com.ibm.icu.text

Class ArabicShaping


public final class ArabicShaping
extends Object

Shape Arabic text on a character basis.

ArabicShaping performs basic operations for "shaping" Arabic text. It is most useful for use with legacy data formats and legacy display technology (simple terminals). All operations are performed on Unicode characters.

Text-based shaping means that some character code points in the text are replaced by others depending on the context. It transforms one kind of text into another. In comparison, modern displays for Arabic text select appropriate, context-dependent font glyphs for each text element, which means that they transform text into a glyph vector.

Text transformations are necessary when modern display technology is not available or when text needs to be transformed to or from legacy formats that use "shaped" characters. Since the Arabic script is cursive, connecting adjacent letters to each other, computers select images for each letter based on the surrounding letters. This usually results in four images per Arabic letter: initial, middle, final, and isolated forms. In Unicode, on the other hand, letters are normally stored abstract, and a display system is expected to select the necessary glyphs. (This makes searching and other text processing easier because the same letter has only one code.) It is possible to mimic this with text transformations because there are characters in Unicode that are rendered as letters with a specific shape (or cursive connectivity). They were included for interoperability with legacy systems and codepages, and for unsophisticated display systems.

A second kind of text transformations is supported for Arabic digits: For compatibility with legacy codepages that only include European digits, it is possible to replace one set of digits by another, changing the character code points. These operations can be performed for either Arabic-Indic Digits (U+0660...U+0669) or Eastern (Extended) Arabic-Indic digits (U+06f0...U+06f9).

Some replacements may result in more or fewer characters (code points). By default, this means that the destination buffer may receive text with a length different from the source length. Some legacy systems rely on the length of the text to be constant. They expect extra spaces to be added or consumed either next to the affected character or at the end of the text.

Field Summary

static int
DIGITS_AN2EN
Digit shaping option: Replace Arabic-Indic digits by European digits (U+0030...U+0039).
static int
DIGITS_EN2AN
Digit shaping option: Replace European digits (U+0030...U+0039) by Arabic-Indic digits.
static int
DIGITS_EN2AN_INIT_AL
Digit shaping option: Replace European digits (U+0030...U+0039) by Arabic-Indic digits if the most recent strongly directional character is an Arabic letter (its Bidi direction value is RIGHT_TO_LEFT_ARABIC).
static int
DIGITS_EN2AN_INIT_LR
Digit shaping option: Replace European digits (U+0030...U+0039) by Arabic-Indic digits if the most recent strongly directional character is an Arabic letter (its Bidi direction value is RIGHT_TO_LEFT_ARABIC).
static int
DIGITS_MASK
Bit mask for digit shaping options.
static int
DIGITS_NOOP
Digit shaping option: do not perform digit shaping.
static int
DIGIT_TYPE_AN
Digit type option: Use Arabic-Indic digits (U+0660...U+0669).
static int
DIGIT_TYPE_AN_EXTENDED
Digit type option: Use Eastern (Extended) Arabic-Indic digits (U+06f0...U+06f9).
static int
DIGIT_TYPE_MASK
Bit mask for digit type options.
static int
LENGTH_FIXED_SPACES_AT_BEGINNING
Memory option: the result must have the same length as the source.
static int
LENGTH_FIXED_SPACES_AT_END
Memory option: the result must have the same length as the source.
static int
LENGTH_FIXED_SPACES_NEAR
Memory option: the result must have the same length as the source.
static int
LENGTH_GROW_SHRINK
Memory option: allow the result to have a different length than the source.
static int
LENGTH_MASK
Bit mask for memory options.
static int
LETTERS_MASK
Bit mask for letter shaping options.
static int
LETTERS_NOOP
Letter shaping option: do not perform letter shaping.
static int
LETTERS_SHAPE
Letter shaping option: replace normative letter characters in the U+0600 (Arabic) block, by shaped ones in the U+FE70 (Presentation Forms B) block.
static int
LETTERS_SHAPE_TASHKEEL_ISOLATED
Letter shaping option: replace normative letter characters in the U+0600 (Arabic) block, except for the TASHKEEL characters at U+064B...U+0652, by shaped ones in the U+Fe70 (Presentation Forms B) block.
static int
LETTERS_UNSHAPE
Letter shaping option: replace shaped letter characters in the U+FE70 (Presentation Forms B) block by normative ones in the U+0600 (Arabic) block.
static int
TEXT_DIRECTION_LOGICAL
Direction indicator: the source is in logical (keyboard) order.
static int
TEXT_DIRECTION_MASK
Bit mask for direction indicators.
static int
TEXT_DIRECTION_VISUAL_LTR
Direction indicator: the source is in visual (display) order, that is, the leftmost displayed character is stored first.

Constructor Summary

ArabicShaping(int options)
Construct ArabicShaping using the options flags.

Method Summary

boolean
equals(Object rhs)
int
hashCode()
String
shape(String text)
Convert a string, returning the new string.
void
shape(char[] source, int start, int length)
Convert a range of text in place.
int
shape(char[] source, int sourceStart, int sourceLength, char[] dest, int destStart, int destSize)
Convert a range of text in the source array, putting the result into a range of text in the destination array, and return the number of characters written.
String
toString()

Field Details

DIGITS_AN2EN

public static final int DIGITS_AN2EN
Digit shaping option: Replace Arabic-Indic digits by European digits (U+0030...U+0039).
Field Value:
64

DIGITS_EN2AN

public static final int DIGITS_EN2AN
Digit shaping option: Replace European digits (U+0030...U+0039) by Arabic-Indic digits.
Field Value:
32

DIGITS_EN2AN_INIT_AL

public static final int DIGITS_EN2AN_INIT_AL
Digit shaping option: Replace European digits (U+0030...U+0039) by Arabic-Indic digits if the most recent strongly directional character is an Arabic letter (its Bidi direction value is RIGHT_TO_LEFT_ARABIC). The initial state at the start of the text is assumed to be an Arabic, letter, so European digits at the start of the text will change. Compare to DIGITS_ALEN2AN_INT_LR.
Field Value:
128

DIGITS_EN2AN_INIT_LR

public static final int DIGITS_EN2AN_INIT_LR
Digit shaping option: Replace European digits (U+0030...U+0039) by Arabic-Indic digits if the most recent strongly directional character is an Arabic letter (its Bidi direction value is RIGHT_TO_LEFT_ARABIC). The initial state at the start of the text is assumed to be not an Arabic, letter, so European digits at the start of the text will not change. Compare to DIGITS_ALEN2AN_INIT_AL.
Field Value:
96

DIGITS_MASK

public static final int DIGITS_MASK
Bit mask for digit shaping options.
Field Value:
224

DIGITS_NOOP

public static final int DIGITS_NOOP
Digit shaping option: do not perform digit shaping.
Field Value:
0

DIGIT_TYPE_AN

public static final int DIGIT_TYPE_AN
Digit type option: Use Arabic-Indic digits (U+0660...U+0669).
Field Value:
0

DIGIT_TYPE_AN_EXTENDED

public static final int DIGIT_TYPE_AN_EXTENDED
Digit type option: Use Eastern (Extended) Arabic-Indic digits (U+06f0...U+06f9).
Field Value:
256

DIGIT_TYPE_MASK

public static final int DIGIT_TYPE_MASK
Bit mask for digit type options.
Field Value:
256

LENGTH_FIXED_SPACES_AT_BEGINNING

public static final int LENGTH_FIXED_SPACES_AT_BEGINNING
Memory option: the result must have the same length as the source. If more room is necessary, then try to consume spaces at the beginning of the text.
Field Value:
3

LENGTH_FIXED_SPACES_AT_END

public static final int LENGTH_FIXED_SPACES_AT_END
Memory option: the result must have the same length as the source. If more room is necessary, then try to consume spaces at the end of the text.
Field Value:
2

LENGTH_FIXED_SPACES_NEAR

public static final int LENGTH_FIXED_SPACES_NEAR
Memory option: the result must have the same length as the source. If more room is necessary, then try to consume spaces next to modified characters.
Field Value:
1

LENGTH_GROW_SHRINK

public static final int LENGTH_GROW_SHRINK
Memory option: allow the result to have a different length than the source.
Field Value:
0

LENGTH_MASK

public static final int LENGTH_MASK
Bit mask for memory options.
Field Value:
3

LETTERS_MASK

public static final int LETTERS_MASK
Bit mask for letter shaping options.
Field Value:
24

LETTERS_NOOP

public static final int LETTERS_NOOP
Letter shaping option: do not perform letter shaping.
Field Value:
0

LETTERS_SHAPE

public static final int LETTERS_SHAPE
Letter shaping option: replace normative letter characters in the U+0600 (Arabic) block, by shaped ones in the U+FE70 (Presentation Forms B) block. Performs Lam-Alef ligature substitution.
Field Value:
8

LETTERS_SHAPE_TASHKEEL_ISOLATED

public static final int LETTERS_SHAPE_TASHKEEL_ISOLATED
Letter shaping option: replace normative letter characters in the U+0600 (Arabic) block, except for the TASHKEEL characters at U+064B...U+0652, by shaped ones in the U+Fe70 (Presentation Forms B) block. The TASHKEEL characters will always be converted to the isolated forms rather than to their correct shape.
Field Value:
24

LETTERS_UNSHAPE

public static final int LETTERS_UNSHAPE
Letter shaping option: replace shaped letter characters in the U+FE70 (Presentation Forms B) block by normative ones in the U+0600 (Arabic) block. Converts Lam-Alef ligatures to pairs of Lam and Alef characters, consuming spaces if required.
Field Value:
16

TEXT_DIRECTION_LOGICAL

public static final int TEXT_DIRECTION_LOGICAL
Direction indicator: the source is in logical (keyboard) order.
Field Value:
0

TEXT_DIRECTION_MASK

public static final int TEXT_DIRECTION_MASK
Bit mask for direction indicators.
Field Value:
4

TEXT_DIRECTION_VISUAL_LTR

public static final int TEXT_DIRECTION_VISUAL_LTR
Direction indicator: the source is in visual (display) order, that is, the leftmost displayed character is stored first.
Field Value:
4

Constructor Details

ArabicShaping

public ArabicShaping(int options)
Construct ArabicShaping using the options flags. The flags are as follows:
'LENGTH' flags control whether the text can change size, and if not, how to maintain the size of the text when LamAlef ligatures are formed or broken.
'TEXT_DIRECTION' flags control whether the text is read and written in visual order or in logical order.
'LETTERS_SHAPE' flags control whether conversion is to or from presentation forms.
'DIGITS' flags control whether digits are shaped, and whether from European to Arabic-Indic or vice-versa.
'DIGIT_TYPE' flags control whether standard or extended Arabic-Indic digits are used when performing digit conversion.

Method Details

equals

public boolean equals(Object rhs)

hashCode

public int hashCode()

shape

public String shape(String text)
            throws ArabicShapingException
Convert a string, returning the new string.
Parameters:
text - the string to convert
Returns:
the converted string
Throws:
ArabicShapingException - if the string cannot be converted according to the options.

shape

public void shape(char[] source,
                  int start,
                  int length)
            throws ArabicShapingException
Convert a range of text in place. This may only be used if the Length option does not grow or shrink the text.
Parameters:
source - An array containing the input text
start - The start of the range of text to convert
length - The length of the range of text to convert
Throws:
ArabicShapingException - if the text cannot be converted according to the options.

shape

public int shape(char[] source,
                 int sourceStart,
                 int sourceLength,
                 char[] dest,
                 int destStart,
                 int destSize)
            throws ArabicShapingException
Convert a range of text in the source array, putting the result into a range of text in the destination array, and return the number of characters written.
Parameters:
source - An array containing the input text
sourceStart - The start of the range of text to convert
sourceLength - The length of the range of text to convert
dest - The destination array that will receive the result. It may be NULL only if destSize is 0.
destStart - The start of the range of the destination buffer to use.
destSize - The size (capacity) of the destination buffer. If destSize is 0, then no output is produced, but the necessary buffer size is returned ("preflighting"). This does not validate the text against the options, for example, if letters are being unshaped, and spaces are being consumed following lamalef, this will not detect a lamalef without a corresponding space. An error will be thrown when the actual conversion is attempted.
Returns:
The number of chars written to the destination buffer. If an error occurs, then no output was written, or it may be incomplete.
Throws:
ArabicShapingException - if the text cannot be converted according to the options.

toString

public String toString()

Copyright (c) 2006 IBM Corporation and others.