UNICODE::BIDI(3)

NAME
unicode::bidi, unicode::bidi_calc, unicode::bidi_calc_types, unicode::bidi_reorder, unicode::bidi_cleanup, unicode::bidi_logical_order, unicode::bidi_combinings, unicode::bidi_needs_embed, unicode::bidi_embed, unicode::bidi_embed_paragraph_level, unicode::bidi_get_direction, unicode::bidi_override - unicode bi-directional algorithm

SYNOPSIS

#include <courier-unicode.h>

struct unicode::bidi_calc_types {
  bidi_calc_types(const std::u32string & string);
  std::vector<unicode_bidi_type_t> types ;
  void setbnl(std::u32string & string);
}.fi

std::tuple<std::vector<unicode_bidi_level_t>, struct unicode_bidi_direction> unicode::bidi_calc(const unicode::bidi_calc_types &ustring);

std::tuple<std::vector<unicode_bidi_level_t>, struct unicode_bidi_direction> unicode::bidi_calc(const unicode::bidi_calc_types &ustring, unicode_bidi_level_t embedding_level);

int unicode::bidi_reorder(std::u32string &string, std::vector<unicode_bidi_level_t> &embedding_level, const std::function<void (size_t, size_t)> &reorder_callback=[](size_t, size_t){}, size_t starting_pos=0, size_t n=(size_t)-1);

void unicode::bidi_reorder(std::vector<unicode_bidi_level_t> &embedding_level, const std::function<void (size_t, size_t)> &reorder_callback=[](size_t, size_t){}, size_t starting_pos=0, size_t n=(size_t)-1);

void unicode::bidi_cleanup(std::u32string &string, const std::function<void (size_t)> &removed_callback=[](size_t){}, int cleanup_options);

int unicode::bidi_cleanup(std::u32string &string, std::vector <unicode_bidi_level_t> &levels, const std::function<void (size_t)> &removed_callback=[](size_t){}, int cleanup_options=0);

int unicode::bidi_cleanup(std::u32string &string, std::vector <unicode_bidi_level_t> &levels, const std::function<void (size_t)> &removed_callback, int cleanup_options, size_t starting_pos, size_t n);

int unicode::bidi_logical_order(std::u32string &string, std::vector <unicode_bidi_level_t> &levels, unicode_bidi_level_t paragraph_embedding, const std::function<void (size_t, size_t)> &reorder_callback=[](size_t, size_t){}, size_t starting_pos=0, size_t n=(size_t)-1);

void unicode::bidi_combinings(const std::u32string &string, const std::vector <unicode_bidi_level_t> &levels, const std::function <void (unicode_bidi_level_t level, size_t level_start, size_t n_chars, size_t comb_start, size_t n_comb_chars)> &callback);

void unicode::bidi_combinings(const std::u32string &string, const std::function <void (unicode_bidi_level_t level, size_t level_start, size_t n_chars, size_t comb_start, size_t n_comb_chars)> &callback);

void unicode::bidi_logical_order(std::vector <unicode_bidi_level_t> &levels, unicode_bidi_level_t paragraph_embedding, const std::function<void (size_t, size_t)> &reorder_callback, size_t starting_pos=0, size_t n=(size_t)-1);

bool unicode::bidi_needs_embed(const std::u32string &string, const std::vector <unicode_bidi_level_t> &levels, const unicode_bidi_level_t (paragraph_embedding=NULL, size_t starting_pos=0, size_t n=(size_t)-1);

int unicode::bidi_embed(const std::u32string &string, const std::vector <unicode_bidi_level_t> &levels, unicode_bidi_level_t paragraph_embedding, const std::function<void (const char32_t *, size_t, bool)> &callback);

std::u32string unicode::bidi_embed(const std::u32string &string, const std::vector <unicode_bidi_level_t> &levels, unicode_bidi_level_t paragraph_embedding);

char32_t unicode_bidi_embed_paragraph_level(const std::u32string &string, unicode_bidi_level_t paragraph_embedding);

unicode_bidi_direction bidi_get_direction(const std::u32string &string, size_t starting_pos=0, size_t n=(size_t)-1);

std::u32string bidi_override(const std::u32string &string, unicode_bidi_level_t direction, int cleanup_options=0);

DESCRIPTION

These functions implement the C++ interface for the Unicode Bi-Directional algorithm[1]. See the description of the underlying unicode_bidi(3) C library API for more information. C++ specific notes:

    • unicode::bidi_calc returns the directional embedding value buffer and the calculated paragraph embedding level. Its ustring is implicitly converted from a std::u32string:

        std::u32string text;
        auto [levels, direction]=unicode::bidi_calc(text);
    Alternatively a unicode::bidi_calc_types objects gets constructed from the same std::u32string and then passed directly to unicode::bidi_calc:

        std::u32string text;
        unicode::bidi_calc_types types{text};
        types.setbnl(text); // Optional
        // types.types is a std::vector of enum_bidi_types_t values
        auto [levels, direction]=unicode::bidi_calc(types);
    This provides the means to access the intermediate enum_bidi_types_t values that get calculated from the Unicode text string.

        Note
        In all cases the std::u32string cannot be a temporary object, and it must remain in scope until unicode::bidi_calc() returns.

    The optional setbnl() method uses unicode_bidi_setbnl(3) to replace paragraph separators with newline characters, in the unicode string. It requires the same unicode string that was passed to the constructor as a parameter (because the constructor takes a constant reference, but this method modifies the string.

    • Several C functions provide a “dry-run” mode by passing a NULL pointer. The C++ API provides separate overloads, with and without the nullable parameter.

    • Several C functions accept a nullable function pointer, with the NULL function pointer specifying no callback. The C++ functions have a std::function parameter with a default do-nothing closure.

    • Several C functions accept two parameters, a Unicode character pointer and the embedding level buffer, and a single parameter that specifies the size of both. The equivalent C++ function takes two discrete parameters, a std::u32string and a std::vector and returns an int; a negative value if their sizes differ, and 0 if their sizes match, and the requested function completes. The unicode::bidi_embed overload that returns a std::u32string returns an empty string in case of a mismatch.

    • unicode::bidi_reorder reorders the entire string and its embedding_levels by default. The optional starting_pos and n parameters limit the reordering to the indicated subset of the original string (specified as the starting position offset index, and the number of characters).

    • unicode::bidi_reorder, unicode::bidi_cleanup, unicode::bidi_logical_order, unicode::bidi_needs_embed and unicode::bidi_get_direction take two optional parameters (defaulted values or overloaded) specifying an optional starting position and number of characters that define a subset of the original string that gets reordered, cleaned up, or has its direction determined.

    This unicode::bidi_cleanup does not trim off the passed in string and embedding level buffer, since it affects only a subset of the string. The number of times the removed character callback gets invoked indicates how much the substring should be trimmed off.

    • unicode::bidi_override modifies the passed-in string as follows:

        • unicode::bidi_cleanup() is applied with the specified, or defaulted, cleanup_options

        • Either the LRO or an RLO override marker gets prepended to the Unicode string, forcing the entire string to be interpreted in a single rendering direction, when processed by the Unicode bi-directional algorithm.

    unicode::bidi_override makes it possible to use a Unicode-aware application or algorithm in a context that only works with text that's always displayed in a fixed direction, allowing graceful handling of input containing bi-directional text.

  unicode::literals namespace

    using namespace unicode::literals;
    std::u32string foo(std::u32string bar)
    {
    	return bar + LRO;
    }

This namespace contains the following constexpr definitions:

    • char32_t arrays with literal Unicode character strings containing Unicode directional, isolate, and override markers, like LRO, RLO and others.

    • CLEANUP_EXTRA, CLEANUP_BNL, and CLEANUP_CANONICAL options for unicode::bidi_cleanup().

SEE ALSO

courier-unicode(7), unicode_bidi(3).

AUTHOR

Sam Varshavchik
    Author

NOTES

1.  Unicode Bi-Directional algorithm
    https://www.unicode.org/reports/tr9/tr9-42.html