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Bidirectional Text

Bidirectional Text — Types and functions to help with handling bidirectional text

Synopsis

enum                PangoDirection;
PangoDirection      pango_unichar_direction             (gunichar ch);
PangoDirection      pango_find_base_dir                 (const gchar *text,
                                                         gint length);
gboolean            pango_get_mirror_char               (gunichar ch,
                                                         gunichar *mirrored_ch);
enum                PangoBidiType;
PangoBidiType       pango_bidi_type_for_unichar         (gunichar ch);

Description

Pango supports bidirectional text (like Arabic and Hebrew) automatically. Some applications however, need some help to correctly handle bidirectional text.

The PangoDirection type can be used with pango_context_set_base_dir() to instruct Pango about direction of text, though in most cases Pango detects that correctly and automatically. The rest of the facilities in this section are used internally by Pango already, and are provided to help applications that need more direct control over bidirectional setting of text.

Details

enum PangoDirection

typedef enum {
  PANGO_DIRECTION_LTR,
  PANGO_DIRECTION_RTL,
  PANGO_DIRECTION_TTB_LTR,
  PANGO_DIRECTION_TTB_RTL,
  PANGO_DIRECTION_WEAK_LTR,
  PANGO_DIRECTION_WEAK_RTL,
  PANGO_DIRECTION_NEUTRAL
} PangoDirection;

The PangoDirection type represents a direction in the Unicode bidirectional algorithm; not every value in this enumeration makes sense for every usage of PangoDirection; for example, the return value of pango_unichar_direction() and pango_find_base_dir() cannot be PANGO_DIRECTION_WEAK_LTR or PANGO_DIRECTION_WEAK_RTL, since every character is either neutral or has a strong direction; on the other hand PANGO_DIRECTION_NEUTRAL doesn't make sense to pass to pango_itemize_with_base_dir().

The PANGO_DIRECTION_TTB_LTR, PANGO_DIRECTION_TTB_RTL values come from an earlier interpretation of this enumeration as the writing direction of a block of text and are no longer used; See PangoGravity for how vertical text is handled in Pango.

PANGO_DIRECTION_LTR

A strong left-to-right direction

PANGO_DIRECTION_RTL

A strong right-to-left direction

PANGO_DIRECTION_TTB_LTR

Deprecated value; treated the same as PANGO_DIRECTION_RTL.

PANGO_DIRECTION_TTB_RTL

Deprecated value; treated the same as PANGO_DIRECTION_LTR

PANGO_DIRECTION_WEAK_LTR

A weak left-to-right direction

PANGO_DIRECTION_WEAK_RTL

A weak right-to-left direction

PANGO_DIRECTION_NEUTRAL

No direction specified

pango_unichar_direction ()

PangoDirection      pango_unichar_direction             (gunichar ch);

Determines the inherent direction of a character; either PANGO_DIRECTION_LTR, PANGO_DIRECTION_RTL, or PANGO_DIRECTION_NEUTRAL.

This function is useful to categorize characters into left-to-right letters, right-to-left letters, and everything else. If full Unicode bidirectional type of a character is needed, pango_bidi_type_for_gunichar() can be used instead.

ch :

a Unicode character

Returns :

the direction of the character.

pango_find_base_dir ()

PangoDirection      pango_find_base_dir                 (const gchar *text,
                                                         gint length);

Searches a string the first character that has a strong direction, according to the Unicode bidirectional algorithm.

text :

the text to process

length :

length of text in bytes (may be -1 if text is nul-terminated)

Returns :

The direction corresponding to the first strong character. If no such character is found, then PANGO_DIRECTION_NEUTRAL is returned.

Since 1.4


pango_get_mirror_char ()

gboolean            pango_get_mirror_char               (gunichar ch,
                                                         gunichar *mirrored_ch);

Warning

pango_get_mirror_char is deprecated and should not be used in newly-written code.

If ch has the Unicode mirrored property and there is another Unicode character that typically has a glyph that is the mirror image of ch's glyph, puts that character in the address pointed to by mirrored_ch.

Use g_unichar_get_mirror_char() instead; the docs for that function provide full details.

ch :

a Unicode character

mirrored_ch :

location to store the mirrored character

Returns :

TRUE if ch has a mirrored character and mirrored_ch is filled in, FALSE otherwise

enum PangoBidiType

typedef enum {
  /* Strong types */
  PANGO_BIDI_TYPE_L,
  PANGO_BIDI_TYPE_LRE,
  PANGO_BIDI_TYPE_LRO,
  PANGO_BIDI_TYPE_R,
  PANGO_BIDI_TYPE_AL,
  PANGO_BIDI_TYPE_RLE,
  PANGO_BIDI_TYPE_RLO,

  /* Weak types */
  PANGO_BIDI_TYPE_PDF,
  PANGO_BIDI_TYPE_EN,
  PANGO_BIDI_TYPE_ES,
  PANGO_BIDI_TYPE_ET,
  PANGO_BIDI_TYPE_AN,
  PANGO_BIDI_TYPE_CS,
  PANGO_BIDI_TYPE_NSM,
  PANGO_BIDI_TYPE_BN,

  /* Neutral types */
  PANGO_BIDI_TYPE_B,
  PANGO_BIDI_TYPE_S,
  PANGO_BIDI_TYPE_WS,
  PANGO_BIDI_TYPE_ON
} PangoBidiType;

The PangoBidiType type represents the bidirectional character type of a Unicode character as specified by the Unicode bidirectional algorithm.

PANGO_BIDI_TYPE_L

Left-to-Right

PANGO_BIDI_TYPE_LRE

Left-to-Right Embedding

PANGO_BIDI_TYPE_LRO

Left-to-Right Override

PANGO_BIDI_TYPE_R

Right-to-Left

PANGO_BIDI_TYPE_AL

Right-to-Left Arabic

PANGO_BIDI_TYPE_RLE

Right-to-Left Embedding

PANGO_BIDI_TYPE_RLO

Right-to-Left Override

PANGO_BIDI_TYPE_PDF

Pop Directional Format

PANGO_BIDI_TYPE_EN

European Number

PANGO_BIDI_TYPE_ES

European Number Separator

PANGO_BIDI_TYPE_ET

European Number Terminator

PANGO_BIDI_TYPE_AN

Arabic Number

PANGO_BIDI_TYPE_CS

Common Number Separator

PANGO_BIDI_TYPE_NSM

Nonspacing Mark

PANGO_BIDI_TYPE_BN

Boundary Neutral

PANGO_BIDI_TYPE_B

Paragraph Separator

PANGO_BIDI_TYPE_S

Segment Separator

PANGO_BIDI_TYPE_WS

Whitespace

PANGO_BIDI_TYPE_ON

Other Neutrals

Since 1.22


pango_bidi_type_for_unichar ()

PangoBidiType       pango_bidi_type_for_unichar         (gunichar ch);

Determines the normative bidirectional character type of a character, as specified in the Unicode Character Database.

A simplified version of this function is available as pango_unichar_get_direction().

ch :

a Unicode character

Returns :

the bidirectional character type, as used in the Unicode bidirectional algorithm.

Since 1.22

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