2 * Copyright © 2011,2012 Google, Inc.
4 * This is part of HarfBuzz, a text shaping library.
6 * Permission is hereby granted, without written agreement and without
7 * license or royalty fees, to use, copy, modify, and distribute this
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19 * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
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24 * Google Author(s): Behdad Esfahbod
27 #include "hb-ot-shape-normalize-private.hh"
28 #include "hb-ot-shape-complex-private.hh"
29 #include "hb-ot-shape-private.hh"
35 * This file exports one main function: _hb_ot_shape_normalize().
37 * This function closely reflects the Unicode Normalization Algorithm,
40 * Each shaper specifies whether it prefers decomposed (NFD) or composed (NFC).
41 * The logic however tries to use whatever the font can support.
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.
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.
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.
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.
65 * - When a font does not support a character but supports its decomposition,
66 * well, use the decomposition (preferring the canonical decomposition, but
67 * falling back to the compatibility decomposition if necessary). The
68 * compatibility decomposition is really nice to have, for characters like
69 * ellipsis, or various-sized space characters.
71 * - The complex shapers can customize the compose and decompose functions to
72 * offload some of their requirements to the normalizer. For example, the
73 * Indic shaper may want to disallow recomposing of two matras.
75 * - We try compatibility decomposition if decomposing through canonical
76 * decomposition alone failed to find a sequence that the font supports.
77 * We don't try compatibility decomposition recursively during the canonical
78 * decomposition phase. This has minimal impact. There are only a handful
79 * of Greek letter that have canonical decompositions that include characters
80 * with compatibility decomposition. Those can be found using this command:
82 * egrep "`echo -n ';('; grep ';<' UnicodeData.txt | cut -d';' -f1 | tr '\n' '|'; echo ') '`" UnicodeData.txt
86 decompose_unicode (const hb_ot_shape_normalize_context_t *c,
91 return c->unicode->decompose (ab, a, b);
95 compose_unicode (const hb_ot_shape_normalize_context_t *c,
100 return c->unicode->compose (a, b, ab);
104 set_glyph (hb_glyph_info_t &info, hb_font_t *font)
106 font->get_glyph (info.codepoint, 0, &info.glyph_index());
110 output_char (hb_buffer_t *buffer, hb_codepoint_t unichar, hb_codepoint_t glyph)
112 buffer->cur().glyph_index() = glyph;
113 buffer->output_glyph (unichar);
114 _hb_glyph_info_set_unicode_props (&buffer->prev(), buffer->unicode);
118 next_char (hb_buffer_t *buffer, hb_codepoint_t glyph)
120 buffer->cur().glyph_index() = glyph;
121 buffer->next_glyph ();
125 skip_char (hb_buffer_t *buffer)
127 buffer->skip_glyph ();
130 /* Returns 0 if didn't decompose, number of resulting characters otherwise. */
131 static inline unsigned int
132 decompose (const hb_ot_shape_normalize_context_t *c, bool shortest, hb_codepoint_t ab)
134 hb_codepoint_t a, b, a_glyph, b_glyph;
136 if (!c->decompose (c, ab, &a, &b) ||
137 (b && !c->font->get_glyph (b, 0, &b_glyph)))
140 bool has_a = c->font->get_glyph (a, 0, &a_glyph);
141 if (shortest && has_a) {
143 output_char (c->buffer, a, a_glyph);
145 output_char (c->buffer, b, b_glyph);
152 if ((ret = decompose (c, shortest, a))) {
154 output_char (c->buffer, b, b_glyph);
161 output_char (c->buffer, a, a_glyph);
163 output_char (c->buffer, b, b_glyph);
172 /* Returns 0 if didn't decompose, number of resulting characters otherwise. */
174 decompose_compatibility (const hb_ot_shape_normalize_context_t *c, hb_codepoint_t u)
177 hb_codepoint_t decomposed[HB_UNICODE_MAX_DECOMPOSITION_LEN];
178 hb_codepoint_t glyphs[HB_UNICODE_MAX_DECOMPOSITION_LEN];
180 len = c->buffer->unicode->decompose_compatibility (u, decomposed);
184 for (i = 0; i < len; i++)
185 if (!c->font->get_glyph (decomposed[i], 0, &glyphs[i]))
188 for (i = 0; i < len; i++)
189 output_char (c->buffer, decomposed[i], glyphs[i]);
194 /* Returns true if recomposition may be benefitial. */
196 decompose_current_character (const hb_ot_shape_normalize_context_t *c, bool shortest)
198 hb_buffer_t * const buffer = c->buffer;
199 hb_codepoint_t glyph;
200 unsigned int len = 1;
202 /* Kind of a cute waterfall here... */
203 if (shortest && c->font->get_glyph (buffer->cur().codepoint, 0, &glyph))
204 next_char (buffer, glyph);
205 else if ((len = decompose (c, shortest, buffer->cur().codepoint)))
207 else if (!shortest && c->font->get_glyph (buffer->cur().codepoint, 0, &glyph))
208 next_char (buffer, glyph);
209 else if ((len = decompose_compatibility (c, buffer->cur().codepoint)))
212 next_char (buffer, glyph); /* glyph is initialized in earlier branches. */
215 * A recomposition would only be useful if we decomposed into at least three
222 handle_variation_selector_cluster (const hb_ot_shape_normalize_context_t *c, unsigned int end)
224 hb_buffer_t * const buffer = c->buffer;
225 for (; buffer->idx < end - 1;) {
226 if (unlikely (buffer->unicode->is_variation_selector (buffer->cur(+1).codepoint))) {
227 /* The next two lines are some ugly lines... But work. */
228 c->font->get_glyph (buffer->cur().codepoint, buffer->cur(+1).codepoint, &buffer->cur().glyph_index());
229 buffer->replace_glyphs (2, 1, &buffer->cur().codepoint);
231 set_glyph (buffer->cur(), c->font);
232 buffer->next_glyph ();
235 if (likely (buffer->idx < end)) {
236 set_glyph (buffer->cur(), c->font);
237 buffer->next_glyph ();
241 /* Returns true if recomposition may be benefitial. */
243 decompose_multi_char_cluster (const hb_ot_shape_normalize_context_t *c, unsigned int end)
245 hb_buffer_t * const buffer = c->buffer;
246 /* TODO Currently if there's a variation-selector we give-up, it's just too hard. */
247 for (unsigned int i = buffer->idx; i < end; i++)
248 if (unlikely (buffer->unicode->is_variation_selector (buffer->info[i].codepoint))) {
249 handle_variation_selector_cluster (c, end);
253 while (buffer->idx < end)
254 decompose_current_character (c, false);
255 /* We can be smarter here and only return true if there are at least two ccc!=0 marks.
256 * But does not matter. */
261 decompose_cluster (const hb_ot_shape_normalize_context_t *c, bool short_circuit, unsigned int end)
263 if (likely (c->buffer->idx + 1 == end))
264 return decompose_current_character (c, short_circuit);
266 return decompose_multi_char_cluster (c, end);
271 compare_combining_class (const hb_glyph_info_t *pa, const hb_glyph_info_t *pb)
273 unsigned int a = _hb_glyph_info_get_modified_combining_class (pa);
274 unsigned int b = _hb_glyph_info_get_modified_combining_class (pb);
276 return a < b ? -1 : a == b ? 0 : +1;
281 _hb_ot_shape_normalize (const hb_ot_shape_plan_t *plan,
285 hb_ot_shape_normalization_mode_t mode = plan->shaper->normalization_preference ?
286 plan->shaper->normalization_preference (&buffer->props) :
287 HB_OT_SHAPE_NORMALIZATION_MODE_DEFAULT;
288 const hb_ot_shape_normalize_context_t c = {
293 plan->shaper->decompose ? plan->shaper->decompose : decompose_unicode,
294 plan->shaper->compose ? plan->shaper->compose : compose_unicode
297 bool short_circuit = mode != HB_OT_SHAPE_NORMALIZATION_MODE_DECOMPOSED &&
298 mode != HB_OT_SHAPE_NORMALIZATION_MODE_COMPOSED_DIACRITICS_NO_SHORT_CIRCUIT;
299 bool can_use_recompose = false;
302 /* We do a fairly straightforward yet custom normalization process in three
303 * separate rounds: decompose, reorder, recompose (if desired). Currently
304 * this makes two buffer swaps. We can make it faster by moving the last
305 * two rounds into the inner loop for the first round, but it's more readable
309 /* First round, decompose */
311 buffer->clear_output ();
313 for (buffer->idx = 0; buffer->idx < count;)
316 for (end = buffer->idx + 1; end < count; end++)
317 if (buffer->cur().cluster != buffer->info[end].cluster)
320 can_use_recompose = decompose_cluster (&c, short_circuit, end) || can_use_recompose;
322 buffer->swap_buffers ();
325 if (mode != HB_OT_SHAPE_NORMALIZATION_MODE_COMPOSED_FULL && !can_use_recompose)
329 /* Second round, reorder (inplace) */
332 for (unsigned int i = 0; i < count; i++)
334 if (_hb_glyph_info_get_modified_combining_class (&buffer->info[i]) == 0)
338 for (end = i + 1; end < count; end++)
339 if (_hb_glyph_info_get_modified_combining_class (&buffer->info[end]) == 0)
342 /* We are going to do a bubble-sort. Only do this if the
343 * sequence is short. Doing it on long sequences can result
344 * in an O(n^2) DoS. */
350 hb_bubble_sort (buffer->info + i, end - i, compare_combining_class);
356 if (mode == HB_OT_SHAPE_NORMALIZATION_MODE_DECOMPOSED)
359 /* Third round, recompose */
361 /* As noted in the comment earlier, we don't try to combine
362 * ccc=0 chars with their previous Starter. */
364 buffer->clear_output ();
366 unsigned int starter = 0;
367 buffer->next_glyph ();
368 while (buffer->idx < count)
370 hb_codepoint_t composed, glyph;
371 if (/* If mode is NOT COMPOSED_FULL (ie. it's COMPOSED_DIACRITICS), we don't try to
372 * compose a CCC=0 character with it's preceding starter. */
373 (mode == HB_OT_SHAPE_NORMALIZATION_MODE_COMPOSED_FULL ||
374 _hb_glyph_info_get_modified_combining_class (&buffer->cur()) != 0) &&
375 /* If there's anything between the starter and this char, they should have CCC
376 * smaller than this character's. */
377 (starter == buffer->out_len - 1 ||
378 _hb_glyph_info_get_modified_combining_class (&buffer->prev()) < _hb_glyph_info_get_modified_combining_class (&buffer->cur())) &&
381 buffer->out_info[starter].codepoint,
382 buffer->cur().codepoint,
384 /* And the font has glyph for the composite. */
385 font->get_glyph (composed, 0, &glyph))
388 buffer->next_glyph (); /* Copy to out-buffer. */
389 if (unlikely (buffer->in_error))
391 buffer->merge_out_clusters (starter, buffer->out_len);
392 buffer->out_len--; /* Remove the second composable. */
393 buffer->out_info[starter].codepoint = composed; /* Modify starter and carry on. */
394 set_glyph (buffer->out_info[starter], font);
395 _hb_glyph_info_set_unicode_props (&buffer->out_info[starter], buffer->unicode);
400 /* Blocked, or doesn't compose. */
401 buffer->next_glyph ();
403 if (_hb_glyph_info_get_modified_combining_class (&buffer->prev()) == 0)
404 starter = buffer->out_len - 1;
406 buffer->swap_buffers ();