1 : /*
2 : * Copyright © 2011 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-private.hh"
28 : #include "hb-ot-shape-complex-private.hh"
29 :
30 :
31 : /*
32 : * HIGHLEVEL DESIGN:
33 : *
34 : * This file exports one main function: _hb_ot_shape_normalize().
35 : *
36 : * This function closely reflects the Unicode Normalization Algorithm,
37 : * yet it's different. The shaper an either prefer decomposed (NFD) or
38 : * composed (NFC).
39 : *
40 : * In general what happens is that: each grapheme is decomposed in a chain
41 : * of 1:2 decompositions, marks reordered, and then recomposed if desired,
42 : * so far it's like Unicode Normalization. However, the decomposition and
43 : * recomposition only happens if the font supports the resulting characters.
44 : *
45 : * The goals are:
46 : *
47 : * - Try to render all canonically equivalent strings similarly. To really
48 : * achieve this we have to always do the full decomposition and then
49 : * selectively recompose from there. It's kinda too expensive though, so
50 : * we skip some cases. For example, if composed is desired, we simply
51 : * don't touch 1-character clusters that are supported by the font, even
52 : * though their NFC may be different.
53 : *
54 : * - When a font has a precomposed character for a sequence but the 'ccmp'
55 : * feature in the font is not adequate, use the precomposed character
56 : * which typically has better mark positioning.
57 : *
58 : * - When a font does not support a combining mark, but supports it precomposed
59 : * with previous base. This needs the itemizer to have this knowledge too.
60 : * We need ot provide assistance to the itemizer.
61 : *
62 : * - When a font does not support a character but supports its decomposition,
63 : * well, use the decomposition.
64 : *
65 : * - The Indic shaper requests decomposed output. This will handle splitting
66 : * matra for the Indic shaper.
67 : */
68 :
69 : static void
70 0 : output_glyph (hb_ot_shape_context_t *c,
71 : hb_codepoint_t glyph)
72 : {
73 0 : hb_buffer_t *buffer = c->buffer;
74 :
75 0 : buffer->output_glyph (glyph);
76 0 : hb_glyph_info_set_unicode_props (&buffer->out_info[buffer->out_len - 1], buffer->unicode);
77 0 : }
78 :
79 : static bool
80 0 : decompose (hb_ot_shape_context_t *c,
81 : bool shortest,
82 : hb_codepoint_t ab)
83 : {
84 : hb_codepoint_t a, b, glyph;
85 :
86 0 : if (!hb_unicode_decompose (c->buffer->unicode, ab, &a, &b) ||
87 0 : (b && !hb_font_get_glyph (c->font, b, 0, &glyph)))
88 0 : return FALSE;
89 :
90 0 : bool has_a = hb_font_get_glyph (c->font, a, 0, &glyph);
91 0 : if (shortest && has_a) {
92 : /* Output a and b */
93 0 : output_glyph (c, a);
94 0 : if (b)
95 0 : output_glyph (c, b);
96 0 : return TRUE;
97 : }
98 :
99 0 : if (decompose (c, shortest, a)) {
100 0 : if (b)
101 0 : output_glyph (c, b);
102 0 : return TRUE;
103 : }
104 :
105 0 : if (has_a) {
106 0 : output_glyph (c, a);
107 0 : if (b)
108 0 : output_glyph (c, b);
109 0 : return TRUE;
110 : }
111 :
112 0 : return FALSE;
113 : }
114 :
115 : static void
116 0 : decompose_current_glyph (hb_ot_shape_context_t *c,
117 : bool shortest)
118 : {
119 0 : if (decompose (c, shortest, c->buffer->info[c->buffer->idx].codepoint))
120 0 : c->buffer->skip_glyph ();
121 : else
122 0 : c->buffer->next_glyph ();
123 0 : }
124 :
125 : static void
126 0 : decompose_single_char_cluster (hb_ot_shape_context_t *c,
127 : bool will_recompose)
128 : {
129 : hb_codepoint_t glyph;
130 :
131 : /* If recomposing and font supports this, we're good to go */
132 0 : if (will_recompose && hb_font_get_glyph (c->font, c->buffer->info[c->buffer->idx].codepoint, 0, &glyph)) {
133 0 : c->buffer->next_glyph ();
134 0 : return;
135 : }
136 :
137 0 : decompose_current_glyph (c, will_recompose);
138 : }
139 :
140 : static void
141 0 : decompose_multi_char_cluster (hb_ot_shape_context_t *c,
142 : unsigned int end)
143 : {
144 : /* TODO Currently if there's a variation-selector we give-up, it's just too hard. */
145 0 : for (unsigned int i = c->buffer->idx; i < end; i++)
146 0 : if (unlikely (is_variation_selector (c->buffer->info[i].codepoint))) {
147 0 : while (c->buffer->idx < end)
148 0 : c->buffer->next_glyph ();
149 0 : return;
150 : }
151 :
152 0 : while (c->buffer->idx < end)
153 0 : decompose_current_glyph (c, FALSE);
154 : }
155 :
156 : static int
157 0 : compare_combining_class (const hb_glyph_info_t *pa, const hb_glyph_info_t *pb)
158 : {
159 0 : unsigned int a = pa->combining_class();
160 0 : unsigned int b = pb->combining_class();
161 :
162 0 : return a < b ? -1 : a == b ? 0 : +1;
163 : }
164 :
165 : void
166 0 : _hb_ot_shape_normalize (hb_ot_shape_context_t *c)
167 : {
168 0 : hb_buffer_t *buffer = c->buffer;
169 0 : bool recompose = !hb_ot_shape_complex_prefer_decomposed (c->plan->shaper);
170 0 : bool has_multichar_clusters = FALSE;
171 : unsigned int count;
172 :
173 : /* We do a fairly straightforward yet custom normalization process in three
174 : * separate rounds: decompose, reorder, recompose (if desired). Currently
175 : * this makes two buffer swaps. We can make it faster by moving the last
176 : * two rounds into the inner loop for the first round, but it's more readable
177 : * this way. */
178 :
179 :
180 : /* First round, decompose */
181 :
182 0 : buffer->clear_output ();
183 0 : count = buffer->len;
184 0 : for (buffer->idx = 0; buffer->idx < count;)
185 : {
186 : unsigned int end;
187 0 : for (end = buffer->idx + 1; end < count; end++)
188 0 : if (buffer->info[buffer->idx].cluster != buffer->info[end].cluster)
189 0 : break;
190 :
191 0 : if (buffer->idx + 1 == end)
192 0 : decompose_single_char_cluster (c, recompose);
193 : else {
194 0 : decompose_multi_char_cluster (c, end);
195 0 : has_multichar_clusters = TRUE;
196 : }
197 : }
198 0 : buffer->swap_buffers ();
199 :
200 :
201 : /* Technically speaking, two characters with ccc=0 may combine. But all
202 : * those cases are in languages that the indic module handles (which expects
203 : * decomposed), or in Hangul jamo, which again, we want decomposed anyway.
204 : * So we don't bother combining across cluster boundaries. This is a huge
205 : * performance saver if the compose() callback is slow.
206 : *
207 : * TODO: Am I right about Hangul? If I am, we should add a Hangul module
208 : * that requests decomposed. If for Hangul we end up wanting composed, we
209 : * can do that in the Hangul module.
210 : */
211 :
212 0 : if (!has_multichar_clusters)
213 0 : return; /* Done! */
214 :
215 :
216 : /* Second round, reorder (inplace) */
217 :
218 0 : count = buffer->len;
219 0 : for (unsigned int i = 0; i < count; i++)
220 : {
221 0 : if (buffer->info[i].combining_class() == 0)
222 0 : continue;
223 :
224 : unsigned int end;
225 0 : for (end = i + 1; end < count; end++)
226 0 : if (buffer->info[end].combining_class() == 0)
227 0 : break;
228 :
229 : /* We are going to do a bubble-sort. Only do this if the
230 : * sequence is short. Doing it on long sequences can result
231 : * in an O(n^2) DoS. */
232 0 : if (end - i > 10) {
233 0 : i = end;
234 0 : continue;
235 : }
236 :
237 0 : hb_bubble_sort (buffer->info + i, end - i, compare_combining_class);
238 :
239 0 : i = end;
240 : }
241 :
242 :
243 0 : if (!recompose)
244 0 : return;
245 :
246 : /* Third round, recompose */
247 :
248 : /* As noted in the comment earlier, we don't try to combine
249 : * ccc=0 chars with their previous Starter. */
250 :
251 0 : buffer->clear_output ();
252 0 : count = buffer->len;
253 0 : unsigned int starter = 0;
254 0 : buffer->next_glyph ();
255 0 : while (buffer->idx < count)
256 : {
257 0 : if (buffer->info[buffer->idx].combining_class() == 0) {
258 0 : starter = buffer->out_len;
259 0 : buffer->next_glyph ();
260 0 : continue;
261 : }
262 :
263 : hb_codepoint_t composed, glyph;
264 0 : if ((buffer->out_info[buffer->out_len - 1].combining_class() >=
265 0 : buffer->info[buffer->idx].combining_class()) ||
266 : !hb_unicode_compose (c->buffer->unicode,
267 0 : buffer->out_info[starter].codepoint,
268 0 : buffer->info[buffer->idx].codepoint,
269 0 : &composed) ||
270 0 : !hb_font_get_glyph (c->font, composed, 0, &glyph))
271 : {
272 : /* Blocked, or doesn't compose. */
273 0 : buffer->next_glyph ();
274 0 : continue;
275 : }
276 :
277 : /* Composes. Modify starter and carry on. */
278 0 : buffer->out_info[starter].codepoint = composed;
279 0 : hb_glyph_info_set_unicode_props (&buffer->out_info[starter], buffer->unicode);
280 :
281 0 : buffer->skip_glyph ();
282 : }
283 0 : buffer->swap_buffers ();
284 :
285 : }
286 :
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