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ubidi.h File Reference

C API: BIDI algorithm. More...

#include "unicode/utypes.h"
#include "unicode/uchar.h"

Go to the source code of this file.


Detailed Description

C API: BIDI algorithm.

BIDI algorithm for ICU

This is an implementation of the Unicode Bidirectional algorithm. The algorithm is defined in the Unicode Technical Report 9, version 5, also described in The Unicode Standard, Version 3.0 .

General remarks about the API:

In functions with an error code parameter, the pErrorCode pointer must be valid and the value that it points to must not indicate a failure before the function call. Otherwise, the function returns immediately. After the function call, the value indicates success or failure.

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 functions 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.

Author:
Markus W. Scherer
Version:
1.0

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:

 *#include "unicode/ubidi.h"

 *typedef enum {
     styleNormal=0, styleSelected=1,
     styleBold=2, styleItalics=4,
     styleSuper=8, styleSub=16
 *} Style;

 *typedef struct { int32_t limit; Style style; } StyleRun;

 *int getTextWidth(const UChar *text, int32_t start, int32_t limit,
                  const StyleRun *styleRuns, int styleRunCount);

 // set *pLimit and *pStyleRunLimit for a line
 // from text[start] and from styleRuns[styleRunStart]
 // using ubidi_getLogicalRun(para, ...)
 *void getLineBreak(const UChar *text, int32_t start, int32_t *pLimit,
                  UBiDi *para,
                  const StyleRun *styleRuns, int styleRunStart, int *pStyleRunLimit,
                  int *pLineWidth);

 // render runs on a line sequentially, always from left to right

 // prepare rendering a new line
 *void startLine(UBiDiDirection textDirection, int lineWidth);

 // render a run of text and advance to the right by the run width
 // the text[start..limit-1] is always in logical order
 *void renderRun(const UChar *text, int32_t start, int32_t limit,
               UBiDiDirection textDirection, Style 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
 *void renderDirectionalRun(const UChar *text,
                           int32_t start, int32_t limit,
                           UBiDiDirection direction,
                           const StyleRun *styleRuns, int styleRunCount) {
     int i;

     // iterate over style runs
     if(direction==UBIDI_LTR) {
         int styleLimit;

         for(i=0; i<styleRunCount; ++i) {
             styleLimit=styleRun[i].limit;
             if(start<styleLimit) {
                 if(styleLimit>limit) { styleLimit=limit; }
                 renderRun(text, start, styleLimit,
                           direction, styleRun[i].style);
                 if(styleLimit==limit) { break; }
                 start=styleLimit;
             }
         }
     } else {
         int styleStart;

         for(i=styleRunCount-1; i>=0; --i) {
             if(i>0) {
                 styleStart=styleRun[i-1].limit;
             } else {
                 styleStart=0;
             }
             if(limit>=styleStart) {
                 if(styleStart<start) { styleStart=start; }
                 renderRun(text, styleStart, limit,
                           direction, styleRun[i].style);
                 if(styleStart==start) { break; }
                 limit=styleStart;
             }
         }
     }
 }

 // the line object represents text[start..limit-1]
 void renderLine(UBiDi *line, const UChar *text,
                 int32_t start, int32_t limit,
                 const StyleRun *styleRuns, int styleRunCount) {
     UBiDiDirection direction=ubidi_getDirection(line);
     if(direction!=UBIDI_MIXED) {
         // unidirectional
         if(styleRunCount<=1) {
             renderRun(text, start, limit, direction, styleRuns[0].style);
         } else {
             renderDirectionalRun(text, start, limit,
                                  direction, styleRuns, styleRunCount);
         }
     } else {
         // mixed-directional
         int32_t count, i, length;
         UBiDiLevel level;

         count=ubidi_countRuns(para, pErrorCode);
         if(U_SUCCESS(*pErrorCode)) {
             if(styleRunCount<=1) {
                 Style style=styleRuns[0].style;

                 // iterate over directional runs
                for(i=0; i<count; ++i) {
                    direction=ubidi_getVisualRun(para, i, &start, &length);
                     renderRun(text, start, start+length, direction, style);
                }
             } else {
                 int32_t j;

                 // iterate over both directional and style runs
                 for(i=0; i<count; ++i) {
                     direction=ubidi_getVisualRun(line, i, &start, &length);
                     renderDirectionalRun(text, start, start+length,
                                          direction, styleRuns, styleRunCount);
                 }
             }
         }
     }
 }

 *void renderParagraph(const UChar *text, int32_t length,
                     UBiDiDirection textDirection,
                      const StyleRun *styleRuns, int styleRunCount,
                      int lineWidth,
                      UErrorCode *pErrorCode) {
     UBiDi *para;

     if(pErrorCode==NULL || U_FAILURE(*pErrorCode) || length<=0) {
         return;
     }

     para=ubidi_openSized(length, 0, pErrorCode);
     if(para==NULL) { return; }

     ubidi_setPara(para, text, length,
                   textDirection ? UBIDI_DEFAULT_RTL : UBIDI_DEFAULT_LTR,
                   NULL, pErrorCode);
     if(U_SUCCESS(*pErrorCode)) {
         UBiDiLevel paraLevel=1&ubidi_getParaLevel(para);
         StyleRun styleRun={ length, styleNormal };
         int width;

         if(styleRuns==NULL || styleRunCount<=0) {
            styleRunCount=1;
             styleRuns=&styleRun;
         }

        // assume styleRuns[styleRunCount-1].limit>=length

         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 {
             UBiDi *line;

             // we need to render several lines
             line=ubidi_openSized(length, 0, pErrorCode);
             if(line!=NULL) {
                 int32_t start=0, limit;
                 int styleRunStart=0, styleRunLimit;

                 for(;;) {
                     limit=length;
                     styleRunLimit=styleRunCount;
                     getLineBreak(text, start, &limit, para,
                                  styleRuns, styleRunStart, &styleRunLimit,
                                 &width);
                     ubidi_setLine(para, start, limit, line, pErrorCode);
                     if(U_SUCCESS(*pErrorCode)) {
                         // prepare rendering a new line
                         // from either left or right
                         startLine(paraLevel, width);

                         renderLine(line, text, start, limit,
                                    styleRuns+styleRunStart,
                                    styleRunLimit-styleRunStart);
                     }
                     if(limit==length) { break; }
                     start=limit;
                     styleRunStart=styleRunLimit-1;
                     if(start>=styleRuns[styleRunStart].limit) {
                         ++styleRunStart;
                     }
                 }

                 ubidi_close(line);
             }
        }
    }

     ubidi_close(para);
 *}
 *

Define Documentation

#define UBIDI_DEFAULT_LTR   0xfe
 

Paragraph level setting.

If there is no strong character, then set the paragraph level to 0 (left-to-right).

#define UBIDI_DEFAULT_RTL   0xff
 

Paragraph level setting.

If there is no strong character, then set the paragraph level to 1 (right-to-left).

#define UBIDI_DO_MIRRORING   2
 

option bit for ubidi_writeReordered(): replace characters with the "mirrored" property in RTL runs by their mirror-image mappings

See also:
ubidi_writeReordered

#define UBIDI_INSERT_LRM_FOR_NUMERIC   4
 

option bit for ubidi_writeReordered(): surround the run with LRMs if necessary; this is part of the approximate "inverse BiDi" algorithm

See also:
ubidi_setInverse

ubidi_writeReordered

#define UBIDI_KEEP_BASE_COMBINING   1
 

option bit for ubidi_writeReordered(): keep combining characters after their base characters in RTL runs

See also:
ubidi_writeReordered

#define UBIDI_LEVEL_OVERRIDE   0x80
 

Bit flag for level input.

Overrides directional properties.

#define UBIDI_MAX_EXPLICIT_LEVEL   61
 

Maximum explicit embedding level.

(The maximum resolved level can be up to UBIDI_MAX_EXPLICIT_LEVEL+1).

#define UBIDI_OUTPUT_REVERSE   16
 

option bit for ubidi_writeReordered(): write the output in reverse order

This has the same effect as calling ubidi_writeReordered() first without this option, and then calling ubidi_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:
ubidi_writeReordered

#define UBIDI_REMOVE_BIDI_CONTROLS   8
 

option bit for ubidi_writeReordered(): remove BiDi control characters (this does not affect UBIDI_INSERT_LRM_FOR_NUMERIC)

See also:
ubidi_writeReordered


Typedef Documentation

typedef uint8_t UBiDiLevel
 

UBiDiLevel is the type of the level values in this BiDi implementation.

It holds an embedding level and indicates the visual direction by its bit 0 (even/odd value).

It can also hold non-level values for the paraLevel and embeddingLevels arguments of ubidi_setPara(); there:

  • bit 7 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 pesudo-level values UBIDI_DEFAULT_LTR and UBIDI_DEFAULT_RTL.

    See also:
    ubidi_setPara

    The related constants are not real, valid level values. UBIDI_DEFAULT_XXX can be used to specify a default for the paragraph level for when the ubidi_setPara() function shall determine it but there is no strongly typed character in the input.

    Note that the value for UBIDI_DEFAULT_LTR is even and the one for UBIDI_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 UBIDI_MAX_EXPLICIT_LEVEL is odd.

    See also:
    UBIDI_DEFAULT_LTR

    UBIDI_DEFAULT_RTL

    UBIDI_LEVEL_OVERRIDE

    UBIDI_MAX_EXPLICIT_LEVEL


Enumeration Type Documentation

enum UBiDiDirection
 

UBiDiDirection values indicate the text direction.

Enumeration values:
UBIDI_LTR  All left-to-right text.

This is a 0 value.

UBIDI_RTL  All right-to-left text.

This is a 1 value.

UBIDI_MIXED  Mixed-directional text.


Function Documentation

U_CAPI void U_EXPORT2 ubidi_close UBiDi pBiDi  ) 
 

ubidi_close() must be called to free the memory associated with a UBiDi object.

Important: If a UBiDi object is the child of another one (its parent), after calling ubidi_setLine(), then the child object must be destroyed (closed) or reused (by calling ubidi_setPara() or ubidi_setLine()) before the parent object.

Parameters:
pBiDi is a UBiDi object.
See also:
ubidi_setPara

ubidi_setLine

U_CAPI int32_t U_EXPORT2 ubidi_countRuns UBiDi pBiDi,
UErrorCode pErrorCode
 

Get the number of runs.

This function may invoke the actual reordering on the UBiDi object, after ubidi_setPara() may have resolved only the levels of the text. Therefore, ubidi_countRuns() may have to allocate memory, and may fail doing so.

Parameters:
pBiDi is the paragraph or line UBiDi object.
pErrorCode must be a valid pointer to an error code value, which must not indicate a failure before the function call.
Returns:
The number of runs.

U_CAPI UBiDiDirection U_EXPORT2 ubidi_getDirection const UBiDi pBiDi  ) 
 

Get the directionality of the text.

Parameters:
pBiDi is the paragraph or line UBiDi object.
Returns:
A UBIDI_XXX value that indicates if the entire text represented by this object is unidirectional, and which direction, or if it is mixed-directional.
See also:
UBiDiDirection

U_CAPI int32_t U_EXPORT2 ubidi_getLength const UBiDi pBiDi  ) 
 

Get the length of the text.

Parameters:
pBiDi is the paragraph or line UBiDi object.
Returns:
The length of the text that the UBiDi object was created for.

U_CAPI UBiDiLevel U_EXPORT2 ubidi_getLevelAt const UBiDi pBiDi,
int32_t  charIndex
 

Get the level for one character.

Parameters:
pBiDi is the paragraph or line UBiDi object.
charIndex the index of a character.
Returns:
The level for the character at charIndex.
See also:
UBiDiLevel

U_CAPI const UBiDiLevel* U_EXPORT2 ubidi_getLevels UBiDi pBiDi,
UErrorCode pErrorCode
 

Get an array of levels for each character.

Note that this function may allocate memory under some circumstances, unlike ubidi_getLevelAt().

Parameters:
pBiDi is the paragraph or line UBiDi object.
pErrorCode must be a valid pointer to an error code value, which must not indicate a failure before the function call.
Returns:
The levels array for the text, or NULL if an error occurs.
See also:
UBiDiLevel

U_CAPI int32_t U_EXPORT2 ubidi_getLogicalIndex UBiDi pBiDi,
int32_t  visualIndex,
UErrorCode pErrorCode
 

Get the logical text position from a visual position.

If such a mapping is used many times on the same UBiDi object, then calling ubidi_getVisualMap() is more efficient.

This is the inverse function to ubidi_getVisualIndex().

Parameters:
pBiDi is the paragraph or line UBiDi object.
visualIndex is the visual position of a character.
pErrorCode must be a valid pointer to an error code value, which must not indicate a failure before the function call.
Returns:
The index of this character in the text.
See also:
ubidi_getVisualMap

ubidi_getVisualIndex

U_CAPI void U_EXPORT2 ubidi_getLogicalMap UBiDi pBiDi,
int32_t *  indexMap,
UErrorCode pErrorCode
 

Get a logical-to-visual index map (array) for the characters in the UBiDi (paragraph or line) object.

Parameters:
pBiDi is the paragraph or line UBiDi object.
indexMap is a pointer to an array of ubidi_getLength() indexes which will reflect the reordering of the characters. The array does not need to be initialized.
The index map will result in indexMap[logicalIndex]==visualIndex.

Parameters:
pErrorCode must be a valid pointer to an error code value, which must not indicate a failure before the function call.
See also:
ubidi_getVisualMap

ubidi_getVisualIndex

U_CAPI void U_EXPORT2 ubidi_getLogicalRun const UBiDi pBiDi,
int32_t  logicalStart,
int32_t *  pLogicalLimit,
UBiDiLevel pLevel
 

Get a logical run.

This function 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:
pBiDi is the paragraph or line UBiDi object.
logicalStart is the first character of the run.
pLogicalLimit will receive the limit of the run. The l-value that you point to here may be the same expression (variable) as the one for logicalStart. This pointer can be NULL if this value is not necessary.
pLevel will receive the level of the run. This pointer can be NULL if this value is not necessary.

U_CAPI UBiDiLevel U_EXPORT2 ubidi_getParaLevel const UBiDi pBiDi  ) 
 

Get the paragraph level of the text.

Parameters:
pBiDi is the paragraph or line UBiDi object.
Returns:
The paragraph level.
See also:
UBiDiLevel

U_CAPI const UChar* U_EXPORT2 ubidi_getText const UBiDi pBiDi  ) 
 

Get the pointer to the text.

Parameters:
pBiDi is the paragraph or line UBiDi object.
Returns:
The pointer to the text that the UBiDi object was created for.
See also:
ubidi_setPara

ubidi_setLine

U_CAPI int32_t U_EXPORT2 ubidi_getVisualIndex UBiDi pBiDi,
int32_t  logicalIndex,
UErrorCode pErrorCode
 

Get the visual position from a logical text position.

If such a mapping is used many times on the same UBiDi object, then calling ubidi_getLogicalMap() is more efficient.

Note that in right-to-left runs, this mapping places modifier letters before base characters and second surrogates before first ones.

Parameters:
pBiDi is the paragraph or line UBiDi object.
logicalIndex is the index of a character in the text.
pErrorCode must be a valid pointer to an error code value, which must not indicate a failure before the function call.
Returns:
The visual position of this character.
See also:
ubidi_getLogicalMap

ubidi_getLogicalIndex

U_CAPI void U_EXPORT2 ubidi_getVisualMap UBiDi pBiDi,
int32_t *  indexMap,
UErrorCode pErrorCode
 

Get a visual-to-logical index map (array) for the characters in the UBiDi (paragraph or line) object.

Parameters:
pBiDi is the paragraph or line UBiDi object.
indexMap is a pointer to an array of ubidi_getLength() indexes which will reflect the reordering of the characters. The array does not need to be initialized.
The index map will result in indexMap[visualIndex]==logicalIndex.

Parameters:
pErrorCode must be a valid pointer to an error code value, which must not indicate a failure before the function call.
See also:
ubidi_getLogicalMap

ubidi_getLogicalIndex

U_CAPI UBiDiDirection U_EXPORT2 ubidi_getVisualRun UBiDi pBiDi,
int32_t  runIndex,
int32_t *  pLogicalStart,
int32_t *  pLength
 

Get one run's logical start, length, and directionality, which can be 0 for LTR or 1 for RTL.

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.

ubidi_countRuns() should be called before the runs are retrieved.

Parameters:
pBiDi is the paragraph or line UBiDi object.
runIndex is the number of the run in visual order, in the range [0..ubidi_countRuns(pBiDi)-1].
pLogicalStart is the first logical character index in the text. The pointer may be NULL if this index is not needed.
pLength is the number of characters (at least one) in the run. The pointer may be NULL if this is not needed.
Returns:
the directionality of the run, UBIDI_LTR==0 or UBIDI_RTL==1, never UBIDI_MIXED.
See also:
ubidi_countRuns
Example:
 int32_t i, count=ubidi_countRuns(pBiDi),
         logicalStart, visualIndex=0, length;
 for(i=0; i<count; ++i) {
    if(UBIDI_LTR==ubidi_getVisualRun(pBiDi, i, &logicalStart, &length)) {
         do { // LTR
             show_char(text[logicalStart++], visualIndex++);
         } while(--length>0);
     } else {
         logicalStart+=length;  // logicalLimit
         do { // RTL
             show_char(text[--logicalStart], visualIndex++);
         } while(--length>0);
     }
 }
 *

Note that in right-to-left runs, code like this places modifier letters before base characters and second surrogates before first ones.

U_CAPI void U_EXPORT2 ubidi_invertMap const int32_t *  srcMap,
int32_t *  destMap,
int32_t  length
 

Invert an index map.

The one-to-one index mapping of the first map is inverted and written to the second one.

Parameters:
srcMap is an array with length indexes which define the original mapping.
destMap is an array with length indexes which will be filled with the inverse mapping.
length is the length of each array.

U_CAPI UBool U_EXPORT2 ubidi_isInverse UBiDi pBiDi  ) 
 

Is this BiDi object set to perform the inverse BiDi algorithm?

Parameters:
pBiDi is a UBiDi object.
See also:
ubidi_setInverse

U_CAPI UBiDi* U_EXPORT2 ubidi_open void   ) 
 

Allocate a UBiDi structure.

Such an object is initially empty. It is assigned the BiDi properties of a paragraph by ubidi_setPara() or the BiDi properties of a line of a paragraph by ubidi_setLine().

This object can be reused for as long as it is not deallocated by calling ubidi_close().

ubidi_set() will allocate additional memory for internal structures as necessary.

Returns:
An empty UBiDi object.

U_CAPI UBiDi* U_EXPORT2 ubidi_openSized int32_t  maxLength,
int32_t  maxRunCount,
UErrorCode pErrorCode
 

Allocate a UBiDi structure with preallocated memory for internal structures.

This function provides a UBiDi object like ubidi_open() with no arguments, but it also preallocates memory for internal structures according to the sizings supplied by the caller.

Subsequent functions will not allocate any more memory, and are thus guaranteed not to fail because of lack of memory.

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 ubidi_open().

Parameters:
maxLength is the maximum paragraph 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 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.

Parameters:
pErrorCode must be a valid pointer to an error code value, which must not indicate a failure before the function call.
Returns:
An empty UBiDi object with preallocated memory.

U_CAPI void U_EXPORT2 ubidi_reorderLogical const UBiDiLevel levels,
int32_t  length,
int32_t *  indexMap
 

This is a convenience function that does not use a UBiDi 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 ubidi_getLogicalMap on a UBiDi object.

Parameters:
levels is an array with length levels that have been determined by the application.
length is the number of levels in the array, or, semantically, the number of objects to be reordered. It must be length>0.
indexMap is a pointer to an array of length indexes which will reflect the reordering of the characters. The array does not need to be initialized.
The index map will result in indexMap[logicalIndex]==visualIndex.

U_CAPI void U_EXPORT2 ubidi_reorderVisual const UBiDiLevel levels,
int32_t  length,
int32_t *  indexMap
 

This is a convenience function that does not use a UBiDi 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 ubidi_getVisualMap on a UBiDi object.

Parameters:
levels is an array with length levels that have been determined by the application.
length is the number of levels in the array, or, semantically, the number of objects to be reordered. It must be length>0.
indexMap is a pointer to an array of length indexes which will reflect the reordering of the characters. The array does not need to be initialized.
The index map will result in indexMap[visualIndex]==logicalIndex.

U_CAPI void U_EXPORT2 ubidi_setInverse UBiDi pBiDi,
UBool  isInverse
 

Modify the operation of the BiDi algorithm such that it approximates an "inverse BiDi" algorithm.

This function must be called before ubidi_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 codepages 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 isInverse set to TRUE, this function changes the behavior of some of the subsequent functions 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 ubidi_getVisualRun(). Since the actual input for "inverse BiDi" is visually ordered text and ubidi_getVisualRun() gets the reordered runs, these are actually the runs of the logically ordered output.

Parameters:
pBiDi is a UBiDi object.
isInverse specifies "forward" or "inverse" BiDi operation
See also:
ubidi_setPara

ubidi_writeReordered

U_CAPI void U_EXPORT2 ubidi_setLine const UBiDi pParaBiDi,
int32_t  start,
int32_t  limit,
UBiDi pLineBiDi,
UErrorCode pErrorCode
 

ubidi_setLine() sets a UBiDi 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 UBiDi object representing this information for a paragraph of text, and by specifying a range of indexes in this paragraph.

In the new line object, the indexes will range from 0 to limit-start.

This is used after calling ubidi_setPara() for a paragraph, and after line-breaking on that paragraph. It is not necessary if the 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 UBiDi object that represents a line.

Important: pLineBiDi shares data with pParaBiDi. You must destroy or reuse pLineBiDi before pParaBiDi. In other words, you must destroy or reuse the UBiDi object for a line before the object for its parent paragraph.

The text pointer that was stored in pParaBiDi is also copied, and start is added to it so that it points to the beginning of the line for this object.

Parameters:
pParaBiDi is the parent paragraph object.
start is the line's first index into the paragraph text.
limit is just behind the line's last index into the paragraph text (its last index +1).
It must be 0<=start<=limit<=paragraph length.
pLineBiDi is the object that will now represent a line of the paragraph.
pErrorCode must be a valid pointer to an error code value, which must not indicate a failure before the function call.
See also:
ubidi_setPara

U_CAPI void U_EXPORT2 ubidi_setPara UBiDi pBiDi,
const UChar text,
int32_t  length,
UBiDiLevel  paraLevel,
UBiDiLevel embeddingLevels,
UErrorCode pErrorCode
 

Perform the Unicode BiDi algorithm.

It is defined in the Unicode Technical Report 9, version 5, also described in The Unicode Standard, Version 3.0 .

This function takes a single plain text paragraph with or without externally specified embedding levels from styled text and computes the left-right-directionality of each character.

If the entire paragraph consists of text of only one direction, then the function 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 must be externally split into separate paragraphs (rule P1). Paragraph separators (B) should appear at most at the very end.

Parameters:
pBiDi A UBiDi object allocated with ubidi_open() which will be set to contain the reordering information, especially the resolved levels for all the characters in text.
text is a pointer to the single-paragraph text that the BiDi algorithm will be performed on (step (P1) of the algorithm is performed externally). The text must be (at least) length long. This pointer is stored in the UBiDi object and can be retrieved with ubidi_getText().
length is the length of the text; if length==-1 then the text must be zero-terminated.
paraLevel specifies the default level for the paragraph; it is typically 0 (LTR) or 1 (RTL). If the function shall determine the paragraph level from the text, then paraLevel can be set to either UBIDI_DEFAULT_LTR or UBIDI_DEFAULT_RTL; if there is no strongly typed character, then the desired default is used (0 for LTR or 1 for RTL). Any other value between 0 and UBIDI_MAX_EXPLICIT_LEVEL is also valid, with odd levels indicating RTL.
embeddingLevels (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 UBIDI_LEVEL_OVERRIDE bit set.
Except for that bit, it must be paraLevel<=embeddingLevels[]<=UBIDI_MAX_EXPLICIT_LEVEL.

Caution: A copy of this pointer, not of the levels, will be stored in the UBiDi object; the embeddingLevels array must not be deallocated before the UBiDi structure is destroyed or reused, and the embeddingLevels should not be modified to avoid unexpected results on subsequent BiDi operations. However, the ubidi_setPara() and ubidi_setLine() functions may modify some or all of the levels.

After the UBiDi object is reused or destroyed, the caller must take care of the deallocation of the embeddingLevels array.

The embeddingLevels array must be at least length long.

Parameters:
pErrorCode must be a valid pointer to an error code value, which must not indicate a failure before the function call.

U_CAPI int32_t U_EXPORT2 ubidi_writeReordered UBiDi pBiDi,
UChar dest,
int32_t  destSize,
uint16_t  options,
UErrorCode pErrorCode
 

Take a UBiDi object containing the reordering information for one paragraph or line of text as set by ubidi_setPara() or ubidi_setLine() and write a reordered string to the destination buffer.

This function preserves the integrity of characters with multiple code units and (optionally) modifier letters. Characters in RTL runs 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; see the description of the destSize and options parameters and of the option bit flags.

Parameters:
pBiDi A pointer to a UBiDi object that is set by ubidi_setPara() or ubidi_setLine() and contains the reordering information for the text that it was defined for, as well as a pointer to that text.
The text was aliased (only the pointer was stored without copying the contents) and must not have been modified since the ubidi_setPara() call.

Parameters:
dest A pointer to where the reordered text is to be copied. The source text and dest[destSize] must not overlap.
destSize The size of the dest buffer, in number of UChars. If the UBIDI_INSERT_LRM_FOR_NUMERIC option is set, then the destination length could be as large as ubidi_getLength(pBiDi)+2*ubidi_countRuns(pBiDi). If the UBIDI_REMOVE_BIDI_CONTROLS option is set, then the destination length may be less than ubidi_getLength(pBiDi). If none of these options is set, then the destination length will be exactly ubidi_getLength(pBiDi).
options 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).
pErrorCode must be a valid pointer to an error code value, which must not indicate a failure before the function call.
Returns:
The length of the output string.

U_CAPI int32_t U_EXPORT2 ubidi_writeReverse const UChar src,
int32_t  srcLength,
UChar dest,
int32_t  destSize,
uint16_t  options,
UErrorCode pErrorCode
 

Reverse a Right-To-Left run of Unicode text.

This function preserves the integrity of characters with multiple code units and (optionally) modifier letters. 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 function is the implementation for reversing RTL runs as part of ubidi_writeReordered(). For detailed descriptions of the parameters, see there. Since no BiDi controls are inserted here, the output string length will never exceed srcLength.

See also:
ubidi_writeReordered
Parameters:
src A pointer to the RTL run text.
srcLength The length of the RTL run.
dest A pointer to where the reordered text is to be copied. src[srcLength] and dest[destSize] must not overlap.
destSize The size of the dest buffer, in number of UChars. If the UBIDI_REMOVE_BIDI_CONTROLS option is set, then the destination length may be less than srcLength. If this option is not set, then the destination length will be exactly srcLength.
options A bit set of options for the reordering that control how the reordered text is written. See ubidi_writeReordered().
pErrorCode must be a valid pointer to an error code value, which must not indicate a failure before the function call.
Returns:
The length of the output string.


Generated on Sun Jan 18 22:55:41 2004 for ICU 2.1 by doxygen 1.3.4