ubidi.h File Reference

C API: Bidi algorithm. More...

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

Go to the source code of this file.

## Namespaces

| icu
| File coll.h.

## Macros

#define | UBIDI_DEFAULT_LTR 0xfe
| Paragraph level setting. More...
#define | UBIDI_DEFAULT_RTL 0xff
| Paragraph level setting. More...
#define | UBIDI_MAX_EXPLICIT_LEVEL 125
| Maximum explicit embedding level. More...
#define | UBIDI_LEVEL_OVERRIDE 0x80
| Bit flag for level input. More...
#define | UBIDI_MAP_NOWHERE (-1)
| Special value which can be returned by the mapping functions when a logical index has no corresponding visual index or vice-versa. More...
#define | UBIDI_KEEP_BASE_COMBINING 1
| option flags for ubidi_writeReordered() More...
#define | UBIDI_DO_MIRRORING 2
| option bit for ubidi_writeReordered(): replace characters with the "mirrored" property in RTL runs by their mirror-image mappings More...
#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 More...
#define | UBIDI_REMOVE_BIDI_CONTROLS 8
| option bit for ubidi_writeReordered(): remove Bidi control characters (this does not affect UBIDI_INSERT_LRM_FOR_NUMERIC) More...
#define | UBIDI_OUTPUT_REVERSE 16
| option bit for ubidi_writeReordered(): write the output in reverse order More...
#define | U_BIDI_CLASS_DEFAULT U_CHAR_DIRECTION_COUNT
| Value returned by `UBiDiClassCallback` callbacks when there is no need to override the standard Bidi class for a given code point. More...

## Typedefs

typedef uint8_t | UBiDiLevel
| UBiDiLevel is the type of the level values in this Bidi implementation. More...
typedef enum UBiDiDirection | UBiDiDirection
typedef struct UBiDi | UBiDi
typedef enum UBiDiReorderingMode | UBiDiReorderingMode
| `UBiDiReorderingMode` values indicate which variant of the Bidi algorithm to use. More...
typedef enum UBiDiReorderingOption | UBiDiReorderingOption
| `UBiDiReorderingOption` values indicate which options are specified to affect the Bidi algorithm. More...
typedef UCharDirection | UBiDiClassCallback(const void *context, UChar32 c)
| Callback type declaration for overriding default Bidi class values with custom ones. More...

## Enumerations

enum | UBiDiDirection { UBIDI_LTR , UBIDI_RTL , UBIDI_MIXED , UBIDI_NEUTRAL }
| `UBiDiDirection` values indicate the text direction. More...
enum | UBiDiReorderingMode { UBIDI_REORDER_DEFAULT = 0 , UBIDI_REORDER_NUMBERS_SPECIAL , UBIDI_REORDER_GROUP_NUMBERS_WITH_R , UBIDI_REORDER_RUNS_ONLY , UBIDI_REORDER_INVERSE_NUMBERS_AS_L , UBIDI_REORDER_INVERSE_LIKE_DIRECT , UBIDI_REORDER_INVERSE_FOR_NUMBERS_SPECIAL , UBIDI_REORDER_COUNT }
| `UBiDiReorderingMode` values indicate which variant of the Bidi algorithm to use. More...
enum | UBiDiReorderingOption { UBIDI_OPTION_DEFAULT = 0 , UBIDI_OPTION_INSERT_MARKS = 1 , UBIDI_OPTION_REMOVE_CONTROLS = 2 , UBIDI_OPTION_STREAMING = 4 }
| `UBiDiReorderingOption` values indicate which options are specified to affect the Bidi algorithm. More...

## Functions

U_CAPI UBiDi * | ubidi_open (void)
| Allocate a `UBiDi` structure. More...
U_CAPI UBiDi * | ubidi_openSized (int32_t maxLength, int32_t maxRunCount, UErrorCode *pErrorCode)
| Allocate a `UBiDi` structure with preallocated memory for internal structures. More...
U_CAPI void | ubidi_close (UBiDi *pBiDi)
| `ubidi_close()` must be called to free the memory associated with a UBiDi object. More...
U_CAPI void | ubidi_setInverse (UBiDi *pBiDi, UBool isInverse)
| Modify the operation of the Bidi algorithm such that it approximates an "inverse Bidi" algorithm. More...
U_CAPI UBool | ubidi_isInverse (UBiDi *pBiDi)
| Is this Bidi object set to perform the inverse Bidi algorithm? More...
U_CAPI void | ubidi_orderParagraphsLTR (UBiDi *pBiDi, UBool orderParagraphsLTR)
| Specify whether block separators must be allocated level zero, so that successive paragraphs will progress from left to right. More...
U_CAPI UBool | ubidi_isOrderParagraphsLTR (UBiDi *pBiDi)
| Is this Bidi object set to allocate level 0 to block separators so that successive paragraphs progress from left to right? More...
U_CAPI void | ubidi_setReorderingMode (UBiDi *pBiDi, UBiDiReorderingMode 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". More...
U_CAPI UBiDiReorderingMode | ubidi_getReorderingMode (UBiDi *pBiDi)
| What is the requested reordering mode for a given Bidi object? More...
U_CAPI void | ubidi_setReorderingOptions (UBiDi *pBiDi, uint32_t reorderingOptions)
| Specify which of the reordering options should be applied during Bidi transformations. More...
U_CAPI uint32_t | ubidi_getReorderingOptions (UBiDi *pBiDi)
| What are the reordering options applied to a given Bidi object? More...
U_CAPI void | ubidi_setContext (UBiDi *pBiDi, const UChar *prologue, int32_t proLength, const UChar *epilogue, int32_t epiLength, UErrorCode *pErrorCode)
| Set the context before a call to ubidi_setPara(). More...
U_CAPI void | ubidi_setPara (UBiDi *pBiDi, const UChar *text, int32_t length, UBiDiLevel paraLevel, UBiDiLevel *embeddingLevels, UErrorCode *pErrorCode)
| Perform the Unicode Bidi algorithm. More...
U_CAPI void | 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. More...
U_CAPI UBiDiDirection | ubidi_getDirection (const UBiDi *pBiDi)
| Get the directionality of the text. More...
U_CAPI UBiDiDirection | ubidi_getBaseDirection (const UChar *text, int32_t length)
| Gets the base direction of the text provided according to the Unicode Bidirectional Algorithm. More...
U_CAPI const UChar * | ubidi_getText (const UBiDi *pBiDi)
| Get the pointer to the text. More...
U_CAPI int32_t | ubidi_getLength (const UBiDi *pBiDi)
| Get the length of the text. More...
U_CAPI UBiDiLevel | ubidi_getParaLevel (const UBiDi *pBiDi)
| Get the paragraph level of the text. More...
U_CAPI int32_t | ubidi_countParagraphs (UBiDi *pBiDi)
| Get the number of paragraphs. More...
U_CAPI int32_t | ubidi_getParagraph (const UBiDi *pBiDi, int32_t charIndex, int32_t *pParaStart, int32_t *pParaLimit, UBiDiLevel *pParaLevel, UErrorCode *pErrorCode)
| Get a paragraph, given a position within the text. More...
U_CAPI void | ubidi_getParagraphByIndex (const UBiDi *pBiDi, int32_t paraIndex, int32_t *pParaStart, int32_t *pParaLimit, UBiDiLevel *pParaLevel, UErrorCode *pErrorCode)
| Get a paragraph, given the index of this paragraph. More...
U_CAPI UBiDiLevel | ubidi_getLevelAt (const UBiDi *pBiDi, int32_t charIndex)
| Get the level for one character. More...
U_CAPI const UBiDiLevel * | ubidi_getLevels (UBiDi *pBiDi, UErrorCode *pErrorCode)
| Get an array of levels for each character. More...
U_CAPI void | ubidi_getLogicalRun (const UBiDi *pBiDi, int32_t logicalPosition, int32_t *pLogicalLimit, UBiDiLevel *pLevel)
| Get a logical run. More...
U_CAPI int32_t | ubidi_countRuns (UBiDi *pBiDi, UErrorCode *pErrorCode)
| Get the number of runs. More...
U_CAPI UBiDiDirection | 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. More...
U_CAPI int32_t | ubidi_getVisualIndex (UBiDi *pBiDi, int32_t logicalIndex, UErrorCode *pErrorCode)
| Get the visual position from a logical text position. More...
U_CAPI int32_t | ubidi_getLogicalIndex (UBiDi *pBiDi, int32_t visualIndex, UErrorCode *pErrorCode)
| Get the logical text position from a visual position. More...
U_CAPI void | 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. More...
U_CAPI void | 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. More...
U_CAPI void | ubidi_reorderLogical (const UBiDiLevel *levels, int32_t length, int32_t *indexMap)
| This is a convenience function that does not use a UBiDi object. More...
U_CAPI void | ubidi_reorderVisual (const UBiDiLevel *levels, int32_t length, int32_t *indexMap)
| This is a convenience function that does not use a UBiDi object. More...
U_CAPI void | ubidi_invertMap (const int32_t *srcMap, int32_t *destMap, int32_t length)
| Invert an index map. More...
U_CAPI int32_t | ubidi_getProcessedLength (const UBiDi *pBiDi)
| Get the length of the source text processed by the last call to `ubidi_setPara()`. More...
U_CAPI int32_t | ubidi_getResultLength (const UBiDi *pBiDi)
| Get the length of the reordered text resulting from the last call to `ubidi_setPara()`. More...
U_CAPI UCharDirection | ubidi_getCustomizedClass (UBiDi *pBiDi, UChar32 c)
| Retrieve the Bidi class for a given code point. More...
U_CAPI void | ubidi_setClassCallback (UBiDi *pBiDi, UBiDiClassCallback *newFn, const void *newContext, UBiDiClassCallback **oldFn, const void **oldContext, UErrorCode *pErrorCode)
| Set the callback function and callback data used by the UBA implementation for Bidi class determination. More...
U_CAPI void | ubidi_getClassCallback (UBiDi *pBiDi, UBiDiClassCallback **fn, const void **context)
| Get the current callback function used for Bidi class determination. More...
U_CAPI int32_t | ubidi_writeReordered (UBiDi *pBiDi, UChar *dest, int32_t destSize, uint16_t options, UErrorCode *pErrorCode)
| Take a `UBiDi` object containing the reordering information for a piece of text (one or more paragraphs) set by `ubidi_setPara()` or for a line of text set by `ubidi_setLine()` and write a reordered string to the destination buffer. More...
U_CAPI int32_t | 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. More...

## 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 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 (u_shapeArabic()) APIs can be used at the core of such "Storage Layout Engines".

### 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:

- 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.

    *#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=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]
      void renderLine(UBiDi *line, const UChar *text,
                      int32_t start, int32_t limit,
                      const StyleRun *styleRuns, int styleRunCount,
                      UErrorCode *pErrorCode) {
          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(line, 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(line, 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, pErrorCode);
              } 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, pErrorCode);
                          }
                          if(limit==length) { break; }
                          start=limit;
                          styleRunStart=styleRunLimit-1;
                          if(start>=styleRuns[styleRunStart].limit) {
                              ++styleRunStart;
                          }
                      }

                      ubidi_close(line);
                  }
             }
         }

          ubidi_close(para);
    *}
    *
    ubidi_openSizedU_CAPI UBiDi * ubidi_openSized(int32_t maxLength, int32_t maxRunCount, UErrorCode *pErrorCode)Allocate a UBiDi structure with preallocated memory for internal structures.
    UBIDI_DEFAULT_RTL#define UBIDI_DEFAULT_RTLParagraph level setting.Definition: ubidi.h:393
    UBIDI_DEFAULT_LTR#define UBIDI_DEFAULT_LTRParagraph level setting.Definition: ubidi.h:366
    ubidi_countRunsU_CAPI int32_t ubidi_countRuns(UBiDi *pBiDi, UErrorCode *pErrorCode)Get the number of runs.
    ubidi_setLineU_CAPI void 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,...
    ubidi_closeU_CAPI void ubidi_close(UBiDi *pBiDi)ubidi_close() must be called to free the memory associated with a UBiDi object.
    UBiDiDirectionUBiDiDirectionUBiDiDirection values indicate the text direction.Definition: ubidi.h:429
    UBIDI_LTR@ UBIDI_LTRLeft-to-right text.Definition: ubidi.h:441
    UBIDI_MIXED@ UBIDI_MIXEDMixed-directional text.Definition: ubidi.h:460
    ubidi_setParaU_CAPI void ubidi_setPara(UBiDi *pBiDi, const UChar *text, int32_t length, UBiDiLevel paraLevel, UBiDiLevel *embeddingLevels, UErrorCode *pErrorCode)Perform the Unicode Bidi algorithm.
    ubidi_getDirectionU_CAPI UBiDiDirection ubidi_getDirection(const UBiDi *pBiDi)Get the directionality of the text.
    UBiDiLeveluint8_t UBiDiLevelUBiDiLevel is the type of the level values in this Bidi implementation.Definition: ubidi.h:340
    ubidi_getParaLevelU_CAPI UBiDiLevel ubidi_getParaLevel(const UBiDi *pBiDi)Get the paragraph level of the text.
    ubidi_getVisualRunU_CAPI UBiDiDirection 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.
    UBiDistruct UBiDi UBiDiDefinition: ubidi.h:486
    UCharchar16_t UCharThe base type for UTF-16 code units and pointers.Definition: umachine.h:386
    NULL#define NULLDefine NULL if necessary, to nullptr for C++ and to ((void *)0) for C.Definition: utypes.h:188
    UErrorCodeUErrorCodeStandard ICU4C error code type, a substitute for exceptions.Definition: utypes.h:415
    U_FAILURE#define U_FAILURE(x)Does the error code indicate a failure?Definition: utypes.h:717
    U_SUCCESS#define U_SUCCESS(x)Does the error code indicate success?Definition: utypes.h:712

Definition in file ubidi.h.

## Macro Definition Documentation

## U_BIDI_CLASS_DEFAULT

#define U_BIDI_CLASS_DEFAULT U_CHAR_DIRECTION_COUNT

Value returned by `UBiDiClassCallback` callbacks when there is no need to override the standard Bidi class for a given code point.

This constant is deprecated; use u_getIntPropertyMaxValue(UCHAR_BIDI_CLASS)+1 instead.

See also
  UBiDiClassCallback

Deprecated:
  ICU 58 The numeric value may change over time, see ICU ticket #12420.

Definition at line 1992 of file ubidi.h.

## UBIDI_DEFAULT_LTR

#define UBIDI_DEFAULT_LTR 0xfe

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 `UBIDI_REORDER_INVERSE_LIKE_DIRECT` or `UBIDI_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 righmost or leftmost strong character of the source text is RTL or Arabic Letter, the direction will be LTR otherwise.

If reordering option `UBIDI_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).

See also
  UBIDI_REORDER_INVERSE_LIKE_DIRECT
  UBIDI_REORDER_INVERSE_FOR_NUMBERS_SPECIAL

Stable:
  ICU 2.0

Definition at line 366 of file ubidi.h.

## UBIDI_DEFAULT_RTL

#define UBIDI_DEFAULT_RTL 0xff

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 `UBIDI_REORDER_INVERSE_LIKE_DIRECT` or `UBIDI_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 righmost 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 `UBIDI_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).

See also
  UBIDI_REORDER_INVERSE_LIKE_DIRECT
  UBIDI_REORDER_INVERSE_FOR_NUMBERS_SPECIAL

Stable:
  ICU 2.0

Definition at line 393 of file ubidi.h.

## UBIDI_DO_MIRRORING

#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

Stable:
  ICU 2.0

Definition at line 1864 of file ubidi.h.

## UBIDI_INSERT_LRM_FOR_NUMERIC

#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

This option does not imply corresponding adjustment of the index mappings.

See also
  ubidi_setInverse
  ubidi_writeReordered

Stable:
  ICU 2.0

Definition at line 1878 of file ubidi.h.

## UBIDI_KEEP_BASE_COMBINING

#define UBIDI_KEEP_BASE_COMBINING 1

option flags for ubidi_writeReordered()

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

See also
  ubidi_writeReordered

Stable:
  ICU 2.0

Definition at line 1854 of file ubidi.h.

## UBIDI_LEVEL_OVERRIDE

#define UBIDI_LEVEL_OVERRIDE 0x80

Bit flag for level input.

Overrides directional properties.

Stable:
  ICU 2.0

Definition at line 408 of file ubidi.h.

## UBIDI_MAP_NOWHERE

#define UBIDI_MAP_NOWHERE (-1)

Special value which can be returned by the mapping functions 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 `UBIDI_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 `UBIDI_OPTION_INSERT_MARKS`.

See also
  ubidi_getVisualIndex
  ubidi_getVisualMap
  ubidi_getLogicalIndex
  ubidi_getLogicalMap

Stable:
  ICU 3.6

Definition at line 423 of file ubidi.h.

## UBIDI_MAX_EXPLICIT_LEVEL

#define UBIDI_MAX_EXPLICIT_LEVEL 125

Maximum explicit embedding level.

Same as the max_depth value in the Unicode Bidirectional Algorithm. (The maximum resolved level can be up to `UBIDI_MAX_EXPLICIT_LEVEL+1`).

Stable:
  ICU 2.0

Definition at line 402 of file ubidi.h.

## UBIDI_OUTPUT_REVERSE

#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

Stable:
  ICU 2.0

Definition at line 1907 of file ubidi.h.

## UBIDI_REMOVE_BIDI_CONTROLS

#define UBIDI_REMOVE_BIDI_CONTROLS 8

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

This option does not imply corresponding adjustment of the index mappings.

See also
  ubidi_writeReordered

Stable:
  ICU 2.0

Definition at line 1891 of file ubidi.h.

## Typedef Documentation

## UBiDi

typedef struct UBiDi UBiDi

Stable:
  ICU 2.0

Definition at line 340 of file ubidi.h.

## UBiDiClassCallback

typedef UCharDirection UBiDiClassCallback(const void *context, UChar32 c)

Callback type declaration for overriding default Bidi class values with custom ones.

Usually, the function pointer will be propagated to a `UBiDi` object by calling the `ubidi_setClassCallback()` function; then the callback will be invoked by the UBA implementation any time the class of a character is to be determined.

Parameters

  context | is a pointer to the callback private data.
  c | is the code point to get a Bidi class for.

Returns
  The directional property / Bidi class for the given code point `c` if the default class has been overridden, or `u_getIntPropertyMaxValue(UCHAR_BIDI_CLASS)+1` if the standard Bidi class value for `c` is to be used.

See also
  ubidi_setClassCallback
  ubidi_getClassCallback

Stable:
  ICU 3.6

Definition at line 2016 of file ubidi.h.

## UBiDiDirection

typedef enum UBiDiDirection UBiDiDirection

Stable:
  ICU 2.0

Definition at line 340 of file ubidi.h.

## UBiDiLevel

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 pseudo-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.

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 UBiDiLevel=uint8_t data type in this API.

See also
  UBIDI_DEFAULT_LTR
  UBIDI_DEFAULT_RTL
  UBIDI_LEVEL_OVERRIDE
  UBIDI_MAX_EXPLICIT_LEVEL

Stable:
  ICU 2.0

Definition at line 340 of file ubidi.h.

## UBiDiReorderingMode

typedef enum UBiDiReorderingMode UBiDiReorderingMode

`UBiDiReorderingMode` values indicate which variant of the Bidi algorithm to use.

See also
  ubidi_setReorderingMode

Stable:
  ICU 3.6

## UBiDiReorderingOption

typedef enum UBiDiReorderingOption UBiDiReorderingOption

`UBiDiReorderingOption` values indicate which options are specified to affect the Bidi algorithm.

See also
  ubidi_setReorderingOptions

Stable:
  ICU 3.6

## Enumeration Type Documentation

## UBiDiDirection

enum UBiDiDirection

`UBiDiDirection` values indicate the text direction.

Stable:
  ICU 2.0

Enumerator

UBIDI_LTR

Left-to-right text.

This is a 0 value.

- As return value for `ubidi_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 `ubidi_getBaseDirection()`, it means that the first strong character of the source string has a left-to-right direction.

Stable:
  ICU 2.0

UBIDI_RTL

Right-to-left text.

This is a 1 value.

- As return value for `ubidi_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 `ubidi_getBaseDirection()`, it means that the first strong character of the source string has a right-to-left direction.

Stable:
  ICU 2.0

UBIDI_MIXED

Mixed-directional text.

As return value for `ubidi_getDirection()`, it means that the source string contains both left-to-right and right-to-left characters.

Stable:
  ICU 2.0

UBIDI_NEUTRAL

No strongly directional text.

As return value for `ubidi_getBaseDirection()`, it means that the source string is missing or empty, or contains neither left-to-right nor right-to-left characters.

Stable:
  ICU 4.6

Definition at line 429 of file ubidi.h.

## UBiDiReorderingMode

enum UBiDiReorderingMode

`UBiDiReorderingMode` values indicate which variant of the Bidi algorithm to use.

See also
  ubidi_setReorderingMode

Stable:
  ICU 3.6

Enumerator

UBIDI_REORDER_DEFAULT

Regular Logical to Visual Bidi algorithm according to Unicode.

This is a 0 value.

Stable:
  ICU 3.6

UBIDI_REORDER_NUMBERS_SPECIAL

Logical to Visual algorithm which handles numbers in a way which mimics the behavior of Windows XP.

Stable:
  ICU 3.6

UBIDI_REORDER_GROUP_NUMBERS_WITH_R

Logical to Visual algorithm grouping numbers with adjacent R characters (reversible algorithm).

Stable:
  ICU 3.6

UBIDI_REORDER_RUNS_ONLY

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 `UBIDI_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.

Stable:
  ICU 3.6

UBIDI_REORDER_INVERSE_NUMBERS_AS_L

Visual to Logical algorithm which handles numbers like L (same algorithm as selected by `ubidi_setInverse(true)`.

See also
  ubidi_setInverse

Stable:
  ICU 3.6

UBIDI_REORDER_INVERSE_LIKE_DIRECT

Visual to Logical algorithm equivalent to the regular Logical to Visual algorithm.

Stable:
  ICU 3.6

UBIDI_REORDER_INVERSE_FOR_NUMBERS_SPECIAL

Inverse Bidi (Visual to Logical) algorithm for the `UBIDI_REORDER_NUMBERS_SPECIAL` Bidi algorithm.

Stable:
  ICU 3.6

UBIDI_REORDER_COUNT

Number of values for reordering mode.

Deprecated:
  ICU 58 The numeric value may change over time, see ICU ticket #12420.

Definition at line 699 of file ubidi.h.

## UBiDiReorderingOption

enum UBiDiReorderingOption

`UBiDiReorderingOption` values indicate which options are specified to affect the Bidi algorithm.

See also
  ubidi_setReorderingOptions

Stable:
  ICU 3.6

Enumerator

UBIDI_OPTION_DEFAULT

option value for `ubidi_setReorderingOptions`: disable all the options which can be set with this function

See also
  ubidi_setReorderingOptions

Stable:
  ICU 3.6

UBIDI_OPTION_INSERT_MARKS

option bit for `ubidi_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 `ubidi_setPara`.

This option is significant only with reordering modes which generate a result with Logical order, specifically:

- `UBIDI_REORDER_RUNS_ONLY`
- `UBIDI_REORDER_INVERSE_NUMBERS_AS_L`
- `UBIDI_REORDER_INVERSE_LIKE_DIRECT`
- `UBIDI_REORDER_INVERSE_FOR_NUMBERS_SPECIAL`

If this option is set in conjunction with reordering mode `UBIDI_REORDER_INVERSE_NUMBERS_AS_L` or with calling `ubidi_setInverse(true)`, it implies option `UBIDI_INSERT_LRM_FOR_NUMERIC` in calls to function `ubidi_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 `UBIDI_OPTION_REMOVE_CONTROLS` set before calling `ubidi_setPara()` or option `UBIDI_REMOVE_BIDI_CONTROLS` in `ubidi_writeReordered`), the result will be identical to the source text in the first transformation.

This option will be ignored if specified together with option `UBIDI_OPTION_REMOVE_CONTROLS`. It inhibits option `UBIDI_REMOVE_BIDI_CONTROLS` in calls to function `ubidi_writeReordered()` and it implies option `UBIDI_INSERT_LRM_FOR_NUMERIC` in calls to function `ubidi_writeReordered()` if the reordering mode is `UBIDI_REORDER_INVERSE_NUMBERS_AS_L`.

See also
  ubidi_setReorderingMode
  ubidi_setReorderingOptions

Stable:
  ICU 3.6

UBIDI_OPTION_REMOVE_CONTROLS

option bit for `ubidi_setReorderingOptions`: remove Bidi control characters

This option must be set or reset before calling `ubidi_setPara`.

This option nullifies option `UBIDI_OPTION_INSERT_MARKS`. It inhibits option `UBIDI_INSERT_LRM_FOR_NUMERIC` in calls to function `ubidi_writeReordered()` and it implies option `UBIDI_REMOVE_BIDI_CONTROLS` in calls to that function.

See also
  ubidi_setReorderingMode
  ubidi_setReorderingOptions

Stable:
  ICU 3.6

UBIDI_OPTION_STREAMING

option bit for `ubidi_setReorderingOptions`: process the output as part of a stream to be continued

This option must be set or reset before calling `ubidi_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, `ubidi_setPara()` may process less than the full source text in order to truncate the text at a meaningful boundary. The caller should call `ubidi_getProcessedLength()` immediately after calling `ubidi_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 `ubidi_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 `UBIDI_OPTION_STREAMING`.

In all cases, this option should be turned off before processing the last part of the text.

When the `UBIDI_OPTION_STREAMING` option is used, it is recommended to call `ubidi_orderParagraphsLTR()` with argument `orderParagraphsLTR` set to `true` before calling `ubidi_setPara` so that later paragraphs may be concatenated to previous paragraphs on the right.

See also
  ubidi_setReorderingMode
  ubidi_setReorderingOptions
  ubidi_getProcessedLength
  ubidi_orderParagraphsLTR

Stable:
  ICU 3.6

Definition at line 914 of file ubidi.h.

## Function Documentation

## ubidi_close()

U_CAPI void ubidi_close | ( | UBiDi * | pBiDi | ) |

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

Important: A parent `UBiDi` object must not be destroyed or reused if it still has children. If a `UBiDi` object has become the child of another one (its parent) by 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

Stable:
  ICU 2.0

## ubidi_countParagraphs()

U_CAPI int32_t ubidi_countParagraphs | ( | UBiDi * | pBiDi | ) |

Get the number of paragraphs.

Parameters

  pBiDi | is the paragraph or line `UBiDi` object.

Returns
  The number of paragraphs.

Stable:
  ICU 3.4

## ubidi_countRuns()

U_CAPI int32_t 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.

Returns
  The number of runs.

Stable:
  ICU 2.0

## ubidi_getBaseDirection()

U_CAPI UBiDiDirection ubidi_getBaseDirection | ( | const UChar * | text,
|  | int32_t | length
| ) |  |

Gets 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, `UBIDI_LTR` is returned. If the first such character has type R or AL, `UBIDI_RTL` is returned. If the string does not contain any character of these types, then `UBIDI_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

  text | is a pointer to the text whose base direction is needed. Note: the text must be (at least) `length` long.
  length | is the length of the text; if `length==-1` then the text must be zero-terminated.

Returns
  `UBIDI_LTR`, `UBIDI_RTL`, `UBIDI_NEUTRAL`

See also
  UBiDiDirection

Stable:
  ICU 4.6

## ubidi_getClassCallback()

U_CAPI void ubidi_getClassCallback | ( | UBiDi * | pBiDi,
|  | UBiDiClassCallback ** | fn,
|  | const void ** | context
| ) |  |

Get the current callback function used for Bidi class determination.

Parameters

  pBiDi | is the paragraph `UBiDi` object.
  fn | fillin: Returns the callback function pointer.
  context | fillin: Returns the callback's private context.

See also
  ubidi_setClassCallback

Stable:
  ICU 3.6

## ubidi_getCustomizedClass()

U_CAPI UCharDirection ubidi_getCustomizedClass | ( | UBiDi * | pBiDi,
|  | UChar32 | c
| ) |  |

Retrieve the Bidi class for a given code point.

If a `UBiDiClassCallback` callback is defined and returns a value other than `u_getIntPropertyMaxValue(UCHAR_BIDI_CLASS)+1`, that value is used; otherwise the default class determination mechanism is invoked.

Parameters

  pBiDi | is the paragraph `UBiDi` object.
  c | is the code point whose Bidi class must be retrieved.

Returns
  The Bidi class for character `c` based on the given `pBiDi` instance.

See also
  UBiDiClassCallback

Stable:
  ICU 3.6

## ubidi_getDirection()

U_CAPI UBiDiDirection ubidi_getDirection | ( | const UBiDi * | pBiDi | ) |

Get the directionality of the text.

Parameters

  pBiDi | is the paragraph or line `UBiDi` object.

Returns
  a value of `UBIDI_LTR`, `UBIDI_RTL` or `UBIDI_MIXED` that indicates if the entire text represented by this object is unidirectional, and which direction, or if it is mixed-directional. Note - The value `UBIDI_NEUTRAL` is never returned from this method.

See also
  UBiDiDirection

Stable:
  ICU 2.0

Referenced by icu::ParagraphLayout::getTextDirection().

## ubidi_getLength()

U_CAPI int32_t 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.

Stable:
  ICU 2.0

## ubidi_getLevelAt()

U_CAPI UBiDiLevel 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. It must be in the range [0..ubidi_getProcessedLength(pBiDi)].

Returns
  The level for the character at charIndex (0 if charIndex is not in the valid range).

See also
  UBiDiLevel
  ubidi_getProcessedLength

Stable:
  ICU 2.0

## ubidi_getLevels()

U_CAPI const UBiDiLevel* 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, whose text length must be strictly positive.
  pErrorCode | must be a valid pointer to an error code value.

Returns
  The levels array for the text, or `NULL` if an error occurs.

See also
  UBiDiLevel
  ubidi_getProcessedLength

Stable:
  ICU 2.0

## ubidi_getLogicalIndex()

U_CAPI int32_t 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.

The value returned may be `UBIDI_MAP_NOWHERE` if there is no logical position because the corresponding text character is a Bidi mark inserted in the output by option `UBIDI_OPTION_INSERT_MARKS`.

This is the inverse function to `ubidi_getVisualIndex()`.

When the visual output is altered by using options of `ubidi_writeReordered()` such as `UBIDI_INSERT_LRM_FOR_NUMERIC`, `UBIDI_KEEP_BASE_COMBINING`, `UBIDI_OUTPUT_REVERSE`, `UBIDI_REMOVE_BIDI_CONTROLS`, the logical position returned may not be correct. It is advised to use, when possible, reordering options such as `UBIDI_OPTION_INSERT_MARKS` and `UBIDI_OPTION_REMOVE_CONTROLS`.

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.

Returns
  The index of this character in the text.

See also
  ubidi_getVisualMap
  ubidi_getVisualIndex
  ubidi_getResultLength

Stable:
  ICU 2.0

## ubidi_getLogicalMap()

U_CAPI void 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.

Some values in the map may be `UBIDI_MAP_NOWHERE` if the corresponding text characters are Bidi controls removed from the visual output by the option `UBIDI_OPTION_REMOVE_CONTROLS`.

When the visual output is altered by using options of `ubidi_writeReordered()` such as `UBIDI_INSERT_LRM_FOR_NUMERIC`, `UBIDI_KEEP_BASE_COMBINING`, `UBIDI_OUTPUT_REVERSE`, `UBIDI_REMOVE_BIDI_CONTROLS`, the visual positions returned may not be correct. It is advised to use, when possible, reordering options such as `UBIDI_OPTION_INSERT_MARKS` and `UBIDI_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 `ubidi_writeReordered()`, optionally with the `UBIDI_KEEP_BASE_COMBINING` option can be considered instead of using the mapping, in order to avoid these issues.

Parameters

  pBiDi | is the paragraph or line `UBiDi` object.
  indexMap | is a pointer to an array of `ubidi_getProcessedLength()` indexes which will reflect the reordering of the characters. If option `UBIDI_OPTION_INSERT_MARKS` is set, the number of elements allocated in `indexMap` must be no less than `ubidi_getResultLength()`. The array does not need to be initialized. The index map will result in `indexMap[logicalIndex]==visualIndex`.
  pErrorCode | must be a valid pointer to an error code value.

See also
  ubidi_getVisualMap
  ubidi_getVisualIndex
  ubidi_getProcessedLength
  ubidi_getResultLength

Stable:
  ICU 2.0

## ubidi_getLogicalRun()

U_CAPI void ubidi_getLogicalRun | ( | const UBiDi * | pBiDi,
|  | int32_t | logicalPosition,
|  | 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.
  logicalPosition | is a logical position within the source text.
  pLogicalLimit | will receive the limit of the corresponding run. The l-value that you point to here may be the same expression (variable) as the one for `logicalPosition`. This pointer can be `NULL` if this value is not necessary.
  pLevel | will receive the level of the corresponding run. This pointer can be `NULL` if this value is not necessary.

See also
  ubidi_getProcessedLength

Stable:
  ICU 2.0

## ubidi_getParagraph()

U_CAPI int32_t ubidi_getParagraph | ( | const UBiDi * | pBiDi,
|  | int32_t | charIndex,
|  | int32_t * | pParaStart,
|  | int32_t * | pParaLimit,
|  | UBiDiLevel * | pParaLevel,
|  | UErrorCode * | pErrorCode
| ) |  |

Get a paragraph, given a position within the text.

This function returns information about a paragraph.
Note: if the paragraph index is known, it is more efficient to retrieve the paragraph information using ubidi_getParagraphByIndex().

Parameters

  pBiDi | is the paragraph or line `UBiDi` object.
  charIndex | is the index of a character within the text, in the range `[0..ubidi_getProcessedLength(pBiDi)-1]`.
  pParaStart | will receive the index of the first character of the paragraph in the text. This pointer can be `NULL` if this value is not necessary.
  pParaLimit | will receive the limit of the paragraph. The l-value that you point to here may be the same expression (variable) as the one for `charIndex`. This pointer can be `NULL` if this value is not necessary.
  pParaLevel | will receive the level of the paragraph. This pointer can be `NULL` if this value is not necessary.
  pErrorCode | must be a valid pointer to an error code value.

Returns
  The index of the paragraph containing the specified position.

See also
  ubidi_getProcessedLength

Stable:
  ICU 3.4

## ubidi_getParagraphByIndex()

U_CAPI void ubidi_getParagraphByIndex | ( | const UBiDi * | pBiDi,
|  | int32_t | paraIndex,
|  | int32_t * | pParaStart,
|  | int32_t * | pParaLimit,
|  | UBiDiLevel * | pParaLevel,
|  | UErrorCode * | pErrorCode
| ) |  |

Get a paragraph, given the index of this paragraph.

This function returns information about a paragraph.

Parameters

  pBiDi | is the paragraph `UBiDi` object.
  paraIndex | is the number of the paragraph, in the range `[0..ubidi_countParagraphs(pBiDi)-1]`.
  pParaStart | will receive the index of the first character of the paragraph in the text. This pointer can be `NULL` if this value is not necessary.
  pParaLimit | will receive the limit of the paragraph. This pointer can be `NULL` if this value is not necessary.
  pParaLevel | will receive the level of the paragraph. This pointer can be `NULL` if this value is not necessary.
  pErrorCode | must be a valid pointer to an error code value.

Stable:
  ICU 3.4

## ubidi_getParaLevel()

U_CAPI UBiDiLevel 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. If there are multiple paragraphs, their level may vary if the required paraLevel is UBIDI_DEFAULT_LTR or UBIDI_DEFAULT_RTL. In that case, the level of the first paragraph is returned.

See also
  UBiDiLevel
  ubidi_getParagraph
  ubidi_getParagraphByIndex

Stable:
  ICU 2.0

Referenced by icu::ParagraphLayout::getParagraphLevel().

## ubidi_getProcessedLength()

U_CAPI int32_t ubidi_getProcessedLength | ( | const UBiDi * | pBiDi | ) |

Get the length of the source text processed by the last call to `ubidi_setPara()`.

This length may be different from the length of the source text if option `UBIDI_OPTION_STREAMING` has been set.
Note that whenever the length of the text affects the execution or the result of a function, it is the processed length which must be considered, except for `ubidi_setPara` (which receives unprocessed source text) and `ubidi_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 of `ubidi_setLine`
- maximum value of the `charIndex` argument of `ubidi_getParagraph`
- maximum value of the `charIndex` argument of `ubidi_getLevelAt`
- number of elements in the array returned by `ubidi_getLevels`
- maximum value of the `logicalStart` argument of `ubidi_getLogicalRun`
- maximum value of the `logicalIndex` argument of `ubidi_getVisualIndex`
- number of elements filled in the `*indexMap` argument of `ubidi_getLogicalMap`
- length of text processed by `ubidi_writeReordered`

Parameters

  pBiDi | is the paragraph `UBiDi` object.

Returns
  The length of the part of the source text processed by the last call to `ubidi_setPara`.

See also
  ubidi_setPara
  UBIDI_OPTION_STREAMING

Stable:
  ICU 3.6

## ubidi_getReorderingMode()

U_CAPI UBiDiReorderingMode ubidi_getReorderingMode | ( | UBiDi * | pBiDi | ) |

What is the requested reordering mode for a given Bidi object?

Parameters

  pBiDi | is a `UBiDi` object.

Returns
  the current reordering mode of the Bidi object

See also
  ubidi_setReorderingMode

Stable:
  ICU 3.6

## ubidi_getReorderingOptions()

U_CAPI uint32_t ubidi_getReorderingOptions | ( | UBiDi * | pBiDi | ) |

What are the reordering options applied to a given Bidi object?

Parameters

  pBiDi | is a `UBiDi` object.

Returns
  the current reordering options of the Bidi object

See also
  ubidi_setReorderingOptions

Stable:
  ICU 3.6

## ubidi_getResultLength()

U_CAPI int32_t ubidi_getResultLength | ( | const UBiDi * | pBiDi | ) |

Get the length of the reordered text resulting from the last call to `ubidi_setPara()`.

This length may be different from the length of the source text if option `UBIDI_OPTION_INSERT_MARKS` or option `UBIDI_OPTION_REMOVE_CONTROLS` has been set.
This resulting length is the one to consider in the following cases:

- maximum value of the `visualIndex` argument of `ubidi_getLogicalIndex`
- number of elements of the `*indexMap` argument of `ubidi_getVisualMap`

Note that this length stays identical to the source text length if Bidi marks are inserted or removed using option bits of `ubidi_writeReordered`, or if option `UBIDI_REORDER_INVERSE_NUMBERS_AS_L` has been set.

Parameters

  pBiDi | is the paragraph `UBiDi` object.

Returns
  The length of the reordered text resulting from the last call to `ubidi_setPara`.

See also
  ubidi_setPara
  UBIDI_OPTION_INSERT_MARKS
  UBIDI_OPTION_REMOVE_CONTROLS

Stable:
  ICU 3.6

## ubidi_getText()

U_CAPI const UChar* 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

Stable:
  ICU 2.0

## ubidi_getVisualIndex()

U_CAPI int32_t 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.

The value returned may be `UBIDI_MAP_NOWHERE` if there is no visual position because the corresponding text character is a Bidi control removed from output by the option `UBIDI_OPTION_REMOVE_CONTROLS`.

When the visual output is altered by using options of `ubidi_writeReordered()` such as `UBIDI_INSERT_LRM_FOR_NUMERIC`, `UBIDI_KEEP_BASE_COMBINING`, `UBIDI_OUTPUT_REVERSE`, `UBIDI_REMOVE_BIDI_CONTROLS`, the visual position returned may not be correct. It is advised to use, when possible, reordering options such as `UBIDI_OPTION_INSERT_MARKS` and `UBIDI_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 `ubidi_writeReordered()`, optionally with the `UBIDI_KEEP_BASE_COMBINING` option can be considered instead of using the mapping, in order to avoid these issues.

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.

Returns
  The visual position of this character.

See also
  ubidi_getLogicalMap
  ubidi_getLogicalIndex
  ubidi_getProcessedLength

Stable:
  ICU 2.0

## ubidi_getVisualMap()

U_CAPI void 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.

Some values in the map may be `UBIDI_MAP_NOWHERE` if the corresponding text characters are Bidi marks inserted in the visual output by the option `UBIDI_OPTION_INSERT_MARKS`.

When the visual output is altered by using options of `ubidi_writeReordered()` such as `UBIDI_INSERT_LRM_FOR_NUMERIC`, `UBIDI_KEEP_BASE_COMBINING`, `UBIDI_OUTPUT_REVERSE`, `UBIDI_REMOVE_BIDI_CONTROLS`, the logical positions returned may not be correct. It is advised to use, when possible, reordering options such as `UBIDI_OPTION_INSERT_MARKS` and `UBIDI_OPTION_REMOVE_CONTROLS`.

Parameters

  pBiDi | is the paragraph or line `UBiDi` object.
  indexMap | is a pointer to an array of `ubidi_getResultLength()` indexes which will reflect the reordering of the characters. If option `UBIDI_OPTION_REMOVE_CONTROLS` is set, the number of elements allocated in `indexMap` must be no less than `ubidi_getProcessedLength()`. The array does not need to be initialized. The index map will result in `indexMap[visualIndex]==logicalIndex`.
  pErrorCode | must be a valid pointer to an error code value.

See also
  ubidi_getLogicalMap
  ubidi_getLogicalIndex
  ubidi_getProcessedLength
  ubidi_getResultLength

Stable:
  ICU 2.0

## ubidi_getVisualRun()

U_CAPI UBiDiDirection 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`, never `UBIDI_NEUTRAL`.

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 second surrogates before first ones (which is generally a bad idea) and combining characters before base characters.

Use of `ubidi_writeReordered()`, optionally with the `UBIDI_KEEP_BASE_COMBINING` option, can be considered in order to avoid these issues.

Stable:
  ICU 2.0

## ubidi_invertMap()

U_CAPI void ubidi_invertMap | ( | const int32_t * | srcMap,
|  | int32_t * | destMap,
|  | int32_t | length
| ) |  |

Invert an index map.

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

Parameters

  srcMap

  is an array with `length` elements which defines the original mapping from a source array containing `length` elements 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 `UBIDI_MAP_NOWHERE`. All elements must be >=0 or equal to `UBIDI_MAP_NOWHERE`. Some elements may have a value >= `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 `UBIDI_MAP_NOWHERE`).

  destMap

  is an array with a number of elements equal to 1 + the highest value in `srcMap`. `destMap` will be filled with the inverse mapping. If element with index i in `srcMap` has a value k different from `UBIDI_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 `UBIDI_MAP_NOWHERE`.

  length | is the length of each array.

See also
  UBIDI_MAP_NOWHERE

Stable:
  ICU 2.0

## ubidi_isInverse()

U_CAPI UBool ubidi_isInverse | ( | UBiDi * | pBiDi | ) |

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

Note: calling this function after setting the reordering mode with `ubidi_setReorderingMode` will return `true` if the reordering mode was set to `UBIDI_REORDER_INVERSE_NUMBERS_AS_L`, `false` for all other values.

Parameters

  pBiDi | is a `UBiDi` object.

Returns
  true if the Bidi object is set to perform the inverse Bidi algorithm by handling numbers as L.

See also
  ubidi_setInverse
  ubidi_setReorderingMode

Stable:
  ICU 2.0

## ubidi_isOrderParagraphsLTR()

U_CAPI UBool ubidi_isOrderParagraphsLTR | ( | UBiDi * | pBiDi | ) |

Is this Bidi object set to allocate level 0 to block separators so that successive paragraphs progress from left to right?

Parameters

  pBiDi | is a `UBiDi` object.

Returns
  true if the Bidi object is set to allocate level 0 to block separators.

See also
  ubidi_orderParagraphsLTR

Stable:
  ICU 3.4

## ubidi_open()

U_CAPI UBiDi* ubidi_open | ( | void |  | ) |

Allocate a `UBiDi` structure.

Such an object is initially empty. It is assigned the Bidi properties of a piece of text containing one or more paragraphs by `ubidi_setPara()` or the Bidi properties of a line within a paragraph by `ubidi_setLine()`.

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

`ubidi_setPara()` and `ubidi_setLine()` will allocate additional memory for internal structures as necessary.

Returns
  An empty `UBiDi` object.

Stable:
  ICU 2.0

## ubidi_openSized()

U_CAPI UBiDi* 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 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

  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.

  pErrorCode | must be a valid pointer to an error code value.

Returns
  An empty `UBiDi` object with preallocated memory.

Stable:
  ICU 2.0

## ubidi_orderParagraphsLTR()

U_CAPI void ubidi_orderParagraphsLTR | ( | UBiDi * | pBiDi,
|  | UBool | orderParagraphsLTR
| ) |  |

Specify whether block separators must be allocated level zero, so that successive paragraphs will progress from left to right.

This function must be called before `ubidi_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

  pBiDi | is a `UBiDi` object.
  orderParagraphsLTR | specifies whether paragraph separators (B) must receive level 0, so that successive paragraphs progress from left to right.

See also
  ubidi_setPara

Stable:
  ICU 3.4

## ubidi_reorderLogical()

U_CAPI void 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`.

Stable:
  ICU 2.0

## ubidi_reorderVisual()

U_CAPI void 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`.

Stable:
  ICU 2.0

## ubidi_setClassCallback()

U_CAPI void ubidi_setClassCallback | ( | UBiDi * | pBiDi,
|  | UBiDiClassCallback * | newFn,
|  | const void * | newContext,
|  | UBiDiClassCallback ** | oldFn,
|  | const void ** | oldContext,
|  | UErrorCode * | pErrorCode
| ) |  |

Set the callback function and callback data used by the UBA implementation for Bidi class determination.

This may be useful for assigning Bidi classes to PUA characters, or for special application needs. For instance, an application may want to handle all spaces like L or R characters (according to the base direction) when creating the visual ordering of logical lines which are part of a report organized in columns: there should not be interaction between adjacent cells.

Parameters

  pBiDi | is the paragraph `UBiDi` object.
  newFn | is the new callback function pointer.
  newContext | is the new callback context pointer. This can be NULL.
  oldFn | fillin: Returns the old callback function pointer. This can be NULL.
  oldContext | fillin: Returns the old callback's context. This can be NULL.
  pErrorCode | must be a valid pointer to an error code value.

See also
  ubidi_getClassCallback

Stable:
  ICU 3.6

## ubidi_setContext()

U_CAPI void ubidi_setContext | ( | UBiDi * | pBiDi,
|  | const UChar * | prologue,
|  | int32_t | proLength,
|  | const UChar * | epilogue,
|  | int32_t | epiLength,
|  | UErrorCode * | pErrorCode
| ) |  |

Set the context before a call to ubidi_setPara().

ubidi_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 ubidi_setPara(). The characters specified as prologue and epilogue should not be modified by the calling program until the call to ubidi_setPara() has returned. If successive calls to ubidi_setPara() all need specification of a context, ubidi_setContext() must be called before each call to ubidi_setPara(). In other words, a context is not "remembered" after the following successful call to ubidi_setPara().

If a call to ubidi_setPara() specifies UBIDI_DEFAULT_LTR or UBIDI_DEFAULT_RTL as paraLevel and is preceded by a call to ubidi_setContext() which specifies a prologue, the paragraph level will be computed taking in consideration the text in the prologue.

When ubidi_setPara() is called without a previous call to ubidi_setContext, the main text is handled as if preceded and followed by strong directional characters at the current paragraph level. Calling ubidi_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 ubidi_setContext() with specification of an epilogue will change the behavior of ubidi_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 `ubidi_setContext` is called repeatedly without calling `ubidi_setPara`, the earlier calls have no effect, only the last call will be remembered for the next call to `ubidi_setPara`.

Note 2: calling `ubidi_setContext(pBiDi, NULL, 0, NULL, 0, &errorCode)` cancels any previous setting of non-empty prologue or epilogue. The next call to `ubidi_setPara()` will process no prologue or epilogue.

Note 3: users must be aware that even after setting the context before a call to ubidi_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 = "<code>abc DE</code>"
epilogue = none
main text = "<code>FGH xyz</code>"
paraLevel = UBIDI_LTR
display without prologue = "<code>HGF xyz</code>" ("HGF" is adjacent to "xyz")
display with prologue = "<code>abc HGFED xyz</code>" ("HGF" is not adjacent to "xyz")

Parameters

  pBiDi | is a paragraph `UBiDi` object.
  prologue | is a pointer to the text which precedes the text that will be specified in a coming call to ubidi_setPara(). If there is no prologue to consider, then `proLength` must be zero and this pointer can be NULL.
  proLength | is the length of the prologue; if `proLength==-1` then the prologue must be zero-terminated. Otherwise proLength must be >= 0. If `proLength==0`, it means that there is no prologue to consider.
  epilogue | is a pointer to the text which follows the text that will be specified in a coming call to ubidi_setPara(). If there is no epilogue to consider, then `epiLength` must be zero and this pointer can be NULL.
  epiLength | is the length of the epilogue; if `epiLength==-1` then the epilogue must be zero-terminated. Otherwise epiLength must be >= 0. If `epiLength==0`, it means that there is no epilogue to consider.
  pErrorCode | must be a valid pointer to an error code value.

See also
  ubidi_setPara

Stable:
  ICU 4.8

## ubidi_setInverse()

U_CAPI void 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 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 `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.

Calling this function with argument `isInverse` set to `true` is equivalent to calling `ubidi_setReorderingMode` with argument `reorderingMode` set to `UBIDI_REORDER_INVERSE_NUMBERS_AS_L`.
Calling this function with argument `isInverse` set to `false` is equivalent to calling `ubidi_setReorderingMode` with argument `reorderingMode` set to `UBIDI_REORDER_DEFAULT`.

Parameters

  pBiDi | is a `UBiDi` object.
  isInverse | specifies "forward" or "inverse" Bidi operation.

See also
  ubidi_setPara
  ubidi_writeReordered
  ubidi_setReorderingMode

Stable:
  ICU 2.0

## ubidi_setLine()

U_CAPI void 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 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 `ubidi_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 `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. It must have been set by a successful call to ubidi_setPara.
  start | is the line's first index into the text.
  limit | is just behind the line's last index into the text (its last index +1). It must be `0<=start<limit<=`containing paragraph limit. If the specified line crosses a paragraph boundary, the function will terminate with error code U_ILLEGAL_ARGUMENT_ERROR.
  pLineBiDi | is the object that will now represent a line of the text.
  pErrorCode | must be a valid pointer to an error code value.

See also
  ubidi_setPara
  ubidi_getProcessedLength

Stable:
  ICU 2.0

## ubidi_setPara()

U_CAPI void 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 Standard Annex #9, version 13, also described in The Unicode Standard, Version 4.0 .

This function 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 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 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.

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 text that the Bidi algorithm will be performed on. This pointer is stored in the UBiDi object and can be retrieved with `ubidi_getText()`. Note: the text must be (at least) `length` long.
  length | is the length of the text; if `length==-1` then the text must be zero-terminated.

  paraLevel

  specifies the default level for the text; 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 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 `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.
  Aside from that bit, it must be `paraLevel<=embeddingLevels[]<=UBIDI_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 `UBIDI_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 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.
  Note: the `embeddingLevels` array must be at least `length` long. This pointer can be `NULL` if this value is not necessary.

  pErrorCode | must be a valid pointer to an error code value.

Stable:
  ICU 2.0

## ubidi_setReorderingMode()

U_CAPI void ubidi_setReorderingMode | ( | UBiDi * | pBiDi,
|  | UBiDiReorderingMode | 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 function must be called before `ubidi_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 `UBIDI_REORDER_DEFAULT`, this function changes the behavior of some of the subsequent functions 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 `UBIDI_REORDER_DEFAULT`, the standard Bidi Logical to Visual algorithm is applied.

- When the reordering mode is set to `UBIDI_REORDER_NUMBERS_SPECIAL`, the algorithm used to perform Bidi transformations when calling `ubidi_setPara` 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 `UBIDI_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 `UBIDI_REORDER_RUNS_ONLY`, a "Logical to Logical" transformation must be performed:

  - If the default text level of the source text (argument `paraLevel` in `ubidi_setPara`) 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 be needed when logical text which is basically Arabic or Hebrew, with possible included numbers or phrases in English, has to be displayed as if it had an even embedding level (this can happen if the displaying application treats all text as if it was basically LTR).
  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.

- When the reordering mode is set to `UBIDI_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 option `UBIDI_INSERT_LRM_FOR_NUMERIC` can be used with function `ubidi_writeReordered` to this end. This mode is equivalent to calling `ubidi_setInverse()` with argument `isInverse` set to `true`.

- When the reordering mode is set to `UBIDI_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 mode `UBIDI_REORDER_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 mode `UBIDI_REORDER_INVERSE_NUMBERS_AS_L`.
  When used in conjunction with option `UBIDI_OPTION_INSERT_MARKS`, this mode generally adds Bidi marks to the output significantly more sparingly than mode `UBIDI_REORDER_INVERSE_NUMBERS_AS_L` with option `UBIDI_INSERT_LRM_FOR_NUMERIC` in calls to `ubidi_writeReordered`.

- When the reordering mode is set to `UBIDI_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 `UBIDI_REORDER_INVERSE`), output runs should be retrieved using `ubidi_getVisualRun()`, and the output text with `ubidi_writeReordered()`. The caller should keep in mind that in "inverse Bidi" modes the input is actually visually ordered text and reordered output returned by `ubidi_getVisualRun()` or `ubidi_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 `UBIDI_OUTPUT_REVERSE` of `ubidi_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 `UBIDI_REORDER_RUNS_ONLY`.

Parameters

  pBiDi | is a `UBiDi` object.
  reorderingMode | specifies the required variant of the Bidi algorithm.

See also
  UBiDiReorderingMode
  ubidi_setInverse
  ubidi_setPara
  ubidi_writeReordered

Stable:
  ICU 3.6

## ubidi_setReorderingOptions()

U_CAPI void ubidi_setReorderingOptions | ( | UBiDi * | pBiDi,
|  | uint32_t | reorderingOptions
| ) |  |

Specify which of the reordering options should be applied during Bidi transformations.

Parameters

  pBiDi | is a `UBiDi` object.
  reorderingOptions | is a combination of zero or more of the following options: `UBIDI_OPTION_DEFAULT`, `UBIDI_OPTION_INSERT_MARKS`, `UBIDI_OPTION_REMOVE_CONTROLS`, `UBIDI_OPTION_STREAMING`.

See also
  ubidi_getReorderingOptions

Stable:
  ICU 3.6

## ubidi_writeReordered()

U_CAPI int32_t ubidi_writeReordered | ( | UBiDi * | pBiDi,
|  | UChar * | dest,
|  | int32_t | destSize,
|  | uint16_t | options,
|  | UErrorCode * | pErrorCode
| ) |  |

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

This function 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 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.
  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_getProcessedLength(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). The available options are: `UBIDI_DO_MIRRORING`, `UBIDI_INSERT_LRM_FOR_NUMERIC`, `UBIDI_KEEP_BASE_COMBINING`, `UBIDI_OUTPUT_REVERSE`, `UBIDI_REMOVE_BIDI_CONTROLS`

  pErrorCode | must be a valid pointer to an error code value.

Returns
  The length of the output string.

See also
  ubidi_getProcessedLength

Stable:
  ICU 2.0

## ubidi_writeReverse()

U_CAPI int32_t 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) 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 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 the `options` parameter in `ubidi_writeReordered()`.
  pErrorCode | must be a valid pointer to an error code value.

Returns
  The length of the output string.

Stable:
  ICU 2.0