1 /*
2 * Copyright © 2011,2012 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-fallback-private.hh"
28 #include "hb-ot-layout-gsubgpos-private.hh"
29
30 static unsigned int
recategorize_combining_class(hb_codepoint_t u,unsigned int klass)31 recategorize_combining_class (hb_codepoint_t u,
32 unsigned int klass)
33 {
34 if (klass >= 200)
35 return klass;
36
37 /* Thai / Lao need some per-character work. */
38 if ((u & ~0xFF) == 0x0E00u)
39 {
40 if (unlikely (klass == 0))
41 {
42 switch (u)
43 {
44 case 0x0E31u:
45 case 0x0E34u:
46 case 0x0E35u:
47 case 0x0E36u:
48 case 0x0E37u:
49 case 0x0E47u:
50 case 0x0E4Cu:
51 case 0x0E4Du:
52 case 0x0E4Eu:
53 klass = HB_UNICODE_COMBINING_CLASS_ABOVE_RIGHT;
54 break;
55
56 case 0x0EB1u:
57 case 0x0EB4u:
58 case 0x0EB5u:
59 case 0x0EB6u:
60 case 0x0EB7u:
61 case 0x0EBBu:
62 case 0x0ECCu:
63 case 0x0ECDu:
64 klass = HB_UNICODE_COMBINING_CLASS_ABOVE;
65 break;
66
67 case 0x0EBCu:
68 klass = HB_UNICODE_COMBINING_CLASS_BELOW;
69 break;
70 }
71 } else {
72 /* Thai virama is below-right */
73 if (u == 0x0E3Au)
74 klass = HB_UNICODE_COMBINING_CLASS_BELOW_RIGHT;
75 }
76 }
77
78 switch (klass)
79 {
80
81 /* Hebrew */
82
83 case HB_MODIFIED_COMBINING_CLASS_CCC10: /* sheva */
84 case HB_MODIFIED_COMBINING_CLASS_CCC11: /* hataf segol */
85 case HB_MODIFIED_COMBINING_CLASS_CCC12: /* hataf patah */
86 case HB_MODIFIED_COMBINING_CLASS_CCC13: /* hataf qamats */
87 case HB_MODIFIED_COMBINING_CLASS_CCC14: /* hiriq */
88 case HB_MODIFIED_COMBINING_CLASS_CCC15: /* tsere */
89 case HB_MODIFIED_COMBINING_CLASS_CCC16: /* segol */
90 case HB_MODIFIED_COMBINING_CLASS_CCC17: /* patah */
91 case HB_MODIFIED_COMBINING_CLASS_CCC18: /* qamats */
92 case HB_MODIFIED_COMBINING_CLASS_CCC20: /* qubuts */
93 case HB_MODIFIED_COMBINING_CLASS_CCC22: /* meteg */
94 return HB_UNICODE_COMBINING_CLASS_BELOW;
95
96 case HB_MODIFIED_COMBINING_CLASS_CCC23: /* rafe */
97 return HB_UNICODE_COMBINING_CLASS_ATTACHED_ABOVE;
98
99 case HB_MODIFIED_COMBINING_CLASS_CCC24: /* shin dot */
100 return HB_UNICODE_COMBINING_CLASS_ABOVE_RIGHT;
101
102 case HB_MODIFIED_COMBINING_CLASS_CCC25: /* sin dot */
103 case HB_MODIFIED_COMBINING_CLASS_CCC19: /* holam */
104 return HB_UNICODE_COMBINING_CLASS_ABOVE_LEFT;
105
106 case HB_MODIFIED_COMBINING_CLASS_CCC26: /* point varika */
107 return HB_UNICODE_COMBINING_CLASS_ABOVE;
108
109 case HB_MODIFIED_COMBINING_CLASS_CCC21: /* dagesh */
110 break;
111
112
113 /* Arabic and Syriac */
114
115 case HB_MODIFIED_COMBINING_CLASS_CCC27: /* fathatan */
116 case HB_MODIFIED_COMBINING_CLASS_CCC28: /* dammatan */
117 case HB_MODIFIED_COMBINING_CLASS_CCC30: /* fatha */
118 case HB_MODIFIED_COMBINING_CLASS_CCC31: /* damma */
119 case HB_MODIFIED_COMBINING_CLASS_CCC33: /* shadda */
120 case HB_MODIFIED_COMBINING_CLASS_CCC34: /* sukun */
121 case HB_MODIFIED_COMBINING_CLASS_CCC35: /* superscript alef */
122 case HB_MODIFIED_COMBINING_CLASS_CCC36: /* superscript alaph */
123 return HB_UNICODE_COMBINING_CLASS_ABOVE;
124
125 case HB_MODIFIED_COMBINING_CLASS_CCC29: /* kasratan */
126 case HB_MODIFIED_COMBINING_CLASS_CCC32: /* kasra */
127 return HB_UNICODE_COMBINING_CLASS_BELOW;
128
129
130 /* Thai */
131
132 case HB_MODIFIED_COMBINING_CLASS_CCC103: /* sara u / sara uu */
133 return HB_UNICODE_COMBINING_CLASS_BELOW_RIGHT;
134
135 case HB_MODIFIED_COMBINING_CLASS_CCC107: /* mai */
136 return HB_UNICODE_COMBINING_CLASS_ABOVE_RIGHT;
137
138
139 /* Lao */
140
141 case HB_MODIFIED_COMBINING_CLASS_CCC118: /* sign u / sign uu */
142 return HB_UNICODE_COMBINING_CLASS_BELOW;
143
144 case HB_MODIFIED_COMBINING_CLASS_CCC122: /* mai */
145 return HB_UNICODE_COMBINING_CLASS_ABOVE;
146
147
148 /* Tibetan */
149
150 case HB_MODIFIED_COMBINING_CLASS_CCC129: /* sign aa */
151 return HB_UNICODE_COMBINING_CLASS_BELOW;
152
153 case HB_MODIFIED_COMBINING_CLASS_CCC130: /* sign i*/
154 return HB_UNICODE_COMBINING_CLASS_ABOVE;
155
156 case HB_MODIFIED_COMBINING_CLASS_CCC132: /* sign u */
157 return HB_UNICODE_COMBINING_CLASS_BELOW;
158
159 }
160
161 return klass;
162 }
163
164 void
_hb_ot_shape_fallback_position_recategorize_marks(const hb_ot_shape_plan_t * plan HB_UNUSED,hb_font_t * font HB_UNUSED,hb_buffer_t * buffer)165 _hb_ot_shape_fallback_position_recategorize_marks (const hb_ot_shape_plan_t *plan HB_UNUSED,
166 hb_font_t *font HB_UNUSED,
167 hb_buffer_t *buffer)
168 {
169 unsigned int count = buffer->len;
170 hb_glyph_info_t *info = buffer->info;
171 for (unsigned int i = 0; i < count; i++)
172 if (_hb_glyph_info_get_general_category (&info[i]) == HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK) {
173 unsigned int combining_class = _hb_glyph_info_get_modified_combining_class (&info[i]);
174 combining_class = recategorize_combining_class (info[i].codepoint, combining_class);
175 _hb_glyph_info_set_modified_combining_class (&info[i], combining_class);
176 }
177 }
178
179
180 static void
zero_mark_advances(hb_buffer_t * buffer,unsigned int start,unsigned int end)181 zero_mark_advances (hb_buffer_t *buffer,
182 unsigned int start,
183 unsigned int end)
184 {
185 hb_glyph_info_t *info = buffer->info;
186 for (unsigned int i = start; i < end; i++)
187 if (_hb_glyph_info_get_general_category (&info[i]) == HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK)
188 {
189 buffer->pos[i].x_advance = 0;
190 buffer->pos[i].y_advance = 0;
191 }
192 }
193
194 static inline void
position_mark(const hb_ot_shape_plan_t * plan,hb_font_t * font,hb_buffer_t * buffer,hb_glyph_extents_t & base_extents,unsigned int i,unsigned int combining_class)195 position_mark (const hb_ot_shape_plan_t *plan,
196 hb_font_t *font,
197 hb_buffer_t *buffer,
198 hb_glyph_extents_t &base_extents,
199 unsigned int i,
200 unsigned int combining_class)
201 {
202 hb_glyph_extents_t mark_extents;
203 if (!font->get_glyph_extents (buffer->info[i].codepoint,
204 &mark_extents))
205 return;
206
207 hb_position_t y_gap = font->y_scale / 16;
208
209 hb_glyph_position_t &pos = buffer->pos[i];
210 pos.x_offset = pos.y_offset = 0;
211
212
213 /* We dont position LEFT and RIGHT marks. */
214
215 /* X positioning */
216 switch (combining_class)
217 {
218 case HB_UNICODE_COMBINING_CLASS_DOUBLE_BELOW:
219 case HB_UNICODE_COMBINING_CLASS_DOUBLE_ABOVE:
220 if (buffer->props.direction == HB_DIRECTION_LTR) {
221 pos.x_offset += base_extents.x_bearing - mark_extents.width / 2 - mark_extents.x_bearing;
222 break;
223 } else if (buffer->props.direction == HB_DIRECTION_RTL) {
224 pos.x_offset += base_extents.x_bearing + base_extents.width - mark_extents.width / 2 - mark_extents.x_bearing;
225 break;
226 }
227 HB_FALLTHROUGH;
228
229 default:
230 case HB_UNICODE_COMBINING_CLASS_ATTACHED_BELOW:
231 case HB_UNICODE_COMBINING_CLASS_ATTACHED_ABOVE:
232 case HB_UNICODE_COMBINING_CLASS_BELOW:
233 case HB_UNICODE_COMBINING_CLASS_ABOVE:
234 /* Center align. */
235 pos.x_offset += base_extents.x_bearing + (base_extents.width - mark_extents.width) / 2 - mark_extents.x_bearing;
236 break;
237
238 case HB_UNICODE_COMBINING_CLASS_ATTACHED_BELOW_LEFT:
239 case HB_UNICODE_COMBINING_CLASS_BELOW_LEFT:
240 case HB_UNICODE_COMBINING_CLASS_ABOVE_LEFT:
241 /* Left align. */
242 pos.x_offset += base_extents.x_bearing - mark_extents.x_bearing;
243 break;
244
245 case HB_UNICODE_COMBINING_CLASS_ATTACHED_ABOVE_RIGHT:
246 case HB_UNICODE_COMBINING_CLASS_BELOW_RIGHT:
247 case HB_UNICODE_COMBINING_CLASS_ABOVE_RIGHT:
248 /* Right align. */
249 pos.x_offset += base_extents.x_bearing + base_extents.width - mark_extents.width - mark_extents.x_bearing;
250 break;
251 }
252
253 /* Y positioning */
254 switch (combining_class)
255 {
256 case HB_UNICODE_COMBINING_CLASS_DOUBLE_BELOW:
257 case HB_UNICODE_COMBINING_CLASS_BELOW_LEFT:
258 case HB_UNICODE_COMBINING_CLASS_BELOW:
259 case HB_UNICODE_COMBINING_CLASS_BELOW_RIGHT:
260 /* Add gap, fall-through. */
261 base_extents.height -= y_gap;
262 HB_FALLTHROUGH;
263
264 case HB_UNICODE_COMBINING_CLASS_ATTACHED_BELOW_LEFT:
265 case HB_UNICODE_COMBINING_CLASS_ATTACHED_BELOW:
266 pos.y_offset = base_extents.y_bearing + base_extents.height - mark_extents.y_bearing;
267 /* Never shift up "below" marks. */
268 if ((y_gap > 0) == (pos.y_offset > 0))
269 {
270 base_extents.height -= pos.y_offset;
271 pos.y_offset = 0;
272 }
273 base_extents.height += mark_extents.height;
274 break;
275
276 case HB_UNICODE_COMBINING_CLASS_DOUBLE_ABOVE:
277 case HB_UNICODE_COMBINING_CLASS_ABOVE_LEFT:
278 case HB_UNICODE_COMBINING_CLASS_ABOVE:
279 case HB_UNICODE_COMBINING_CLASS_ABOVE_RIGHT:
280 /* Add gap, fall-through. */
281 base_extents.y_bearing += y_gap;
282 base_extents.height -= y_gap;
283 HB_FALLTHROUGH;
284
285 case HB_UNICODE_COMBINING_CLASS_ATTACHED_ABOVE:
286 case HB_UNICODE_COMBINING_CLASS_ATTACHED_ABOVE_RIGHT:
287 pos.y_offset = base_extents.y_bearing - (mark_extents.y_bearing + mark_extents.height);
288 /* Don't shift down "above" marks too much. */
289 if ((y_gap > 0) != (pos.y_offset > 0))
290 {
291 unsigned int correction = -pos.y_offset / 2;
292 base_extents.y_bearing += correction;
293 base_extents.height -= correction;
294 pos.y_offset += correction;
295 }
296 base_extents.y_bearing -= mark_extents.height;
297 base_extents.height += mark_extents.height;
298 break;
299 }
300 }
301
302 static inline void
position_around_base(const hb_ot_shape_plan_t * plan,hb_font_t * font,hb_buffer_t * buffer,unsigned int base,unsigned int end)303 position_around_base (const hb_ot_shape_plan_t *plan,
304 hb_font_t *font,
305 hb_buffer_t *buffer,
306 unsigned int base,
307 unsigned int end)
308 {
309 hb_direction_t horiz_dir = HB_DIRECTION_INVALID;
310 hb_glyph_extents_t base_extents;
311 if (!font->get_glyph_extents (buffer->info[base].codepoint,
312 &base_extents))
313 {
314 /* If extents don't work, zero marks and go home. */
315 zero_mark_advances (buffer, base + 1, end);
316 return;
317 }
318 base_extents.x_bearing += buffer->pos[base].x_offset;
319 base_extents.y_bearing += buffer->pos[base].y_offset;
320
321 unsigned int lig_id = _hb_glyph_info_get_lig_id (&buffer->info[base]);
322 unsigned int num_lig_components = _hb_glyph_info_get_lig_num_comps (&buffer->info[base]);
323
324 hb_position_t x_offset = 0, y_offset = 0;
325 if (HB_DIRECTION_IS_FORWARD (buffer->props.direction)) {
326 x_offset -= buffer->pos[base].x_advance;
327 y_offset -= buffer->pos[base].y_advance;
328 }
329
330 hb_glyph_extents_t component_extents = base_extents;
331 unsigned int last_lig_component = (unsigned int) -1;
332 unsigned int last_combining_class = 255;
333 hb_glyph_extents_t cluster_extents = base_extents; /* Initialization is just to shut gcc up. */
334 hb_glyph_info_t *info = buffer->info;
335 for (unsigned int i = base + 1; i < end; i++)
336 if (_hb_glyph_info_get_modified_combining_class (&info[i]))
337 {
338 if (num_lig_components > 1) {
339 unsigned int this_lig_id = _hb_glyph_info_get_lig_id (&info[i]);
340 unsigned int this_lig_component = _hb_glyph_info_get_lig_comp (&info[i]) - 1;
341 /* Conditions for attaching to the last component. */
342 if (!lig_id || lig_id != this_lig_id || this_lig_component >= num_lig_components)
343 this_lig_component = num_lig_components - 1;
344 if (last_lig_component != this_lig_component)
345 {
346 last_lig_component = this_lig_component;
347 last_combining_class = 255;
348 component_extents = base_extents;
349 if (unlikely (horiz_dir == HB_DIRECTION_INVALID)) {
350 if (HB_DIRECTION_IS_HORIZONTAL (plan->props.direction))
351 horiz_dir = plan->props.direction;
352 else
353 horiz_dir = hb_script_get_horizontal_direction (plan->props.script);
354 }
355 if (horiz_dir == HB_DIRECTION_LTR)
356 component_extents.x_bearing += (this_lig_component * component_extents.width) / num_lig_components;
357 else
358 component_extents.x_bearing += ((num_lig_components - 1 - this_lig_component) * component_extents.width) / num_lig_components;
359 component_extents.width /= num_lig_components;
360 }
361 }
362
363 unsigned int this_combining_class = _hb_glyph_info_get_modified_combining_class (&info[i]);
364 if (last_combining_class != this_combining_class)
365 {
366 last_combining_class = this_combining_class;
367 cluster_extents = component_extents;
368 }
369
370 position_mark (plan, font, buffer, cluster_extents, i, this_combining_class);
371
372 buffer->pos[i].x_advance = 0;
373 buffer->pos[i].y_advance = 0;
374 buffer->pos[i].x_offset += x_offset;
375 buffer->pos[i].y_offset += y_offset;
376
377 } else {
378 if (HB_DIRECTION_IS_FORWARD (buffer->props.direction)) {
379 x_offset -= buffer->pos[i].x_advance;
380 y_offset -= buffer->pos[i].y_advance;
381 } else {
382 x_offset += buffer->pos[i].x_advance;
383 y_offset += buffer->pos[i].y_advance;
384 }
385 }
386 }
387
388 static inline void
position_cluster(const hb_ot_shape_plan_t * plan,hb_font_t * font,hb_buffer_t * buffer,unsigned int start,unsigned int end)389 position_cluster (const hb_ot_shape_plan_t *plan,
390 hb_font_t *font,
391 hb_buffer_t *buffer,
392 unsigned int start,
393 unsigned int end)
394 {
395 if (end - start < 2)
396 return;
397
398 /* Find the base glyph */
399 hb_glyph_info_t *info = buffer->info;
400 for (unsigned int i = start; i < end; i++)
401 if (!HB_UNICODE_GENERAL_CATEGORY_IS_MARK (_hb_glyph_info_get_general_category (&info[i])))
402 {
403 /* Find mark glyphs */
404 unsigned int j;
405 for (j = i + 1; j < end; j++)
406 if (!HB_UNICODE_GENERAL_CATEGORY_IS_MARK (_hb_glyph_info_get_general_category (&info[j])))
407 break;
408
409 position_around_base (plan, font, buffer, i, j);
410
411 i = j - 1;
412 }
413 }
414
415 void
_hb_ot_shape_fallback_position(const hb_ot_shape_plan_t * plan,hb_font_t * font,hb_buffer_t * buffer)416 _hb_ot_shape_fallback_position (const hb_ot_shape_plan_t *plan,
417 hb_font_t *font,
418 hb_buffer_t *buffer)
419 {
420 _hb_buffer_assert_gsubgpos_vars (buffer);
421
422 unsigned int start = 0;
423 unsigned int count = buffer->len;
424 hb_glyph_info_t *info = buffer->info;
425 for (unsigned int i = 1; i < count; i++)
426 if (likely (!HB_UNICODE_GENERAL_CATEGORY_IS_MARK (_hb_glyph_info_get_general_category (&info[i])))) {
427 position_cluster (plan, font, buffer, start, i);
428 start = i;
429 }
430 position_cluster (plan, font, buffer, start, count);
431 }
432
433
434 /* Performs old-style TrueType kerning. */
435 void
_hb_ot_shape_fallback_kern(const hb_ot_shape_plan_t * plan,hb_font_t * font,hb_buffer_t * buffer)436 _hb_ot_shape_fallback_kern (const hb_ot_shape_plan_t *plan,
437 hb_font_t *font,
438 hb_buffer_t *buffer)
439 {
440 if (!plan->has_kern) return;
441
442 OT::hb_apply_context_t c (1, font, buffer);
443 c.set_lookup_mask (plan->kern_mask);
444 c.set_lookup_props (OT::LookupFlag::IgnoreMarks);
445 OT::hb_apply_context_t::skipping_iterator_t &skippy_iter = c.iter_input;
446 skippy_iter.init (&c);
447
448 unsigned int count = buffer->len;
449 hb_glyph_info_t *info = buffer->info;
450 hb_glyph_position_t *pos = buffer->pos;
451 for (unsigned int idx = 0; idx < count;)
452 {
453 skippy_iter.reset (idx, 1);
454 if (!skippy_iter.next ())
455 {
456 idx++;
457 continue;
458 }
459
460 hb_position_t x_kern, y_kern;
461 font->get_glyph_kerning_for_direction (info[idx].codepoint,
462 info[skippy_iter.idx].codepoint,
463 buffer->props.direction,
464 &x_kern, &y_kern);
465
466 if (x_kern)
467 {
468 hb_position_t kern1 = x_kern >> 1;
469 hb_position_t kern2 = x_kern - kern1;
470 pos[idx].x_advance += kern1;
471 pos[skippy_iter.idx].x_advance += kern2;
472 pos[skippy_iter.idx].x_offset += kern2;
473 }
474
475 if (y_kern)
476 {
477 hb_position_t kern1 = y_kern >> 1;
478 hb_position_t kern2 = y_kern - kern1;
479 pos[idx].y_advance += kern1;
480 pos[skippy_iter.idx].y_advance += kern2;
481 pos[skippy_iter.idx].y_offset += kern2;
482 }
483
484 idx = skippy_iter.idx;
485 }
486 }
487
488
489 /* Adjusts width of various spaces. */
490 void
_hb_ot_shape_fallback_spaces(const hb_ot_shape_plan_t * plan,hb_font_t * font,hb_buffer_t * buffer)491 _hb_ot_shape_fallback_spaces (const hb_ot_shape_plan_t *plan,
492 hb_font_t *font,
493 hb_buffer_t *buffer)
494 {
495 if (!HB_DIRECTION_IS_HORIZONTAL (buffer->props.direction))
496 return;
497
498 hb_glyph_info_t *info = buffer->info;
499 hb_glyph_position_t *pos = buffer->pos;
500 unsigned int count = buffer->len;
501 for (unsigned int i = 0; i < count; i++)
502 if (_hb_glyph_info_is_unicode_space (&info[i]) && !_hb_glyph_info_ligated (&info[i]))
503 {
504 hb_unicode_funcs_t::space_t space_type = _hb_glyph_info_get_unicode_space_fallback_type (&info[i]);
505 hb_codepoint_t glyph;
506 typedef hb_unicode_funcs_t t;
507 switch (space_type)
508 {
509 case t::NOT_SPACE: /* Shouldn't happen. */
510 case t::SPACE:
511 break;
512
513 case t::SPACE_EM:
514 case t::SPACE_EM_2:
515 case t::SPACE_EM_3:
516 case t::SPACE_EM_4:
517 case t::SPACE_EM_5:
518 case t::SPACE_EM_6:
519 case t::SPACE_EM_16:
520 pos[i].x_advance = (font->x_scale + ((int) space_type)/2) / (int) space_type;
521 break;
522
523 case t::SPACE_4_EM_18:
524 pos[i].x_advance = font->x_scale * 4 / 18;
525 break;
526
527 case t::SPACE_FIGURE:
528 for (char u = '0'; u <= '9'; u++)
529 if (font->get_nominal_glyph (u, &glyph))
530 {
531 pos[i].x_advance = font->get_glyph_h_advance (glyph);
532 break;
533 }
534 break;
535
536 case t::SPACE_PUNCTUATION:
537 if (font->get_nominal_glyph ('.', &glyph))
538 pos[i].x_advance = font->get_glyph_h_advance (glyph);
539 else if (font->get_nominal_glyph (',', &glyph))
540 pos[i].x_advance = font->get_glyph_h_advance (glyph);
541 break;
542
543 case t::SPACE_NARROW:
544 /* Half-space?
545 * Unicode doc http://www.unicode.org/charts/PDF/U2000.pdf says ~1/4 or 1/5 of EM.
546 * However, in my testing, many fonts have their regular space being about that
547 * size. To me, a percentage of the space width makes more sense. Half is as
548 * good as any. */
549 pos[i].x_advance /= 2;
550 break;
551 }
552 }
553 }
554