LineBreaker.cpp revision abae97a39c26e191e350575932611a90e6b04d06
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// Multiplier for hyphen penalty on last line. 41const float LAST_LINE_PENALTY_MULTIPLIER = 4.0f; 42// Penalty assigned to each line break (to try to minimize number of lines) 43// TODO: when we implement full justification (so spaces can shrink and stretch), this is 44// probably not the most appropriate method. 45const float LINE_PENALTY_MULTIPLIER = 2.0f; 46 47// Very long words trigger O(n^2) behavior in hyphenation, so we disable hyphenation for 48// unreasonably long words. This is somewhat of a heuristic because extremely long words 49// are possible in some languages. This does mean that very long real words can get 50// broken by desperate breaks, with no hyphens. 51const size_t LONGEST_HYPHENATED_WORD = 45; 52 53// When the text buffer is within this limit, capacity of vectors is retained at finish(), 54// to avoid allocation. 55const size_t MAX_TEXT_BUF_RETAIN = 32678; 56 57void LineBreaker::setLocale(const icu::Locale& locale, Hyphenator* hyphenator) { 58 delete mBreakIterator; 59 UErrorCode status = U_ZERO_ERROR; 60 mBreakIterator = icu::BreakIterator::createLineInstance(locale, status); 61 // TODO: check status 62 63 // TODO: load actual resource dependent on locale; letting Minikin do it is a hack 64 mHyphenator = hyphenator; 65} 66 67void LineBreaker::setText() { 68 UErrorCode status = U_ZERO_ERROR; 69 utext_openUChars(&mUText, mTextBuf.data(), mTextBuf.size(), &status); 70 mBreakIterator->setText(&mUText, status); 71 mBreakIterator->first(); 72 73 // handle initial break here because addStyleRun may never be called 74 mBreakIterator->next(); 75 mCandidates.clear(); 76 Candidate cand = {0, 0, 0.0, 0.0, 0.0, 0.0, 0, 0}; 77 mCandidates.push_back(cand); 78 79 // reset greedy breaker state 80 mBreaks.clear(); 81 mWidths.clear(); 82 mFlags.clear(); 83 mLastBreak = 0; 84 mBestBreak = 0; 85 mBestScore = SCORE_INFTY; 86 mPreBreak = 0; 87 mFirstTabIndex = INT_MAX; 88} 89 90void LineBreaker::setLineWidths(float firstWidth, int firstWidthLineCount, float restWidth) { 91 mLineWidths.setWidths(firstWidth, firstWidthLineCount, restWidth); 92} 93 94 95void LineBreaker::setIndents(const std::vector<float>& indents) { 96 mLineWidths.setIndents(indents); 97} 98 99// This function determines whether a character is a space that disappears at end of line. 100// It is the Unicode set: [[:General_Category=Space_Separator:]-[:Line_Break=Glue:]], 101// plus '\n'. 102// Note: all such characters are in the BMP, so it's ok to use code units for this. 103static bool isLineEndSpace(uint16_t c) { 104 return c == '\n' || c == ' ' || c == 0x1680 || (0x2000 <= c && c <= 0x200A && c != 0x2007) || 105 c == 0x205F || c == 0x3000; 106} 107 108// Ordinarily, this method measures the text in the range given. However, when paint 109// is nullptr, it assumes the widths have already been calculated and stored in the 110// width buffer. 111// This method finds the candidate word breaks (using the ICU break iterator) and sends them 112// to addCandidate. 113float LineBreaker::addStyleRun(MinikinPaint* paint, const FontCollection* typeface, 114 FontStyle style, size_t start, size_t end, bool isRtl) { 115 Layout layout; // performance TODO: move layout to self object to reduce allocation cost? 116 float width = 0.0f; 117 int bidiFlags = isRtl ? kBidi_Force_RTL : kBidi_Force_LTR; 118 119 float hyphenPenalty = 0.0; 120 if (paint != nullptr) { 121 layout.setFontCollection(typeface); 122 layout.doLayout(mTextBuf.data(), start, end - start, mTextBuf.size(), bidiFlags, style, 123 *paint); 124 layout.getAdvances(mCharWidths.data() + start); 125 width = layout.getAdvance(); 126 127 // a heuristic that seems to perform well 128 hyphenPenalty = 0.5 * paint->size * paint->scaleX * mLineWidths.getLineWidth(0); 129 if (mHyphenationFrequency == kHyphenationFrequency_Normal) { 130 hyphenPenalty *= 4.0; // TODO: Replace with a better value after some testing 131 } 132 133 mLinePenalty = std::max(mLinePenalty, hyphenPenalty * LINE_PENALTY_MULTIPLIER); 134 } 135 136 size_t current = (size_t)mBreakIterator->current(); 137 size_t wordEnd = start; 138 size_t lastBreak = start; 139 ParaWidth lastBreakWidth = mWidth; 140 ParaWidth postBreak = mWidth; 141 for (size_t i = start; i < end; i++) { 142 uint16_t c = mTextBuf[i]; 143 if (c == CHAR_TAB) { 144 mWidth = mPreBreak + mTabStops.nextTab(mWidth - mPreBreak); 145 if (mFirstTabIndex == INT_MAX) { 146 mFirstTabIndex = (int)i; 147 } 148 // fall back to greedy; other modes don't know how to deal with tabs 149 mStrategy = kBreakStrategy_Greedy; 150 } else { 151 mWidth += mCharWidths[i]; 152 if (!isLineEndSpace(c)) { 153 postBreak = mWidth; 154 wordEnd = i + 1; 155 } 156 } 157 if (i + 1 == current) { 158 // Override ICU's treatment of soft hyphen as a break opportunity, because we want it 159 // to be a hyphen break, with penalty and drawing behavior. 160 if (c != CHAR_SOFT_HYPHEN) { 161 if (paint != nullptr && mHyphenator != nullptr && 162 mHyphenationFrequency != kHyphenationFrequency_None && 163 wordEnd > lastBreak && wordEnd - lastBreak <= LONGEST_HYPHENATED_WORD) { 164 mHyphenator->hyphenate(&mHyphBuf, &mTextBuf[lastBreak], wordEnd - lastBreak); 165 #if VERBOSE_DEBUG 166 std::string hyphenatedString; 167 for (size_t j = lastBreak; j < wordEnd; j++) { 168 if (mHyphBuf[j - lastBreak]) hyphenatedString.push_back('-'); 169 // Note: only works with ASCII, should do UTF-8 conversion here 170 hyphenatedString.push_back(buffer()[j]); 171 } 172 ALOGD("hyphenated string: %s", hyphenatedString.c_str()); 173 #endif 174 175 // measure hyphenated substrings 176 for (size_t j = lastBreak; j < wordEnd; j++) { 177 uint8_t hyph = mHyphBuf[j - lastBreak]; 178 if (hyph) { 179 paint->hyphenEdit = hyph; 180 layout.doLayout(mTextBuf.data(), lastBreak, j - lastBreak, 181 mTextBuf.size(), bidiFlags, style, *paint); 182 ParaWidth hyphPostBreak = lastBreakWidth + layout.getAdvance(); 183 paint->hyphenEdit = 0; 184 layout.doLayout(mTextBuf.data(), j, wordEnd - j, 185 mTextBuf.size(), bidiFlags, style, *paint); 186 ParaWidth hyphPreBreak = postBreak - layout.getAdvance(); 187 addWordBreak(j, hyphPreBreak, hyphPostBreak, hyphenPenalty, hyph); 188 } 189 } 190 } 191 192 // Skip break for zero-width characters. 193 if (current == mTextBuf.size() || mCharWidths[current] > 0) { 194 addWordBreak(current, mWidth, postBreak, 0.0, 0); 195 } 196 lastBreak = current; 197 lastBreakWidth = mWidth; 198 } 199 current = (size_t)mBreakIterator->next(); 200 } 201 } 202 203 return width; 204} 205 206// add a word break (possibly for a hyphenated fragment), and add desperate breaks if 207// needed (ie when word exceeds current line width) 208void LineBreaker::addWordBreak(size_t offset, ParaWidth preBreak, ParaWidth postBreak, 209 float penalty, uint8_t hyph) { 210 Candidate cand; 211 ParaWidth width = mCandidates.back().preBreak; 212 if (postBreak - width > currentLineWidth()) { 213 // Add desperate breaks. 214 // Note: these breaks are based on the shaping of the (non-broken) original text; they 215 // are imprecise especially in the presence of kerning, ligatures, and Arabic shaping. 216 size_t i = mCandidates.back().offset; 217 width += mCharWidths[i++]; 218 for (; i < offset; i++) { 219 float w = mCharWidths[i]; 220 if (w > 0) { 221 cand.offset = i; 222 cand.preBreak = width; 223 cand.postBreak = width; 224 cand.penalty = SCORE_DESPERATE; 225 cand.hyphenEdit = 0; 226#if VERBOSE_DEBUG 227 ALOGD("desperate cand: %d %g:%g", 228 mCandidates.size(), cand.postBreak, cand.preBreak); 229#endif 230 addCandidate(cand); 231 width += w; 232 } 233 } 234 } 235 236 cand.offset = offset; 237 cand.preBreak = preBreak; 238 cand.postBreak = postBreak; 239 cand.penalty = penalty; 240 cand.hyphenEdit = hyph; 241#if VERBOSE_DEBUG 242 ALOGD("cand: %d %g:%g", mCandidates.size(), cand.postBreak, cand.preBreak); 243#endif 244 addCandidate(cand); 245} 246 247// TODO performance: could avoid populating mCandidates if greedy only 248void LineBreaker::addCandidate(Candidate cand) { 249 size_t candIndex = mCandidates.size(); 250 mCandidates.push_back(cand); 251 if (cand.postBreak - mPreBreak > currentLineWidth()) { 252 // This break would create an overfull line, pick the best break and break there (greedy) 253 if (mBestBreak == mLastBreak) { 254 mBestBreak = candIndex; 255 } 256 pushBreak(mCandidates[mBestBreak].offset, mCandidates[mBestBreak].postBreak - mPreBreak, 257 mCandidates[mBestBreak].hyphenEdit); 258 mBestScore = SCORE_INFTY; 259#if VERBOSE_DEBUG 260 ALOGD("break: %d %g", mBreaks.back(), mWidths.back()); 261#endif 262 mLastBreak = mBestBreak; 263 mPreBreak = mCandidates[mBestBreak].preBreak; 264 } 265 if (cand.penalty <= mBestScore) { 266 mBestBreak = candIndex; 267 mBestScore = cand.penalty; 268 } 269} 270 271void LineBreaker::pushBreak(int offset, float width, uint8_t hyph) { 272 mBreaks.push_back(offset); 273 mWidths.push_back(width); 274 int flags = (mFirstTabIndex < mBreaks.back()) << kTab_Shift; 275 flags |= hyph; 276 mFlags.push_back(flags); 277 mFirstTabIndex = INT_MAX; 278} 279 280void LineBreaker::addReplacement(size_t start, size_t end, float width) { 281 mCharWidths[start] = width; 282 std::fill(&mCharWidths[start + 1], &mCharWidths[end], 0.0f); 283 addStyleRun(nullptr, nullptr, FontStyle(), start, end, false); 284} 285 286float LineBreaker::currentLineWidth() const { 287 return mLineWidths.getLineWidth(mBreaks.size()); 288} 289 290void LineBreaker::computeBreaksGreedy() { 291 // All breaks but the last have been added in addCandidate already. 292 size_t nCand = mCandidates.size(); 293 if (nCand == 1 || mLastBreak != nCand - 1) { 294 pushBreak(mCandidates[nCand - 1].offset, mCandidates[nCand - 1].postBreak - mPreBreak, 0); 295 // don't need to update mBestScore, because we're done 296#if VERBOSE_DEBUG 297 ALOGD("final break: %d %g", mBreaks.back(), mWidths.back()); 298#endif 299 } 300} 301 302// Follow "prev" links in mCandidates array, and copy to result arrays. 303void LineBreaker::finishBreaksOptimal() { 304 // clear existing greedy break result 305 mBreaks.clear(); 306 mWidths.clear(); 307 mFlags.clear(); 308 size_t nCand = mCandidates.size(); 309 size_t prev; 310 for (size_t i = nCand - 1; i > 0; i = prev) { 311 prev = mCandidates[i].prev; 312 mBreaks.push_back(mCandidates[i].offset); 313 mWidths.push_back(mCandidates[i].postBreak - mCandidates[prev].preBreak); 314 mFlags.push_back(mCandidates[i].hyphenEdit); 315 } 316 std::reverse(mBreaks.begin(), mBreaks.end()); 317 std::reverse(mWidths.begin(), mWidths.end()); 318 std::reverse(mFlags.begin(), mFlags.end()); 319} 320 321void LineBreaker::computeBreaksOptimal(bool isRectangle) { 322 size_t active = 0; 323 size_t nCand = mCandidates.size(); 324 float width = mLineWidths.getLineWidth(0); 325 for (size_t i = 1; i < nCand; i++) { 326 bool atEnd = i == nCand - 1; 327 float best = SCORE_INFTY; 328 size_t bestPrev = 0; 329 size_t lineNumberLast = 0; 330 331 if (!isRectangle) { 332 size_t lineNumberLast = mCandidates[active].lineNumber; 333 width = mLineWidths.getLineWidth(lineNumberLast); 334 } 335 ParaWidth leftEdge = mCandidates[i].postBreak - width; 336 float bestHope = 0; 337 338 for (size_t j = active; j < i; j++) { 339 if (!isRectangle) { 340 size_t lineNumber = mCandidates[j].lineNumber; 341 if (lineNumber != lineNumberLast) { 342 float widthNew = mLineWidths.getLineWidth(lineNumber); 343 if (widthNew != width) { 344 leftEdge = mCandidates[i].postBreak - width; 345 bestHope = 0; 346 width = widthNew; 347 } 348 lineNumberLast = lineNumber; 349 } 350 } 351 float jScore = mCandidates[j].score; 352 if (jScore + bestHope >= best) continue; 353 float delta = mCandidates[j].preBreak - leftEdge; 354 355 // compute width score for line 356 float widthScore = 0.0f; 357 if (delta < 0) { 358 widthScore = SCORE_OVERFULL; 359 } else if (atEnd && mStrategy != kBreakStrategy_Balanced) { 360 // increase penalty for hyphen on last line 361 widthScore = LAST_LINE_PENALTY_MULTIPLIER * mCandidates[j].penalty; 362 } else { 363 widthScore = delta * delta; 364 } 365 366 if (delta < 0) { 367 active = j + 1; 368 } else { 369 bestHope = widthScore; 370 } 371 372 float score = jScore + widthScore; 373 if (score <= best) { 374 best = score; 375 bestPrev = j; 376 } 377 } 378 mCandidates[i].score = best + mCandidates[i].penalty + mLinePenalty; 379 mCandidates[i].prev = bestPrev; 380 mCandidates[i].lineNumber = mCandidates[bestPrev].lineNumber + 1; 381 } 382 finishBreaksOptimal(); 383} 384 385size_t LineBreaker::computeBreaks() { 386 if (mStrategy == kBreakStrategy_Greedy) { 387 computeBreaksGreedy(); 388 } else { 389 computeBreaksOptimal(mLineWidths.isConstant()); 390 } 391 return mBreaks.size(); 392} 393 394void LineBreaker::finish() { 395 mWidth = 0; 396 mCandidates.clear(); 397 mBreaks.clear(); 398 mWidths.clear(); 399 mFlags.clear(); 400 if (mTextBuf.size() > MAX_TEXT_BUF_RETAIN) { 401 mTextBuf.clear(); 402 mTextBuf.shrink_to_fit(); 403 mCharWidths.clear(); 404 mCharWidths.shrink_to_fit(); 405 mHyphBuf.clear(); 406 mHyphBuf.shrink_to_fit(); 407 mCandidates.shrink_to_fit(); 408 mBreaks.shrink_to_fit(); 409 mWidths.shrink_to_fit(); 410 mFlags.shrink_to_fit(); 411 } 412 mStrategy = kBreakStrategy_Greedy; 413 mHyphenationFrequency = kHyphenationFrequency_Normal; 414 mLinePenalty = 0.0f; 415} 416 417} // namespace android 418