com.pd4ml.html.doc.bidi

Class BidiOrder

java.lang.Object

com.pd4ml.html.doc.bidi.BidiOrder

public final class BidiOrder
extends Object

Reference implementation of the Unicode 3.0 Bidi algorithm.

This implementation is not optimized for performance. It is intended as a reference implementation that closely follows the specification of the Bidirectional Algorithm in The Unicode Standard version 3.0.

Input:
There are two levels of input to the algorithm, since clients may prefer to supply some information from out-of-band sources rather than relying on the default behavior.

1. unicode type array
2. unicode type array, with externally supplied base line direction

Output:
Output is separated into several stages as well, to better enable clients to evaluate various aspects of implementation conformance.

1. levels array over entire paragraph
2. reordering array over entire paragraph
3. levels array over line
4. reordering array over line

Note that for conformance, algorithms are only required to generate correct reordering and character directionality (odd or even levels) over a line. Generating identical level arrays over a line is not required. Bidi explicit format codes (LRE, RLE, LRO, RLO, PDF) and BN can be assigned arbitrary levels and positions as long as the other text matches.

As the algorithm is defined to operate on a single paragraph at a time, this implementation is written to handle single paragraphs. Thus rule P1 is presumed by this implementation-- the data provided to the implementation is assumed to be a single paragraph, and either contains no 'B' codes, or a single 'B' code at the end of the input. 'B' is allowed as input to illustrate how the algorithm assigns it a level.

Also note that rules L3 and L4 depend on the rendering engine that uses the result of the bidi algorithm. This implementation assumes that the rendering engine expects combining marks in visual order (e.g. to the left of their base character in RTL runs) and that it adjust the glyphs used to render mirrored characters that are in RTL runs so that they render appropriately.

Author:

Doug Felt

Field Summary

Fields

Modifier and Type	Field and Description
static byte	AL Right-to-Left Arabic
static byte	AN Arabic Number
static byte	B Paragraph Separator
static byte	BN Boundary Neutral
static byte	CS Common Number Separator
static byte	EN European Number
static byte	ES European Number Separator
static byte	ET European Number Terminator
static byte	L Left-to-right
static byte	LRE Left-to-Right Embedding
static byte	LRO Left-to-Right Override
static byte	NSM Non-Spacing Mark
static byte	ON Other Neutrals
static byte	PDF Pop Directional Format
static byte	R Right-to-Left
static byte	RLE Right-to-Left Embedding
static byte	RLO Right-to-Left Override
static byte	S Segment Separator
static byte	TYPE_MAX Maximum bidi type value.
static byte	TYPE_MIN Minimum bidi type value.
static byte	WS Whitespace

Constructor Summary

Constructors

Constructor and Description
BidiOrder(byte[] types) Initialize using an array of direction types.
BidiOrder(byte[] types, byte paragraphEmbeddingLevel) Initialize using an array of direction types and an externally supplied paragraph embedding level.
BidiOrder(char[] text, int offset, int length, byte paragraphEmbeddingLevel)

Method Summary

Modifier and Type	Method and Description
byte	getBaseLevel()
static byte	getDirection(char c)
byte[]	getLevels()
byte[]	getLevels(int[] linebreaks) Return levels array breaking lines at offsets in linebreaks.
int[]	getReordering(int[] linebreaks)

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

L

public static final byte L

Left-to-right

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Constant Field Values

LRE

public static final byte LRE

Left-to-Right Embedding

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Constant Field Values

LRO

public static final byte LRO

Left-to-Right Override

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Constant Field Values

R

public static final byte R

Right-to-Left

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Constant Field Values

AL

public static final byte AL

Right-to-Left Arabic

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Constant Field Values

RLE

public static final byte RLE

Right-to-Left Embedding

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Constant Field Values

RLO

public static final byte RLO

Right-to-Left Override

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Constant Field Values

PDF

public static final byte PDF

Pop Directional Format

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Constant Field Values

EN

public static final byte EN

European Number

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Constant Field Values

ES

public static final byte ES

European Number Separator

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ET

public static final byte ET

European Number Terminator

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Constant Field Values

AN

public static final byte AN

Arabic Number

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Constant Field Values

CS

public static final byte CS

Common Number Separator

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Constant Field Values

NSM

public static final byte NSM

Non-Spacing Mark

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Constant Field Values

BN

public static final byte BN

Boundary Neutral

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Constant Field Values

B

public static final byte B

Paragraph Separator

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Constant Field Values

S

public static final byte S

Segment Separator

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Constant Field Values

WS

public static final byte WS

Whitespace

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ON

public static final byte ON

Other Neutrals

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TYPE_MIN

public static final byte TYPE_MIN

Minimum bidi type value.

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Constant Field Values

TYPE_MAX

public static final byte TYPE_MAX

Maximum bidi type value.

See Also:

Constant Field Values

Constructor Detail

BidiOrder

public BidiOrder(byte[] types)

Initialize using an array of direction types. Types range from TYPE_MIN to TYPE_MAX inclusive and represent the direction codes of the characters in the text.

Parameters:

types - the types array

BidiOrder

public BidiOrder(byte[] types,
                 byte paragraphEmbeddingLevel)

Initialize using an array of direction types and an externally supplied paragraph embedding level. The embedding level may be -1, 0, or 1. -1 means to apply the default algorithm (rules P2 and P3), 0 is for LTR paragraphs, and 1 is for RTL paragraphs.

Parameters:

types - the types array

paragraphEmbeddingLevel - the externally supplied paragraph embedding level.

BidiOrder

public BidiOrder(char[] text,
                 int offset,
                 int length,
                 byte paragraphEmbeddingLevel)

Method Detail

getDirection

public static final byte getDirection(char c)

getLevels

public byte[] getLevels()

getLevels

public byte[] getLevels(int[] linebreaks)

Return levels array breaking lines at offsets in linebreaks.
Rule L1.

The returned levels array contains the resolved level for each bidi code passed to the constructor.

The linebreaks array must include at least one value. The values must be in strictly increasing order (no duplicates) between 1 and the length of the text, inclusive. The last value must be the length of the text.

Parameters:

linebreaks - the offsets at which to break the paragraph

Returns:

the resolved levels of the text

getReordering

public int[] getReordering(int[] linebreaks)

Parameters:

linebreaks - the offsets at which to break the paragraph.

Returns:

reordering array breaking lines at offsets in linebreaks.

The reordering array maps from a visual index to a logical index. Lines are concatenated from left to right. So for example, the fifth character from the left on the third line is

 getReordering(linebreaks)[linebreaks[1] + 4]

(linebreaks[1] is the position after the last character of the second line, which is also the index of the first character on the third line, and adding four gets the fifth character from the left).

The linebreaks array must include at least one value. The values must be in strictly increasing order (no duplicates) between 1 and the length of the text, inclusive. The last value must be the length of the text.

getBaseLevel

public byte getBaseLevel()

Returns:

the base level of the paragraph.