void
    166 nuke_joiners (const hb_ot_shape_plan_t *plan,
    167 	      hb_font_t *font,
    168 	      hb_buffer_t *buffer);
    169 
    170 static void
    171 arabic_fallback_shape (const hb_ot_shape_plan_t *plan,
    172 		       hb_font_t *font,
    173 		       hb_buffer_t *buffer);
    174 
    175 static void
    176 record_stch (const hb_ot_shape_plan_t *plan,
    177 	     hb_font_t *font,
    178 	     hb_buffer_t *buffer);
    179 
    180 static void
    181 collect_features_arabic (hb_ot_shape_planner_t *plan)
    182 {
    183   hb_ot_map_builder_t *map = &plan->map;
    184 
    185   /* We apply features according to the Arabic spec, with pauses
    186    * in between most.
    187    *
    188    * The pause between init/medi/... and rlig is required.  See eg:
    189    * https://bugzilla.mozilla.org/show_bug.cgi?id=644184
    190    *
    191    * The pauses between init/medi/... themselves are not necessarily
    192    * needed as only one of those features is applied to any character.
    193    * The only difference it makes is when fonts have contextual
    194    * substitutions.  We now follow the order of the spec, which makes
    195    * for better experience if that's what Uniscribe is doing.
    196    *
    197    * At least for Arabic, looks like Uniscribe has a pause between
    198    * rlig and calt.  Otherwise the IranNastaliq's ALLAH ligature won't
    199    * work.  However, testing shows that rlig and calt are applied
    200    * together for Mongolian in Uniscribe.  As such, we only add a
    201    * pause for Arabic, not other scripts.
    202    */
    203 
    204   map->add_gsub_pause (nuke_joiners);
    205 
    206   map->add_global_bool_feature (HB_TAG('s','t','c','h'));
    207   map->add_gsub_pause (record_stch);
    208 
    209   map->add_global_bool_feature (HB_TAG('c','c','m','p'));
    210   map->add_global_bool_feature (HB_TAG('l','o','c','l'));
    211 
    212   map->add_gsub_pause (NULL);
    213 
    214   for (unsigned int i = 0; i < ARABIC_NUM_FEATURES; i++)
    215   {
    216     bool has_fallback = plan->props.script == HB_SCRIPT_ARABIC && !FEATURE_IS_SYRIAC (arabic_features[i]);
    217     map->add_feature (arabic_features[i], 1, has_fallback ? F_HAS_FALLBACK : F_NONE);
    218     map->add_gsub_pause (NULL);
    219   }
    220 
    221   map->add_feature (HB_TAG('r','l','i','g'), 1, F_GLOBAL|F_HAS_FALLBACK);
    222   if (plan->props.script == HB_SCRIPT_ARABIC)
    223     map->add_gsub_pause (arabic_fallback_shape);
    224 
    225   map->add_global_bool_feature (HB_TAG('c','a','l','t'));
    226 
    227   /* The spec includes 'cswh'.  Earlier versions of Windows
    228    * used to enable this by default, but testing suggests
    229    * that Windows 8 and later do not enable it by default,
    230    * and spec now says 'Off by default'.
    231    * We disabled this in ae23c24c32.
    232    * Note that IranNastaliq uses this feature extensively
    233    * to fixup broken glyph sequences.  Oh well...
    234    * Test case: U+0643,U+0640,U+0631. */
    235   //map->add_gsub_pause (NULL);
    236   //map->add_global_bool_feature (HB_TAG('c','s','w','h'));
    237   map->add_global_bool_feature (HB_TAG('m','s','e','t'));
    238 }
    239 
    240 #include "hb-ot-shape-complex-arabic-fallback.hh"
    241 
    242 struct arabic_shape_plan_t
    243 {
    244   ASSERT_POD ();
    245 
    246   /* The "+ 1" in the next array is to accommodate for the "NONE" command,
    247    * which is not an OpenType feature, but this simplifies the code by not
    248    * having to do a "if (... < NONE) ..." and just rely on the fact that
    249    * mask_array[NONE] == 0. */
    250   hb_mask_t mask_array[ARABIC_NUM_FEATURES + 1];
    251 
    252   arabic_fallback_plan_t *fallback_plan;
    253 
    254   unsigned int do_fallback : 1;
    255   unsigned int has_stch : 1;
    256 };
    257 
    258 void *
    259 data_create_arabic (const hb_ot_shape_plan_t *plan)
    260 {
    261   arabic_shape_plan_t *arabic_plan = (arabic_shape_plan_t *) calloc (1, sizeof (arabic_shape_plan_t));
    262   if (unlikely (!arabic_plan))
    263     return NULL;
    264 
    265   arabic_plan->do_fallback = plan->props.script == HB_SCRIPT_ARABIC;
    266   arabic_plan->has_stch = !!plan->map.get_1_mask (HB_TAG ('s','t','c','h'));
    267   for (unsigned int i = 0; i < ARABIC_NUM_FEATURES; i++) {
    268     arabic_plan->mask_array[i] = plan->map.get_1_mask (arabic_features[i]);
    269     arabic_plan->do_fallback = arabic_plan->do_fallback &&
    270 			       (FEATURE_IS_SYRIAC (arabic_features[i]) ||
    271 			        plan->map.needs_fallback (arabic_features[i]));
    272   }
    273 
    274   return arabic_plan;
    275 }
    276 
    277 void
    278 data_destroy_arabic (void *data)
    279 {
    280   arabic_shape_plan_t *arabic_plan = (arabic_shape_plan_t *) data;
    281 
    282   arabic_fallback_plan_destroy (arabic_plan->fallback_plan);
    283 
    284   free (data);
    285 }
    286 
    287 static void
    288 arabic_joining (hb_buffer_t *buffer)
    289 {
    290   unsigned int count = buffer->len;
    291   hb_glyph_info_t *info = buffer->info;
    292   unsigned int prev = (unsigned int) -1, state = 0;
    293 
    294   /* Check pre-context */
    295   for (unsigned int i = 0; i < buffer->context_len[0]; i++)
    296   {
    297     unsigned int this_type = get_joining_type (buffer->context[0][i], buffer->unicode->general_category (buffer->context[0][i]));
    298 
    299     if (unlikely (this_type == JOINING_TYPE_T))
    300       continue;
    301 
    302     const arabic_state_table_entry *entry = &arabic_state_table[state][this_type];
    303     state = entry->next_state;
    304     break;
    305   }
    306 
    307   for (unsigned int i = 0; i < count; i++)
    308   {
    309     unsigned int this_type = get_joining_type (info[i].codepoint, _hb_glyph_info_get_general_category (&info[i]));
    310 
    311     if (unlikely (this_type == JOINING_TYPE_T)) {
    312       info[i].arabic_shaping_action() = NONE;
    313       continue;
    314     }
    315 
    316     const arabic_state_table_entry *entry = &arabic_state_table[state][this_type];
    317 
    318     if (entry->prev_action != NONE && prev != (unsigned int) -1)
    319       info[prev].arabic_shaping_action() = entry->prev_action;
    320 
    321     info[i].arabic_shaping_action() = entry->curr_action;
    322 
    323     prev = i;
    324     state = entry->next_state;
    325   }
    326 
    327   for (unsigned int i = 0; i < buffer->context_len[1]; i++)
    328   {
    329     unsigned int this_type = get_joining_type (buffer->context[1][i], buffer->unicode->general_category (buffer->context[1][i]));
    330 
    331     if (unlikely (this_type == JOINING_TYPE_T))
    332       continue;
    333 
    334     const arabic_state_table_entry *entry = &arabic_state_table[state][this_type];
    335     if (entry->prev_action != NONE && prev != (unsigned int) -1)
    336       info[prev].arabic_shaping_action() = entry->prev_action;
    337     break;
    338   }
    339 }
    340 
    341 static void
    342 mongolian_variation_selectors (hb_buffer_t *buffer)
    343 {
    344   /* Copy arabic_shaping_action() from base to Mongolian variation selectors. */
    345   unsigned int count = buffer->len;
    346   hb_glyph_info_t *info = buffer->info;
    347   for (unsigned int i = 1; i < count; i++)
    348     if (unlikely (hb_in_range (info[i].codepoint, 0x180Bu, 0x180Du)))
    349       info[i].arabic_shaping_action() = info[i - 1].arabic_shaping_action();
    350 }
    351 
    352 void
    353 setup_masks_arabic_plan (const arabic_shape_plan_t *arabic_plan,
    354 			 hb_buffer_t               *buffer,
    355 			 hb_script_t                script)
    356 {
    357   HB_BUFFER_ALLOCATE_VAR (buffer, arabic_shaping_action);
    358 
    359   arabic_joining (buffer);
    360   if (script == HB_SCRIPT_MONGOLIAN)
    361     mongolian_variation_selectors (buffer);
    362 
    363   unsigned int count = buffer->len;
    364   hb_glyph_info_t *info = buffer->info;
    365   for (unsigned int i = 0; i < count; i++)
    366     info[i].mask |= arabic_plan->mask_array[info[i].arabic_shaping_action()];
    367 }
    368 
    369 static void
    370 setup_masks_arabic (const hb_ot_shape_plan_t *plan,
    371 		    hb_buffer_t              *buffer,
    372 		    hb_font_t                *font HB_UNUSED)
    373 {
    374   const arabic_shape_plan_t *arabic_plan = (const arabic_shape_plan_t *) plan->data;
    375   setup_masks_arabic_plan (arabic_plan, buffer, plan->props.script);
    376 }
    377 
    378 
    379 static void
    380 nuke_joiners (const hb_ot_shape_plan_t *plan HB_UNUSED,
    381 	      hb_font_t *font HB_UNUSED,
    382 	      hb_buffer_t *buffer)
    383 {
    384   unsigned int count = buffer->len;
    385   hb_glyph_info_t *info = buffer->info;
    386   for (unsigned int i = 0; i < count; i++)
    387     if (_hb_glyph_info_is_zwj (&info[i]))
    388       _hb_glyph_info_flip_joiners (&info[i]);
    389 }
    390 
    391 static void
    392 arabic_fallback_shape (const hb_ot_shape_plan_t *plan,
    393 		       hb_font_t *font,
    394 		       hb_buffer_t *buffer)
    395 {
    396   const arabic_shape_plan_t *arabic_plan = (const arabic_shape_plan_t *) plan->data;
    397 
    398   if (!arabic_plan->do_fallback)
    399     return;
    400 
    401 retry:
    402   arabic_fallback_plan_t *fallback_plan = (arabic_fallback_plan_t *) hb_atomic_ptr_get (&arabic_plan->fallback_plan);
    403   if (unlikely (!fallback_plan))
    404   {
    405     /* This sucks.  We need a font to build the fallback plan... */
    406     fallback_plan = arabic_fallback_plan_create (plan, font);
    407     if (unlikely (!hb_atomic_ptr_cmpexch (&(const_cast<arabic_shape_plan_t *> (arabic_plan))->fallback_plan, NULL, fallback_plan))) {
    408       arabic_fallback_plan_destroy (fallback_plan);
    409       goto retry;
    410     }
    411   }
    412 
    413   arabic_fallback_plan_shape (fallback_plan, font, buffer);
    414 }
    415 
    416 /*
    417  * Stretch feature: "stch".
    418  * See example here:
    419  * https://www.microsoft.com/typography/OpenTypeDev/syriac/intro.htm
    420  * We implement this in a generic way, such that the Arabic subtending
    421  * marks can use it as well.
    422  */
    423 
    424 static void
    425 record_stch (const hb_ot_shape_plan_t *plan,
    426 	     hb_font_t *font,
    427 	     hb_buffer_t *buffer)
    428 {
    429   const arabic_shape_plan_t *arabic_plan = (const arabic_shape_plan_t *) plan->data;
    430   if (!arabic_plan->has_stch)
    431     return;
    432 
    433   /* 'stch' feature was just applied.  Look for anything that multiplied,
    434    * and record it for stch treatment later.  Note that rtlm, frac, etc
    435    * are applied before stch, but we assume that they didn't result in
    436    * anything multiplying into 5 pieces, so it's safe-ish... */
    437 
    438   unsigned int count = buffer->len;
    439   hb_glyph_info_t *info = buffer->info;
    440   for (unsigned int i = 0; i < count; i++)
    441     if (unlikely (_hb_glyph_info_multiplied (&info[i])))
    442     {
    443       unsigned int comp = _hb_glyph_info_get_lig_comp (&info[i]);
    444       info[i].arabic_shaping_action() = comp % 2 ? STCH_REPEATING : STCH_FIXED;
    445       buffer->scratch_flags |= HB_BUFFER_SCRATCH_FLAG_ARABIC_HAS_STCH;
    446     }
    447 }
    448 
    449 static void
    450 apply_stch (const hb_ot_shape_plan_t *plan,
    451 	    hb_buffer_t              *buffer,
    452 	    hb_font_t                *font)
    453 {
    454   if (likely (!(buffer->scratch_flags & HB_BUFFER_SCRATCH_FLAG_ARABIC_HAS_STCH)))
    455     return;
    456 
    457   /* The Arabic shaper currently always processes in RTL mode, so we should
    458    * stretch / position the stretched pieces to the left / preceding glyphs. */
    459 
    460   /* We do a two pass implementation:
    461    * First pass calculates the exact number of extra glyphs we need,
    462    * We then enlarge buffer to have that much room,
    463    * Second pass applies the stretch, copying things to the end of buffer.
    464    */
    465 
    466   int sign = font->x_scale < 0 ? -1 : +1;
    467   unsigned int extra_glyphs_needed = 0; // Set during MEASURE, used during CUT
    468   typedef enum { MEASURE, CUT } step_t;
    469 
    470   for (step_t step = MEASURE; step <= CUT; step = (step_t) (step + 1))
    471   {
    472     unsigned int count = buffer->len;
    473     hb_glyph_info_t *info = buffer->info;
    474     hb_glyph_position_t *pos = buffer->pos;
    475     unsigned int new_len = count + extra_glyphs_needed; // write head during CUT
    476     unsigned int j = new_len;
    477     for (unsigned int i = count; i; i--)
    478     {
    479       if (!hb_in_range<unsigned> (info[i - 1].arabic_shaping_action(), STCH_FIXED, STCH_REPEATING))
    480       {
    481         if (step == CUT)
    482 	{
    483 	  --j;
    484 	  info[j] = info[i - 1];
    485 	  pos[j] = pos[i - 1];
    486 	}
    487         continue;
    488       }
    489 
    490       /* Yay, justification! */
    491 
    492       hb_position_t w_total = 0; // Total to be filled
    493       hb_position_t w_fixed = 0; // Sum of fixed tiles
    494       hb_position_t w_repeating = 0; // Sum of repeating tiles
    495       int n_fixed = 0;
    496       int n_repeating = 0;
    497 
    498       unsigned int end = i;
    499       while (i &&
    500 	     hb_in_range<unsigned> (info[i - 1].arabic_shaping_action(), STCH_FIXED, STCH_REPEATING))
    501       {
    502 	i--;
    503 	hb_position_t width = font->get_glyph_h_advance (info[i].codepoint);
    504 	if (info[i].arabic_shaping_action() == STCH_FIXED)
    505 	{
    506 	  w_fixed += width;
    507 	  n_fixed++;
    508 	}
    509 	else
    510 	{
    511 	  w_repeating += width;
    512 	  n_repeating++;
    513 	}
    514       }
    515       unsigned int start = i;
    516       unsigned int context = i;
    517       while (context &&
    518 	     !hb_in_range<unsigned> (info[context - 1].arabic_shaping_action(), STCH_FIXED, STCH_REPEATING) &&
    519 	     (_hb_glyph_info_is_default_ignorable (&info[context - 1]) ||
    520 	      HB_ARABIC_GENERAL_CATEGORY_IS_WORD (_hb_glyph_info_get_general_category (&info[context - 1]))))
    521       {
    522 	context--;
    523 	w_total += pos[context].x_advance;
    524       }
    525       i++; // Don't touch i again.
    526 
    527       DEBUG_MSG (ARABIC, NULL, "%s stretch at (%d,%d,%d)",
    528 		 step == MEASURE ? "measuring" : "cutting", context, start, end);
    529       DEBUG_MSG (ARABIC, NULL, "rest of word:    count=%d width %d", start - context, w_total);
    530       DEBUG_MSG (ARABIC, NULL, "fixed tiles:     count=%d width=%d", n_fixed, w_fixed);
    531       DEBUG_MSG (ARABIC, NULL, "repeating tiles: count=%d width=%d", n_repeating, w_repeating);
    532 
    533       /* Number of additional times to repeat each repeating tile. */
    534       int n_copies = 0;
    535 
    536       hb_position_t w_remaining = w_total - w_fixed;
    537       if (sign * w_remaining > sign * w_repeating && sign * w_repeating > 0)
    538 	n_copies = (sign * w_remaining) / (sign * w_repeating) - 1;
    539 
    540       /* See if we can improve the fit by adding an extra repeat and squeezing them together a bit. */
    541       hb_position_t extra_repeat_overlap = 0;
    542       hb_position_t shortfall = sign * w_remaining - sign * w_repeating * (n_copies + 1);
    543       if (shortfall > 0)
    544       {
    545         ++n_copies;
    546         hb_position_t excess = (n_copies + 1) * sign * w_repeating - sign * w_remaining;
    547         if (excess > 0)
    548           extra_repeat_overlap = excess / (n_copies * n_repeating);
    549       }
    550 
    551       if (step == MEASURE)
    552       {
    553 	extra_glyphs_needed += n_copies * n_repeating;
    554 	DEBUG_MSG (ARABIC, NULL, "will add extra %d copies of repeating tiles", n_copies);
    555       }
    556       else
    557       {
    558 	hb_position_t x_offset = 0;
    559 	for (unsigned int k = end; k > start; k--)
    560 	{
    561 	  hb_position_t width = font->get_glyph_h_advance (info[k - 1].codepoint);
    562 
    563 	  unsigned int repeat = 1;
    564 	  if (info[k - 1].arabic_shaping_action() == STCH_REPEATING)
    565 	    repeat += n_copies;
    566 
    567 	  DEBUG_MSG (ARABIC, NULL, "appending %d copies of glyph %d; j=%d",
    568 		     repeat, info[k - 1].codepoint, j);
    569 	  for (unsigned int n = 0; n < repeat; n++)
    570 	  {
    571 	    x_offset -= width;
    572 	    if (n > 0)
    573 	      x_offset += extra_repeat_overlap;
    574 	    pos[k - 1].x_offset = x_offset;
    575 	    /* Append copy. */
    576 	    --j;
    577 	    info[j] = info[k - 1];
    578 	    pos[j] = pos[k - 1];
    579 	  }
    580 	}
    581       }
    582     }
    583 
    584     if (step == MEASURE)
    585     {
    586       if (unlikely (!buffer->ensure (count + extra_glyphs_needed)))
    587         break;
    588     }
    589     else
    590     {
    591       assert (j == 0);
    592       buffer->len = new_len;
    593     }
    594   }
    595 }
    596 
    597 
    598 static void
    599 postprocess_glyphs_arabic (const hb_ot_shape_plan_t *plan,
    600 			   hb_buffer_t              *buffer,
    601 			   hb_font_t                *font)
    602 {
    603   apply_stch (plan, buffer, font);
    604 
    605   HB_BUFFER_DEALLOCATE_VAR (buffer, arabic_shaping_action);
    606 }
    607 
    608 const hb_ot_complex_shaper_t _hb_ot_complex_shaper_arabic =
    609 {
    610   "arabic",
    611   collect_features_arabic,
    612   NULL, /* override_features */
    613   data_create_arabic,
    614   data_destroy_arabic,
    615   NULL, /* preprocess_text */
    616   postprocess_glyphs_arabic,
    617   HB_OT_SHAPE_NORMALIZATION_MODE_DEFAULT,
    618   NULL, /* decompose */
    619   NULL, /* compose */
    620   setup_masks_arabic,
    621   NULL, /* disable_otl */
    622   HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_LATE,
    623   true, /* fallback_position */
    624 };
    625