* A Bidi object provides information on the bidirectional reordering of the text * used to create it. This is required, for example, to properly display Arabic * or Hebrew text. These languages are inherently mixed directional, as they order * numbers from left-to-right while ordering most other text from right-to-left. *
* Once created, a Bidi object can be queried to see if the text it represents is * all left-to-right or all right-to-left. Such objects are very lightweight and * this text is relatively easy to process. *
* If there are multiple runs of text, information about the runs can be accessed * by indexing to get the start, limit, and level of a run. The level represents * both the direction and the 'nesting level' of a directional run. Odd levels * are right-to-left, while even levels are left-to-right. So for example level * 0 represents left-to-right text, while level 1 represents right-to-left text, and * level 2 represents left-to-right text embedded in a right-to-left run. * * @since 1.4 */ public final class Bidi { /** Constant indicating base direction is left-to-right. */ public static final int DIRECTION_LEFT_TO_RIGHT = 0; /** Constant indicating base direction is right-to-left. */ public static final int DIRECTION_RIGHT_TO_LEFT = 1; /** * 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. */ public static final int DIRECTION_DEFAULT_LEFT_TO_RIGHT = -2; /** * 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. */ public static final int DIRECTION_DEFAULT_RIGHT_TO_LEFT = -1; private BidiBase bidiBase; /** * Create Bidi from the given paragraph of text and base direction. * @param paragraph a paragraph of text * @param flags 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. */ public Bidi(String paragraph, int flags) { if (paragraph == null) { throw new IllegalArgumentException("paragraph is null"); } bidiBase = new BidiBase(paragraph.toCharArray(), 0, null, 0, paragraph.length(), flags); } /** * 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 computes 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 from -1 to -62 indicate overrides at the absolute value * of the level. Positive values from 1 to 62 indicate embeddings. 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.
*
* @param paragraph a paragraph of text with optional character and paragraph attribute information
*
* @see java.awt.font.TextAttribute#BIDI_EMBEDDING
* @see java.awt.font.TextAttribute#NUMERIC_SHAPING
* @see java.awt.font.TextAttribute#RUN_DIRECTION
*/
public Bidi(AttributedCharacterIterator paragraph) {
if (paragraph == null) {
throw new IllegalArgumentException("paragraph is null");
}
bidiBase = new BidiBase(0, 0);
bidiBase.setPara(paragraph);
}
/**
* 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 from -1 to -61 indicate overrides at the absolute value
* of the level. Positive values from 1 to 61 indicate embeddings. Where values are
* zero, the base embedding level as determined by the base direction is assumed.
* @param text an array containing the paragraph of text to process.
* @param textStart the index into the text array of the start of the paragraph.
* @param embeddings 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.
* @param embStart the index into the embedding array of the start of the paragraph.
* @param paragraphLength the length of the paragraph in the text and embeddings arrays.
* @param flags 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.
*/
public Bidi(char[] text, int textStart, byte[] embeddings, int embStart, int paragraphLength, int flags) {
if (text == null) {
throw new IllegalArgumentException("text is null");
}
if (paragraphLength < 0) {
throw new IllegalArgumentException("bad length: " + paragraphLength);
}
if (textStart < 0 || paragraphLength > text.length - textStart) {
throw new IllegalArgumentException("bad range: " + textStart +
" length: " + paragraphLength +
" for text of length: " + text.length);
}
if (embeddings != null && (embStart < 0 || paragraphLength > embeddings.length - embStart)) {
throw new IllegalArgumentException("bad range: " + embStart +
" length: " + paragraphLength +
" for embeddings of length: " + text.length);
}
bidiBase = new BidiBase(text, textStart, embeddings, embStart, paragraphLength, flags);
}
/**
* 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.
* @param lineStart the offset from the start of the paragraph to the start of the line.
* @param lineLimit the offset from the start of the paragraph to the limit of the line.
*/
public Bidi createLineBidi(int lineStart, int lineLimit) {
AttributedString astr = new AttributedString("");
Bidi newBidi = new Bidi(astr.getIterator());
return bidiBase.setLine(this, bidiBase, newBidi, newBidi.bidiBase,lineStart, lineLimit);
}
/**
* 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.
* @return true if the line is not left-to-right or right-to-left.
*/
public boolean isMixed() {
return bidiBase.isMixed();
}
/**
* Return true if the line is all left-to-right text and the base direction is left-to-right.
* @return true if the line is all left-to-right text and the base direction is left-to-right
*/
public boolean isLeftToRight() {
return bidiBase.isLeftToRight();
}
/**
* Return true if the line is all right-to-left text, and the base direction is right-to-left.
* @return true if the line is all right-to-left text, and the base direction is right-to-left
*/
public boolean isRightToLeft() {
return bidiBase.isRightToLeft();
}
/**
* Return the length of text in the line.
* @return the length of text in the line
*/
public int getLength() {
return bidiBase.getLength();
}
/**
* Return true if the base direction is left-to-right.
* @return true if the base direction is left-to-right
*/
public boolean baseIsLeftToRight() {
return bidiBase.baseIsLeftToRight();
}
/**
* Return the base level (0 if left-to-right, 1 if right-to-left).
* @return the base level
*/
public int getBaseLevel() {
return bidiBase.getParaLevel();
}
/**
* Return the resolved level of the character at offset. If offset is <0 or >=
* the length of the line, return the base direction level.
* @param offset the index of the character for which to return the level
* @return the resolved level of the character at offset
*/
public int getLevelAt(int offset) {
return bidiBase.getLevelAt(offset);
}
/**
* Return the number of level runs.
* @return the number of level runs
*/
public int getRunCount() {
return bidiBase.countRuns();
}
/**
* Return the level of the nth logical run in this line.
* @param run the index of the run, between 0 and getRunCount()
* @return the level of the run
*/
public int getRunLevel(int run) {
return bidiBase.getRunLevel(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.
* @param run the index of the run, between 0 and getRunCount()
* @return the start of the run
*/
public int getRunStart(int run) {
return bidiBase.getRunStart(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.
* @param run the index of the run, between 0 and getRunCount()
* @return limit the limit of the run
*/
public int getRunLimit(int run) {
return bidiBase.getRunLimit(run);
}
/**
* 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 function to return true.
*
* @param text the text containing the characters to test
* @param start the start of the range of characters to test
* @param limit the limit of the range of characters to test
* @return true if the range of characters requires bidi analysis
*/
public static boolean requiresBidi(char[] text, int start, int limit) {
return BidiBase.requiresBidi(text, start, limit);
}
/**
* Reorder the objects in the array into visual order based on their levels.
* This is a utility function 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).
*
* @param levels an array representing the bidi level of each object
* @param levelStart the start position in the levels array
* @param objects the array of objects to be reordered into visual order
* @param objectStart the start position in the objects array
* @param count the number of objects to reorder
*/
public static void reorderVisually(byte[] levels, int levelStart, Object[] objects, int objectStart, int count) {
BidiBase.reorderVisually(levels, levelStart, objects, objectStart, count);
}
/**
* Display the bidi internal state, used in debugging.
*/
public String toString() {
return bidiBase.toString();
}
}