gfx/harfbuzz/src/hb-ot-shaper-arabic.cc

   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.hh"
  28
  29 #ifndef HB_NO_OT_SHAPE
  30
  31 #include "hb-ot-shaper-arabic.hh"
  32 #include "hb-ot-shape.hh"
  33
  34
  35 /* buffer var allocations */
  36 #define arabic_shaping_action() ot_shaper_var_u8_auxiliary() /* arabic shaping action */
  37
  38 #define HB_BUFFER_SCRATCH_FLAG_ARABIC_HAS_STCH HB_BUFFER_SCRATCH_FLAG_SHAPER0
  39
  40 /* See:
  41  * https://github.com/harfbuzz/harfbuzz/commit/6e6f82b6f3dde0fc6c3c7d991d9ec6cfff57823d#commitcomment-14248516 */
  42 #define HB_ARABIC_GENERAL_CATEGORY_IS_WORD(gen_cat) \
  43         (FLAG_UNSAFE (gen_cat) & \
  44          (FLAG (HB_UNICODE_GENERAL_CATEGORY_UNASSIGNED) | \
  45           FLAG (HB_UNICODE_GENERAL_CATEGORY_PRIVATE_USE) | \
  46           /*FLAG (HB_UNICODE_GENERAL_CATEGORY_LOWERCASE_LETTER) |*/ \
  47           FLAG (HB_UNICODE_GENERAL_CATEGORY_MODIFIER_LETTER) | \
  48           FLAG (HB_UNICODE_GENERAL_CATEGORY_OTHER_LETTER) | \
  49           /*FLAG (HB_UNICODE_GENERAL_CATEGORY_TITLECASE_LETTER) |*/ \
  50           /*FLAG (HB_UNICODE_GENERAL_CATEGORY_UPPERCASE_LETTER) |*/ \
  51           FLAG (HB_UNICODE_GENERAL_CATEGORY_SPACING_MARK) | \
  52           FLAG (HB_UNICODE_GENERAL_CATEGORY_ENCLOSING_MARK) | \
  53           FLAG (HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK) | \
  54           FLAG (HB_UNICODE_GENERAL_CATEGORY_DECIMAL_NUMBER) | \
  55           FLAG (HB_UNICODE_GENERAL_CATEGORY_LETTER_NUMBER) | \
  56           FLAG (HB_UNICODE_GENERAL_CATEGORY_OTHER_NUMBER) | \
  57           FLAG (HB_UNICODE_GENERAL_CATEGORY_CURRENCY_SYMBOL) | \
  58           FLAG (HB_UNICODE_GENERAL_CATEGORY_MODIFIER_SYMBOL) | \
  59           FLAG (HB_UNICODE_GENERAL_CATEGORY_MATH_SYMBOL) | \
  60           FLAG (HB_UNICODE_GENERAL_CATEGORY_OTHER_SYMBOL)))
  61
  62
  63 /*
  64  * Joining types:
  65  */
  66
  67 /*
  68  * Bits used in the joining tables
  69  */
  70 enum hb_arabic_joining_type_t {
  71   JOINING_TYPE_U                = 0,
  72   JOINING_TYPE_L                = 1,
  73   JOINING_TYPE_R                = 2,
  74   JOINING_TYPE_D                = 3,
  75   JOINING_TYPE_C                = JOINING_TYPE_D,
  76   JOINING_GROUP_ALAPH           = 4,
  77   JOINING_GROUP_DALATH_RISH     = 5,
  78   NUM_STATE_MACHINE_COLS        = 6,
  79
  80   JOINING_TYPE_T = 7,
  81   JOINING_TYPE_X = 8  /* means: use general-category to choose between U or T. */
  82 };
  83
  84 #include "hb-ot-shaper-arabic-table.hh"
  85
  86 static unsigned int get_joining_type (hb_codepoint_t u, hb_unicode_general_category_t gen_cat)
  87 {
  88   unsigned int j_type = joining_type(u);
  89   if (likely (j_type != JOINING_TYPE_X))
  90     return j_type;
  91
  92   return (FLAG_UNSAFE(gen_cat) &
  93           (FLAG(HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK) |
  94            FLAG(HB_UNICODE_GENERAL_CATEGORY_ENCLOSING_MARK) |
  95            FLAG(HB_UNICODE_GENERAL_CATEGORY_FORMAT))
  96          ) ?  JOINING_TYPE_T : JOINING_TYPE_U;
  97 }
  98
  99 #define FEATURE_IS_SYRIAC(tag) hb_in_range<unsigned char> ((unsigned char) (tag), '2', '3')
 100
 101 static const hb_tag_t arabic_features[] =
 102 {
 103   HB_TAG('i','s','o','l'),
 104   HB_TAG('f','i','n','a'),
 105   HB_TAG('f','i','n','2'),
 106   HB_TAG('f','i','n','3'),
 107   HB_TAG('m','e','d','i'),
 108   HB_TAG('m','e','d','2'),
 109   HB_TAG('i','n','i','t'),
 110   HB_TAG_NONE
 111 };
 112
 113
 114 /* Same order as the feature array */
 115 enum arabic_action_t {
 116   ISOL,
 117   FINA,
 118   FIN2,
 119   FIN3,
 120   MEDI,
 121   MED2,
 122   INIT,
 123
 124   NONE,
 125
 126   ARABIC_NUM_FEATURES = NONE,
 127
 128   /* We abuse the same byte for other things... */
 129   STCH_FIXED,
 130   STCH_REPEATING,
 131 };
 132
 133 static const struct arabic_state_table_entry {
 134         uint8_t prev_action;
 135         uint8_t curr_action;
 136         uint16_t next_state;
 137 } arabic_state_table[][NUM_STATE_MACHINE_COLS] =
 138 {
 139   /*   jt_U,          jt_L,          jt_R,          jt_D,          jg_ALAPH,      jg_DALATH_RISH */
 140
 141   /* State 0: prev was U, not willing to join. */
 142   { {NONE,NONE,0}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,6}, },
 143
 144   /* State 1: prev was R or ISOL/ALAPH, not willing to join. */
 145   { {NONE,NONE,0}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,2}, {NONE,FIN2,5}, {NONE,ISOL,6}, },
 146
 147   /* State 2: prev was D/L in ISOL form, willing to join. */
 148   { {NONE,NONE,0}, {NONE,ISOL,2}, {INIT,FINA,1}, {INIT,FINA,3}, {INIT,FINA,4}, {INIT,FINA,6}, },
 149
 150   /* State 3: prev was D in FINA form, willing to join. */
 151   { {NONE,NONE,0}, {NONE,ISOL,2}, {MEDI,FINA,1}, {MEDI,FINA,3}, {MEDI,FINA,4}, {MEDI,FINA,6}, },
 152
 153   /* State 4: prev was FINA ALAPH, not willing to join. */
 154   { {NONE,NONE,0}, {NONE,ISOL,2}, {MED2,ISOL,1}, {MED2,ISOL,2}, {MED2,FIN2,5}, {MED2,ISOL,6}, },
 155
 156   /* State 5: prev was FIN2/FIN3 ALAPH, not willing to join. */
 157   { {NONE,NONE,0}, {NONE,ISOL,2}, {ISOL,ISOL,1}, {ISOL,ISOL,2}, {ISOL,FIN2,5}, {ISOL,ISOL,6}, },
 158
 159   /* State 6: prev was DALATH/RISH, not willing to join. */
 160   { {NONE,NONE,0}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,2}, {NONE,FIN3,5}, {NONE,ISOL,6}, }
 161 };
 162
 163
 164 static bool
 165 arabic_fallback_shape (const hb_ot_shape_plan_t *plan,
 166                        hb_font_t *font,
 167                        hb_buffer_t *buffer);
 168
 169 static bool
 170 record_stch (const hb_ot_shape_plan_t *plan,
 171              hb_font_t *font,
 172              hb_buffer_t *buffer);
 173
 174 static bool
 175 deallocate_buffer_var (const hb_ot_shape_plan_t *plan,
 176                        hb_font_t *font,
 177                        hb_buffer_t *buffer)
 178 {
 179   HB_BUFFER_DEALLOCATE_VAR (buffer, arabic_shaping_action);
 180   return false;
 181 }
 182
 183 static void
 184 collect_features_arabic (hb_ot_shape_planner_t *plan)
 185 {
 186   hb_ot_map_builder_t *map = &plan->map;
 187
 188   /* We apply features according to the Arabic spec, with pauses
 189    * in between most.
 190    *
 191    * The pause between init/medi/... and rlig is required.  See eg:
 192    * https://bugzilla.mozilla.org/show_bug.cgi?id=644184
 193    *
 194    * The pauses between init/medi/... themselves are not necessarily
 195    * needed as only one of those features is applied to any character.
 196    * The only difference it makes is when fonts have contextual
 197    * substitutions.  We now follow the order of the spec, which makes
 198    * for better experience if that's what Uniscribe is doing.
 199    *
 200    * At least for Arabic, looks like Uniscribe has a pause between
 201    * rlig and calt.  Otherwise the IranNastaliq's ALLAH ligature won't
 202    * work.  However, testing shows that rlig and calt are applied
 203    * together for Mongolian in Uniscribe.  As such, we only add a
 204    * pause for Arabic, not other scripts.
 205    */
 206
 207
 208   map->enable_feature (HB_TAG('s','t','c','h'));
 209   map->add_gsub_pause (record_stch);
 210
 211   map->enable_feature (HB_TAG('c','c','m','p'), F_MANUAL_ZWJ);
 212   map->enable_feature (HB_TAG('l','o','c','l'), F_MANUAL_ZWJ);
 213
 214   map->add_gsub_pause (nullptr);
 215
 216   for (unsigned int i = 0; i < ARABIC_NUM_FEATURES; i++)
 217   {
 218     bool has_fallback = plan->props.script == HB_SCRIPT_ARABIC && !FEATURE_IS_SYRIAC (arabic_features[i]);
 219     map->add_feature (arabic_features[i], F_MANUAL_ZWJ | (has_fallback ? F_HAS_FALLBACK : F_NONE));
 220     map->add_gsub_pause (nullptr);
 221   }
 222    map->add_gsub_pause (deallocate_buffer_var);
 223
 224   /* Normally, Unicode says a ZWNJ means "don't ligate".  In Arabic script
 225    * however, it says a ZWJ should also mean "don't ligate".  So we run
 226    * the main ligating features as MANUAL_ZWJ. */
 227
 228   map->enable_feature (HB_TAG('r','l','i','g'), F_MANUAL_ZWJ | F_HAS_FALLBACK);
 229
 230   if (plan->props.script == HB_SCRIPT_ARABIC)
 231     map->add_gsub_pause (arabic_fallback_shape);
 232
 233    map->enable_feature (HB_TAG('c','a','l','t'), F_MANUAL_ZWJ);
 234    /* https://github.com/harfbuzz/harfbuzz/issues/1573 */
 235    if (!map->has_feature (HB_TAG('r','c','l','t')))
 236    {
 237      map->add_gsub_pause (nullptr);
 238      map->enable_feature (HB_TAG('r','c','l','t'), F_MANUAL_ZWJ);
 239    }
 240
 241    map->enable_feature (HB_TAG('l','i','g','a'), F_MANUAL_ZWJ);
 242    map->enable_feature (HB_TAG('c','l','i','g'), F_MANUAL_ZWJ);
 243
 244   /* The spec includes 'cswh'.  Earlier versions of Windows
 245    * used to enable this by default, but testing suggests
 246    * that Windows 8 and later do not enable it by default,
 247    * and spec now says 'Off by default'.
 248    * We disabled this in ae23c24c32.
 249    * Note that IranNastaliq uses this feature extensively
 250    * to fixup broken glyph sequences.  Oh well...
 251    * Test case: U+0643,U+0640,U+0631. */
 252   //map->enable_feature (HB_TAG('c','s','w','h'), F_MANUAL_ZWJ);
 253   map->enable_feature (HB_TAG('m','s','e','t'), F_MANUAL_ZWJ);
 254 }
 255
 256 #include "hb-ot-shaper-arabic-fallback.hh"
 257
 258 struct arabic_shape_plan_t
 259 {
 260   /* The "+ 1" in the next array is to accommodate for the "NONE" command,
 261    * which is not an OpenType feature, but this simplifies the code by not
 262    * having to do a "if (... < NONE) ..." and just rely on the fact that
 263    * mask_array[NONE] == 0. */
 264   hb_mask_t mask_array[ARABIC_NUM_FEATURES + 1];
 265
 266   hb_atomic_ptr_t<arabic_fallback_plan_t> fallback_plan;
 267
 268   unsigned int do_fallback : 1;
 269   unsigned int has_stch : 1;
 270 };
 271
 272 void *
 273 data_create_arabic (const hb_ot_shape_plan_t *plan)
 274 {
 275   arabic_shape_plan_t *arabic_plan = (arabic_shape_plan_t *) hb_calloc (1, sizeof (arabic_shape_plan_t));
 276   if (unlikely (!arabic_plan))
 277     return nullptr;
 278
 279   arabic_plan->do_fallback = plan->props.script == HB_SCRIPT_ARABIC;
 280   arabic_plan->has_stch = !!plan->map.get_1_mask (HB_TAG ('s','t','c','h'));
 281   for (unsigned int i = 0; i < ARABIC_NUM_FEATURES; i++) {
 282     arabic_plan->mask_array[i] = plan->map.get_1_mask (arabic_features[i]);
 283     arabic_plan->do_fallback = arabic_plan->do_fallback &&
 284                                (FEATURE_IS_SYRIAC (arabic_features[i]) ||
 285                                 plan->map.needs_fallback (arabic_features[i]));
 286   }
 287
 288   return arabic_plan;
 289 }
 290
 291 void
 292 data_destroy_arabic (void *data)
 293 {
 294   arabic_shape_plan_t *arabic_plan = (arabic_shape_plan_t *) data;
 295
 296   arabic_fallback_plan_destroy (arabic_plan->fallback_plan);
 297
 298   hb_free (data);
 299 }
 300
 301 static void
 302 arabic_joining (hb_buffer_t *buffer)
 303 {
 304   unsigned int count = buffer->len;
 305   hb_glyph_info_t *info = buffer->info;
 306   unsigned int prev = UINT_MAX, state = 0;
 307
 308   /* Check pre-context */
 309   for (unsigned int i = 0; i < buffer->context_len[0]; i++)
 310   {
 311     unsigned int this_type = get_joining_type (buffer->context[0][i], buffer->unicode->general_category (buffer->context[0][i]));
 312
 313     if (unlikely (this_type == JOINING_TYPE_T))
 314       continue;
 315
 316     const arabic_state_table_entry *entry = &arabic_state_table[state][this_type];
 317     state = entry->next_state;
 318     break;
 319   }
 320
 321   for (unsigned int i = 0; i < count; i++)
 322   {
 323     unsigned int this_type = get_joining_type (info[i].codepoint, _hb_glyph_info_get_general_category (&info[i]));
 324
 325     if (unlikely (this_type == JOINING_TYPE_T)) {
 326       info[i].arabic_shaping_action() = NONE;
 327       continue;
 328     }
 329
 330     const arabic_state_table_entry *entry = &arabic_state_table[state][this_type];
 331
 332     if (entry->prev_action != NONE && prev != UINT_MAX)
 333     {
 334       info[prev].arabic_shaping_action() = entry->prev_action;
 335       buffer->safe_to_insert_tatweel (prev, i + 1);
 336     }
 337     else
 338     {
 339       if (prev == UINT_MAX)
 340       {
 341         if (this_type >= JOINING_TYPE_R)
 342           buffer->unsafe_to_concat_from_outbuffer (0, i + 1);
 343       }
 344       else
 345       {
 346         if (this_type >= JOINING_TYPE_R ||
 347             (2 <= state && state <= 5) /* States that have a possible prev_action. */)
 348           buffer->unsafe_to_concat (prev, i + 1);
 349       }
 350     }
 351
 352     info[i].arabic_shaping_action() = entry->curr_action;
 353
 354     prev = i;
 355     state = entry->next_state;
 356   }
 357
 358   for (unsigned int i = 0; i < buffer->context_len[1]; i++)
 359   {
 360     unsigned int this_type = get_joining_type (buffer->context[1][i], buffer->unicode->general_category (buffer->context[1][i]));
 361
 362     if (unlikely (this_type == JOINING_TYPE_T))
 363       continue;
 364
 365     const arabic_state_table_entry *entry = &arabic_state_table[state][this_type];
 366     if (entry->prev_action != NONE && prev != UINT_MAX)
 367     {
 368       info[prev].arabic_shaping_action() = entry->prev_action;
 369       buffer->safe_to_insert_tatweel (prev, buffer->len);
 370     }
 371     else if (2 <= state && state <= 5) /* States that have a possible prev_action. */
 372     {
 373       buffer->unsafe_to_concat (prev, buffer->len);
 374     }
 375     break;
 376   }
 377 }
 378
 379 static void
 380 mongolian_variation_selectors (hb_buffer_t *buffer)
 381 {
 382   /* Copy arabic_shaping_action() from base to Mongolian variation selectors. */
 383   unsigned int count = buffer->len;
 384   hb_glyph_info_t *info = buffer->info;
 385   for (unsigned int i = 1; i < count; i++)
 386     if (unlikely (hb_in_ranges<hb_codepoint_t> (info[i].codepoint, 0x180Bu, 0x180Du, 0x180Fu, 0x180Fu)))
 387       info[i].arabic_shaping_action() = info[i - 1].arabic_shaping_action();
 388 }
 389
 390 void
 391 setup_masks_arabic_plan (const arabic_shape_plan_t *arabic_plan,
 392                          hb_buffer_t               *buffer,
 393                          hb_script_t                script)
 394 {
 395   HB_BUFFER_ALLOCATE_VAR (buffer, arabic_shaping_action);
 396
 397   arabic_joining (buffer);
 398   if (script == HB_SCRIPT_MONGOLIAN)
 399     mongolian_variation_selectors (buffer);
 400
 401   unsigned int count = buffer->len;
 402   hb_glyph_info_t *info = buffer->info;
 403   for (unsigned int i = 0; i < count; i++)
 404     info[i].mask |= arabic_plan->mask_array[info[i].arabic_shaping_action()];
 405 }
 406
 407 static void
 408 setup_masks_arabic (const hb_ot_shape_plan_t *plan,
 409                     hb_buffer_t              *buffer,
 410                     hb_font_t                *font HB_UNUSED)
 411 {
 412   const arabic_shape_plan_t *arabic_plan = (const arabic_shape_plan_t *) plan->data;
 413   setup_masks_arabic_plan (arabic_plan, buffer, plan->props.script);
 414 }
 415
 416 static bool
 417 arabic_fallback_shape (const hb_ot_shape_plan_t *plan,
 418                        hb_font_t *font,
 419                        hb_buffer_t *buffer)
 420 {
 421 #ifdef HB_NO_OT_SHAPER_ARABIC_FALLBACK
 422   return false;
 423 #endif
 424
 425   const arabic_shape_plan_t *arabic_plan = (const arabic_shape_plan_t *) plan->data;
 426
 427   if (!arabic_plan->do_fallback)
 428     return false;
 429
 430 retry:
 431   arabic_fallback_plan_t *fallback_plan = arabic_plan->fallback_plan;
 432   if (unlikely (!fallback_plan))
 433   {
 434     /* This sucks.  We need a font to build the fallback plan... */
 435     fallback_plan = arabic_fallback_plan_create (plan, font);
 436     if (unlikely (!arabic_plan->fallback_plan.cmpexch (nullptr, fallback_plan)))
 437     {
 438       arabic_fallback_plan_destroy (fallback_plan);
 439       goto retry;
 440     }
 441   }
 442
 443   arabic_fallback_plan_shape (fallback_plan, font, buffer);
 444   return true;
 445 }
 446
 447 /*
 448  * Stretch feature: "stch".
 449  * See example here:
 450  * https://docs.microsoft.com/en-us/typography/script-development/syriac
 451  * We implement this in a generic way, such that the Arabic subtending
 452  * marks can use it as well.
 453  */
 454
 455 static bool
 456 record_stch (const hb_ot_shape_plan_t *plan,
 457              hb_font_t *font HB_UNUSED,
 458              hb_buffer_t *buffer)
 459 {
 460   const arabic_shape_plan_t *arabic_plan = (const arabic_shape_plan_t *) plan->data;
 461   if (!arabic_plan->has_stch)
 462     return false;
 463
 464   /* 'stch' feature was just applied.  Look for anything that multiplied,
 465    * and record it for stch treatment later.  Note that rtlm, frac, etc
 466    * are applied before stch, but we assume that they didn't result in
 467    * anything multiplying into 5 pieces, so it's safe-ish... */
 468
 469   unsigned int count = buffer->len;
 470   hb_glyph_info_t *info = buffer->info;
 471   for (unsigned int i = 0; i < count; i++)
 472     if (unlikely (_hb_glyph_info_multiplied (&info[i])))
 473     {
 474       unsigned int comp = _hb_glyph_info_get_lig_comp (&info[i]);
 475       info[i].arabic_shaping_action() = comp % 2 ? STCH_REPEATING : STCH_FIXED;
 476       buffer->scratch_flags |= HB_BUFFER_SCRATCH_FLAG_ARABIC_HAS_STCH;
 477     }
 478   return false;
 479 }
 480
 481 static void
 482 apply_stch (const hb_ot_shape_plan_t *plan HB_UNUSED,
 483             hb_buffer_t              *buffer,
 484             hb_font_t                *font)
 485 {
 486   if (likely (!(buffer->scratch_flags & HB_BUFFER_SCRATCH_FLAG_ARABIC_HAS_STCH)))
 487     return;
 488
 489   bool rtl = buffer->props.direction == HB_DIRECTION_RTL;
 490
 491   if (!rtl)
 492     buffer->reverse ();
 493
 494   /* We do a two pass implementation:
 495    * First pass calculates the exact number of extra glyphs we need,
 496    * We then enlarge buffer to have that much room,
 497    * Second pass applies the stretch, copying things to the end of buffer.
 498    */
 499
 500   int sign = font->x_scale < 0 ? -1 : +1;
 501   unsigned int extra_glyphs_needed = 0; // Set during MEASURE, used during CUT
 502   enum { MEASURE, CUT } /* step_t */;
 503
 504   for (unsigned int step = MEASURE; step <= CUT; step = step + 1)
 505   {
 506     unsigned int count = buffer->len;
 507     hb_glyph_info_t *info = buffer->info;
 508     hb_glyph_position_t *pos = buffer->pos;
 509     unsigned int new_len = count + extra_glyphs_needed; // write head during CUT
 510     unsigned int j = new_len;
 511     for (unsigned int i = count; i; i--)
 512     {
 513       if (!hb_in_range<uint8_t> (info[i - 1].arabic_shaping_action(), STCH_FIXED, STCH_REPEATING))
 514       {
 515         if (step == CUT)
 516         {
 517           --j;
 518           info[j] = info[i - 1];
 519           pos[j] = pos[i - 1];
 520         }
 521         continue;
 522       }
 523
 524       /* Yay, justification! */
 525
 526       hb_position_t w_total = 0; // Total to be filled
 527       hb_position_t w_fixed = 0; // Sum of fixed tiles
 528       hb_position_t w_repeating = 0; // Sum of repeating tiles
 529       int n_fixed = 0;
 530       int n_repeating = 0;
 531
 532       unsigned int end = i;
 533       while (i &&
 534              hb_in_range<uint8_t> (info[i - 1].arabic_shaping_action(), STCH_FIXED, STCH_REPEATING))
 535       {
 536         i--;
 537         hb_position_t width = font->get_glyph_h_advance (info[i].codepoint);
 538         if (info[i].arabic_shaping_action() == STCH_FIXED)
 539         {
 540           w_fixed += width;
 541           n_fixed++;
 542         }
 543         else
 544         {
 545           w_repeating += width;
 546           n_repeating++;
 547         }
 548       }
 549       unsigned int start = i;
 550       unsigned int context = i;
 551       while (context &&
 552              !hb_in_range<uint8_t> (info[context - 1].arabic_shaping_action(), STCH_FIXED, STCH_REPEATING) &&
 553              (_hb_glyph_info_is_default_ignorable (&info[context - 1]) ||
 554               HB_ARABIC_GENERAL_CATEGORY_IS_WORD (_hb_glyph_info_get_general_category (&info[context - 1]))))
 555       {
 556         context--;
 557         w_total += pos[context].x_advance;
 558       }
 559       i++; // Don't touch i again.
 560
 561       DEBUG_MSG (ARABIC, nullptr, "%s stretch at (%u,%u,%u)",
 562                  step == MEASURE ? "measuring" : "cutting", context, start, end);
 563       DEBUG_MSG (ARABIC, nullptr, "rest of word:    count=%u width %d", start - context, w_total);
 564       DEBUG_MSG (ARABIC, nullptr, "fixed tiles:     count=%d width=%d", n_fixed, w_fixed);
 565       DEBUG_MSG (ARABIC, nullptr, "repeating tiles: count=%d width=%d", n_repeating, w_repeating);
 566
 567       /* Number of additional times to repeat each repeating tile. */
 568       int n_copies = 0;
 569
 570       hb_position_t w_remaining = w_total - w_fixed;
 571       if (sign * w_remaining > sign * w_repeating && sign * w_repeating > 0)
 572         n_copies = (sign * w_remaining) / (sign * w_repeating) - 1;
 573
 574       /* See if we can improve the fit by adding an extra repeat and squeezing them together a bit. */
 575       hb_position_t extra_repeat_overlap = 0;
 576       hb_position_t shortfall = sign * w_remaining - sign * w_repeating * (n_copies + 1);
 577       if (shortfall > 0 && n_repeating > 0)
 578       {
 579         ++n_copies;
 580         hb_position_t excess = (n_copies + 1) * sign * w_repeating - sign * w_remaining;
 581         if (excess > 0)
 582         {
 583           extra_repeat_overlap = excess / (n_copies * n_repeating);
 584           w_remaining = 0;
 585         }
 586       }
 587
 588       if (step == MEASURE)
 589       {
 590         extra_glyphs_needed += n_copies * n_repeating;
 591         DEBUG_MSG (ARABIC, nullptr, "will add extra %d copies of repeating tiles", n_copies);
 592       }
 593       else
 594       {
 595         buffer->unsafe_to_break (context, end);
 596         hb_position_t x_offset = w_remaining / 2;
 597         for (unsigned int k = end; k > start; k--)
 598         {
 599           hb_position_t width = font->get_glyph_h_advance (info[k - 1].codepoint);
 600
 601           unsigned int repeat = 1;
 602           if (info[k - 1].arabic_shaping_action() == STCH_REPEATING)
 603             repeat += n_copies;
 604
 605           DEBUG_MSG (ARABIC, nullptr, "appending %u copies of glyph %u; j=%u",
 606                      repeat, info[k - 1].codepoint, j);
 607           pos[k - 1].x_advance = 0;
 608           for (unsigned int n = 0; n < repeat; n++)
 609           {
 610             if (rtl)
 611             {
 612               x_offset -= width;
 613               if (n > 0)
 614                 x_offset += extra_repeat_overlap;
 615             }
 616             pos[k - 1].x_offset = x_offset;
 617             /* Append copy. */
 618             --j;
 619             info[j] = info[k - 1];
 620             pos[j] = pos[k - 1];
 621
 622             if (!rtl)
 623             {
 624               x_offset += width;
 625               if (n > 0)
 626                 x_offset -= extra_repeat_overlap;
 627             }
 628           }
 629         }
 630       }
 631     }
 632
 633     if (step == MEASURE)
 634     {
 635       if (unlikely (!buffer->ensure (count + extra_glyphs_needed)))
 636         break;
 637     }
 638     else
 639     {
 640       assert (j == 0);
 641       buffer->len = new_len;
 642     }
 643   }
 644
 645   if (!rtl)
 646     buffer->reverse ();
 647 }
 648
 649
 650 static void
 651 postprocess_glyphs_arabic (const hb_ot_shape_plan_t *plan,
 652                            hb_buffer_t              *buffer,
 653                            hb_font_t                *font)
 654 {
 655   apply_stch (plan, buffer, font);
 656 }
 657
 658 /* https://www.unicode.org/reports/tr53/ */
 659
 660 static hb_codepoint_t
 661 modifier_combining_marks[] =
 662 {
 663   0x0654u, /* ARABIC HAMZA ABOVE */
 664   0x0655u, /* ARABIC HAMZA BELOW */
 665   0x0658u, /* ARABIC MARK NOON GHUNNA */
 666   0x06DCu, /* ARABIC SMALL HIGH SEEN */
 667   0x06E3u, /* ARABIC SMALL LOW SEEN */
 668   0x06E7u, /* ARABIC SMALL HIGH YEH */
 669   0x06E8u, /* ARABIC SMALL HIGH NOON */
 670   0x08CAu, /* ARABIC SMALL HIGH FARSI YEH */
 671   0x08CBu, /* ARABIC SMALL HIGH YEH BARREE WITH TWO DOTS BELOW */
 672   0x08CDu, /* ARABIC SMALL HIGH ZAH */
 673   0x08CEu, /* ARABIC LARGE ROUND DOT ABOVE */
 674   0x08CFu, /* ARABIC LARGE ROUND DOT BELOW */
 675   0x08D3u, /* ARABIC SMALL LOW WAW */
 676   0x08F3u, /* ARABIC SMALL HIGH WAW */
 677 };
 678
 679 static inline bool
 680 info_is_mcm (const hb_glyph_info_t &info)
 681 {
 682   hb_codepoint_t u = info.codepoint;
 683   for (unsigned int i = 0; i < ARRAY_LENGTH (modifier_combining_marks); i++)
 684     if (u == modifier_combining_marks[i])
 685       return true;
 686   return false;
 687 }
 688
 689 static void
 690 reorder_marks_arabic (const hb_ot_shape_plan_t *plan HB_UNUSED,
 691                       hb_buffer_t              *buffer,
 692                       unsigned int              start,
 693                       unsigned int              end)
 694 {
 695   hb_glyph_info_t *info = buffer->info;
 696
 697   DEBUG_MSG (ARABIC, buffer, "Reordering marks from %u to %u", start, end);
 698
 699   unsigned int i = start;
 700   for (unsigned int cc = 220; cc <= 230; cc += 10)
 701   {
 702     DEBUG_MSG (ARABIC, buffer, "Looking for %u's starting at %u", cc, i);
 703     while (i < end && info_cc(info[i]) < cc)
 704       i++;
 705     DEBUG_MSG (ARABIC, buffer, "Looking for %u's stopped at %u", cc, i);
 706
 707     if (i == end)
 708       break;
 709
 710     if (info_cc(info[i]) > cc)
 711       continue;
 712
 713     unsigned int j = i;
 714     while (j < end && info_cc(info[j]) == cc && info_is_mcm (info[j]))
 715       j++;
 716
 717     if (i == j)
 718       continue;
 719
 720     DEBUG_MSG (ARABIC, buffer, "Found %u's from %u to %u", cc, i, j);
 721
 722     /* Shift it! */
 723     DEBUG_MSG (ARABIC, buffer, "Shifting %u's: %u %u", cc, i, j);
 724     hb_glyph_info_t temp[HB_OT_SHAPE_MAX_COMBINING_MARKS];
 725     assert (j - i <= ARRAY_LENGTH (temp));
 726     buffer->merge_clusters (start, j);
 727     memmove (temp, &info[i], (j - i) * sizeof (hb_glyph_info_t));
 728     memmove (&info[start + j - i], &info[start], (i - start) * sizeof (hb_glyph_info_t));
 729     memmove (&info[start], temp, (j - i) * sizeof (hb_glyph_info_t));
 730
 731     /* Renumber CC such that the reordered sequence is still sorted.
 732      * 22 and 26 are chosen because they are smaller than all Arabic categories,
 733      * and are folded back to 220/230 respectively during fallback mark positioning.
 734      *
 735      * We do this because the CGJ-handling logic in the normalizer relies on
 736      * mark sequences having an increasing order even after this reordering.
 737      * https://github.com/harfbuzz/harfbuzz/issues/554
 738      * This, however, does break some obscure sequences, where the normalizer
 739      * might compose a sequence that it should not.  For example, in the seequence
 740      * ALEF, HAMZAH, MADDAH, we should NOT try to compose ALEF+MADDAH, but with this
 741      * renumbering, we will.
 742      */
 743     unsigned int new_start = start + j - i;
 744     unsigned int new_cc = cc == 220 ? HB_MODIFIED_COMBINING_CLASS_CCC22 : HB_MODIFIED_COMBINING_CLASS_CCC26;
 745     while (start < new_start)
 746     {
 747       _hb_glyph_info_set_modified_combining_class (&info[start], new_cc);
 748       start++;
 749     }
 750
 751     i = j;
 752   }
 753 }
 754
 755 const hb_ot_shaper_t _hb_ot_shaper_arabic =
 756 {
 757   collect_features_arabic,
 758   nullptr, /* override_features */
 759   data_create_arabic,
 760   data_destroy_arabic,
 761   nullptr, /* preprocess_text */
 762   postprocess_glyphs_arabic,
 763   nullptr, /* decompose */
 764   nullptr, /* compose */
 765   setup_masks_arabic,
 766   reorder_marks_arabic,
 767   HB_TAG_NONE, /* gpos_tag */
 768   HB_OT_SHAPE_NORMALIZATION_MODE_DEFAULT,
 769   HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_LATE,
 770   true, /* fallback_position */
 771 };
 772
 773
 774 #endif