Bidi
public
class
Bidi
extends Object
java.lang.Object | |
↳ | android.icu.text.Bidi |
Bidi algorithm for ICU
This is an implementation of the Unicode Bidirectional Algorithm. The algorithm is defined in the Unicode Standard Annex #9.Note: Libraries that perform a bidirectional algorithm and reorder strings accordingly are sometimes called "Storage Layout Engines". ICU's Bidi and shaping (ArabicShaping) classes can be used at the core of such "Storage Layout Engines".
General remarks about the API:
The "limit" of a sequence of characters is the position just after their last character, i.e., one more than that position.Some of the API methods provide access to "runs". Such a "run" is defined as a sequence of characters that are at the same embedding level after performing the Bidi algorithm.
Basic concept: paragraph
A piece of text can be divided into several paragraphs by characters with the Bidi classBlock Separator
. For handling of
paragraphs, see:
Basic concept: text direction
The direction of a piece of text may be:Basic concept: levels
Levels in this API represent embedding levels according to the Unicode Bidirectional Algorithm. Their low-order bit (even/odd value) indicates the visual direction.
Levels can be abstract values when used for the
paraLevel
and embeddingLevels
arguments of setPara()
; there:
- the high-order bit of an
embeddingLevels[]
value indicates whether the using application is specifying the level of a character to override whatever the Bidi implementation would resolve it to. paraLevel
can be set to the pseudo-level valuesLEVEL_DEFAULT_LTR
andLEVEL_DEFAULT_RTL
.
The related constants are not real, valid level values.
DEFAULT_XXX
can be used to specify
a default for the paragraph level for
when the setPara()
method
shall determine it but there is no
strongly typed character in the input.
Note that the value for LEVEL_DEFAULT_LTR
is even
and the one for LEVEL_DEFAULT_RTL
is odd,
just like with normal LTR and RTL level values -
these special values are designed that way. Also, the implementation
assumes that MAX_EXPLICIT_LEVEL is odd.
Note: The numeric values of the related constants will not change: They are tied to the use of 7-bit byte values (plus the override bit) and of the byte data type in this API.
See Also:
Basic concept: Reordering Mode
Reordering mode values indicate which variant of the Bidi algorithm to use. See Also:setReorderingMode(int)
REORDER_DEFAULT
REORDER_NUMBERS_SPECIAL
REORDER_GROUP_NUMBERS_WITH_R
REORDER_RUNS_ONLY
REORDER_INVERSE_NUMBERS_AS_L
REORDER_INVERSE_LIKE_DIRECT
REORDER_INVERSE_FOR_NUMBERS_SPECIAL
Basic concept: Reordering Options
Reordering options can be applied during Bidi text transformations. See Also:setReorderingOptions(int)
OPTION_DEFAULT
OPTION_INSERT_MARKS
OPTION_REMOVE_CONTROLS
OPTION_STREAMING
Sample code for the ICU Bidi API
Rendering a paragraph with the ICU Bidi API
This is (hypothetical) sample code that illustrates how the ICU Bidi API could be used to render a paragraph of text. Rendering code depends highly on the graphics system, therefore this sample code must make a lot of assumptions, which may or may not match any existing graphics system's properties.The basic assumptions are:
- Rendering is done from left to right on a horizontal line.
- A run of single-style, unidirectional text can be rendered at once.
- Such a run of text is passed to the graphics system with characters (code units) in logical order.
- The line-breaking algorithm is very complicated and Locale-dependent - and therefore its implementation omitted from this sample code.
package android.icu.dev.test.bidi; import android.icu.text.Bidi; import android.icu.text.BidiRun; public class Sample { static final int styleNormal = 0; static final int styleSelected = 1; static final int styleBold = 2; static final int styleItalics = 4; static final int styleSuper=8; static final int styleSub = 16; static class StyleRun { int limit; int style; public StyleRun(int limit, int style) { this.limit = limit; this.style = style; } } static class Bounds { int start; int limit; public Bounds(int start, int limit) { this.start = start; this.limit = limit; } } static int getTextWidth(String text, int start, int limit, StyleRun[] styleRuns, int styleRunCount) { // simplistic way to compute the width return limit - start; } // set limit and StyleRun limit for a line // from text[start] and from styleRuns[styleRunStart] // using Bidi.getLogicalRun(...) // returns line width static int getLineBreak(String text, Bounds line, Bidi para, StyleRun styleRuns[], Bounds styleRun) { // dummy return return 0; } // render runs on a line sequentially, always from left to right // prepare rendering a new line static void startLine(byte textDirection, int lineWidth) { System.out.println(); } // render a run of text and advance to the right by the run width // the text[start..limit-1] is always in logical order static void renderRun(String text, int start, int limit, byte textDirection, int style) { } // We could compute a cross-product // from the style runs with the directional runs // and then reorder it. // Instead, here we iterate over each run type // and render the intersections - // with shortcuts in simple (and common) cases. // renderParagraph() is the main function. // render a directional run with // (possibly) multiple style runs intersecting with it static void renderDirectionalRun(String text, int start, int limit, byte direction, StyleRun styleRuns[], int styleRunCount) { int i; // iterate over style runs if (direction == Bidi.LTR) { int styleLimit; for (i = 0; i < styleRunCount; ++i) { styleLimit = styleRuns[i].limit; if (start < styleLimit) { if (styleLimit > limit) { styleLimit = limit; } renderRun(text, start, styleLimit, direction, styleRuns[i].style); if (styleLimit == limit) { break; } start = styleLimit; } } } else { int styleStart; for (i = styleRunCount-1; i >= 0; --i) { if (i > 0) { styleStart = styleRuns[i-1].limit; } else { styleStart = 0; } if (limit >= styleStart) { if (styleStart < start) { styleStart = start; } renderRun(text, styleStart, limit, direction, styleRuns[i].style); if (styleStart == start) { break; } limit = styleStart; } } } } // the line object represents text[start..limit-1] static void renderLine(Bidi line, String text, int start, int limit, StyleRun styleRuns[], int styleRunCount) { byte direction = line.getDirection(); if (direction != Bidi.MIXED) { // unidirectional if (styleRunCount <= 1) { renderRun(text, start, limit, direction, styleRuns[0].style); } else { renderDirectionalRun(text, start, limit, direction, styleRuns, styleRunCount); } } else { // mixed-directional int count, i; BidiRun run; try { count = line.countRuns(); } catch (IllegalStateException e) { e.printStackTrace(); return; } if (styleRunCount <= 1) { int style = styleRuns[0].style; // iterate over directional runs for (i = 0; i < count; ++i) { run = line.getVisualRun(i); renderRun(text, run.getStart(), run.getLimit(), run.getDirection(), style); } } else { // iterate over both directional and style runs for (i = 0; i < count; ++i) { run = line.getVisualRun(i); renderDirectionalRun(text, run.getStart(), run.getLimit(), run.getDirection(), styleRuns, styleRunCount); } } } } static void renderParagraph(String text, byte textDirection, StyleRun styleRuns[], int styleRunCount, int lineWidth) { int length = text.length(); Bidi para = new Bidi(); try { para.setPara(text, textDirection != 0 ? Bidi.LEVEL_DEFAULT_RTL : Bidi.LEVEL_DEFAULT_LTR, null); } catch (Exception e) { e.printStackTrace(); return; } byte paraLevel = (byte)(1 & para.getParaLevel()); StyleRun styleRun = new StyleRun(length, styleNormal); if (styleRuns == null || styleRunCount <= 0) { styleRuns = new StyleRun[1]; styleRunCount = 1; styleRuns[0] = styleRun; } // assume styleRuns[styleRunCount-1].limit>=length int width = getTextWidth(text, 0, length, styleRuns, styleRunCount); if (width <= lineWidth) { // everything fits onto one line // prepare rendering a new line from either left or right startLine(paraLevel, width); renderLine(para, text, 0, length, styleRuns, styleRunCount); } else { // we need to render several lines Bidi line = new Bidi(length, 0); int start = 0, limit; int styleRunStart = 0, styleRunLimit; for (;;) { limit = length; styleRunLimit = styleRunCount; width = getLineBreak(text, new Bounds(start, limit), para, styleRuns, new Bounds(styleRunStart, styleRunLimit)); try { line = para.setLine(start, limit); } catch (Exception e) { e.printStackTrace(); return; } // prepare rendering a new line // from either left or right startLine(paraLevel, width); if (styleRunStart > 0) { int newRunCount = styleRuns.length - styleRunStart; StyleRun[] newRuns = new StyleRun[newRunCount]; System.arraycopy(styleRuns, styleRunStart, newRuns, 0, newRunCount); renderLine(line, text, start, limit, newRuns, styleRunLimit - styleRunStart); } else { renderLine(line, text, start, limit, styleRuns, styleRunLimit - styleRunStart); } if (limit == length) { break; } start = limit; styleRunStart = styleRunLimit - 1; if (start >= styleRuns[styleRunStart].limit) { ++styleRunStart; } } } } public static void main(String[] args) { renderParagraph("Some Latin text...", Bidi.LTR, null, 0, 80); renderParagraph("Some Hebrew text...", Bidi.RTL, null, 0, 60); } }
Summary
Constants | |
---|---|
int |
DIRECTION_DEFAULT_LEFT_TO_RIGHT
Constant indicating that the base direction depends on the first strong directional character in the text according to the Unicode Bidirectional Algorithm. |
int |
DIRECTION_DEFAULT_RIGHT_TO_LEFT
Constant indicating that the base direction depends on the first strong directional character in the text according to the Unicode Bidirectional Algorithm. |
int |
DIRECTION_LEFT_TO_RIGHT
Constant indicating base direction is left-to-right. |
int |
DIRECTION_RIGHT_TO_LEFT
Constant indicating base direction is right-to-left. |
short |
DO_MIRRORING
option bit for writeReordered(): replace characters with the "mirrored" property in RTL runs by their mirror-image mappings |
short |
INSERT_LRM_FOR_NUMERIC
option bit for writeReordered(): surround the run with LRMs if necessary; this is part of the approximate "inverse Bidi" algorithm This option does not imply corresponding adjustment of the index mappings. |
short |
KEEP_BASE_COMBINING
option bit for writeReordered(): keep combining characters after their base characters in RTL runs |
byte |
LEVEL_DEFAULT_LTR
Paragraph level setting Constant indicating that the base direction depends on the first strong directional character in the text according to the Unicode Bidirectional Algorithm. |
byte |
LEVEL_DEFAULT_RTL
Paragraph level setting Constant indicating that the base direction depends on the first strong directional character in the text according to the Unicode Bidirectional Algorithm. |
byte |
LEVEL_OVERRIDE
Bit flag for level input. |
byte |
LTR
Left-to-right text. |
int |
MAP_NOWHERE
Special value which can be returned by the mapping methods when a logical index has no corresponding visual index or vice-versa. |
byte |
MAX_EXPLICIT_LEVEL
Maximum explicit embedding level. |
byte |
MIXED
Mixed-directional text. |
byte |
NEUTRAL
No strongly directional text. |
int |
OPTION_DEFAULT
Option value for |
int |
OPTION_INSERT_MARKS
Option bit for This option must be set or reset before calling
|
int |
OPTION_REMOVE_CONTROLS
Option bit for This option must be set or reset before calling
|
int |
OPTION_STREAMING
Option bit for This option must be set or reset before calling
|
short |
OUTPUT_REVERSE
option bit for writeReordered(): write the output in reverse order This has the same effect as calling |
short |
REMOVE_BIDI_CONTROLS
option bit for writeReordered(): remove Bidi control characters (this does not affect INSERT_LRM_FOR_NUMERIC) This option does not imply corresponding adjustment of the index mappings. |
short |
REORDER_DEFAULT
Reordering mode: Regular Logical to Visual Bidi algorithm according to Unicode. |
short |
REORDER_GROUP_NUMBERS_WITH_R
Reordering mode: Logical to Visual algorithm grouping numbers with adjacent R characters (reversible algorithm). |
short |
REORDER_INVERSE_FOR_NUMBERS_SPECIAL
Reordering mode: Inverse Bidi (Visual to Logical) algorithm for the
|
short |
REORDER_INVERSE_LIKE_DIRECT
Reordering mode: Visual to Logical algorithm equivalent to the regular Logical to Visual algorithm. |
short |
REORDER_INVERSE_NUMBERS_AS_L
Reordering mode: Visual to Logical algorithm which handles numbers
like L (same algorithm as selected by |
short |
REORDER_NUMBERS_SPECIAL
Reordering mode: Logical to Visual algorithm which handles numbers in a way which mimicks the behavior of Windows XP. |
short |
REORDER_RUNS_ONLY
Reordering mode: Reorder runs only to transform a Logical LTR string to the logical RTL string with the same display, or vice-versa. |
byte |
RTL
Right-to-left text. |
Public constructors | |
---|---|
Bidi()
Allocate a |
|
Bidi(int maxLength, int maxRunCount)
Allocate a |
|
Bidi(String paragraph, int flags)
Create Bidi from the given paragraph of text and base direction. |
|
Bidi(AttributedCharacterIterator paragraph)
Create Bidi from the given paragraph of text. |
|
Bidi(char[] text, int textStart, byte[] embeddings, int embStart, int paragraphLength, int flags)
Create Bidi from the given text, embedding, and direction information. |
Public methods | |
---|---|
boolean
|
baseIsLeftToRight()
Return true if the base direction is left-to-right |
int
|
countParagraphs()
Get the number of paragraphs. |
int
|
countRuns()
Get the number of runs. |
Bidi
|
createLineBidi(int lineStart, int lineLimit)
Create a Bidi object representing the bidi information on a line of text within the paragraph represented by the current Bidi. |
static
byte
|
getBaseDirection(CharSequence paragraph)
Get the base direction of the text provided according to the Unicode Bidirectional Algorithm. |
int
|
getBaseLevel()
Return the base level (0 if left-to-right, 1 if right-to-left). |
BidiClassifier
|
getCustomClassifier()
Gets the current custom class classifier used for Bidi class determination. |
int
|
getCustomizedClass(int c)
Retrieves the Bidi class for a given code point. |
byte
|
getDirection()
Get the directionality of the text. |
int
|
getLength()
Get the length of the text. |
byte
|
getLevelAt(int charIndex)
Get the level for one character. |
byte[]
|
getLevels()
Get an array of levels for each character. |
int
|
getLogicalIndex(int visualIndex)
Get the logical text position from a visual position. |
int[]
|
getLogicalMap()
Get a logical-to-visual index map (array) for the characters in the
|
BidiRun
|
getLogicalRun(int logicalPosition)
Get a logical run. |
byte
|
getParaLevel()
Get the paragraph level of the text. |
BidiRun
|
getParagraph(int charIndex)
Get a paragraph, given a position within the text. |
BidiRun
|
getParagraphByIndex(int paraIndex)
Get a paragraph, given the index of this paragraph. |
int
|
getParagraphIndex(int charIndex)
Get the index of a paragraph, given a position within the text. |
int
|
getProcessedLength()
Get the length of the source text processed by the last call to
|
int
|
getReorderingMode()
What is the requested reordering mode for a given Bidi object? |
int
|
getReorderingOptions()
What are the reordering options applied to a given Bidi object? |
int
|
getResultLength()
Get the length of the reordered text resulting from the last call to
|
int
|
getRunCount()
Return the number of level runs. |
int
|
getRunLevel(int run)
Return the level of the nth logical run in this line. |
int
|
getRunLimit(int run)
Return the index of the character past the end of the nth logical run in this line, as an offset from the start of the line. |
int
|
getRunStart(int run)
Return the index of the character at the start of the nth logical run in this line, as an offset from the start of the line. |
char[]
|
getText()
Get the text. |
String
|
getTextAsString()
Get the text. |
int
|
getVisualIndex(int logicalIndex)
Get the visual position from a logical text position. |
int[]
|
getVisualMap()
Get a visual-to-logical index map (array) for the characters in the
|
BidiRun
|
getVisualRun(int runIndex)
Get a |
static
int[]
|
invertMap(int[] srcMap)
Invert an index map. |
boolean
|
isInverse()
Is this Note: calling this method after setting the reordering mode with
|
boolean
|
isLeftToRight()
Return true if the line is all left-to-right text and the base direction is left-to-right. |
boolean
|
isMixed()
Return true if the line is not left-to-right or right-to-left. |
boolean
|
isOrderParagraphsLTR()
Is this |
boolean
|
isRightToLeft()
Return true if the line is all right-to-left text, and the base direction is right-to-left |
void
|
orderParagraphsLTR(boolean ordarParaLTR)
Specify whether block separators must be allocated level zero, so that successive paragraphs will progress from left to right. |
static
int[]
|
reorderLogical(byte[] levels)
This is a convenience method that does not use a |
static
int[]
|
reorderVisual(byte[] levels)
This is a convenience method that does not use a |
static
void
|
reorderVisually(byte[] levels, int levelStart, Object[] objects, int objectStart, int count)
Reorder the objects in the array into visual order based on their levels. |
static
boolean
|
requiresBidi(char[] text, int start, int limit)
Return true if the specified text requires bidi analysis. |
void
|
setContext(String prologue, String epilogue)
Set the context before a call to setPara(). |
void
|
setCustomClassifier(BidiClassifier classifier)
Set a custom Bidi classifier used by the UBA implementation for Bidi class determination. |
void
|
setInverse(boolean isInverse)
Modify the operation of the Bidi algorithm such that it approximates an "inverse Bidi" algorithm. |
Bidi
|
setLine(int start, int limit)
|
void
|
setPara(AttributedCharacterIterator paragraph)
Perform the Unicode Bidi algorithm on a given paragraph, as defined in the Unicode Standard Annex #9, version 13, also described in The Unicode Standard, Version 4.0 . |
void
|
setPara(char[] chars, byte paraLevel, byte[] embeddingLevels)
Perform the Unicode Bidi algorithm. |
void
|
setPara(String text, byte paraLevel, byte[] embeddingLevels)
Perform the Unicode Bidi algorithm. |
void
|
setReorderingMode(int reorderingMode)
Modify the operation of the Bidi algorithm such that it implements some variant to the basic Bidi algorithm or approximates an "inverse Bidi" algorithm, depending on different values of the "reordering mode". |
void
|
setReorderingOptions(int options)
Specify which of the reordering options should be applied during Bidi transformations. |
String
|
writeReordered(int options)
Take a |
static
String
|
writeReverse(String src, int options)
Reverse a Right-To-Left run of Unicode text. |
Inherited methods | |
---|---|
Constants
DIRECTION_DEFAULT_LEFT_TO_RIGHT
public static final int DIRECTION_DEFAULT_LEFT_TO_RIGHT
Constant indicating that the base direction depends on the first strong directional character in the text according to the Unicode Bidirectional Algorithm. If no strong directional character is present, the base direction is left-to-right.
Constant Value: 126 (0x0000007e)
DIRECTION_DEFAULT_RIGHT_TO_LEFT
public static final int DIRECTION_DEFAULT_RIGHT_TO_LEFT
Constant indicating that the base direction depends on the first strong directional character in the text according to the Unicode Bidirectional Algorithm. If no strong directional character is present, the base direction is right-to-left.
Constant Value: 127 (0x0000007f)
DIRECTION_LEFT_TO_RIGHT
public static final int DIRECTION_LEFT_TO_RIGHT
Constant indicating base direction is left-to-right.
Constant Value: 0 (0x00000000)
DIRECTION_RIGHT_TO_LEFT
public static final int DIRECTION_RIGHT_TO_LEFT
Constant indicating base direction is right-to-left.
Constant Value: 1 (0x00000001)
DO_MIRRORING
public static final short DO_MIRRORING
option bit for writeReordered(): replace characters with the "mirrored" property in RTL runs by their mirror-image mappings
See also:
Constant Value: 2 (0x00000002)
INSERT_LRM_FOR_NUMERIC
public static final short INSERT_LRM_FOR_NUMERIC
option bit for writeReordered(): surround the run with LRMs if necessary; this is part of the approximate "inverse Bidi" algorithm
This option does not imply corresponding adjustment of the index mappings.
See also:
Constant Value: 4 (0x00000004)
KEEP_BASE_COMBINING
public static final short KEEP_BASE_COMBINING
option bit for writeReordered(): keep combining characters after their base characters in RTL runs
See also:
Constant Value: 1 (0x00000001)
LEVEL_DEFAULT_LTR
public static final byte LEVEL_DEFAULT_LTR
Paragraph level setting
Constant indicating that the base direction depends on the first strong directional character in the text according to the Unicode Bidirectional Algorithm. If no strong directional character is present, then set the paragraph level to 0 (left-to-right).
If this value is used in conjunction with reordering modes
REORDER_INVERSE_LIKE_DIRECT
or
REORDER_INVERSE_FOR_NUMBERS_SPECIAL
, the text to reorder
is assumed to be visual LTR, and the text after reordering is required
to be the corresponding logical string with appropriate contextual
direction. The direction of the result string will be RTL if either
the rightmost or leftmost strong character of the source text is RTL
or Arabic Letter, the direction will be LTR otherwise.
If reordering option OPTION_INSERT_MARKS
is set, an RLM may
be added at the beginning of the result string to ensure round trip
(that the result string, when reordered back to visual, will produce
the original source text).
Constant Value: 126 (0x0000007e)
LEVEL_DEFAULT_RTL
public static final byte LEVEL_DEFAULT_RTL
Paragraph level setting
Constant indicating that the base direction depends on the first strong directional character in the text according to the Unicode Bidirectional Algorithm. If no strong directional character is present, then set the paragraph level to 1 (right-to-left).
If this value is used in conjunction with reordering modes
REORDER_INVERSE_LIKE_DIRECT
or
REORDER_INVERSE_FOR_NUMBERS_SPECIAL
, the text to reorder
is assumed to be visual LTR, and the text after reordering is required
to be the corresponding logical string with appropriate contextual
direction. The direction of the result string will be RTL if either
the rightmost or leftmost strong character of the source text is RTL
or Arabic Letter, or if the text contains no strong character;
the direction will be LTR otherwise.
If reordering option OPTION_INSERT_MARKS
is set, an RLM may
be added at the beginning of the result string to ensure round trip
(that the result string, when reordered back to visual, will produce
the original source text).
Constant Value: 127 (0x0000007f)
LEVEL_OVERRIDE
public static final byte LEVEL_OVERRIDE
Bit flag for level input. Overrides directional properties.
Constant Value: -128 (0xffffff80)
LTR
public static final byte LTR
Left-to-right text.
- As return value for
getDirection()
, it means that the source string contains no right-to-left characters, or that the source string is empty and the paragraph level is even. - As return value for
getBaseDirection()
, it means that the first strong character of the source string has a left-to-right direction.
Constant Value: 0 (0x00000000)
MAP_NOWHERE
public static final int MAP_NOWHERE
Special value which can be returned by the mapping methods when a
logical index has no corresponding visual index or vice-versa. This may
happen for the logical-to-visual mapping of a Bidi control when option
OPTION_REMOVE_CONTROLS
is
specified. This can also happen for the visual-to-logical mapping of a
Bidi mark (LRM or RLM) inserted by option
OPTION_INSERT_MARKS
.
See also:
Constant Value: -1 (0xffffffff)
MAX_EXPLICIT_LEVEL
public static final byte MAX_EXPLICIT_LEVEL
Maximum explicit embedding level.
Same as the max_depth value in the
Unicode Bidirectional Algorithm.
(The maximum resolved level can be up to MAX_EXPLICIT_LEVEL+1
).
Constant Value: 125 (0x0000007d)
MIXED
public static final byte MIXED
Mixed-directional text.
As return value for getDirection()
, it means
that the source string contains both left-to-right and
right-to-left characters.
Constant Value: 2 (0x00000002)
NEUTRAL
public static final byte NEUTRAL
No strongly directional text.
As return value for getBaseDirection()
, it means
that the source string is missing or empty, or contains neither
left-to-right nor right-to-left characters.
Constant Value: 3 (0x00000003)
OPTION_DEFAULT
public static final int OPTION_DEFAULT
Option value for setReorderingOptions
:
disable all the options which can be set with this method
See also:
Constant Value: 0 (0x00000000)
OPTION_INSERT_MARKS
public static final int OPTION_INSERT_MARKS
Option bit for setReorderingOptions
:
insert Bidi marks (LRM or RLM) when needed to ensure correct result of
a reordering to a Logical order
This option must be set or reset before calling
setPara
.
This option is significant only with reordering modes which generate a result with Logical order, specifically.
REORDER_RUNS_ONLY
REORDER_INVERSE_NUMBERS_AS_L
REORDER_INVERSE_LIKE_DIRECT
REORDER_INVERSE_FOR_NUMBERS_SPECIAL
If this option is set in conjunction with reordering mode
REORDER_INVERSE_NUMBERS_AS_L
or with calling
setInverse(true)
, it implies option
INSERT_LRM_FOR_NUMERIC
in calls to method
writeReordered()
.
For other reordering modes, a minimum number of LRM or RLM characters
will be added to the source text after reordering it so as to ensure
round trip, i.e. when applying the inverse reordering mode on the
resulting logical text with removal of Bidi marks
(option OPTION_REMOVE_CONTROLS
set before calling
setPara()
or option
REMOVE_BIDI_CONTROLS
in
writeReordered
), the result will be identical to the
source text in the first transformation.
This option will be ignored if specified together with option
OPTION_REMOVE_CONTROLS
. It inhibits option
REMOVE_BIDI_CONTROLS
in calls to method
writeReordered()
and it implies option
INSERT_LRM_FOR_NUMERIC
in calls to method
writeReordered()
if the reordering mode is
REORDER_INVERSE_NUMBERS_AS_L
.
See also:
Constant Value: 1 (0x00000001)
OPTION_REMOVE_CONTROLS
public static final int OPTION_REMOVE_CONTROLS
Option bit for setReorderingOptions
:
remove Bidi control characters
This option must be set or reset before calling
setPara
.
This option nullifies option
OPTION_INSERT_MARKS
. It inhibits option
INSERT_LRM_FOR_NUMERIC
in calls to method
writeReordered()
and it implies option
REMOVE_BIDI_CONTROLS
in calls to that method.
See also:
Constant Value: 2 (0x00000002)
OPTION_STREAMING
public static final int OPTION_STREAMING
Option bit for setReorderingOptions
:
process the output as part of a stream to be continued
This option must be set or reset before calling
setPara
.
This option specifies that the caller is interested in processing large text object in parts. The results of the successive calls are expected to be concatenated by the caller. Only the call for the last part will have this option bit off.
When this option bit is on, setPara()
may process
less than the full source text in order to truncate the text at a
meaningful boundary. The caller should call
getProcessedLength()
immediately after calling
setPara()
in order to determine how much of the source
text has been processed. Source text beyond that length should be
resubmitted in following calls to setPara
. The
processed length may be less than the length of the source text if a
character preceding the last character of the source text constitutes a
reasonable boundary (like a block separator) for text to be continued.
If the last character of the source text constitutes a reasonable
boundary, the whole text will be processed at once.
If nowhere in the source text there exists
such a reasonable boundary, the processed length will be zero.
The caller should check for such an occurrence and do one of the following:
- submit a larger amount of text with a better chance to include a reasonable boundary.
- resubmit the same text after turning off option
OPTION_STREAMING
.
When the OPTION_STREAMING
option is used, it is
recommended to call orderParagraphsLTR(true)
before calling
setPara()
so that later paragraphs may be concatenated to
previous paragraphs on the right.
Constant Value: 4 (0x00000004)
OUTPUT_REVERSE
public static final short OUTPUT_REVERSE
option bit for writeReordered(): write the output in reverse order
This has the same effect as calling writeReordered()
first without this option, and then calling
writeReverse()
without mirroring.
Doing this in the same step is faster and avoids a temporary buffer.
An example for using this option is output to a character terminal that
is designed for RTL scripts and stores text in reverse order.
See also:
Constant Value: 16 (0x00000010)
REMOVE_BIDI_CONTROLS
public static final short REMOVE_BIDI_CONTROLS
option bit for writeReordered(): remove Bidi control characters (this does not affect INSERT_LRM_FOR_NUMERIC)
This option does not imply corresponding adjustment of the index mappings.
Constant Value: 8 (0x00000008)
REORDER_DEFAULT
public static final short REORDER_DEFAULT
Reordering mode: Regular Logical to Visual Bidi algorithm according to Unicode.
See also:
Constant Value: 0 (0x00000000)
REORDER_GROUP_NUMBERS_WITH_R
public static final short REORDER_GROUP_NUMBERS_WITH_R
Reordering mode: Logical to Visual algorithm grouping numbers with adjacent R characters (reversible algorithm).
See also:
Constant Value: 2 (0x00000002)
REORDER_INVERSE_FOR_NUMBERS_SPECIAL
public static final short REORDER_INVERSE_FOR_NUMBERS_SPECIAL
Reordering mode: Inverse Bidi (Visual to Logical) algorithm for the
REORDER_NUMBERS_SPECIAL
Bidi algorithm.
See also:
Constant Value: 6 (0x00000006)
REORDER_INVERSE_LIKE_DIRECT
public static final short REORDER_INVERSE_LIKE_DIRECT
Reordering mode: Visual to Logical algorithm equivalent to the regular Logical to Visual algorithm.
See also:
Constant Value: 5 (0x00000005)
REORDER_INVERSE_NUMBERS_AS_L
public static final short REORDER_INVERSE_NUMBERS_AS_L
Reordering mode: Visual to Logical algorithm which handles numbers
like L (same algorithm as selected by setInverse(true)
.
Constant Value: 4 (0x00000004)
REORDER_NUMBERS_SPECIAL
public static final short REORDER_NUMBERS_SPECIAL
Reordering mode: Logical to Visual algorithm which handles numbers in a way which mimicks the behavior of Windows XP.
See also:
Constant Value: 1 (0x00000001)
REORDER_RUNS_ONLY
public static final short REORDER_RUNS_ONLY
Reordering mode: Reorder runs only to transform a Logical LTR string
to the logical RTL string with the same display, or vice-versa.
If this mode is set together with option
OPTION_INSERT_MARKS
, some Bidi controls in the source
text may be removed and other controls may be added to produce the
minimum combination which has the required display.
Constant Value: 3 (0x00000003)
RTL
public static final byte RTL
Right-to-left text.
- As return value for
getDirection()
, it means that the source string contains no left-to-right characters, or that the source string is empty and the paragraph level is odd. - As return value for
getBaseDirection()
, it means that the first strong character of the source string has a right-to-left direction.
Constant Value: 1 (0x00000001)
Public constructors
Bidi
public Bidi ()
Allocate a Bidi
object.
Such an object is initially empty. It is assigned
the Bidi properties of a piece of text containing one or more paragraphs
by setPara()
or the Bidi properties of a line within a paragraph by
setLine()
.
This object can be reused.
setPara()
and setLine()
will allocate
additional memory for internal structures as necessary.
Bidi
public Bidi (int maxLength, int maxRunCount)
Allocate a Bidi
object with preallocated memory
for internal structures.
This method provides a Bidi
object like the default constructor
but it also preallocates memory for internal structures
according to the sizings supplied by the caller.
The preallocation can be limited to some of the internal memory
by setting some values to 0 here. That means that if, e.g.,
maxRunCount
cannot be reasonably predetermined and should not
be set to maxLength
(the only failproof value) to avoid
wasting memory, then maxRunCount
could be set to 0 here
and the internal structures that are associated with it will be allocated
on demand, just like with the default constructor.
Parameters | |
---|---|
maxLength |
int : is the maximum text or line length that internal memory
will be preallocated for. An attempt to associate this object with a
longer text will fail, unless this value is 0, which leaves the allocation
up to the implementation. |
maxRunCount |
int : is the maximum anticipated number of same-level runs
that internal memory will be preallocated for. An attempt to access
visual runs on an object that was not preallocated for as many runs
as the text was actually resolved to will fail,
unless this value is 0, which leaves the allocation up to the implementation.The number of runs depends on the actual text and maybe anywhere between 1 and maxLength . It is typically small. |
Throws | |
---|---|
IllegalArgumentException |
if maxLength or maxRunCount is less than 0 |
Bidi
public Bidi (String paragraph, int flags)
Create Bidi from the given paragraph of text and base direction.
Parameters | |
---|---|
paragraph |
String : a paragraph of text |
flags |
int : a collection of flags that control the algorithm. The
algorithm understands the flags DIRECTION_LEFT_TO_RIGHT,
DIRECTION_RIGHT_TO_LEFT, DIRECTION_DEFAULT_LEFT_TO_RIGHT, and
DIRECTION_DEFAULT_RIGHT_TO_LEFT. Other values are reserved. |
Bidi
public Bidi (AttributedCharacterIterator paragraph)
Create Bidi from the given paragraph of text.
The RUN_DIRECTION attribute in the text, if present, determines the base direction (left-to-right or right-to-left). If not present, the base direction is computed using the Unicode Bidirectional Algorithm, defaulting to left-to-right if there are no strong directional characters in the text. This attribute, if present, must be applied to all the text in the paragraph.
The BIDI_EMBEDDING attribute in the text, if present, represents
embedding level information.
Negative values indicate overrides at the absolute value of the level.
Positive values indicate embeddings. (See MAX_EXPLICIT_LEVEL
.)
Where values are zero or not defined, the base
embedding level as determined by the base direction is assumed.
The NUMERIC_SHAPING attribute in the text, if present, converts European digits to other decimal digits before running the bidi algorithm. This attribute, if present, must be applied to all the text in the paragraph.
Note: this constructor calls setPara() internally.
Parameters | |
---|---|
paragraph |
AttributedCharacterIterator : a paragraph of text with optional character and
paragraph attribute information |
Bidi
public Bidi (char[] text, int textStart, byte[] embeddings, int embStart, int paragraphLength, int flags)
Create Bidi from the given text, embedding, and direction information.
The embeddings array may be null. If present, the values represent
embedding level information.
Negative values indicate overrides at the absolute value of the level.
Positive values indicate embeddings. (See MAX_EXPLICIT_LEVEL
.)
Where values are zero, the base embedding level
as determined by the base direction is assumed,
except for paragraph separators which remain at 0 to prevent reordering of paragraphs.
Note: This constructor calls setPara() internally,
after converting the java.text.Bidi-style embeddings with negative overrides
into ICU-style embeddings with bit fields for LEVEL_OVERRIDE
and the level.
Parameters | |
---|---|
text |
char : an array containing the paragraph of text to process. |
textStart |
int : the index into the text array of the start of the
paragraph. |
embeddings |
byte : an array containing embedding values for each character
in the paragraph. This can be null, in which case it is assumed
that there is no external embedding information. |
embStart |
int : the index into the embedding array of the start of the
paragraph. |
paragraphLength |
int : the length of the paragraph in the text and
embeddings arrays. |
flags |
int : a collection of flags that control the algorithm. The
algorithm understands the flags DIRECTION_LEFT_TO_RIGHT,
DIRECTION_RIGHT_TO_LEFT, DIRECTION_DEFAULT_LEFT_TO_RIGHT, and
DIRECTION_DEFAULT_RIGHT_TO_LEFT. Other values are reserved. |
Throws | |
---|---|
IllegalArgumentException |
if the values in embeddings are not within the allowed range |
Public methods
baseIsLeftToRight
public boolean baseIsLeftToRight ()
Return true if the base direction is left-to-right
Returns | |
---|---|
boolean |
true if the base direction is left-to-right |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
countParagraphs
public int countParagraphs ()
Get the number of paragraphs.
Returns | |
---|---|
int |
The number of paragraphs. |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
countRuns
public int countRuns ()
Get the number of runs.
This method may invoke the actual reordering on the
Bidi
object, after setPara()
may have resolved only the levels of the text. Therefore,
countRuns()
may have to allocate memory,
and may throw an exception if it fails to do so.
Returns | |
---|---|
int |
The number of runs. |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
createLineBidi
public Bidi createLineBidi (int lineStart, int lineLimit)
Create a Bidi object representing the bidi information on a line of text within the paragraph represented by the current Bidi. This call is not required if the entire paragraph fits on one line.
Parameters | |
---|---|
lineStart |
int : the offset from the start of the paragraph to the start
of the line. |
lineLimit |
int : the offset from the start of the paragraph to the limit
of the line. |
Returns | |
---|---|
Bidi |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara |
IllegalArgumentException |
if lineStart and lineLimit are not in the range
0<=lineStart<lineLimit<=getProcessedLength() ,
or if the specified line crosses a paragraph boundary |
getBaseDirection
public static byte getBaseDirection (CharSequence paragraph)
Get the base direction of the text provided according to the Unicode Bidirectional Algorithm. The base direction is derived from the first character in the string with bidirectional character type L, R, or AL. If the first such character has type L, LTR is returned. If the first such character has type R or AL, RTL is returned. If the string does not contain any character of these types, then NEUTRAL is returned. This is a lightweight function for use when only the base direction is needed and no further bidi processing of the text is needed.
Parameters | |
---|---|
paragraph |
CharSequence : the text whose paragraph level direction is needed. |
Returns | |
---|---|
byte |
LTR, RTL, NEUTRAL |
getBaseLevel
public int getBaseLevel ()
Return the base level (0 if left-to-right, 1 if right-to-left).
Returns | |
---|---|
int |
the base level |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
getCustomClassifier
public BidiClassifier getCustomClassifier ()
Gets the current custom class classifier used for Bidi class determination.
Returns | |
---|---|
BidiClassifier |
An instance of class BidiClassifier |
See also:
getCustomizedClass
public int getCustomizedClass (int c)
Retrieves the Bidi class for a given code point.
If a BidiClassifier
is defined and returns a value
other than UCharacter.getIntPropertyMaxValue(UProperty.BIDI_CLASS)+1
,
that value is used; otherwise the default class determination mechanism is invoked.
Parameters | |
---|---|
c |
int : The code point to get a Bidi class for. |
Returns | |
---|---|
int |
The Bidi class for the character c that is in effect
for this Bidi instance. |
See also:
getDirection
public byte getDirection ()
Get the directionality of the text.
Returns | |
---|---|
byte |
a value of LTR , RTL or MIXED
that indicates if the entire text
represented by this object is unidirectional,
and which direction, or if it is mixed-directional. |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
getLength
public int getLength ()
Get the length of the text.
Returns | |
---|---|
int |
The length of the text that the Bidi object was
created for. |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
getLevelAt
public byte getLevelAt (int charIndex)
Get the level for one character.
Parameters | |
---|---|
charIndex |
int : the index of a character. |
Returns | |
---|---|
byte |
The level for the character at charIndex . |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
IllegalArgumentException |
if charIndex is not in the range
0<=charIndex<getProcessedLength() |
See also:
getLevels
public byte[] getLevels ()
Get an array of levels for each character.
Note that this method may allocate memory under some
circumstances, unlike getLevelAt()
.
Returns | |
---|---|
byte[] |
The levels array for the text,
or null if an error occurs. |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
getLogicalIndex
public int getLogicalIndex (int visualIndex)
Get the logical text position from a visual position.
If such a mapping is used many times on the same
Bidi
object, then calling
getVisualMap()
is more efficient.
The value returned may be MAP_NOWHERE
if there is no
logical position because the corresponding text character is a Bidi
mark inserted in the output by option
OPTION_INSERT_MARKS
.
This is the inverse method to getVisualIndex()
.
When the visual output is altered by using options of
writeReordered()
such as INSERT_LRM_FOR_NUMERIC
,
KEEP_BASE_COMBINING
, OUTPUT_REVERSE
,
REMOVE_BIDI_CONTROLS
, the logical position returned may not
be correct. It is advised to use, when possible, reordering options
such as OPTION_INSERT_MARKS
and OPTION_REMOVE_CONTROLS
.
Parameters | |
---|---|
visualIndex |
int : is the visual position of a character. |
Returns | |
---|---|
int |
The index of this character in the text. |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
IllegalArgumentException |
if visualIndex is not in
the range 0<=visualIndex<getResultLength() |
getLogicalMap
public int[] getLogicalMap ()
Get a logical-to-visual index map (array) for the characters in the
Bidi
(paragraph or line) object.
Some values in the map may be MAP_NOWHERE
if the
corresponding text characters are Bidi controls removed from the visual
output by the option OPTION_REMOVE_CONTROLS
.
When the visual output is altered by using options of
writeReordered()
such as INSERT_LRM_FOR_NUMERIC
,
KEEP_BASE_COMBINING
, OUTPUT_REVERSE
,
REMOVE_BIDI_CONTROLS
, the visual positions returned may not
be correct. It is advised to use, when possible, reordering options
such as OPTION_INSERT_MARKS
and OPTION_REMOVE_CONTROLS
.
Note that in right-to-left runs, this mapping places
second surrogates before first ones (which is generally a bad idea)
and combining characters before base characters.
Use of
, optionally with the
writeReordered(int)
option can be considered instead
of using the mapping, in order to avoid these issues.KEEP_BASE_COMBINING
Returns | |
---|---|
int[] |
an array of getProcessedLength()
indexes which will reflect the reordering of the characters.The index map will result in indexMap[logicalIndex]==visualIndex , where
indexMap represents the returned array. |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
getLogicalRun
public BidiRun getLogicalRun (int logicalPosition)
Get a logical run. This method returns information about a run and is used to retrieve runs in logical order.
This is especially useful for line-breaking on a paragraph.
Parameters | |
---|---|
logicalPosition |
int : is a logical position within the source text. |
Returns | |
---|---|
BidiRun |
a BidiRun object filled with start containing
the first character of the run, limit containing
the limit of the run, and embeddingLevel containing
the level of the run. |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
IllegalArgumentException |
if logicalPosition is not in the range
0<=logicalPosition<getProcessedLength() |
getParaLevel
public byte getParaLevel ()
Get the paragraph level of the text.
Returns | |
---|---|
byte |
The paragraph level. If there are multiple paragraphs, their level may vary if the required paraLevel is LEVEL_DEFAULT_LTR or LEVEL_DEFAULT_RTL. In that case, the level of the first paragraph is returned. |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
getParagraph
public BidiRun getParagraph (int charIndex)
Get a paragraph, given a position within the text.
This method returns information about a paragraph.
Note: if the paragraph index is known, it is more efficient to
retrieve the paragraph information using getParagraphByIndex().
Parameters | |
---|---|
charIndex |
int : is the index of a character within the text, in the
range [0..getProcessedLength()-1] . |
Returns | |
---|---|
BidiRun |
a BidiRun object with the details of the paragraph:start will receive the index of the first character
of the paragraph in the text.limit will receive the limit of the paragraph.embeddingLevel will receive the level of the paragraph. |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
IllegalArgumentException |
if charIndex is not within the legal range |
getParagraphByIndex
public BidiRun getParagraphByIndex (int paraIndex)
Get a paragraph, given the index of this paragraph. This method returns information about a paragraph.
Parameters | |
---|---|
paraIndex |
int : is the number of the paragraph, in the
range [0..countParagraphs()-1] . |
Returns | |
---|---|
BidiRun |
a BidiRun object with the details of the paragraph:start will receive the index of the first character
of the paragraph in the text.limit will receive the limit of the paragraph.embeddingLevel will receive the level of the paragraph. |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
IllegalArgumentException |
if paraIndex is not in the range
[0..countParagraphs()-1] |
See also:
getParagraphIndex
public int getParagraphIndex (int charIndex)
Get the index of a paragraph, given a position within the text.
Parameters | |
---|---|
charIndex |
int : is the index of a character within the text, in the
range [0..getProcessedLength()-1] . |
Returns | |
---|---|
int |
The index of the paragraph containing the specified position, starting from 0. |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
IllegalArgumentException |
if charIndex is not within the legal range |
See also:
getProcessedLength
public int getProcessedLength ()
Get the length of the source text processed by the last call to
setPara()
. This length may be different from the length of
the source text if option OPTION_STREAMING
has been
set.
Note that whenever the length of the text affects the execution or the
result of a method, it is the processed length which must be considered,
except for setPara
(which receives unprocessed source text)
and getLength
(which returns the original length of the
source text).
In particular, the processed length is the one to consider in the
following cases:
- maximum value of the
limit
argument ofsetLine
- maximum value of the
charIndex
argument ofgetParagraph
- maximum value of the
charIndex
argument ofgetLevelAt
- number of elements in the array returned by
getLevels
- maximum value of the
logicalStart
argument ofgetLogicalRun
- maximum value of the
logicalIndex
argument ofgetVisualIndex
- number of elements returned by
getLogicalMap
- length of text processed by
writeReordered
Returns | |
---|---|
int |
The length of the part of the source text processed by
the last call to setPara . |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
getReorderingMode
public int getReorderingMode ()
What is the requested reordering mode for a given Bidi object?
Returns | |
---|---|
int |
the current reordering mode of the Bidi object |
See also:
getReorderingOptions
public int getReorderingOptions ()
What are the reordering options applied to a given Bidi object?
Returns | |
---|---|
int |
the current reordering options of the Bidi object |
See also:
getResultLength
public int getResultLength ()
Get the length of the reordered text resulting from the last call to
setPara()
. This length may be different from the length
of the source text if option OPTION_INSERT_MARKS
or option OPTION_REMOVE_CONTROLS
has been set.
This resulting length is the one to consider in the following cases:
- maximum value of the
visualIndex
argument ofgetLogicalIndex
- number of elements returned by
getVisualMap
writeReordered
, or if option
REORDER_INVERSE_NUMBERS_AS_L
has been set.
Returns | |
---|---|
int |
The length of the reordered text resulting from
the last call to setPara . |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
getRunCount
public int getRunCount ()
Return the number of level runs.
Returns | |
---|---|
int |
the number of level runs |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
getRunLevel
public int getRunLevel (int run)
Return the level of the nth logical run in this line.
Parameters | |
---|---|
run |
int : the index of the run, between 0 and countRuns()-1 |
Returns | |
---|---|
int |
the level of the run |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
IllegalArgumentException |
if run is not in
the range 0<=run<countRuns() |
getRunLimit
public int getRunLimit (int run)
Return the index of the character past the end of the nth logical run in this line, as an offset from the start of the line. For example, this will return the length of the line for the last run on the line.
Parameters | |
---|---|
run |
int : the index of the run, between 0 and countRuns() |
Returns | |
---|---|
int |
the limit of the run |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
IllegalArgumentException |
if run is not in
the range 0<=run<countRuns() |
getRunStart
public int getRunStart (int run)
Return the index of the character at the start of the nth logical run in this line, as an offset from the start of the line.
Parameters | |
---|---|
run |
int : the index of the run, between 0 and countRuns() |
Returns | |
---|---|
int |
the start of the run |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
IllegalArgumentException |
if run is not in
the range 0<=run<countRuns() |
getText
public char[] getText ()
Get the text.
Returns | |
---|---|
char[] |
A char array containing the text that the
Bidi object was created for. |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
getTextAsString
public String getTextAsString ()
Get the text.
Returns | |
---|---|
String |
A String containing the text that the
Bidi object was created for. |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
getVisualIndex
public int getVisualIndex (int logicalIndex)
Get the visual position from a logical text position.
If such a mapping is used many times on the same
Bidi
object, then calling
getLogicalMap()
is more efficient.
The value returned may be MAP_NOWHERE
if there is no
visual position because the corresponding text character is a Bidi
control removed from output by the option
OPTION_REMOVE_CONTROLS
.
When the visual output is altered by using options of
writeReordered()
such as INSERT_LRM_FOR_NUMERIC
,
KEEP_BASE_COMBINING
, OUTPUT_REVERSE
,
REMOVE_BIDI_CONTROLS
, the visual position returned may not
be correct. It is advised to use, when possible, reordering options
such as OPTION_INSERT_MARKS
and OPTION_REMOVE_CONTROLS
.
Note that in right-to-left runs, this mapping places
second surrogates before first ones (which is generally a bad idea)
and combining characters before base characters.
Use of
, optionally with the
writeReordered(int)
option can be considered instead
of using the mapping, in order to avoid these issues.KEEP_BASE_COMBINING
Parameters | |
---|---|
logicalIndex |
int : is the index of a character in the text. |
Returns | |
---|---|
int |
The visual position of this character. |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
IllegalArgumentException |
if logicalIndex is not in
the range 0<=logicalIndex<getProcessedLength() |
getVisualMap
public int[] getVisualMap ()
Get a visual-to-logical index map (array) for the characters in the
Bidi
(paragraph or line) object.
Some values in the map may be MAP_NOWHERE
if the
corresponding text characters are Bidi marks inserted in the visual
output by the option OPTION_INSERT_MARKS
.
When the visual output is altered by using options of
writeReordered()
such as INSERT_LRM_FOR_NUMERIC
,
KEEP_BASE_COMBINING
, OUTPUT_REVERSE
,
REMOVE_BIDI_CONTROLS
, the logical positions returned may not
be correct. It is advised to use, when possible, reordering options
such as OPTION_INSERT_MARKS
and OPTION_REMOVE_CONTROLS
.
Returns | |
---|---|
int[] |
an array of getResultLength()
indexes which will reflect the reordering of the characters.The index map will result in indexMap[visualIndex]==logicalIndex , where
indexMap represents the returned array. |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
getVisualRun
public BidiRun getVisualRun (int runIndex)
Get a BidiRun
object according to its index. BidiRun methods
may be used to retrieve the run's logical start, length and level,
which can be even for an LTR run or odd for an RTL run.
In an RTL run, the character at the logical start is
visually on the right of the displayed run.
The length is the number of characters in the run.
countRuns()
is normally called
before the runs are retrieved.
Example:
Bidi bidi = new Bidi(); String text = "abc 123 DEFG xyz"; bidi.setPara(text, Bidi.RTL, null); int i, count=bidi.countRuns(), logicalStart, visualIndex=0, length; BidiRun run; for (i = 0; i < count; ++i) { run = bidi.getVisualRun(i); logicalStart = run.getStart(); length = run.getLength(); if (Bidi.LTR == run.getEmbeddingLevel()) { do { // LTR show_char(text.charAt(logicalStart++), visualIndex++); } while (--length > 0); } else { logicalStart += length; // logicalLimit do { // RTL show_char(text.charAt(--logicalStart), visualIndex++); } while (--length > 0); } }
Note that in right-to-left runs, code like this places second surrogates before first ones (which is generally a bad idea) and combining characters before base characters.
Use of
, optionally with the
writeReordered(int)
option, can be considered in
order to avoid these issues.KEEP_BASE_COMBINING
Parameters | |
---|---|
runIndex |
int : is the number of the run in visual order, in the
range [0..countRuns()-1] . |
Returns | |
---|---|
BidiRun |
a BidiRun object containing the details of the run. The
directionality of the run is
LTR==0 or RTL==1 ,
never MIXED . |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
IllegalArgumentException |
if runIndex is not in
the range 0<=runIndex<countRuns() |
invertMap
public static int[] invertMap (int[] srcMap)
Invert an index map. The index mapping of the argument map is inverted and returned as an array of indexes that we will call the inverse map.
Parameters | |
---|---|
srcMap |
int : is an array whose elements define the original mapping
from a source array to a destination array.
Some elements of the source array may have no mapping in the
destination array. In that case, their value will be
the special value MAP_NOWHERE .
All elements must be >=0 or equal to MAP_NOWHERE .
Some elements in the source map may have a value greater than the
srcMap.length if the destination array has more elements than the
source array.
There must be no duplicate indexes (two or more elements with the
same value except MAP_NOWHERE ). |
Returns | |
---|---|
int[] |
an array representing the inverse map.
This array has a number of elements equal to 1 + the highest
value in srcMap .
For elements of the result array which have no matching elements
in the source array, the corresponding elements in the inverse
map will receive a value equal to MAP_NOWHERE .
If element with index i in srcMap has a value k different
from MAP_NOWHERE , this means that element i of
the source array maps to element k in the destination array.
The inverse map will have value i in its k-th element.
For all elements of the destination array which do not map to
an element in the source array, the corresponding element in the
inverse map will have a value equal to MAP_NOWHERE . |
See also:
isInverse
public boolean isInverse ()
Is this Bidi
object set to perform the inverse Bidi
algorithm?
Note: calling this method after setting the reordering mode with
setReorderingMode
will return true
if the
reordering mode was set to
REORDER_INVERSE_NUMBERS_AS_L
, false
for all other values.
Returns | |
---|---|
boolean |
true if the Bidi object is set to
perform the inverse Bidi algorithm by handling numbers as L. |
isLeftToRight
public boolean isLeftToRight ()
Return true if the line is all left-to-right text and the base direction is left-to-right.
Returns | |
---|---|
boolean |
true if the line is all left-to-right text and the base direction is left-to-right. |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara |
isMixed
public boolean isMixed ()
Return true if the line is not left-to-right or right-to-left. This means it either has mixed runs of left-to-right and right-to-left text, or the base direction differs from the direction of the only run of text.
Returns | |
---|---|
boolean |
true if the line is not left-to-right or right-to-left. |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara |
isOrderParagraphsLTR
public boolean isOrderParagraphsLTR ()
Is this Bidi
object set to allocate level 0 to block
separators so that successive paragraphs progress from left to right?
Returns | |
---|---|
boolean |
true if the Bidi object is set to
allocate level 0 to block separators. |
isRightToLeft
public boolean isRightToLeft ()
Return true if the line is all right-to-left text, and the base direction is right-to-left
Returns | |
---|---|
boolean |
true if the line is all right-to-left text, and the base direction is right-to-left |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara |
orderParagraphsLTR
public void orderParagraphsLTR (boolean ordarParaLTR)
Specify whether block separators must be allocated level zero,
so that successive paragraphs will progress from left to right.
This method must be called before setPara()
.
Paragraph separators (B) may appear in the text. Setting them to level zero
means that all paragraph separators (including one possibly appearing
in the last text position) are kept in the reordered text after the text
that they follow in the source text.
When this feature is not enabled, a paragraph separator at the last
position of the text before reordering will go to the first position
of the reordered text when the paragraph level is odd.
Parameters | |
---|---|
ordarParaLTR |
boolean : specifies whether paragraph separators (B) must
receive level 0, so that successive paragraphs progress from left to right. |
See also:
reorderLogical
public static int[] reorderLogical (byte[] levels)
This is a convenience method that does not use a Bidi
object.
It is intended to be used for when an application has determined the levels
of objects (character sequences) and just needs to have them reordered (L2).
This is equivalent to using getLogicalMap()
on a
Bidi
object.
Parameters | |
---|---|
levels |
byte : is an array of levels that have been determined by
the application. |
Returns | |
---|---|
int[] |
an array of levels.length
indexes which will reflect the reordering of the characters.
The index map will result in
|
reorderVisual
public static int[] reorderVisual (byte[] levels)
This is a convenience method that does not use a Bidi
object.
It is intended to be used for when an application has determined the levels
of objects (character sequences) and just needs to have them reordered (L2).
This is equivalent to using getVisualMap()
on a
Bidi
object.
Parameters | |
---|---|
levels |
byte : is an array of levels that have been determined by
the application. |
Returns | |
---|---|
int[] |
an array of levels.length
indexes which will reflect the reordering of the characters.
The index map will result in
|
reorderVisually
public static void reorderVisually (byte[] levels, int levelStart, Object[] objects, int objectStart, int count)
Reorder the objects in the array into visual order based on their levels.
This is a utility method to use when you have a collection of objects
representing runs of text in logical order, each run containing text at a
single level. The elements at index
from
objectStart
up to objectStart + count
in the
objects array will be reordered into visual order assuming
each run of text has the level indicated by the corresponding element in
the levels array (at index - objectStart + levelStart
).
Parameters | |
---|---|
levels |
byte : an array representing the bidi level of each object |
levelStart |
int : the start position in the levels array |
objects |
Object : the array of objects to be reordered into visual order |
objectStart |
int : the start position in the objects array |
count |
int : the number of objects to reorder |
requiresBidi
public static boolean requiresBidi (char[] text, int start, int limit)
Return true if the specified text requires bidi analysis. If this returns false, the text will display left-to-right. Clients can then avoid constructing a Bidi object. Text in the Arabic Presentation Forms area of Unicode is presumed to already be shaped and ordered for display, and so will not cause this method to return true.
Parameters | |
---|---|
text |
char : the text containing the characters to test |
start |
int : the start of the range of characters to test |
limit |
int : the limit of the range of characters to test |
Returns | |
---|---|
boolean |
true if the range of characters requires bidi analysis |
setContext
public void setContext (String prologue, String epilogue)
Set the context before a call to setPara().
setPara() computes the left-right directionality for a given piece of text which is supplied as one of its arguments. Sometimes this piece of text (the "main text") should be considered in context, because text appearing before ("prologue") and/or after ("epilogue") the main text may affect the result of this computation.
This function specifies the prologue and/or the epilogue for the next call to setPara(). If successive calls to setPara() all need specification of a context, setContext() must be called before each call to setPara(). In other words, a context is not "remembered" after the following successful call to setPara().
If a call to setPara() specifies DEFAULT_LTR or DEFAULT_RTL as paraLevel and is preceded by a call to setContext() which specifies a prologue, the paragraph level will be computed taking in consideration the text in the prologue.
When setPara() is called without a previous call to setContext, the main text is handled as if preceded and followed by strong directional characters at the current paragraph level. Calling setContext() with specification of a prologue will change this behavior by handling the main text as if preceded by the last strong character appearing in the prologue, if any. Calling setContext() with specification of an epilogue will change the behavior of setPara() by handling the main text as if followed by the first strong character or digit appearing in the epilogue, if any.
Note 1: if setContext
is called repeatedly without
calling setPara
, the earlier calls have no effect,
only the last call will be remembered for the next call to
setPara
.
Note 2: calling setContext(null, null)
cancels any previous setting of non-empty prologue or epilogue.
The next call to setPara()
will process no
prologue or epilogue.
Note 3: users must be aware that even after setting the context
before a call to setPara() to perform e.g. a logical to visual
transformation, the resulting string may not be identical to what it
would have been if all the text, including prologue and epilogue, had
been processed together.
Example (upper case letters represent RTL characters):
prologue = "abc DE
"
epilogue = none
main text = "FGH xyz
"
paraLevel = LTR
display without prologue = "HGF xyz
"
("HGF" is adjacent to "xyz")
display with prologue = "abc HGFED xyz
"
("HGF" is not adjacent to "xyz")
Parameters | |
---|---|
prologue |
String : is the text which precedes the text that
will be specified in a coming call to setPara().
If there is no prologue to consider,
this parameter can be null . |
epilogue |
String : is the text which follows the text that
will be specified in a coming call to setPara().
If there is no epilogue to consider,
this parameter can be null . |
See also:
setCustomClassifier
public void setCustomClassifier (BidiClassifier classifier)
Set a custom Bidi classifier used by the UBA implementation for Bidi class determination.
Parameters | |
---|---|
classifier |
BidiClassifier : A new custom classifier. This can be null. |
See also:
setInverse
public void setInverse (boolean isInverse)
Modify the operation of the Bidi algorithm such that it
approximates an "inverse Bidi" algorithm. This method
must be called before setPara()
.
The normal operation of the Bidi algorithm as described in the Unicode Technical Report is to take text stored in logical (keyboard, typing) order and to determine the reordering of it for visual rendering. Some legacy systems store text in visual order, and for operations with standard, Unicode-based algorithms, the text needs to be transformed to logical order. This is effectively the inverse algorithm of the described Bidi algorithm. Note that there is no standard algorithm for this "inverse Bidi" and that the current implementation provides only an approximation of "inverse Bidi".
With isInversed
set to true
,
this method changes the behavior of some of the subsequent methods
in a way that they can be used for the inverse Bidi algorithm.
Specifically, runs of text with numeric characters will be treated in a
special way and may need to be surrounded with LRM characters when they are
written in reordered sequence.
Output runs should be retrieved using getVisualRun()
.
Since the actual input for "inverse Bidi" is visually ordered text and
getVisualRun()
gets the reordered runs, these are actually
the runs of the logically ordered output.
Calling this method with argument isInverse
set to
true
is equivalent to calling setReorderingMode
with argument reorderingMode
set to REORDER_INVERSE_NUMBERS_AS_L
.
Calling this method with argument isInverse
set to
false
is equivalent to calling setReorderingMode
with argument reorderingMode
set to REORDER_DEFAULT
.
Parameters | |
---|---|
isInverse |
boolean : specifies "forward" or "inverse" Bidi operation. |
setLine
public Bidi setLine (int start, int limit)
setLine()
returns a Bidi
object to
contain the reordering information, especially the resolved levels,
for all the characters in a line of text. This line of text is
specified by referring to a Bidi
object representing
this information for a piece of text containing one or more paragraphs,
and by specifying a range of indexes in this text.
In the new line object, the indexes will range from 0 to limit-start-1
.
This is used after calling setPara()
for a piece of text, and after line-breaking on that text.
It is not necessary if each paragraph is treated as a single line.
After line-breaking, rules (L1) and (L2) for the treatment of
trailing WS and for reordering are performed on
a Bidi
object that represents a line.
Important: the line Bidi
object may
reference data within the global text Bidi
object.
You should not alter the content of the global text object until
you are finished using the line object.
Parameters | |
---|---|
start |
int : is the line's first index into the text. |
limit |
int : is just behind the line's last index into the text
(its last index +1). |
Returns | |
---|---|
Bidi |
a Bidi object that will now represent a line of the text. |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara |
IllegalArgumentException |
if start and limit are not in the range
0<=start<limit<=getProcessedLength() ,
or if the specified line crosses a paragraph boundary |
setPara
public void setPara (AttributedCharacterIterator paragraph)
Perform the Unicode Bidi algorithm on a given paragraph, as defined in the Unicode Standard Annex #9, version 13, also described in The Unicode Standard, Version 4.0 .
This method takes a paragraph of text and computes the left-right-directionality of each character. The text should not contain any Unicode block separators.
The RUN_DIRECTION attribute in the text, if present, determines the base direction (left-to-right or right-to-left). If not present, the base direction is computed using the Unicode Bidirectional Algorithm, defaulting to left-to-right if there are no strong directional characters in the text. This attribute, if present, must be applied to all the text in the paragraph.
The BIDI_EMBEDDING attribute in the text, if present, represents
embedding level information.
Negative values indicate overrides at the absolute value of the level.
Positive values indicate embeddings. (See MAX_EXPLICIT_LEVEL
.)
Where values are zero or not defined, the base
embedding level as determined by the base direction is assumed.
The NUMERIC_SHAPING attribute in the text, if present, converts European
digits to other decimal digits before running the bidi algorithm. This
attribute, if present, must be applied to all the text in the paragraph.
If the entire text is all of the same directionality, then
the method may not perform all the steps described by the algorithm,
i.e., some levels may not be the same as if all steps were performed.
This is not relevant for unidirectional text.
For example, in pure LTR text with numbers the numbers would get
a resolved level of 2 higher than the surrounding text according to
the algorithm. This implementation may set all resolved levels to
the same value in such a case.
Parameters | |
---|---|
paragraph |
AttributedCharacterIterator : a paragraph of text with optional character and
paragraph attribute information |
setPara
public void setPara (char[] chars, byte paraLevel, byte[] embeddingLevels)
Perform the Unicode Bidi algorithm. It is defined in the Unicode Standard Annex #9.
This method takes a piece of plain text containing one or more paragraphs, with or without externally specified embedding levels from styled text and computes the left-right-directionality of each character.
If the entire text is all of the same directionality, then
the method may not perform all the steps described by the algorithm,
i.e., some levels may not be the same as if all steps were performed.
This is not relevant for unidirectional text.
For example, in pure LTR text with numbers the numbers would get
a resolved level of 2 higher than the surrounding text according to
the algorithm. This implementation may set all resolved levels to
the same value in such a case.
The text can be composed of multiple paragraphs. Occurrence of a block separator in the text terminates a paragraph, and whatever comes next starts a new paragraph. The exception to this rule is when a Carriage Return (CR) is followed by a Line Feed (LF). Both CR and LF are block separators, but in that case, the pair of characters is considered as terminating the preceding paragraph, and a new paragraph will be started by a character coming after the LF.
The text is stored internally as an array of characters. Therefore the documentation will refer to indexes of the characters in the text.
Parameters | |
---|---|
chars |
char : contains the text that the Bidi algorithm will be performed
on. This text can be retrieved with getText() or
getTextAsString . |
paraLevel |
byte : specifies the default level for the text;
it is typically 0 (LTR) or 1 (RTL).
If the method shall determine the paragraph level from the text,
then paraLevel can be set to
either LEVEL_DEFAULT_LTR
or LEVEL_DEFAULT_RTL ; if the text contains multiple
paragraphs, the paragraph level shall be determined separately for
each paragraph; if a paragraph does not include any strongly typed
character, then the desired default is used (0 for LTR or 1 for RTL).
Any other value between 0 and MAX_EXPLICIT_LEVEL
is also valid, with odd levels indicating RTL. |
embeddingLevels |
byte : (in) may be used to preset the embedding and
override levels, ignoring characters like LRE and PDF in the text.
A level overrides the directional property of its corresponding
(same index) character if the level has the
LEVEL_OVERRIDE bit set.Aside from that bit, it must be paraLevel<=embeddingLevels[]<=MAX_EXPLICIT_LEVEL ,
except that level 0 is always allowed.
Level 0 for a paragraph separator prevents reordering of paragraphs;
this only works reliably if LEVEL_OVERRIDE
is also set for paragraph separators.
Level 0 for other characters is treated as a wildcard
and is lifted up to the resolved level of the surrounding paragraph.Caution: A reference to this array, not a copy of the levels, will be stored in the Bidi object;
the embeddingLevels
should not be modified to avoid unexpected results on subsequent
Bidi operations. However, the setPara() and
setLine() methods may modify some or all of the
levels.Note: the embeddingLevels array must
have one entry for each character in text . |
Throws | |
---|---|
IllegalArgumentException |
if the values in embeddingLevels are not within the allowed range |
setPara
public void setPara (String text, byte paraLevel, byte[] embeddingLevels)
Perform the Unicode Bidi algorithm. It is defined in the Unicode Standard Annex #9.
This method takes a piece of plain text containing one or more paragraphs, with or without externally specified embedding levels from styled text and computes the left-right-directionality of each character.
If the entire text is all of the same directionality, then
the method may not perform all the steps described by the algorithm,
i.e., some levels may not be the same as if all steps were performed.
This is not relevant for unidirectional text.
For example, in pure LTR text with numbers the numbers would get
a resolved level of 2 higher than the surrounding text according to
the algorithm. This implementation may set all resolved levels to
the same value in such a case.
The text can be composed of multiple paragraphs. Occurrence of a block separator in the text terminates a paragraph, and whatever comes next starts a new paragraph. The exception to this rule is when a Carriage Return (CR) is followed by a Line Feed (LF). Both CR and LF are block separators, but in that case, the pair of characters is considered as terminating the preceding paragraph, and a new paragraph will be started by a character coming after the LF.
Although the text is passed here as a String
, it is
stored internally as an array of characters. Therefore the
documentation will refer to indexes of the characters in the text.
Parameters | |
---|---|
text |
String : contains the text that the Bidi algorithm will be performed
on. This text can be retrieved with getText() or
getTextAsString . |
paraLevel |
byte : specifies the default level for the text;
it is typically 0 (LTR) or 1 (RTL).
If the method shall determine the paragraph level from the text,
then paraLevel can be set to
either LEVEL_DEFAULT_LTR
or LEVEL_DEFAULT_RTL ; if the text contains multiple
paragraphs, the paragraph level shall be determined separately for
each paragraph; if a paragraph does not include any strongly typed
character, then the desired default is used (0 for LTR or 1 for RTL).
Any other value between 0 and MAX_EXPLICIT_LEVEL
is also valid, with odd levels indicating RTL. |
embeddingLevels |
byte : (in) may be used to preset the embedding and override levels,
ignoring characters like LRE and PDF in the text.
A level overrides the directional property of its corresponding
(same index) character if the level has the
LEVEL_OVERRIDE bit set.Aside from that bit, it must be paraLevel<=embeddingLevels[]<=MAX_EXPLICIT_LEVEL ,
except that level 0 is always allowed.
Level 0 for a paragraph separator prevents reordering of paragraphs;
this only works reliably if LEVEL_OVERRIDE
is also set for paragraph separators.
Level 0 for other characters is treated as a wildcard
and is lifted up to the resolved level of the surrounding paragraph.Caution: A reference to this array, not a copy of the levels, will be stored in the Bidi object;
the embeddingLevels
should not be modified to avoid unexpected results on subsequent
Bidi operations. However, the setPara() and
setLine() methods may modify some or all of the
levels.Note: the embeddingLevels array must
have one entry for each character in text . |
Throws | |
---|---|
IllegalArgumentException |
if the values in embeddingLevels are not within the allowed range |
setReorderingMode
public void setReorderingMode (int reorderingMode)
Modify the operation of the Bidi algorithm such that it implements some
variant to the basic Bidi algorithm or approximates an "inverse Bidi"
algorithm, depending on different values of the "reordering mode".
This method must be called before setPara()
, and stays in
effect until called again with a different argument.
The normal operation of the Bidi algorithm as described in the Unicode Standard Annex #9 is to take text stored in logical (keyboard, typing) order and to determine how to reorder it for visual rendering.
With the reordering mode set to a value other than
REORDER_DEFAULT
, this method changes the behavior of some of
the subsequent methods in a way such that they implement an inverse Bidi
algorithm or some other algorithm variants.
Some legacy systems store text in visual order, and for operations with standard, Unicode-based algorithms, the text needs to be transformed into logical order. This is effectively the inverse algorithm of the described Bidi algorithm. Note that there is no standard algorithm for this "inverse Bidi", so a number of variants are implemented here.
In other cases, it may be desirable to emulate some variant of the Logical to Visual algorithm (e.g. one used in MS Windows), or perform a Logical to Logical transformation.
- When the Reordering Mode is set to
REORDER_DEFAULT
, the standard Bidi Logical to Visual algorithm is applied. - When the reordering mode is set to
REORDER_NUMBERS_SPECIAL
, the algorithm used to perform Bidi transformations when callingsetPara
should approximate the algorithm used in Microsoft Windows XP rather than strictly conform to the Unicode Bidi algorithm.
The differences between the basic algorithm and the algorithm addressed by this option are as follows:- Within text at an even embedding level, the sequence "123AB" (where AB represent R or AL letters) is transformed to "123BA" by the Unicode algorithm and to "BA123" by the Windows algorithm.
- Arabic-Indic numbers (AN) are handled by the Windows algorithm just like regular numbers (EN).
- When the reordering mode is set to
REORDER_GROUP_NUMBERS_WITH_R
, numbers located between LTR text and RTL text are associated with the RTL text. For instance, an LTR paragraph with content "abc 123 DEF" (where upper case letters represent RTL characters) will be transformed to "abc FED 123" (and not "abc 123 FED"), "DEF 123 abc" will be transformed to "123 FED abc" and "123 FED abc" will be transformed to "DEF 123 abc". This makes the algorithm reversible and makes it useful when round trip (from visual to logical and back to visual) must be achieved without adding LRM characters. However, this is a variation from the standard Unicode Bidi algorithm.
The source text should not contain Bidi control characters other than LRM or RLM. - When the reordering mode is set to
REORDER_RUNS_ONLY
, a "Logical to Logical" transformation must be performed:- If the default text level of the source text (argument
paraLevel
insetPara
) is even, the source text will be handled as LTR logical text and will be transformed to the RTL logical text which has the same LTR visual display. - If the default level of the source text is odd, the source text will be handled as RTL logical text and will be transformed to the LTR logical text which has the same LTR visual display.
This mode may also be needed in the reverse case, when logical text which is basically English, with possible included phrases in Arabic or Hebrew, has to be displayed as if it had an odd embedding level.
Both cases could be handled by adding LRE or RLE at the head of the text, if the display subsystem supports these formatting controls. If it does not, the problem may be handled by transforming the source text in this mode before displaying it, so that it will be displayed properly.
The source text should not contain Bidi control characters other than LRM or RLM. - If the default text level of the source text (argument
- When the reordering mode is set to
REORDER_INVERSE_NUMBERS_AS_L
, an "inverse Bidi" algorithm is applied. Runs of text with numeric characters will be treated like LTR letters and may need to be surrounded with LRM characters when they are written in reordered sequence (the optionINSERT_LRM_FOR_NUMERIC
can be used with methodwriteReordered
to this end. This mode is equivalent to callingsetInverse()
with argumentisInverse
set totrue
. - When the reordering mode is set to
REORDER_INVERSE_LIKE_DIRECT
, the "direct" Logical to Visual Bidi algorithm is used as an approximation of an "inverse Bidi" algorithm. This mode is similar to modeREORDER_INVERSE_NUMBERS_AS_L
but is closer to the regular Bidi algorithm.
For example, an LTR paragraph with the content "FED 123 456 CBA" (where upper case represents RTL characters) will be transformed to "ABC 456 123 DEF", as opposed to "DEF 123 456 ABC" with modeREORDER_INVERSE_NUMBERS_AS_L
.
When used in conjunction with optionOPTION_INSERT_MARKS
, this mode generally adds Bidi marks to the output significantly more sparingly than modeREORDER_INVERSE_NUMBERS_AS_L
.
with optionINSERT_LRM_FOR_NUMERIC
in calls towriteReordered
. - When the reordering mode is set to
REORDER_INVERSE_FOR_NUMBERS_SPECIAL
, the Logical to Visual Bidi algorithm used in Windows XP is used as an approximation of an "inverse Bidi" algorithm.
For example, an LTR paragraph with the content "abc FED123" (where upper case represents RTL characters) will be transformed to "abc 123DEF.
In all the reordering modes specifying an "inverse Bidi" algorithm
(i.e. those with a name starting with REORDER_INVERSE
),
output runs should be retrieved using getVisualRun()
, and
the output text with writeReordered()
. The caller should
keep in mind that in "inverse Bidi" modes the input is actually visually
ordered text and reordered output returned by getVisualRun()
or writeReordered()
are actually runs or character string
of logically ordered output.
For all the "inverse Bidi" modes, the source text should not contain
Bidi control characters other than LRM or RLM.
Note that option OUTPUT_REVERSE
of
writeReordered
has no useful meaning and should not be used
in conjunction with any value of the reordering mode specifying "inverse
Bidi" or with value REORDER_RUNS_ONLY
.
Parameters | |
---|---|
reorderingMode |
int : specifies the required variant of the Bidi
algorithm. |
setReorderingOptions
public void setReorderingOptions (int options)
Specify which of the reordering options should be applied during Bidi transformations.
Parameters | |
---|---|
options |
int : A combination of zero or more of the following
reordering options:
OPTION_DEFAULT , OPTION_INSERT_MARKS ,
OPTION_REMOVE_CONTROLS , OPTION_STREAMING . |
writeReordered
public String writeReordered (int options)
Take a Bidi
object containing the reordering
information for a piece of text (one or more paragraphs) set by
setPara()
or for a line of text set by setLine()
and return a string containing the reordered text.
The text may have been aliased (only a reference was stored
without copying the contents), thus it must not have been modified
since the setPara()
call.
This method preserves the integrity of characters with multiple
code units and (optionally) combining characters.
Characters in RTL runs can be replaced by mirror-image characters
in the returned string. Note that "real" mirroring has to be done in a
rendering engine by glyph selection and that for many "mirrored"
characters there are no Unicode characters as mirror-image equivalents.
There are also options to insert or remove Bidi control
characters; see the descriptions of the return value and the
options
parameter, and of the option bit flags.
Parameters | |
---|---|
options |
int : A bit set of options for the reordering that control
how the reordered text is written.
The options include mirroring the characters on a code
point basis and inserting LRM characters, which is used
especially for transforming visually stored text
to logically stored text (although this is still an
imperfect implementation of an "inverse Bidi" algorithm
because it uses the "forward Bidi" algorithm at its core).
The available options are:
DO_MIRRORING ,
INSERT_LRM_FOR_NUMERIC ,
KEEP_BASE_COMBINING ,
OUTPUT_REVERSE ,
REMOVE_BIDI_CONTROLS ,
STREAMING |
Returns | |
---|---|
String |
The reordered text.
If the INSERT_LRM_FOR_NUMERIC option is set, then
the length of the returned string could be as large as
getLength()+2*countRuns() .If the REMOVE_BIDI_CONTROLS option is set, then the
length of the returned string may be less than
getLength() .If none of these options is set, then the length of the returned string will be exactly getProcessedLength() . |
Throws | |
---|---|
IllegalStateException |
if this call is not preceded by a successful
call to setPara or setLine |
writeReverse
public static String writeReverse (String src, int options)
Reverse a Right-To-Left run of Unicode text.
This method preserves the integrity of characters with multiple
code units and (optionally) combining characters.
Characters can be replaced by mirror-image characters
in the destination buffer. Note that "real" mirroring has
to be done in a rendering engine by glyph selection
and that for many "mirrored" characters there are no
Unicode characters as mirror-image equivalents.
There are also options to insert or remove Bidi control
characters.
This method is the implementation for reversing RTL runs as part
of writeReordered()
. For detailed descriptions
of the parameters, see there.
Since no Bidi controls are inserted here, the output string length
will never exceed src.length()
.
Parameters | |
---|---|
src |
String : The RTL run text. |
options |
int : A bit set of options for the reordering that control
how the reordered text is written.
See the options parameter in writeReordered() . |
Returns | |
---|---|
String |
The reordered text.
If the REMOVE_BIDI_CONTROLS option
is set, then the length of the returned string may be less than
src.length() . If this option is not set,
then the length of the returned string will be exactly
src.length() . |
Throws | |
---|---|
IllegalArgumentException |
if src is null. |
See also: