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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 
get_joining_type(hb_codepoint_t u,hb_unicode_general_category_t gen_cat)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
collect_features_arabic(hb_ot_shape_planner_t * plan)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 *
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 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
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       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
mongolian_variation_selectors(hb_buffer_t * buffer)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
setup_masks_arabic_plan(const arabic_shape_plan_t * arabic_plan,hb_buffer_t * buffer,hb_script_t script)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
setup_masks_arabic(const hb_ot_shape_plan_t * plan,hb_buffer_t * buffer,hb_font_t * font HB_UNUSED)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
nuke_joiners(const hb_ot_shape_plan_t * plan HB_UNUSED,hb_font_t * font HB_UNUSED,hb_buffer_t * buffer)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
arabic_fallback_shape(const hb_ot_shape_plan_t * plan,hb_font_t * font,hb_buffer_t * buffer)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
record_stch(const hb_ot_shape_plan_t * plan,hb_font_t * font,hb_buffer_t * buffer)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
apply_stch(const hb_ot_shape_plan_t * plan,hb_buffer_t * buffer,hb_font_t * font)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
postprocess_glyphs_arabic(const hb_ot_shape_plan_t * plan,hb_buffer_t * buffer,hb_font_t * font)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