LineBreaker.cpp revision bb86b433f97a301c11800806b1ce5331fa227d4a
1/* 2 * Copyright (C) 2015 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17#define VERBOSE_DEBUG 0 18 19#include <limits> 20 21#define LOG_TAG "Minikin" 22#include <cutils/log.h> 23 24#include <minikin/Layout.h> 25#include <minikin/LineBreaker.h> 26 27using std::vector; 28 29namespace android { 30 31const int CHAR_TAB = 0x0009; 32const uint16_t CHAR_SOFT_HYPHEN = 0x00AD; 33 34// Large scores in a hierarchy; we prefer desperate breaks to an overfull line. All these 35// constants are larger than any reasonable actual width score. 36const float SCORE_INFTY = std::numeric_limits<float>::max(); 37const float SCORE_OVERFULL = 1e12f; 38const float SCORE_DESPERATE = 1e10f; 39 40// When the text buffer is within this limit, capacity of vectors is retained at finish(), 41// to avoid allocation. 42const size_t MAX_TEXT_BUF_RETAIN = 32678; 43 44void LineBreaker::setLocale(const icu::Locale& locale, Hyphenator* hyphenator) { 45 delete mBreakIterator; 46 UErrorCode status = U_ZERO_ERROR; 47 mBreakIterator = icu::BreakIterator::createLineInstance(locale, status); 48 // TODO: check status 49 50 // TODO: load actual resource dependent on locale; letting Minikin do it is a hack 51 mHyphenator = hyphenator; 52} 53 54void LineBreaker::setText() { 55 UErrorCode status = U_ZERO_ERROR; 56 utext_openUChars(&mUText, mTextBuf.data(), mTextBuf.size(), &status); 57 mBreakIterator->setText(&mUText, status); 58 mBreakIterator->first(); 59 60 // handle initial break here because addStyleRun may never be called 61 mBreakIterator->next(); 62 mCandidates.clear(); 63 Candidate cand = {0, 0, 0.0, 0.0, 0.0, 0.0, 0, 0}; 64 mCandidates.push_back(cand); 65 66 // reset greedy breaker state 67 mBreaks.clear(); 68 mWidths.clear(); 69 mFlags.clear(); 70 mLastBreak = 0; 71 mBestBreak = 0; 72 mBestScore = SCORE_INFTY; 73 mPreBreak = 0; 74 mFirstTabIndex = INT_MAX; 75} 76 77void LineBreaker::setLineWidths(float firstWidth, int firstWidthLineCount, float restWidth) { 78 mLineWidths.setWidths(firstWidth, firstWidthLineCount, restWidth); 79} 80 81 82void LineBreaker::setIndents(const std::vector<float>& indents) { 83 mLineWidths.setIndents(indents); 84} 85 86// This function determines whether a character is a space that disappears at end of line. 87// It is the Unicode set: [[:General_Category=Space_Separator:]-[:Line_Break=Glue:]] 88// Note: all such characters are in the BMP, so it's ok to use code units for this. 89static bool isLineEndSpace(uint16_t c) { 90 return c == ' ' || c == 0x1680 || (0x2000 <= c && c <= 0x200A && c != 0x2007) || c == 0x205F || 91 c == 0x3000; 92} 93 94// Ordinarily, this method measures the text in the range given. However, when paint 95// is nullptr, it assumes the widths have already been calculated and stored in the 96// width buffer. 97// This method finds the candidate word breaks (using the ICU break iterator) and sends them 98// to addCandidate. 99float LineBreaker::addStyleRun(MinikinPaint* paint, const FontCollection* typeface, 100 FontStyle style, size_t start, size_t end, bool isRtl) { 101 Layout layout; // performance TODO: move layout to self object to reduce allocation cost? 102 float width = 0.0f; 103 int bidiFlags = isRtl ? kBidi_Force_RTL : kBidi_Force_LTR; 104 105 float hyphenPenalty = 0.0; 106 if (paint != nullptr) { 107 layout.setFontCollection(typeface); 108 layout.doLayout(mTextBuf.data(), start, end - start, mTextBuf.size(), bidiFlags, style, 109 *paint); 110 layout.getAdvances(mCharWidths.data() + start); 111 width = layout.getAdvance(); 112 113 // a heuristic that seems to perform well 114 hyphenPenalty = 0.5 * paint->size * paint->scaleX * mLineWidths.getLineWidth(0); 115 } 116 117 size_t current = (size_t)mBreakIterator->current(); 118 size_t wordEnd = start; 119 size_t lastBreak = start; 120 ParaWidth lastBreakWidth = mWidth; 121 ParaWidth postBreak = mWidth; 122 for (size_t i = start; i < end; i++) { 123 uint16_t c = mTextBuf[i]; 124 if (c == CHAR_TAB) { 125 mWidth = mPreBreak + mTabStops.nextTab(mWidth - mPreBreak); 126 if (mFirstTabIndex == INT_MAX) { 127 mFirstTabIndex = (int)i; 128 } 129 // fall back to greedy; other modes don't know how to deal with tabs 130 mStrategy = kBreakStrategy_Greedy; 131 } else { 132 mWidth += mCharWidths[i]; 133 if (!isLineEndSpace(c)) { 134 postBreak = mWidth; 135 wordEnd = i + 1; 136 } 137 } 138 if (i + 1 == current) { 139 // Override ICU's treatment of soft hyphen as a break opportunity, because we want it 140 // to be a hyphen break, with penalty and drawing behavior. 141 if (c != CHAR_SOFT_HYPHEN) { 142 if (paint != nullptr && mHyphenator != nullptr && wordEnd > lastBreak) { 143 mHyphenator->hyphenate(&mHyphBuf, &mTextBuf[lastBreak], wordEnd - lastBreak); 144 #if VERBOSE_DEBUG 145 std::string hyphenatedString; 146 for (size_t j = lastBreak; j < wordEnd; j++) { 147 if (mHyphBuf[j - lastBreak]) hyphenatedString.push_back('-'); 148 // Note: only works with ASCII, should do UTF-8 conversion here 149 hyphenatedString.push_back(buffer()[j]); 150 } 151 ALOGD("hyphenated string: %s", hyphenatedString.c_str()); 152 #endif 153 154 // measure hyphenated substrings 155 for (size_t j = lastBreak; j < wordEnd; j++) { 156 uint8_t hyph = mHyphBuf[j - lastBreak]; 157 if (hyph) { 158 paint->hyphenEdit = hyph; 159 layout.doLayout(mTextBuf.data(), lastBreak, j - lastBreak, 160 mTextBuf.size(), bidiFlags, style, *paint); 161 ParaWidth hyphPostBreak = lastBreakWidth + layout.getAdvance(); 162 paint->hyphenEdit = 0; 163 layout.doLayout(mTextBuf.data(), j, wordEnd - j, 164 mTextBuf.size(), bidiFlags, style, *paint); 165 ParaWidth hyphPreBreak = postBreak - layout.getAdvance(); 166 addWordBreak(j, hyphPreBreak, hyphPostBreak, hyphenPenalty, hyph); 167 } 168 } 169 } 170 171 // Skip break for zero-width characters. 172 if (current == mTextBuf.size() || mCharWidths[current] > 0) { 173 addWordBreak(current, mWidth, postBreak, 0.0, 0); 174 } 175 lastBreak = current; 176 lastBreakWidth = mWidth; 177 } 178 current = (size_t)mBreakIterator->next(); 179 } 180 } 181 182 return width; 183} 184 185// add a word break (possibly for a hyphenated fragment), and add desperate breaks if 186// needed (ie when word exceeds current line width) 187void LineBreaker::addWordBreak(size_t offset, ParaWidth preBreak, ParaWidth postBreak, 188 float penalty, uint8_t hyph) { 189 Candidate cand; 190 ParaWidth width = mCandidates.back().preBreak; 191 if (postBreak - width > currentLineWidth()) { 192 // Add desperate breaks. 193 // Note: these breaks are based on the shaping of the (non-broken) original text; they 194 // are imprecise especially in the presence of kerning, ligatures, and Arabic shaping. 195 size_t i = mCandidates.back().offset; 196 width += mCharWidths[i++]; 197 for (; i < offset; i++) { 198 float w = mCharWidths[i]; 199 if (w > 0) { 200 cand.offset = i; 201 cand.preBreak = width; 202 cand.postBreak = width; 203 cand.penalty = SCORE_DESPERATE; 204 cand.hyphenEdit = 0; 205#if VERBOSE_DEBUG 206 ALOGD("desperate cand: %d %g:%g", 207 mCandidates.size(), cand.postBreak, cand.preBreak); 208#endif 209 addCandidate(cand); 210 width += w; 211 } 212 } 213 } 214 215 cand.offset = offset; 216 cand.preBreak = preBreak; 217 cand.postBreak = postBreak; 218 cand.penalty = penalty; 219 cand.hyphenEdit = hyph; 220#if VERBOSE_DEBUG 221 ALOGD("cand: %d %g:%g", mCandidates.size(), cand.postBreak, cand.preBreak); 222#endif 223 addCandidate(cand); 224} 225 226// TODO: for justified text, refine with shrink/stretch 227float LineBreaker::computeScore(float delta, bool atEnd) { 228 if (delta < 0) { 229 return SCORE_OVERFULL; 230 } else if (atEnd && mStrategy != kBreakStrategy_Balanced) { 231 return 0.0; 232 } else { 233 return delta * delta; 234 } 235} 236 237// TODO performance: could avoid populating mCandidates if greedy only 238void LineBreaker::addCandidate(Candidate cand) { 239 size_t candIndex = mCandidates.size(); 240 mCandidates.push_back(cand); 241 if (cand.postBreak - mPreBreak > currentLineWidth()) { 242 // This break would create an overfull line, pick the best break and break there (greedy) 243 if (mBestBreak == mLastBreak) { 244 mBestBreak = candIndex; 245 } 246 pushBreak(mCandidates[mBestBreak].offset, mCandidates[mBestBreak].postBreak - mPreBreak, 247 mCandidates[mBestBreak].hyphenEdit); 248 mBestScore = SCORE_INFTY; 249#if VERBOSE_DEBUG 250 ALOGD("break: %d %g", mBreaks.back(), mWidths.back()); 251#endif 252 mLastBreak = mBestBreak; 253 mPreBreak = mCandidates[mBestBreak].preBreak; 254 } 255 if (cand.penalty <= mBestScore) { 256 mBestBreak = candIndex; 257 mBestScore = cand.penalty; 258 } 259} 260 261void LineBreaker::pushBreak(int offset, float width, uint8_t hyph) { 262 mBreaks.push_back(offset); 263 mWidths.push_back(width); 264 int flags = (mFirstTabIndex < mBreaks.back()) << kTab_Shift; 265 flags |= hyph; 266 mFlags.push_back(flags); 267 mFirstTabIndex = INT_MAX; 268} 269 270void LineBreaker::addReplacement(size_t start, size_t end, float width) { 271 mCharWidths[start] = width; 272 std::fill(&mCharWidths[start + 1], &mCharWidths[end], 0.0f); 273 addStyleRun(nullptr, nullptr, FontStyle(), start, end, false); 274} 275 276float LineBreaker::currentLineWidth() const { 277 return mLineWidths.getLineWidth(mBreaks.size()); 278} 279 280void LineBreaker::computeBreaksGreedy() { 281 // All breaks but the last have been added in addCandidate already. 282 size_t nCand = mCandidates.size(); 283 if (nCand == 1 || mLastBreak != nCand - 1) { 284 pushBreak(mCandidates[nCand - 1].offset, mCandidates[nCand - 1].postBreak - mPreBreak, 0); 285 // don't need to update mBestScore, because we're done 286#if VERBOSE_DEBUG 287 ALOGD("final break: %d %g", mBreaks.back(), mWidths.back()); 288#endif 289 } 290} 291 292// Follow "prev" links in mCandidates array, and copy to result arrays. 293void LineBreaker::finishBreaksOptimal() { 294 // clear existing greedy break result 295 mBreaks.clear(); 296 mWidths.clear(); 297 mFlags.clear(); 298 size_t nCand = mCandidates.size(); 299 size_t prev; 300 for (size_t i = nCand - 1; i > 0; i = prev) { 301 prev = mCandidates[i].prev; 302 mBreaks.push_back(mCandidates[i].offset); 303 mWidths.push_back(mCandidates[i].postBreak - mCandidates[prev].preBreak); 304 mFlags.push_back(mCandidates[i].hyphenEdit); 305 } 306 std::reverse(mBreaks.begin(), mBreaks.end()); 307 std::reverse(mWidths.begin(), mWidths.end()); 308 std::reverse(mFlags.begin(), mFlags.end()); 309} 310 311void LineBreaker::computeBreaksOptimal() { 312 size_t active = 0; 313 size_t nCand = mCandidates.size(); 314 for (size_t i = 1; i < nCand; i++) { 315 bool atEnd = i == nCand - 1; 316 float best = SCORE_INFTY; 317 size_t bestPrev = 0; 318 319 size_t lineNumberLast = mCandidates[active].lineNumber; 320 float width = mLineWidths.getLineWidth(lineNumberLast); 321 ParaWidth leftEdge = mCandidates[i].postBreak - width; 322 float bestHope = 0; 323 324 for (size_t j = active; j < i; j++) { 325 size_t lineNumber = mCandidates[j].lineNumber; 326 if (lineNumber != lineNumberLast) { 327 float widthNew = mLineWidths.getLineWidth(lineNumber); 328 if (widthNew != width) { 329 leftEdge = mCandidates[i].postBreak - width; 330 bestHope = 0; 331 width = widthNew; 332 } 333 lineNumberLast = lineNumber; 334 } 335 float jScore = mCandidates[j].score; 336 if (jScore + bestHope >= best) continue; 337 float delta = mCandidates[j].preBreak - leftEdge; 338 339 float widthScore = computeScore(delta, atEnd); 340 if (delta < 0) { 341 active = j + 1; 342 } else { 343 bestHope = widthScore; 344 } 345 346 float score = jScore + widthScore; 347 if (score <= best) { 348 best = score; 349 bestPrev = j; 350 } 351 } 352 mCandidates[i].score = best + mCandidates[i].penalty; 353 mCandidates[i].prev = bestPrev; 354 mCandidates[i].lineNumber = mCandidates[bestPrev].lineNumber + 1; 355 } 356 finishBreaksOptimal(); 357} 358 359void LineBreaker::computeBreaksOptimalRect() { 360 size_t active = 0; 361 size_t nCand = mCandidates.size(); 362 float width = mLineWidths.getLineWidth(0); 363 for (size_t i = 1; i < nCand; i++) { 364 bool atEnd = i == nCand - 1; 365 float best = SCORE_INFTY; 366 size_t bestPrev = 0; 367 368 // Width-based component of score increases as line gets shorter, so score will always be 369 // at least this. 370 float bestHope = 0; 371 372 ParaWidth leftEdge = mCandidates[i].postBreak - width; 373 for (size_t j = active; j < i; j++) { 374 // TODO performance: can break if bestHope >= best; worth it? 375 float jScore = mCandidates[j].score; 376 if (jScore + bestHope >= best) continue; 377 float delta = mCandidates[j].preBreak - leftEdge; 378 379 float widthScore = computeScore(delta, atEnd); 380 if (delta < 0) { 381 active = j + 1; 382 } else { 383 bestHope = widthScore; 384 } 385 386 float score = jScore + widthScore; 387 if (score <= best) { 388 best = score; 389 bestPrev = j; 390 } 391 } 392 mCandidates[i].score = best + mCandidates[i].penalty; 393 mCandidates[i].prev = bestPrev; 394 } 395 finishBreaksOptimal(); 396} 397 398size_t LineBreaker::computeBreaks() { 399 if (mStrategy == kBreakStrategy_Greedy) { 400 computeBreaksGreedy(); 401 } else if (mLineWidths.isConstant()) { 402 computeBreaksOptimalRect(); 403 } else { 404 computeBreaksOptimal(); 405 } 406 return mBreaks.size(); 407} 408 409void LineBreaker::finish() { 410 mWidth = 0; 411 mCandidates.clear(); 412 mBreaks.clear(); 413 mWidths.clear(); 414 mFlags.clear(); 415 if (mTextBuf.size() > MAX_TEXT_BUF_RETAIN) { 416 mTextBuf.clear(); 417 mTextBuf.shrink_to_fit(); 418 mCharWidths.clear(); 419 mCharWidths.shrink_to_fit(); 420 mHyphBuf.clear(); 421 mHyphBuf.shrink_to_fit(); 422 mCandidates.shrink_to_fit(); 423 mBreaks.shrink_to_fit(); 424 mWidths.shrink_to_fit(); 425 mFlags.shrink_to_fit(); 426 } 427 mStrategy = kBreakStrategy_Greedy; 428} 429 430} // namespace android 431