LineBreaker.h revision 5cdad92c300a65cab89b172e952186f0c5870657
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/** 18 * A module for breaking paragraphs into lines, supporting high quality 19 * hyphenation and justification. 20 */ 21 22#ifndef MINIKIN_LINE_BREAKER_H 23#define MINIKIN_LINE_BREAKER_H 24 25#include "unicode/brkiter.h" 26#include "unicode/locid.h" 27#include <cmath> 28#include <vector> 29#include "minikin/Hyphenator.h" 30 31namespace android { 32 33enum BreakStrategy { 34 kBreakStrategy_Greedy = 0, 35 kBreakStrategy_HighQuality = 1, 36 kBreakStrategy_Balanced = 2 37}; 38 39// TODO: want to generalize to be able to handle array of line widths 40class LineWidths { 41 public: 42 void setWidths(float firstWidth, int firstWidthLineCount, float restWidth) { 43 mFirstWidth = firstWidth; 44 mFirstWidthLineCount = firstWidthLineCount; 45 mRestWidth = restWidth; 46 } 47 bool isConstant() const { 48 // technically mFirstWidthLineCount == 0 would count too, but doesn't actually happen 49 return mRestWidth == mFirstWidth; 50 } 51 float getLineWidth(int line) const { 52 return (line < mFirstWidthLineCount) ? mFirstWidth : mRestWidth; 53 } 54 private: 55 float mFirstWidth; 56 int mFirstWidthLineCount; 57 float mRestWidth; 58}; 59 60class TabStops { 61 public: 62 void set(const int* stops, size_t nStops, int tabWidth) { 63 if (stops != nullptr) { 64 mStops.assign(stops, stops + nStops); 65 } else { 66 mStops.clear(); 67 } 68 mTabWidth = tabWidth; 69 } 70 float nextTab(float widthSoFar) const { 71 for (size_t i = 0; i < mStops.size(); i++) { 72 if (mStops[i] > widthSoFar) { 73 return mStops[i]; 74 } 75 } 76 return floor(widthSoFar / mTabWidth + 1) * mTabWidth; 77 } 78 private: 79 std::vector<int> mStops; 80 int mTabWidth; 81}; 82 83class LineBreaker { 84 public: 85 const static int kTab_Shift = 29; // keep synchronized with TAB_MASK in StaticLayout.java 86 87 ~LineBreaker() { 88 utext_close(&mUText); 89 delete mBreakIterator; 90 } 91 92 // Note: Locale persists across multiple invocations (it is not cleaned up by finish()), 93 // explicitly to avoid the cost of creating ICU BreakIterator objects. It should always 94 // be set on the first invocation, but callers are encouraged not to call again unless 95 // locale has actually changed. 96 // That logic could be here but it's better for performance that it's upstream because of 97 // the cost of constructing and comparing the ICU Locale object. 98 // Note: caller is responsible for managing lifetime of hyphenator 99 void setLocale(const icu::Locale& locale, Hyphenator* hyphenator); 100 101 void resize(size_t size) { 102 mTextBuf.resize(size); 103 mCharWidths.resize(size); 104 } 105 106 size_t size() const { 107 return mTextBuf.size(); 108 } 109 110 uint16_t* buffer() { 111 return mTextBuf.data(); 112 } 113 114 float* charWidths() { 115 return mCharWidths.data(); 116 } 117 118 // set text to current contents of buffer 119 void setText(); 120 121 void setLineWidths(float firstWidth, int firstWidthLineCount, float restWidth); 122 123 void setTabStops(const int* stops, size_t nStops, int tabWidth) { 124 mTabStops.set(stops, nStops, tabWidth); 125 } 126 127 BreakStrategy getStrategy() const { return mStrategy; } 128 129 void setStrategy(BreakStrategy strategy) { mStrategy = strategy; } 130 131 // TODO: this class is actually fairly close to being general and not tied to using 132 // Minikin to do the shaping of the strings. The main thing that would need to be changed 133 // is having some kind of callback (or virtual class, or maybe even template), which could 134 // easily be instantiated with Minikin's Layout. Future work for when needed. 135 float addStyleRun(MinikinPaint* paint, const FontCollection* typeface, FontStyle style, 136 size_t start, size_t end, bool isRtl); 137 138 void addReplacement(size_t start, size_t end, float width); 139 140 size_t computeBreaks(); 141 142 const int* getBreaks() const { 143 return mBreaks.data(); 144 } 145 146 const float* getWidths() const { 147 return mWidths.data(); 148 } 149 150 const int* getFlags() const { 151 return mFlags.data(); 152 } 153 154 void finish(); 155 156 private: 157 // ParaWidth is used to hold cumulative width from beginning of paragraph. Note that for 158 // very large paragraphs, accuracy could degrade using only 32-bit float. Note however 159 // that float is used extensively on the Java side for this. This is a typedef so that 160 // we can easily change it based on performance/accuracy tradeoff. 161 typedef double ParaWidth; 162 163 // A single candidate break 164 struct Candidate { 165 size_t offset; // offset to text buffer, in code units 166 size_t prev; // index to previous break 167 ParaWidth preBreak; 168 ParaWidth postBreak; 169 float penalty; // penalty of this break (for example, hyphen penalty) 170 float score; // best score found for this break 171 size_t lineNumber; // only updated for non-constant line widths 172 uint8_t hyphenEdit; 173 }; 174 175 float currentLineWidth() const; 176 177 // compute shrink/stretch penalty for line 178 float computeScore(float delta, bool atEnd); 179 180 void addWordBreak(size_t offset, ParaWidth preBreak, ParaWidth postBreak, float penalty, 181 uint8_t hyph); 182 183 void addCandidate(Candidate cand); 184 185 // push an actual break to the output. Takes care of setting flags for tab 186 void pushBreak(int offset, float width, uint8_t hyph); 187 188 void computeBreaksGreedy(); 189 190 void computeBreaksOptimal(); 191 192 // special case when LineWidth is constant (layout is rectangle) 193 void computeBreaksOptimalRect(); 194 195 void finishBreaksOptimal(); 196 197 icu::BreakIterator* mBreakIterator = nullptr; 198 UText mUText = UTEXT_INITIALIZER; 199 std::vector<uint16_t>mTextBuf; 200 std::vector<float>mCharWidths; 201 202 Hyphenator* mHyphenator; 203 std::vector<uint8_t> mHyphBuf; 204 205 // layout parameters 206 BreakStrategy mStrategy = kBreakStrategy_Greedy; 207 LineWidths mLineWidths; 208 TabStops mTabStops; 209 210 // result of line breaking 211 std::vector<int> mBreaks; 212 std::vector<float> mWidths; 213 std::vector<int> mFlags; 214 215 ParaWidth mWidth = 0; 216 std::vector<Candidate> mCandidates; 217 218 // the following are state for greedy breaker (updated while adding style runs) 219 size_t mLastBreak; 220 size_t mBestBreak; 221 float mBestScore; 222 ParaWidth mPreBreak; // prebreak of last break 223 int mFirstTabIndex; 224}; 225 226} // namespace android 227 228#endif // MINIKIN_LINE_BREAKER_H 229