tor-browser

nsLineBreaker.h (12423B)

---

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef NSLINEBREAKER_H_
#define NSLINEBREAKER_H_

#include "mozilla/intl/LineBreaker.h"
#include "mozilla/intl/Segmenter.h"
#include "nsString.h"
#include "nsTArray.h"

class nsAtom;
class nsHyphenator;

/**
* A receiver of line break data.
*/
class nsILineBreakSink {
public:
 /**
  * Sets the break data for a substring of the associated text chunk.
  * One or more of these calls will be performed; the union of all substrings
  * will cover the entire text chunk. Substrings may overlap (i.e., we may
  * set the break-before state of a character more than once).
  * @param aBreakBefore the break-before states for the characters in the
  * substring. These are enum values from gfxTextRun::CompressedGlyph:
  *    FLAG_BREAK_TYPE_NONE     - no linebreak is allowed here
  *    FLAG_BREAK_TYPE_NORMAL   - a normal (whitespace) linebreak
  *    FLAG_BREAK_TYPE_HYPHEN   - a hyphenation point
  */
 virtual void SetBreaks(uint32_t aStart, uint32_t aLength,
                        uint8_t* aBreakBefore) = 0;

 /**
  * Indicates which characters should be capitalized. Only called if
  * BREAK_NEED_CAPITALIZATION was requested.
  */
 virtual void SetCapitalization(uint32_t aStart, uint32_t aLength,
                                bool* aCapitalize) = 0;
};

/**
* A line-breaking state machine. You feed text into it via AppendText calls
* and it computes the possible line breaks. Because break decisions can
* require a lot of context, the breaks for a piece of text are sometimes not
* known until later text has been seen (or all text ends). So breaks are
* returned via a call to SetBreaks on the nsILineBreakSink object passed
* with each text chunk, which might happen during the corresponding AppendText
* call, or might happen during a later AppendText call or even a Reset()
* call.
*
* The linebreak results MUST NOT depend on how the text is broken up
* into AppendText calls.
*
* The current strategy is that we break the overall text into
* whitespace-delimited "words". Then those words are passed to the LineBreaker
* for deeper analysis if they might contain breakable characters.
*
* This class also handles detection of which characters should be capitalized
* for text-transform:capitalize. This is a good place to handle that because
* we have all the context we need.
*/
class nsLineBreaker {
public:
 nsLineBreaker();
 ~nsLineBreaker();

 static inline bool IsSpace(char16_t u) {
   return mozilla::intl::NS_IsSpace(u);
 }

 // Helper also used by nsCaseTransformTextRunFactory::TransformString.
 // aChar is the current character to be examined;
 // aCapitalizeNext is a state variable: initialize it to true at start-of-
 // text, then pass it back to this function as each successive character is
 // considered.
 static bool ShouldCapitalize(uint32_t aChar, bool& aCapitalizeNext);

 // Break opportunities exist at the end of each run of breakable whitespace
 // (see IsSpace above). Break opportunities can also exist between pairs of
 // non-whitespace characters, as determined by mozilla::intl::LineBreaker.
 // We pass a whitespace-
 // delimited word to LineBreaker if it contains at least one character
 // that has breakable line breaking classes.
 // We provide flags to control on a per-chunk basis where breaks are allowed.
 // At any character boundary, exactly one text chunk governs whether a
 // break is allowed at that boundary.
 //
 // We operate on text after whitespace processing has been applied, so
 // other characters (e.g. tabs and newlines) may have been converted to
 // spaces.

 /**
  * Flags passed with each chunk of text.
  */
 enum {
   /*
    * Do not introduce a break opportunity at the start of this chunk of text.
    */
   BREAK_SUPPRESS_INITIAL = 0x01,
   /**
    * Do not introduce a break opportunity in the interior of this chunk of
    * text. Also, whitespace in this chunk is treated as non-breakable.
    */
   BREAK_SUPPRESS_INSIDE = 0x02,
   /**
    * The sink currently is already set up to have no breaks in it;
    * if no breaks are possible, nsLineBreaker does not need to call
    * SetBreaks on it. This is useful when handling large quantities of
    * preformatted text; the textruns will never have any breaks set on them,
    * and there is no need to ever actually scan the text for breaks, except
    * at the end of textruns in case context is needed for following breakable
    * text.
    */
   BREAK_SKIP_SETTING_NO_BREAKS = 0x04,
   /**
    * We need to be notified of characters that should be capitalized
    * (as in text-transform:capitalize) in this chunk of text.
    */
   BREAK_NEED_CAPITALIZATION = 0x08,
   /**
    * Auto-hyphenation is enabled, so we need to get a hyphenator
    * (if available) and use it to find breakpoints.
    */
   BREAK_USE_AUTO_HYPHENATION = 0x10
 };

 /**
  * Append "invisible whitespace". This acts like whitespace, but there is
  * no actual text associated with it. Only the BREAK_SUPPRESS_INSIDE flag
  * is relevant here.
  */
 nsresult AppendInvisibleWhitespace(uint32_t aFlags);

 /**
  * Feed Unicode text into the linebreaker for analysis. aLength must be
  * nonzero.
  * @param aSink can be null if the breaks are not actually needed (we may
  * still be setting up state for later breaks)
  */
 nsresult AppendText(nsAtom* aHyphenationLanguage, const char16_t* aText,
                     uint32_t aLength, uint32_t aFlags,
                     nsILineBreakSink* aSink);
 /**
  * Feed 8-bit text into the linebreaker for analysis. aLength must be nonzero.
  * @param aSink can be null if the breaks are not actually needed (we may
  * still be setting up state for later breaks)
  */
 nsresult AppendText(nsAtom* aHyphenationLanguage, const uint8_t* aText,
                     uint32_t aLength, uint32_t aFlags,
                     nsILineBreakSink* aSink);
 /**
  * Reset all state. This means the current run has ended; any outstanding
  * calls through nsILineBreakSink are made, and all outstanding references to
  * nsILineBreakSink objects are dropped.
  * After this call, this linebreaker can be reused.
  * This must be called at least once between any call to AppendText() and
  * destroying the object.
  * @param aTrailingBreak this is set to true when there is a break opportunity
  * at the end of the text. This will normally only be declared true when there
  * is breakable whitespace at the end.
  */
 nsresult Reset(bool* aTrailingBreak);

 /*
  * Set word-break mode for line breaker. This is set by word-break property.
  */
 void SetWordBreak(mozilla::intl::WordBreakRule aMode) {
   // If current word is non-empty and mode is changing, flush the breaker.
   if (aMode != mWordBreak && !mCurrentWord.IsEmpty()) {
     nsresult rv = FlushCurrentWord();
     if (NS_FAILED(rv)) {
       NS_WARNING("FlushCurrentWord failed, line-breaks may be wrong");
     }
     // If previous mode was break-all, we should allow a break here.
     // XXX (jfkthame) css-text spec seems unclear on this, raised question in
     // https://github.com/w3c/csswg-drafts/issues/3897
     if (mWordBreak == mozilla::intl::WordBreakRule::BreakAll) {
       mBreakHere = true;
     }
   }
   mWordBreak = aMode;
 }

 /*
  * Set line-break rule strictness mode for line breaker. This is set by the
  * line-break property.
  */
 void SetStrictness(mozilla::intl::LineBreakRule aMode) {
   if (aMode != mLineBreak && !mCurrentWord.IsEmpty()) {
     nsresult rv = FlushCurrentWord();
     if (NS_FAILED(rv)) {
       NS_WARNING("FlushCurrentWord failed, line-breaks may be wrong");
     }
     // If previous mode was anywhere, we should allow a break here.
     if (mLineBreak == mozilla::intl::LineBreakRule::Anywhere) {
       mBreakHere = true;
     }
   }
   mLineBreak = aMode;
 }

 /**
  * Return whether the line-breaker has a buffered "current word" that may
  * be extended with additional word-forming characters.
  */
 bool InWord() const { return !mCurrentWord.IsEmpty(); }

 /**
  * Set the word-continuation state, which will suppress capitalization of
  * the next letter that might otherwise apply.
  */
 void SetWordContinuation(bool aContinuation) {
   mWordContinuation = aContinuation;
 }

 /**
  * Set the hyphenate-limit-chars values. Values are clamped to be <= 255.
  */
 void SetHyphenateLimitChars(uint32_t aWordLength, uint32_t aStartLength,
                             uint32_t aEndLength) {
   mHyphenateLimitWord = std::min(255u, aWordLength);
   mHyphenateLimitStart = std::min(255u, aStartLength);
   mHyphenateLimitEnd = std::min(255u, aEndLength);
 }

private:
 // This is a list of text sources that make up the "current word" (i.e.,
 // run of text which does not contain any whitespace). All the mLengths
 // are are nonzero, these cannot overlap.
 struct TextItem {
   TextItem(nsILineBreakSink* aSink, uint32_t aSinkOffset, uint32_t aLength,
            uint32_t aFlags)
       : mSink(aSink),
         mSinkOffset(aSinkOffset),
         mLength(aLength),
         mFlags(aFlags) {}

   nsILineBreakSink* mSink;
   uint32_t mSinkOffset;
   uint32_t mLength;
   uint32_t mFlags;
 };

 // State for the nonwhitespace "word" that started in previous text and hasn't
 // finished yet.

 // When the current word ends, this computes the linebreak opportunities
 // *inside* the word (excluding either end) and sets them through the
 // appropriate sink(s). Then we clear the current word state.
 nsresult FlushCurrentWord();

 void UpdateCurrentWordLanguage(nsAtom* aHyphenationLanguage);

 void FindHyphenationPoints(nsHyphenator* aHyphenator,
                            const char16_t* aTextStart,
                            const char16_t* aTextLimit, uint8_t* aBreakState);

 inline constexpr bool IsSegmentSpace(char16_t u) const {
   if (mLegacyBehavior) {
     return nsLineBreaker::IsSpace(u);
   }

   return u == 0x0020 ||  // SPACE u
          u == 0x0009 ||  // CHARACTER TABULATION
          u == 0x000D;    // CARRIAGE RETURN
 }

 AutoTArray<char16_t, 100> mCurrentWord;
 // All the items that contribute to mCurrentWord
 AutoTArray<TextItem, 2> mTextItems;
 nsAtom* mCurrentWordLanguage = nullptr;

 // Constraints from CSS `hyphenate-limit-chars` property, to block the use of
 // auto-hyphenation if the word is too short, or at positions too near the
 // beginning/end of the word.
 // (Note that per CSS Text spec, these counts ignore combining marks, etc.,
 // so they are not purely codepoint or character counts.)
 // (Zero values would have no effect; but text-frame code will update the
 // values from CSS before calling the line-breaker.)
 uint8_t mHyphenateLimitWord = 0;   // Min word length to auto-hyphenate
 uint8_t mHyphenateLimitStart = 0;  // Min number of chars before the break
 uint8_t mHyphenateLimitEnd = 0;    // Min number of chars after the break

 bool mCurrentWordContainsMixedLang = false;
 bool mCurrentWordMightBeBreakable = false;
 bool mScriptIsChineseOrJapanese = false;

 // True if the previous character was breakable whitespace
 bool mAfterBreakableSpace = false;
 // True if a break must be allowed at the current position because
 // a run of breakable whitespace ends here
 bool mBreakHere = false;
 // Break rules for letters from the "word-break" property.
 mozilla::intl::WordBreakRule mWordBreak =
     mozilla::intl::WordBreakRule::Normal;
 // Line breaking strictness from the "line-break" property.
 mozilla::intl::LineBreakRule mLineBreak = mozilla::intl::LineBreakRule::Auto;
 // Should the text be treated as continuing a word-in-progress (for purposes
 // of initial capitalization)? Normally this is set to false whenever we
 // start using a linebreaker, but it may be set to true if the line-breaker
 // has been explicitly flushed mid-word.
 bool mWordContinuation = false;
 // True if using old line segmenter.
 const bool mLegacyBehavior;
};

#endif /*NSLINEBREAKER_H_*/