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-normalize-private.hh"
28 #include "hb-ot-shape-complex-private.hh"
29 #include "hb-ot-shape-private.hh"
30
31
32 /*
33 * HIGHLEVEL DESIGN:
34 *
35 * This file exports one main function: _hb_ot_shape_normalize().
36 *
37 * This function closely reflects the Unicode Normalization Algorithm,
38 * yet it's different.
39 *
40 * Each shaper specifies whether it prefers decomposed (NFD) or composed (NFC).
41 * The logic however tries to use whatever the font can support.
42 *
43 * In general what happens is that: each grapheme is decomposed in a chain
44 * of 1:2 decompositions, marks reordered, and then recomposed if desired,
45 * so far it's like Unicode Normalization. However, the decomposition and
46 * recomposition only happens if the font supports the resulting characters.
47 *
48 * The goals are:
49 *
50 * - Try to render all canonically equivalent strings similarly. To really
51 * achieve this we have to always do the full decomposition and then
52 * selectively recompose from there. It's kinda too expensive though, so
53 * we skip some cases. For example, if composed is desired, we simply
54 * don't touch 1-character clusters that are supported by the font, even
55 * though their NFC may be different.
56 *
57 * - When a font has a precomposed character for a sequence but the 'ccmp'
58 * feature in the font is not adequate, use the precomposed character
59 * which typically has better mark positioning.
60 *
61 * - When a font does not support a combining mark, but supports it precomposed
62 * with previous base, use that. This needs the itemizer to have this
63 * knowledge too. We need to provide assistance to the itemizer.
64 *
65 * - When a font does not support a character but supports its canonical
66 * decomposition, well, use the decomposition.
67 *
68 * - The complex shapers can customize the compose and decompose functions to
69 * offload some of their requirements to the normalizer. For example, the
70 * Indic shaper may want to disallow recomposing of two matras.
71 */
72
73 static bool
74 decompose_unicode (const hb_ot_shape_normalize_context_t *c,
75 hb_codepoint_t ab,
76 hb_codepoint_t *a,
77 hb_codepoint_t *b)
78 {
79 return (bool) c->unicode->decompose (ab, a, b);
80 }
81
82 static bool
83 compose_unicode (const hb_ot_shape_normalize_context_t *c,
84 hb_codepoint_t a,
85 hb_codepoint_t b,
86 hb_codepoint_t *ab)
87 {
88 return (bool) c->unicode->compose (a, b, ab);
89 }
90
91 static inline void
92 set_glyph (hb_glyph_info_t &info, hb_font_t *font)
93 {
94 (void) font->get_nominal_glyph (info.codepoint, &info.glyph_index());
95 }
96
97 static inline void
98 output_char (hb_buffer_t *buffer, hb_codepoint_t unichar, hb_codepoint_t glyph)
99 {
100 buffer->cur().glyph_index() = glyph;
101 buffer->output_glyph (unichar); /* This is very confusing indeed. */
102 _hb_glyph_info_set_unicode_props (&buffer->prev(), buffer);
103 }
104
105 static inline void
106 next_char (hb_buffer_t *buffer, hb_codepoint_t glyph)
107 {
108 buffer->cur().glyph_index() = glyph;
109 buffer->next_glyph ();
110 }
111
112 static inline void
113 skip_char (hb_buffer_t *buffer)
114 {
115 buffer->skip_glyph ();
116 }
117
118 /* Returns 0 if didn't decompose, number of resulting characters otherwise. */
119 static inline unsigned int
120 decompose (const hb_ot_shape_normalize_context_t *c, bool shortest, hb_codepoint_t ab)
121 {
122 hb_codepoint_t a, b, a_glyph, b_glyph;
123 hb_buffer_t * const buffer = c->buffer;
124 hb_font_t * const font = c->font;
125
126 if (!c->decompose (c, ab, &a, &b) ||
127 (b && !font->get_nominal_glyph (b, &b_glyph)))
128 return 0;
129
130 bool has_a = (bool) font->get_nominal_glyph (a, &a_glyph);
131 if (shortest && has_a) {
132 /* Output a and b */
133 output_char (buffer, a, a_glyph);
134 if (likely (b)) {
135 output_char (buffer, b, b_glyph);
136 return 2;
137 }
138 return 1;
139 }
140
141 unsigned int ret;
142 if ((ret = decompose (c, shortest, a))) {
143 if (b) {
144 output_char (buffer, b, b_glyph);
145 return ret + 1;
146 }
147 return ret;
148 }
149
150 if (has_a) {
151 output_char (buffer, a, a_glyph);
152 if (likely (b)) {
153 output_char (buffer, b, b_glyph);
154 return 2;
155 }
156 return 1;
157 }
158
159 return 0;
160 }
161
162 static inline void
163 decompose_current_character (const hb_ot_shape_normalize_context_t *c, bool shortest)
164 {
165 hb_buffer_t * const buffer = c->buffer;
166 hb_codepoint_t u = buffer->cur().codepoint;
167 hb_codepoint_t glyph;
168
169 if (shortest && c->font->get_nominal_glyph (u, &glyph))
170 {
171 next_char (buffer, glyph);
172 return;
173 }
174
175 if (decompose (c, shortest, u))
176 {
177 skip_char (buffer);
178 return;
179 }
180
181 if (!shortest && c->font->get_nominal_glyph (u, &glyph))
182 {
183 next_char (buffer, glyph);
184 return;
185 }
186
187 if (_hb_glyph_info_is_unicode_space (&buffer->cur()))
188 {
189 hb_codepoint_t space_glyph;
190 hb_unicode_funcs_t::space_t space_type = buffer->unicode->space_fallback_type (u);
191 if (space_type != hb_unicode_funcs_t::NOT_SPACE && c->font->get_nominal_glyph (0x0020u, &space_glyph))
192 {
193 _hb_glyph_info_set_unicode_space_fallback_type (&buffer->cur(), space_type);
194 next_char (buffer, space_glyph);
195 buffer->scratch_flags |= HB_BUFFER_SCRATCH_FLAG_HAS_SPACE_FALLBACK;
196 return;
197 }
198 }
199
200 if (u == 0x2011u)
201 {
202 /* U+2011 is the only sensible character that is a no-break version of another character
203 * and not a space. The space ones are handled already. Handle this lone one. */
204 hb_codepoint_t other_glyph;
205 if (c->font->get_nominal_glyph (0x2010u, &other_glyph))
206 {
207 next_char (buffer, other_glyph);
208 return;
209 }
210 }
211
212 next_char (buffer, glyph); /* glyph is initialized in earlier branches. */
213 }
214
215 static inline void
216 handle_variation_selector_cluster (const hb_ot_shape_normalize_context_t *c, unsigned int end, bool short_circuit)
217 {
218 /* TODO Currently if there's a variation-selector we give-up, it's just too hard. */
219 hb_buffer_t * const buffer = c->buffer;
220 hb_font_t * const font = c->font;
221 for (; buffer->idx < end - 1 && !buffer->in_error;) {
222 if (unlikely (buffer->unicode->is_variation_selector (buffer->cur(+1).codepoint))) {
223 /* The next two lines are some ugly lines... But work. */
224 if (font->get_variation_glyph (buffer->cur().codepoint, buffer->cur(+1).codepoint, &buffer->cur().glyph_index()))
225 {
226 buffer->replace_glyphs (2, 1, &buffer->cur().codepoint);
227 }
228 else
229 {
230 /* Just pass on the two characters separately, let GSUB do its magic. */
231 set_glyph (buffer->cur(), font);
232 buffer->next_glyph ();
233 set_glyph (buffer->cur(), font);
234 buffer->next_glyph ();
235 }
236 /* Skip any further variation selectors. */
237 while (buffer->idx < end && unlikely (buffer->unicode->is_variation_selector (buffer->cur().codepoint)))
238 {
239 set_glyph (buffer->cur(), font);
240 buffer->next_glyph ();
241 }
242 } else {
243 set_glyph (buffer->cur(), font);
244 buffer->next_glyph ();
245 }
246 }
247 if (likely (buffer->idx < end)) {
248 set_glyph (buffer->cur(), font);
249 buffer->next_glyph ();
250 }
251 }
252
253 static inline void
254 decompose_multi_char_cluster (const hb_ot_shape_normalize_context_t *c, unsigned int end, bool short_circuit)
255 {
256 hb_buffer_t * const buffer = c->buffer;
257 for (unsigned int i = buffer->idx; i < end && !buffer->in_error; i++)
258 if (unlikely (buffer->unicode->is_variation_selector (buffer->info[i].codepoint))) {
259 handle_variation_selector_cluster (c, end, short_circuit);
260 return;
261 }
262
263 while (buffer->idx < end && !buffer->in_error)
264 decompose_current_character (c, short_circuit);
265 }
266
267 static inline void
268 decompose_cluster (const hb_ot_shape_normalize_context_t *c, unsigned int end, bool might_short_circuit, bool always_short_circuit)
269 {
270 if (likely (c->buffer->idx + 1 == end))
271 decompose_current_character (c, might_short_circuit);
272 else
273 decompose_multi_char_cluster (c, end, always_short_circuit);
274 }
275
276
277 static int
278 compare_combining_class (const hb_glyph_info_t *pa, const hb_glyph_info_t *pb)
279 {
280 unsigned int a = _hb_glyph_info_get_modified_combining_class (pa);
281 unsigned int b = _hb_glyph_info_get_modified_combining_class (pb);
282
283 return a < b ? -1 : a == b ? 0 : +1;
284 }
285
286
287 void
288 _hb_ot_shape_normalize (const hb_ot_shape_plan_t *plan,
289 hb_buffer_t *buffer,
290 hb_font_t *font)
291 {
292 if (unlikely (!buffer->len)) return;
293
294 _hb_buffer_assert_unicode_vars (buffer);
295
296 hb_ot_shape_normalization_mode_t mode = plan->shaper->normalization_preference;
297 const hb_ot_shape_normalize_context_t c = {
298 plan,
299 buffer,
300 font,
301 buffer->unicode,
302 plan->shaper->decompose ? plan->shaper->decompose : decompose_unicode,
303 plan->shaper->compose ? plan->shaper->compose : compose_unicode
304 };
305
306 bool always_short_circuit = mode == HB_OT_SHAPE_NORMALIZATION_MODE_NONE;
307 bool might_short_circuit = always_short_circuit ||
308 (mode != HB_OT_SHAPE_NORMALIZATION_MODE_DECOMPOSED &&
309 mode != HB_OT_SHAPE_NORMALIZATION_MODE_COMPOSED_DIACRITICS_NO_SHORT_CIRCUIT);
310 unsigned int count;
311
312 /* We do a fairly straightforward yet custom normalization process in three
313 * separate rounds: decompose, reorder, recompose (if desired). Currently
314 * this makes two buffer swaps. We can make it faster by moving the last
315 * two rounds into the inner loop for the first round, but it's more readable
316 * this way. */
317
318
319 /* First round, decompose */
320
321 buffer->clear_output ();
322 count = buffer->len;
323 for (buffer->idx = 0; buffer->idx < count && !buffer->in_error;)
324 {
325 unsigned int end;
326 for (end = buffer->idx + 1; end < count; end++)
327 if (likely (!HB_UNICODE_GENERAL_CATEGORY_IS_MARK (_hb_glyph_info_get_general_category (&buffer->info[end]))))
328 break;
329
330 decompose_cluster (&c, end, might_short_circuit, always_short_circuit);
331 }
332 buffer->swap_buffers ();
333
334
335 /* Second round, reorder (inplace) */
336
337 count = buffer->len;
338 for (unsigned int i = 0; i < count; i++)
339 {
340 if (_hb_glyph_info_get_modified_combining_class (&buffer->info[i]) == 0)
341 continue;
342
343 unsigned int end;
344 for (end = i + 1; end < count; end++)
345 if (_hb_glyph_info_get_modified_combining_class (&buffer->info[end]) == 0)
346 break;
347
348 /* We are going to do a O(n^2). Only do this if the sequence is short,
349 * but not too short ;). */
350 if (end - i < 2 || end - i > HB_OT_SHAPE_COMPLEX_MAX_COMBINING_MARKS) {
351 i = end;
352 continue;
353 }
354
355 buffer->sort (i, end, compare_combining_class);
356
357 if (plan->shaper->reorder_marks)
358 plan->shaper->reorder_marks (plan, buffer, i, end);
359
360 i = end;
361 }
362
363
364 if (mode == HB_OT_SHAPE_NORMALIZATION_MODE_NONE ||
365 mode == HB_OT_SHAPE_NORMALIZATION_MODE_DECOMPOSED)
366 return;
367
368 /* Third round, recompose */
369
370 /* As noted in the comment earlier, we don't try to combine
371 * ccc=0 chars with their previous Starter. */
372
373 buffer->clear_output ();
374 count = buffer->len;
375 unsigned int starter = 0;
376 bool combine = true;
377 buffer->next_glyph ();
378 while (buffer->idx < count && !buffer->in_error)
379 {
380 hb_codepoint_t composed, glyph;
381 if (combine &&
382 /* We don't try to compose a non-mark character with it's preceding starter.
383 * This is both an optimization to avoid trying to compose every two neighboring
384 * glyphs in most scripts AND a desired feature for Hangul. Apparently Hangul
385 * fonts are not designed to mix-and-match pre-composed syllables and Jamo. */
386 HB_UNICODE_GENERAL_CATEGORY_IS_MARK (_hb_glyph_info_get_general_category (&buffer->cur())))
387 {
388 if (/* If there's anything between the starter and this char, they should have CCC
389 * smaller than this character's. */
390 (starter == buffer->out_len - 1 ||
391 info_cc (buffer->prev()) < info_cc (buffer->cur())) &&
392 /* And compose. */
393 c.compose (&c,
394 buffer->out_info[starter].codepoint,
395 buffer->cur().codepoint,
396 &composed) &&
397 /* And the font has glyph for the composite. */
398 font->get_nominal_glyph (composed, &glyph))
399 {
400 /* Composes. */
401 buffer->next_glyph (); /* Copy to out-buffer. */
402 if (unlikely (buffer->in_error))
403 return;
404 buffer->merge_out_clusters (starter, buffer->out_len);
405 buffer->out_len--; /* Remove the second composable. */
406 /* Modify starter and carry on. */
407 buffer->out_info[starter].codepoint = composed;
408 buffer->out_info[starter].glyph_index() = glyph;
409 _hb_glyph_info_set_unicode_props (&buffer->out_info[starter], buffer);
410
411 continue;
412 }
413 else if (/* We sometimes custom-tailor the sorted order of marks. In that case, stop
414 * trying to combine as soon as combining-class drops. */
415 starter < buffer->out_len - 1 &&
416 info_cc (buffer->prev()) > info_cc (buffer->cur()))
417 combine = false;
418 }
419
420 /* Blocked, or doesn't compose. */
421 buffer->next_glyph ();
422
423 if (info_cc (buffer->prev()) == 0)
424 {
425 starter = buffer->out_len - 1;
426 combine = true;
427 }
428 }
429 buffer->swap_buffers ();
430
431 }