Text::Bidi(3) Unicode bidi algorithm using libfribidi


version 2.11


# Each displayed line is a "paragraph"
use Text::Bidi qw(log2vis);
($par, $map, $visual) = log2vis($logical);
# or just
$visual = log2vis(...);
# For real paragraphs, need to specify the display width
($par, $map, $visual) = log2vis($logical, $width);
# object oriented approach allows one to display line by line
$p = new Text::Bidi::Paragraph $logical;
$visual = $p->visual($off, $len);


The following functions can be exported (nothing is exported by default):
  • ``log2vis''
  • ``is_bidi''
  • ``get_mirror_char''
  • ``get_bidi_type_name''
  • ``fribidi_version''
  • ``unicode_version''
  • ``fribidi_version_num''

All of them can be exported together using the ":all" tag.


This module provides basic support for the Unicode bidirectional (Bidi) text algorithm, for displaying text consisting of both left-to-right and right-to-left written languages (such as Hebrew and Arabic.) It does so via a swig interface file to the libfribidi library.

The fundamental purpose of the bidi algorithm is to reorder text given in logical order into text in visually correct order, suitable for display using standard printing commands. ``Logical order'' means that the characters are given in the order in which they would be read if printed correctly. The direction of the text is determined by properties of the Unicode characters, usually without additional hints. See <http://www.unicode.org/unicode/reports/tr9/> for more details on the problem and the algorithm.

Standard usage

The bidi algorithm works in two stages. The first is on the level of a paragraph, where the direction of each character is computed. The second is on the level of the lines to be displayed. The main practical difference is that the first stage requires only the text of the paragraph, while the second requires knowledge of the width of the displayed lines. The module (or the library) does not determine how the text is broken into paragraphs.

The full interface is provided by Text::Bidi::Paragraph, see there for details. This module provides an abbreviation, ``log2vis'', which combines creating a paragraph object with calling ``visual'' in Text::Bidi::Paragraph on it. It is particularly useful in the case that the whole paragraph should be displayed at once, and the display width is known:

    $visual = log2vis($logical, $width);

There are more options (see ``log2vis''), but this is essentially it. The rest of this documentation will probably be useful only to people who are familiar with libfribidi and who wish to extend or modify the module.

The object-oriented approach

All functions here can be called using either a procedural or an object oriented approach. For example, you may do either

        $visual = log2vis($logical);


        $bidi = new Text::Bidi;
        $visual = $bidi->log2vis($logical);

The advantages of the second form is that it is easier to move to a sub-class, and that two or more objects with different parameters can be used simultaneously. If you are interested in deriving from this class, please see ``SUBCLASSING''.



    say $tb->get_bidi_type_name($Text::Bidi::Type::LTR); # says 'LTR'

Return the string representation of a Bidi character type, as in fribidi_get_bidi_type_name(3). Note that for the above example, one needs to use Text::Bidi::Constants.


    ($p, $visual) = log2vis($logical[,$width[,$dir[,$flags]]]);

Convert the input paragraph $logical to visual. This constructs a Text::Bidi::Paragraph object, and calls ``visual'' in Text::Bidi::Paragraph several times, as required. $width is the maximum width of a line, defaulting to the whole length of the paragraph. $dir is the base direction of the paragraph, determined automatically if not provided. $flags is as in ``visual'' in Text::Bidi::Paragraph. The paragraph will be justified to the right if it is RTL.

The output consists of the Text::Bidi::Paragraph object $p and the visual string $visual.


    my $bidi = is_bidi($logical);

Returns true if the input $logical contains bidi characters. Otherwise, the output of the bidi algorithm will be identical to the input, hence this helps if we want to short-circuit.


    my $mir = get_mirror_char('['); # $mir == ']'

Return the mirror character of the input, possibly itself.


    say fribidi_version();

Returns the version information for the fribidi library


    say fribidi_version_num();

Returns the version number for the fribidi library


    say unicode_version();

Returns the Unicode version used by the fribidi library


The rest of the documentation is only interesting if you would like to derive from this class. The methods listed under ``METHODS'' are wrappers around the similarly named functions in libfribidi, and may be useful for this purpose.

If you do sub-class this class, and would like the procedural interface to use your functions, put a line like

        $Text::Bidi::GlobalClass = __PACKAGE__;

in your module.



    $tb = new Text::Bidi [tie_byte => ..., tie_long => ...];

Create a new Text::Bidi object. If the tie_byte or tie_long options are given, they should be the names (strings) of the classes used as dual life arrays, most probably derived class of Text::Bidi::Array::Byte and Text::Bidi::Array::Long, respectively.

This method is probably of little interest for standard (procedural) use.


    $la = $tb->utf8_to_internal($str);

Convert the Perl string $str into the representation used by libfribidi. The result will be a Text::Bidi::Array::Long.


    $str = $tb->internal_to_utf8($la);

Convert the long array $la, representing a string encoded in to format used by libfribidi, into a Perl string. The array $la can be either a Text::Bidi::Array::Long, or anything that can be used to construct it.


    $types = $tb->get_bidi_types($internal);

Returns a Text::Bidi::Array::Long with the list of Bidi types of the text given by $internal, a representation of the paragraph text, as returned by utf8_to_internal(). Wraps fribidi_get_bidi_types(3).


    $types = $tb->get_joining_types($internal);

Returns a Text::Bidi::Array::Byte with the list of joining types of the text given by $internal, a representation of the paragraph text, as returned by ``utf8_to_internal''. Wraps fribidi_get_joining_types(3).


    say $tb->get_joining_type_name($Text::Bidi::Joining::U); # says 'U'

Return the string representation of a joining character type, as in fribidi_get_joining_type_name(3). Note that for the above example, one needs to use Text::Bidi::Constants.


   ($odir, $lvl) = $tb->get_par_embedding_levels($types[, $dir]);

Return the embedding levels of the characters, whose types are given by $types. $types is a Text::Bidi::Array::Long of Bidi types, as returned by ``get_bidi_types''. $dir is the base paragraph direction. If not given, it defaults to "FRIBIDI_PAR_ON" (neutral).

The output is the resolved paragraph direction $odir, and the Text::Bidi::Array::Byte array $lvl of embedding levels.


    $props = $tb->join_arabic($bidi_types, $lvl, $join_types);

Returns a Text::Bidi::Array::Byte with $props, as returned by fribidi_join_arabic(3). The inputs are $bidi_types, as returned by ``get_bidi_types'', $lvl, as returned by ``get_par_embedding_levels'', and $join_types as returned by ``get_joining_types''. Wraps fribidi_join_arabic(3).


    ($newp, $shaped) = $tb->shaped($flags, $lvl, $prop, $internal);

Returns the internal representation of the paragraph, with shaping applied. The internal representation of the original paragraph (as returned by ``utf8_to_internal'') should be passed in $internal, while the embedding levels (as returned by ``get_par_embedding_levels'') should be in $lvl. See the documentation of fribidi-arabic.h for $flags, but as a special case, a value of "undef" here skips shaping (returning ($prop, $internal)), while any other false value becomes the default. $prop is as returned by ``join_arabic''. This method wraps fribidi_shape_arabic(3).


    $mirrored = $tb->mirrored($lvl, $internal);

Returns the internal representation of the paragraph, with mirroring applied. The internal representation of the original paragraph (as returned by ``utf8_to_internal'') should be passed in $internal, while the embedding levels (as returned by ``get_par_embedding_levels'') should be in $lvl. This method wraps fribidi_shape_mirroring(3).


    $str = $tb->reorder($in, $map[, $offset[, $len]]);
    say $tb->reorder([qw(A B C)], [2, 0, 1]); # says CAB

View the array ref $map as a permutation, and permute the list (of characters) $in according to it. The result is joined, to obtain a string. If $offset and $len are given, returns only that part of the resulting string.


    ($elout, $mout) = $tb->reorder_map($types, $offset, $len, $par,
                                       $map, $el, $flags);

Compute the reordering map for bidi types given by $types, for the interval starting with $offset of length $len. Note that this part of the algorithm depends on the interval in an essential way. $types is an array of types, as computed by ``get_bidi_types''. The other arguments are optional:

The base paragraph direction. Computed via ``get_par_embedding_levels'' if not defined.
An array ref (or a Text::Bidi::Array::Long) from a previous call (with a different interval). The method is called repeatedly for the same paragraph, with different intervals, and the reordering map is updated for the given interval. If not defined, initialised to the identity map.
The embedding levels. If not given, computed by a call to ``get_par_embedding_levels''.
A specification of flags, as described in fribidi_reorder_line(3). The flags can be given either as a number (using "$Text::Bidi::Flags::.." from Text::Bidi::Constants), or as a hashref of the form "{REORDER_NSM => 1}". Defaults to "FRIBIDI_FLAGS_DEFAULT".

The output consists of the modified map $mout (a Text::Bidi::Array::Long), and possibly modified embedding levels $elout.

method remove_bidi_marks

    ($v, $to, $from, $levels) = 
        $tb->remove_bidi_marks($v[, $to[, $from[, $levels]]])

Remove the explicit bidi marks from $v. The optional arguments, if given, are the map from the logical to the visual string, the inverse map, and embedding levels, respectively, as returned by ``reorder_map''. The inverse map $from can be obtained from the direct one $to by a command like:

    @$from[@$map] = 0..$#$map

Each of the arguments can be "undef", in which case it will be skipped. This implements step X9, see fribidi_remove_bidi_marks(3).


There are no real tests for any of this.

Shaping is not supported (probably), since I don't know what it is. Help welcome!


Moshe Kamensky <[email protected]>


This software is copyright (c) 2015 by Moshe Kamensky.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.