gecko/content/base/public/nsLineBreaker.h

176 lines
7.2 KiB
C++

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is Novell code.
*
* The Initial Developer of the Original Code is Novell.
* Portions created by the Initial Developer are Copyright (C) 2006
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
* Robert O'Callahan <robert@ocallahan.org> (Original Author)
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU General Public License Version 2 or later (the "GPL"), or
* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of either the GPL or the LGPL, and not to allow others to
* use your version of this file under the terms of the MPL, indicate your
* decision by deleting the provisions above and replace them with the notice
* and other provisions required by the GPL or the LGPL. If you do not delete
* the provisions above, a recipient may use your version of this file under
* the terms of any one of the MPL, the GPL or the LGPL.
*
* ***** END LICENSE BLOCK ***** */
#ifndef NSLINEBREAKER_H_
#define NSLINEBREAKER_H_
#include "nsString.h"
#include "nsTArray.h"
class nsIAtom;
/**
* 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.
*/
virtual void SetBreaks(PRUint32 aStart, PRUint32 aLength, PRPackedBool* aBreakBefore) = 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 for words that contain a CJK character,
* we break within the word using JISx4051 rules.
* XXX This approach is not very good and we should replace it with something
* better, such as some variant of UAX#14.
*/
class nsLineBreaker {
public:
nsLineBreaker();
~nsLineBreaker();
// We need finegrained control of the line breaking behaviour to ensure
// that we get tricky CSS semantics right (in particular, the way we currently
// interpret and implement them; there's some ambiguity in the spec). The
// rules for CSS 'white-space' are slightly different for breaks induced by
// whitespace and space induced by nonwhitespace. Breaks induced by
// whitespace are always controlled by the
// 'white-space' property of the text node containing the
// whitespace. Breaks induced by non-whitespace where the break is between
// two nodes are controled by the 'white-space' property on the nearest
// common ancestor node. Therefore we provide separate control over
// a) whether whitespace in this text induces breaks b) whether we can
// break between nonwhitespace inside this text and c) whether we can break
// between nonwhitespace between the last text and this text.
//
// "Whitespace" below means Unicode ZWSP (U+200B) and ASCII space (U+0020). We
// operate on text after whitespace processing has been applied, so
// other characters (e.g. tabs and newlines) may have been converted to
// spaces.
enum {
/**
* Allow breaks where a non-whitespace character in this block of text
* is preceded by a whitespace character.
*/
BREAK_WHITESPACE_END = 0x01,
/**
* Allow breaks between eligible nonwhitespace characters when the break
* is in the interior of this block of text.
*/
BREAK_NONWHITESPACE_INSIDE = 0x02,
/**
* Allow break between eligible nonwhitespace characters when the break
* is at the beginning of this block of text.
*/
BREAK_NONWHITESPACE_BEFORE = 0x04
};
/**
* Feed Unicode text into the linebreaker for analysis.
* If aLength is zero, then we assume the string is "invisible whitespace"
* which can induce breaks.
*/
nsresult AppendText(nsIAtom* aLangGroup, const PRUnichar* aText, PRUint32 aLength,
PRUint32 aFlags, nsILineBreakSink* aSink);
/**
* Feed 8-bit text into the linebreaker for analysis.
* If aLength is zero, then we assume the string is "invisible whitespace"
* which can induce breaks.
*/
nsresult AppendText(nsIAtom* aLangGroup, const PRUint8* aText, PRUint32 aLength,
PRUint32 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.
*/
nsresult Reset() { return FlushCurrentWord(); }
private:
struct TextItem {
TextItem(nsILineBreakSink* aSink, PRUint32 aSinkOffset, PRUint32 aLength,
PRUint32 aFlags)
: mSink(aSink), mSinkOffset(aSinkOffset), mLength(aLength), mFlags(aFlags) {}
nsILineBreakSink* mSink;
PRUint32 mSinkOffset;
PRUint32 mLength;
PRUint32 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();
nsAutoTArray<PRUnichar,100> mCurrentWord;
// All the items that contribute to mCurrentWord
nsAutoTArray<TextItem,2> mTextItems;
PRPackedBool mCurrentWordContainsCJK;
// When mCurrentWord is empty, this indicates whether we should allow a break
// before the next text if it starts with non-whitespace.
PRPackedBool mBreakBeforeNonWhitespace;
};
#endif /*NSLINEBREAKER_H_*/