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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.hh"
28 #include "hb-ot-shape-complex-arabic.hh"
29 #include "hb-ot-shape.hh"
30 
31 
32 /* buffer var allocations */
33 #define arabic_shaping_action() complex_var_u8_0() /* arabic shaping action */
34 
35 #define HB_BUFFER_SCRATCH_FLAG_ARABIC_HAS_STCH HB_BUFFER_SCRATCH_FLAG_COMPLEX0
36 
37 /* See:
38  * https://github.com/harfbuzz/harfbuzz/commit/6e6f82b6f3dde0fc6c3c7d991d9ec6cfff57823d#commitcomment-14248516 */
39 #define HB_ARABIC_GENERAL_CATEGORY_IS_WORD(gen_cat) \
40 	(FLAG_UNSAFE (gen_cat) & \
41 	 (FLAG (HB_UNICODE_GENERAL_CATEGORY_UNASSIGNED) | \
42 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_PRIVATE_USE) | \
43 	  /*FLAG (HB_UNICODE_GENERAL_CATEGORY_LOWERCASE_LETTER) |*/ \
44 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_MODIFIER_LETTER) | \
45 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_OTHER_LETTER) | \
46 	  /*FLAG (HB_UNICODE_GENERAL_CATEGORY_TITLECASE_LETTER) |*/ \
47 	  /*FLAG (HB_UNICODE_GENERAL_CATEGORY_UPPERCASE_LETTER) |*/ \
48 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_SPACING_MARK) | \
49 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_ENCLOSING_MARK) | \
50 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK) | \
51 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_DECIMAL_NUMBER) | \
52 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_LETTER_NUMBER) | \
53 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_OTHER_NUMBER) | \
54 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_CURRENCY_SYMBOL) | \
55 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_MODIFIER_SYMBOL) | \
56 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_MATH_SYMBOL) | \
57 	  FLAG (HB_UNICODE_GENERAL_CATEGORY_OTHER_SYMBOL)))
58 
59 
60 /*
61  * Joining types:
62  */
63 
64 /*
65  * Bits used in the joining tables
66  */
67 enum hb_arabic_joining_type_t {
68   JOINING_TYPE_U		= 0,
69   JOINING_TYPE_L		= 1,
70   JOINING_TYPE_R		= 2,
71   JOINING_TYPE_D		= 3,
72   JOINING_TYPE_C		= JOINING_TYPE_D,
73   JOINING_GROUP_ALAPH		= 4,
74   JOINING_GROUP_DALATH_RISH	= 5,
75   NUM_STATE_MACHINE_COLS	= 6,
76 
77   JOINING_TYPE_T = 7,
78   JOINING_TYPE_X = 8  /* means: use general-category to choose between U or T. */
79 };
80 
81 #include "hb-ot-shape-complex-arabic-table.hh"
82 
get_joining_type(hb_codepoint_t u,hb_unicode_general_category_t gen_cat)83 static unsigned int get_joining_type (hb_codepoint_t u, hb_unicode_general_category_t gen_cat)
84 {
85   unsigned int j_type = joining_type(u);
86   if (likely (j_type != JOINING_TYPE_X))
87     return j_type;
88 
89   return (FLAG_UNSAFE(gen_cat) &
90 	  (FLAG(HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK) |
91 	   FLAG(HB_UNICODE_GENERAL_CATEGORY_ENCLOSING_MARK) |
92 	   FLAG(HB_UNICODE_GENERAL_CATEGORY_FORMAT))
93 	 ) ?  JOINING_TYPE_T : JOINING_TYPE_U;
94 }
95 
96 #define FEATURE_IS_SYRIAC(tag) hb_in_range<unsigned char> ((unsigned char) (tag), '2', '3')
97 
98 static const hb_tag_t arabic_features[] =
99 {
100   HB_TAG('i','s','o','l'),
101   HB_TAG('f','i','n','a'),
102   HB_TAG('f','i','n','2'),
103   HB_TAG('f','i','n','3'),
104   HB_TAG('m','e','d','i'),
105   HB_TAG('m','e','d','2'),
106   HB_TAG('i','n','i','t'),
107   HB_TAG_NONE
108 };
109 
110 
111 /* Same order as the feature array */
112 enum arabic_action_t {
113   ISOL,
114   FINA,
115   FIN2,
116   FIN3,
117   MEDI,
118   MED2,
119   INIT,
120 
121   NONE,
122 
123   ARABIC_NUM_FEATURES = NONE,
124 
125   /* We abuse the same byte for other things... */
126   STCH_FIXED,
127   STCH_REPEATING,
128 };
129 
130 static const struct arabic_state_table_entry {
131 	uint8_t prev_action;
132 	uint8_t curr_action;
133 	uint16_t next_state;
134 } arabic_state_table[][NUM_STATE_MACHINE_COLS] =
135 {
136   /*   jt_U,          jt_L,          jt_R,          jt_D,          jg_ALAPH,      jg_DALATH_RISH */
137 
138   /* State 0: prev was U, not willing to join. */
139   { {NONE,NONE,0}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,6}, },
140 
141   /* State 1: prev was R or ISOL/ALAPH, not willing to join. */
142   { {NONE,NONE,0}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,2}, {NONE,FIN2,5}, {NONE,ISOL,6}, },
143 
144   /* State 2: prev was D/L in ISOL form, willing to join. */
145   { {NONE,NONE,0}, {NONE,ISOL,2}, {INIT,FINA,1}, {INIT,FINA,3}, {INIT,FINA,4}, {INIT,FINA,6}, },
146 
147   /* State 3: prev was D in FINA form, willing to join. */
148   { {NONE,NONE,0}, {NONE,ISOL,2}, {MEDI,FINA,1}, {MEDI,FINA,3}, {MEDI,FINA,4}, {MEDI,FINA,6}, },
149 
150   /* State 4: prev was FINA ALAPH, not willing to join. */
151   { {NONE,NONE,0}, {NONE,ISOL,2}, {MED2,ISOL,1}, {MED2,ISOL,2}, {MED2,FIN2,5}, {MED2,ISOL,6}, },
152 
153   /* State 5: prev was FIN2/FIN3 ALAPH, not willing to join. */
154   { {NONE,NONE,0}, {NONE,ISOL,2}, {ISOL,ISOL,1}, {ISOL,ISOL,2}, {ISOL,FIN2,5}, {ISOL,ISOL,6}, },
155 
156   /* State 6: prev was DALATH/RISH, not willing to join. */
157   { {NONE,NONE,0}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,2}, {NONE,FIN3,5}, {NONE,ISOL,6}, }
158 };
159 
160 
161 static void
162 arabic_fallback_shape (const hb_ot_shape_plan_t *plan,
163 		       hb_font_t *font,
164 		       hb_buffer_t *buffer);
165 
166 static void
167 record_stch (const hb_ot_shape_plan_t *plan,
168 	     hb_font_t *font,
169 	     hb_buffer_t *buffer);
170 
171 static void
collect_features_arabic(hb_ot_shape_planner_t * plan)172 collect_features_arabic (hb_ot_shape_planner_t *plan)
173 {
174   hb_ot_map_builder_t *map = &plan->map;
175 
176   /* We apply features according to the Arabic spec, with pauses
177    * in between most.
178    *
179    * The pause between init/medi/... and rlig is required.  See eg:
180    * https://bugzilla.mozilla.org/show_bug.cgi?id=644184
181    *
182    * The pauses between init/medi/... themselves are not necessarily
183    * needed as only one of those features is applied to any character.
184    * The only difference it makes is when fonts have contextual
185    * substitutions.  We now follow the order of the spec, which makes
186    * for better experience if that's what Uniscribe is doing.
187    *
188    * At least for Arabic, looks like Uniscribe has a pause between
189    * rlig and calt.  Otherwise the IranNastaliq's ALLAH ligature won't
190    * work.  However, testing shows that rlig and calt are applied
191    * together for Mongolian in Uniscribe.  As such, we only add a
192    * pause for Arabic, not other scripts.
193    *
194    * A pause after calt is required to make KFGQPC Uthmanic Script HAFS
195    * work correctly.  See https://github.com/harfbuzz/harfbuzz/issues/505
196    */
197 
198 
199   map->enable_feature (HB_TAG('s','t','c','h'));
200   map->add_gsub_pause (record_stch);
201 
202   map->enable_feature (HB_TAG('c','c','m','p'));
203   map->enable_feature (HB_TAG('l','o','c','l'));
204 
205   map->add_gsub_pause (nullptr);
206 
207   for (unsigned int i = 0; i < ARABIC_NUM_FEATURES; i++)
208   {
209     bool has_fallback = plan->props.script == HB_SCRIPT_ARABIC && !FEATURE_IS_SYRIAC (arabic_features[i]);
210     map->add_feature (arabic_features[i], has_fallback ? F_HAS_FALLBACK : F_NONE);
211     map->add_gsub_pause (nullptr);
212   }
213 
214   /* Normally, Unicode says a ZWNJ means "don't ligate".  In Arabic script
215    * however, it says a ZWJ should also mean "don't ligate".  So we run
216    * the main ligating features as MANUAL_ZWJ. */
217 
218   map->enable_feature (HB_TAG('r','l','i','g'), F_MANUAL_ZWJ | F_HAS_FALLBACK);
219 
220   if (plan->props.script == HB_SCRIPT_ARABIC)
221     map->add_gsub_pause (arabic_fallback_shape);
222 
223   /* No pause after rclt.  See 98460779bae19e4d64d29461ff154b3527bf8420. */
224   map->enable_feature (HB_TAG('r','c','l','t'), F_MANUAL_ZWJ);
225   map->enable_feature (HB_TAG('c','a','l','t'), F_MANUAL_ZWJ);
226   map->add_gsub_pause (nullptr);
227 
228   /* And undo here. */
229 
230   /* The spec includes 'cswh'.  Earlier versions of Windows
231    * used to enable this by default, but testing suggests
232    * that Windows 8 and later do not enable it by default,
233    * and spec now says 'Off by default'.
234    * We disabled this in ae23c24c32.
235    * Note that IranNastaliq uses this feature extensively
236    * to fixup broken glyph sequences.  Oh well...
237    * Test case: U+0643,U+0640,U+0631. */
238   //map->enable_feature (HB_TAG('c','s','w','h'));
239   map->enable_feature (HB_TAG('m','s','e','t'));
240 }
241 
242 #include "hb-ot-shape-complex-arabic-fallback.hh"
243 
244 struct arabic_shape_plan_t
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   hb_atomic_ptr_t<arabic_fallback_plan_t> fallback_plan;
253 
254   unsigned int do_fallback : 1;
255   unsigned int has_stch : 1;
256 };
257 
258 void *
data_create_arabic(const hb_ot_shape_plan_t * plan)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 nullptr;
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
data_destroy_arabic(void * data)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
arabic_joining(hb_buffer_t * buffer)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     {
320       info[prev].arabic_shaping_action() = entry->prev_action;
321       buffer->unsafe_to_break (prev, i + 1);
322     }
323 
324     info[i].arabic_shaping_action() = entry->curr_action;
325 
326     prev = i;
327     state = entry->next_state;
328   }
329 
330   for (unsigned int i = 0; i < buffer->context_len[1]; i++)
331   {
332     unsigned int this_type = get_joining_type (buffer->context[1][i], buffer->unicode->general_category (buffer->context[1][i]));
333 
334     if (unlikely (this_type == JOINING_TYPE_T))
335       continue;
336 
337     const arabic_state_table_entry *entry = &arabic_state_table[state][this_type];
338     if (entry->prev_action != NONE && prev != (unsigned int) -1)
339       info[prev].arabic_shaping_action() = entry->prev_action;
340     break;
341   }
342 }
343 
344 static void
mongolian_variation_selectors(hb_buffer_t * buffer)345 mongolian_variation_selectors (hb_buffer_t *buffer)
346 {
347   /* Copy arabic_shaping_action() from base to Mongolian variation selectors. */
348   unsigned int count = buffer->len;
349   hb_glyph_info_t *info = buffer->info;
350   for (unsigned int i = 1; i < count; i++)
351     if (unlikely (hb_in_range<hb_codepoint_t> (info[i].codepoint, 0x180Bu, 0x180Du)))
352       info[i].arabic_shaping_action() = info[i - 1].arabic_shaping_action();
353 }
354 
355 void
setup_masks_arabic_plan(const arabic_shape_plan_t * arabic_plan,hb_buffer_t * buffer,hb_script_t script)356 setup_masks_arabic_plan (const arabic_shape_plan_t *arabic_plan,
357 			 hb_buffer_t               *buffer,
358 			 hb_script_t                script)
359 {
360   HB_BUFFER_ALLOCATE_VAR (buffer, arabic_shaping_action);
361 
362   arabic_joining (buffer);
363   if (script == HB_SCRIPT_MONGOLIAN)
364     mongolian_variation_selectors (buffer);
365 
366   unsigned int count = buffer->len;
367   hb_glyph_info_t *info = buffer->info;
368   for (unsigned int i = 0; i < count; i++)
369     info[i].mask |= arabic_plan->mask_array[info[i].arabic_shaping_action()];
370 }
371 
372 static void
setup_masks_arabic(const hb_ot_shape_plan_t * plan,hb_buffer_t * buffer,hb_font_t * font HB_UNUSED)373 setup_masks_arabic (const hb_ot_shape_plan_t *plan,
374 		    hb_buffer_t              *buffer,
375 		    hb_font_t                *font HB_UNUSED)
376 {
377   const arabic_shape_plan_t *arabic_plan = (const arabic_shape_plan_t *) plan->data;
378   setup_masks_arabic_plan (arabic_plan, buffer, plan->props.script);
379 }
380 
381 static void
arabic_fallback_shape(const hb_ot_shape_plan_t * plan,hb_font_t * font,hb_buffer_t * buffer)382 arabic_fallback_shape (const hb_ot_shape_plan_t *plan,
383 		       hb_font_t *font,
384 		       hb_buffer_t *buffer)
385 {
386   const arabic_shape_plan_t *arabic_plan = (const arabic_shape_plan_t *) plan->data;
387 
388   if (!arabic_plan->do_fallback)
389     return;
390 
391 retry:
392   arabic_fallback_plan_t *fallback_plan = arabic_plan->fallback_plan;
393   if (unlikely (!fallback_plan))
394   {
395     /* This sucks.  We need a font to build the fallback plan... */
396     fallback_plan = arabic_fallback_plan_create (plan, font);
397     if (unlikely (!arabic_plan->fallback_plan.cmpexch (nullptr, fallback_plan)))
398     {
399       arabic_fallback_plan_destroy (fallback_plan);
400       goto retry;
401     }
402   }
403 
404   arabic_fallback_plan_shape (fallback_plan, font, buffer);
405 }
406 
407 /*
408  * Stretch feature: "stch".
409  * See example here:
410  * https://docs.microsoft.com/en-us/typography/script-development/syriac
411  * We implement this in a generic way, such that the Arabic subtending
412  * marks can use it as well.
413  */
414 
415 static void
record_stch(const hb_ot_shape_plan_t * plan,hb_font_t * font HB_UNUSED,hb_buffer_t * buffer)416 record_stch (const hb_ot_shape_plan_t *plan,
417 	     hb_font_t *font HB_UNUSED,
418 	     hb_buffer_t *buffer)
419 {
420   const arabic_shape_plan_t *arabic_plan = (const arabic_shape_plan_t *) plan->data;
421   if (!arabic_plan->has_stch)
422     return;
423 
424   /* 'stch' feature was just applied.  Look for anything that multiplied,
425    * and record it for stch treatment later.  Note that rtlm, frac, etc
426    * are applied before stch, but we assume that they didn't result in
427    * anything multiplying into 5 pieces, so it's safe-ish... */
428 
429   unsigned int count = buffer->len;
430   hb_glyph_info_t *info = buffer->info;
431   for (unsigned int i = 0; i < count; i++)
432     if (unlikely (_hb_glyph_info_multiplied (&info[i])))
433     {
434       unsigned int comp = _hb_glyph_info_get_lig_comp (&info[i]);
435       info[i].arabic_shaping_action() = comp % 2 ? STCH_REPEATING : STCH_FIXED;
436       buffer->scratch_flags |= HB_BUFFER_SCRATCH_FLAG_ARABIC_HAS_STCH;
437     }
438 }
439 
440 static void
apply_stch(const hb_ot_shape_plan_t * plan HB_UNUSED,hb_buffer_t * buffer,hb_font_t * font)441 apply_stch (const hb_ot_shape_plan_t *plan HB_UNUSED,
442 	    hb_buffer_t              *buffer,
443 	    hb_font_t                *font)
444 {
445   if (likely (!(buffer->scratch_flags & HB_BUFFER_SCRATCH_FLAG_ARABIC_HAS_STCH)))
446     return;
447 
448   /* The Arabic shaper currently always processes in RTL mode, so we should
449    * stretch / position the stretched pieces to the left / preceding glyphs. */
450 
451   /* We do a two pass implementation:
452    * First pass calculates the exact number of extra glyphs we need,
453    * We then enlarge buffer to have that much room,
454    * Second pass applies the stretch, copying things to the end of buffer.
455    */
456 
457   int sign = font->x_scale < 0 ? -1 : +1;
458   unsigned int extra_glyphs_needed = 0; // Set during MEASURE, used during CUT
459   enum { MEASURE, CUT } /* step_t */;
460 
461   for (unsigned int step = MEASURE; step <= CUT; step = step + 1)
462   {
463     unsigned int count = buffer->len;
464     hb_glyph_info_t *info = buffer->info;
465     hb_glyph_position_t *pos = buffer->pos;
466     unsigned int new_len = count + extra_glyphs_needed; // write head during CUT
467     unsigned int j = new_len;
468     for (unsigned int i = count; i; i--)
469     {
470       if (!hb_in_range<unsigned> (info[i - 1].arabic_shaping_action(), STCH_FIXED, STCH_REPEATING))
471       {
472         if (step == CUT)
473 	{
474 	  --j;
475 	  info[j] = info[i - 1];
476 	  pos[j] = pos[i - 1];
477 	}
478         continue;
479       }
480 
481       /* Yay, justification! */
482 
483       hb_position_t w_total = 0; // Total to be filled
484       hb_position_t w_fixed = 0; // Sum of fixed tiles
485       hb_position_t w_repeating = 0; // Sum of repeating tiles
486       int n_fixed = 0;
487       int n_repeating = 0;
488 
489       unsigned int end = i;
490       while (i &&
491 	     hb_in_range<unsigned> (info[i - 1].arabic_shaping_action(), STCH_FIXED, STCH_REPEATING))
492       {
493 	i--;
494 	hb_position_t width = font->get_glyph_h_advance (info[i].codepoint);
495 	if (info[i].arabic_shaping_action() == STCH_FIXED)
496 	{
497 	  w_fixed += width;
498 	  n_fixed++;
499 	}
500 	else
501 	{
502 	  w_repeating += width;
503 	  n_repeating++;
504 	}
505       }
506       unsigned int start = i;
507       unsigned int context = i;
508       while (context &&
509 	     !hb_in_range<unsigned> (info[context - 1].arabic_shaping_action(), STCH_FIXED, STCH_REPEATING) &&
510 	     (_hb_glyph_info_is_default_ignorable (&info[context - 1]) ||
511 	      HB_ARABIC_GENERAL_CATEGORY_IS_WORD (_hb_glyph_info_get_general_category (&info[context - 1]))))
512       {
513 	context--;
514 	w_total += pos[context].x_advance;
515       }
516       i++; // Don't touch i again.
517 
518       DEBUG_MSG (ARABIC, nullptr, "%s stretch at (%d,%d,%d)",
519 		 step == MEASURE ? "measuring" : "cutting", context, start, end);
520       DEBUG_MSG (ARABIC, nullptr, "rest of word:    count=%d width %d", start - context, w_total);
521       DEBUG_MSG (ARABIC, nullptr, "fixed tiles:     count=%d width=%d", n_fixed, w_fixed);
522       DEBUG_MSG (ARABIC, nullptr, "repeating tiles: count=%d width=%d", n_repeating, w_repeating);
523 
524       /* Number of additional times to repeat each repeating tile. */
525       int n_copies = 0;
526 
527       hb_position_t w_remaining = w_total - w_fixed;
528       if (sign * w_remaining > sign * w_repeating && sign * w_repeating > 0)
529 	n_copies = (sign * w_remaining) / (sign * w_repeating) - 1;
530 
531       /* See if we can improve the fit by adding an extra repeat and squeezing them together a bit. */
532       hb_position_t extra_repeat_overlap = 0;
533       hb_position_t shortfall = sign * w_remaining - sign * w_repeating * (n_copies + 1);
534       if (shortfall > 0 && n_repeating > 0)
535       {
536         ++n_copies;
537         hb_position_t excess = (n_copies + 1) * sign * w_repeating - sign * w_remaining;
538         if (excess > 0)
539           extra_repeat_overlap = excess / (n_copies * n_repeating);
540       }
541 
542       if (step == MEASURE)
543       {
544 	extra_glyphs_needed += n_copies * n_repeating;
545 	DEBUG_MSG (ARABIC, nullptr, "will add extra %d copies of repeating tiles", n_copies);
546       }
547       else
548       {
549 	buffer->unsafe_to_break (context, end);
550 	hb_position_t x_offset = 0;
551 	for (unsigned int k = end; k > start; k--)
552 	{
553 	  hb_position_t width = font->get_glyph_h_advance (info[k - 1].codepoint);
554 
555 	  unsigned int repeat = 1;
556 	  if (info[k - 1].arabic_shaping_action() == STCH_REPEATING)
557 	    repeat += n_copies;
558 
559 	  DEBUG_MSG (ARABIC, nullptr, "appending %d copies of glyph %d; j=%d",
560 		     repeat, info[k - 1].codepoint, j);
561 	  for (unsigned int n = 0; n < repeat; n++)
562 	  {
563 	    x_offset -= width;
564 	    if (n > 0)
565 	      x_offset += extra_repeat_overlap;
566 	    pos[k - 1].x_offset = x_offset;
567 	    /* Append copy. */
568 	    --j;
569 	    info[j] = info[k - 1];
570 	    pos[j] = pos[k - 1];
571 	  }
572 	}
573       }
574     }
575 
576     if (step == MEASURE)
577     {
578       if (unlikely (!buffer->ensure (count + extra_glyphs_needed)))
579         break;
580     }
581     else
582     {
583       assert (j == 0);
584       buffer->len = new_len;
585     }
586   }
587 }
588 
589 
590 static void
postprocess_glyphs_arabic(const hb_ot_shape_plan_t * plan,hb_buffer_t * buffer,hb_font_t * font)591 postprocess_glyphs_arabic (const hb_ot_shape_plan_t *plan,
592 			   hb_buffer_t              *buffer,
593 			   hb_font_t                *font)
594 {
595   apply_stch (plan, buffer, font);
596 
597   HB_BUFFER_DEALLOCATE_VAR (buffer, arabic_shaping_action);
598 }
599 
600 /* http://www.unicode.org/reports/tr53/ */
601 
602 static hb_codepoint_t
603 modifier_combining_marks[] =
604 {
605   0x0654u, /* ARABIC HAMZA ABOVE */
606   0x0655u, /* ARABIC HAMZA BELOW */
607   0x0658u, /* ARABIC MARK NOON GHUNNA */
608   0x06DCu, /* ARABIC SMALL HIGH SEEN */
609   0x06E3u, /* ARABIC SMALL LOW SEEN */
610   0x06E7u, /* ARABIC SMALL HIGH YEH */
611   0x06E8u, /* ARABIC SMALL HIGH NOON */
612   0x08D3u, /* ARABIC SMALL LOW WAW */
613   0x08F3u, /* ARABIC SMALL HIGH WAW */
614 };
615 
616 static inline bool
info_is_mcm(const hb_glyph_info_t & info)617 info_is_mcm (const hb_glyph_info_t &info)
618 {
619   hb_codepoint_t u = info.codepoint;
620   for (unsigned int i = 0; i < ARRAY_LENGTH (modifier_combining_marks); i++)
621     if (u == modifier_combining_marks[i])
622       return true;
623   return false;
624 }
625 
626 static void
reorder_marks_arabic(const hb_ot_shape_plan_t * plan HB_UNUSED,hb_buffer_t * buffer,unsigned int start,unsigned int end)627 reorder_marks_arabic (const hb_ot_shape_plan_t *plan HB_UNUSED,
628 		      hb_buffer_t              *buffer,
629 		      unsigned int              start,
630 		      unsigned int              end)
631 {
632   hb_glyph_info_t *info = buffer->info;
633 
634   DEBUG_MSG (ARABIC, buffer, "Reordering marks from %d to %d", start, end);
635 
636   unsigned int i = start;
637   for (unsigned int cc = 220; cc <= 230; cc += 10)
638   {
639     DEBUG_MSG (ARABIC, buffer, "Looking for %d's starting at %d", cc, i);
640     while (i < end && info_cc(info[i]) < cc)
641       i++;
642     DEBUG_MSG (ARABIC, buffer, "Looking for %d's stopped at %d", cc, i);
643 
644     if (i == end)
645       break;
646 
647     if (info_cc(info[i]) > cc)
648       continue;
649 
650     unsigned int j = i;
651     while (j < end && info_cc(info[j]) == cc && info_is_mcm (info[j]))
652       j++;
653 
654     if (i == j)
655       continue;
656 
657     DEBUG_MSG (ARABIC, buffer, "Found %d's from %d to %d", cc, i, j);
658 
659     /* Shift it! */
660     DEBUG_MSG (ARABIC, buffer, "Shifting %d's: %d %d", cc, i, j);
661     hb_glyph_info_t temp[HB_OT_SHAPE_COMPLEX_MAX_COMBINING_MARKS];
662     assert (j - i <= ARRAY_LENGTH (temp));
663     buffer->merge_clusters (start, j);
664     memmove (temp, &info[i], (j - i) * sizeof (hb_glyph_info_t));
665     memmove (&info[start + j - i], &info[start], (i - start) * sizeof (hb_glyph_info_t));
666     memmove (&info[start], temp, (j - i) * sizeof (hb_glyph_info_t));
667 
668     /* Renumber CC such that the reordered sequence is still sorted.
669      * 22 and 26 are chosen because they are smaller than all Arabic categories,
670      * and are folded back to 220/230 respectively during fallback mark positioning.
671      *
672      * We do this because the CGJ-handling logic in the normalizer relies on
673      * mark sequences having an increasing order even after this reordering.
674      * https://github.com/harfbuzz/harfbuzz/issues/554
675      * This, however, does break some obscure sequences, where the normalizer
676      * might compose a sequence that it should not.  For example, in the seequence
677      * ALEF, HAMZAH, MADDAH, we should NOT try to compose ALEF+MADDAH, but with this
678      * renumbering, we will.
679      */
680     unsigned int new_start = start + j - i;
681     unsigned int new_cc = cc == 220 ? HB_MODIFIED_COMBINING_CLASS_CCC22 : HB_MODIFIED_COMBINING_CLASS_CCC26;
682     while (start < new_start)
683     {
684       _hb_glyph_info_set_modified_combining_class (&info[start], new_cc);
685       start++;
686     }
687 
688     i = j;
689   }
690 }
691 
692 const hb_ot_complex_shaper_t _hb_ot_complex_shaper_arabic =
693 {
694   collect_features_arabic,
695   nullptr, /* override_features */
696   data_create_arabic,
697   data_destroy_arabic,
698   nullptr, /* preprocess_text */
699   postprocess_glyphs_arabic,
700   HB_OT_SHAPE_NORMALIZATION_MODE_DEFAULT,
701   nullptr, /* decompose */
702   nullptr, /* compose */
703   setup_masks_arabic,
704   HB_TAG_NONE, /* gpos_tag */
705   reorder_marks_arabic,
706   HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_LATE,
707   true, /* fallback_position */
708 };
709