OpenType Font Handling

## OpenType Font Handling OpenType Font Handling — Obtaining information from OpenType tables |

## Synopsis

    typedef     PangoOTTag;
                PangoOTInfo;
                PangoOTBuffer;
                PangoOTGlyph;
                PangoOTRuleset;
    enum        PangoOTTableType;
    PangoOTInfo* pango_ot_info_get              (FT_Face face);
    gboolean    pango_ot_info_find_script       (PangoOTInfo *info,
                                                 PangoOTTableType table_type,
                                                 PangoOTTag script_tag,
                                                 guint *script_index);
    gboolean    pango_ot_info_find_language     (PangoOTInfo *info,
                                                 PangoOTTableType table_type,
                                                 guint script_index,
                                                 PangoOTTag language_tag,
                                                 guint *language_index,
                                                 guint *required_feature_index);
    gboolean    pango_ot_info_find_feature      (PangoOTInfo *info,
                                                 PangoOTTableType table_type,
                                                 PangoOTTag feature_tag,
                                                 guint script_index,
                                                 guint language_index,
                                                 guint *feature_index);
    PangoOTTag* pango_ot_info_list_scripts      (PangoOTInfo *info,
                                                 PangoOTTableType table_type);
    PangoOTTag* pango_ot_info_list_languages    (PangoOTInfo *info,
                                                 PangoOTTableType table_type,
                                                 guint script_index,
                                                 PangoOTTag language_tag);
    PangoOTTag* pango_ot_info_list_features     (PangoOTInfo *info,
                                                 PangoOTTableType table_type,
                                                 PangoOTTag tag,
                                                 guint script_index,
                                                 guint language_index);
    PangoOTBuffer* pango_ot_buffer_new          (PangoFcFont *font);
    void        pango_ot_buffer_destroy         (PangoOTBuffer *buffer);
    void        pango_ot_buffer_clear           (PangoOTBuffer *buffer);
    void        pango_ot_buffer_add_glyph       (PangoOTBuffer *buffer,
                                                 guint glyph_index,
                                                 guint properties,
                                                 guint cluster);
    void        pango_ot_buffer_set_rtl         (PangoOTBuffer *buffer,
                                                 gboolean rtl);
    void        pango_ot_buffer_set_zero_width_marks
                                                (PangoOTBuffer *buffer,
                                                 gboolean zero_width_marks);
    void        pango_ot_buffer_get_glyphs      (PangoOTBuffer *buffer,
                                                 PangoOTGlyph **glyphs,
                                                 int *n_glyphs);
    void        pango_ot_buffer_output          (PangoOTBuffer *buffer,
                                                 PangoGlyphString *glyphs);
    PangoOTRuleset* pango_ot_ruleset_new        (PangoOTInfo *info);
    void        pango_ot_ruleset_add_feature    (PangoOTRuleset *ruleset,
                                                 PangoOTTableType table_type,
                                                 guint feature_index,
                                                 gulong property_bit);
    void        pango_ot_ruleset_substitute     (PangoOTRuleset *ruleset,
                                                 PangoOTBuffer *buffer);
    void        pango_ot_ruleset_position       (PangoOTRuleset *ruleset,
                                                 PangoOTBuffer *buffer);

## Description

## Details

### PangoOTTag

    typedef guint32  PangoOTTag;

The PangoOTTag typedef is used to represent TrueType and OpenType four letter tags inside Pango. Use the ``FT_MAKE_TAG()`` macro defined in the FreeType2 header `freetype/freetype.h` to create PangoOTTags manually.

### PangoOTInfo

    typedef struct _PangoOTInfo PangoOTInfo;

The PangoOTInfo struct contains the various tables associated with an OpenType font. It contains only private fields and should only be accessed via the `pango_ot_info_*` functions which are documented below. To obtain a PangoOTInfo, use `pango_ot_info_new()`.

### PangoOTBuffer

    typedef struct _PangoOTBuffer PangoOTBuffer;

### PangoOTGlyph

    typedef struct {
      guint    glyph;
      guint    properties;
      guint    cluster;
      gushort  component;
      gushort  ligID;
      gushort  property_cache;    /* Internal */
    } PangoOTGlyph;

### PangoOTRuleset

    typedef struct _PangoOTRuleset PangoOTRuleset;

The PangoOTRuleSet structure holds a set of features selected from the tables in an OpenType font. (A feature is an operation such as adjusting glyph positioning that should be applied to a text feature such as a certain type of accent.) A PangoOTRuleSet is created with `pango_ot_ruleset_new()`, features are addded to it with `pango_ot_ruleset_add_feature()`, then it is applied to a PangoGlyphString with `pango_ot_ruleset_shape()`.

### enum PangoOTTableType

    typedef enum
    {
      PANGO_OT_TABLE_GSUB,
      PANGO_OT_TABLE_GPOS
    } PangoOTTableType;

The PangoOTTableType enumeration values are used to identify the various OpenType tables in the `pango_ot_info_*` functions.

`PANGO_OT_TABLE_GSUB` | The GSUB table.
`PANGO_OT_TABLE_GPOS` | The GPOS table.

### pango_ot_info_get ()

    PangoOTInfo* pango_ot_info_get              (FT_Face face);

Returns the PangoOTInfo structure for the given FreeType font.

`face` : | a FT_Face.
Returns : | the PangoOTInfo for `face`. This object will have the same lifetime as FT_Face.

Since 1.2

### pango_ot_info_find_script ()

    gboolean    pango_ot_info_find_script       (PangoOTInfo *info,
                                                 PangoOTTableType table_type,
                                                 PangoOTTag script_tag,
                                                 guint *script_index);

Finds the index of a script.

`info` : | a PangoOTInfo.
`table_type` : | the table type to obtain information about.
`script_tag` : | the tag of the script to find.
`script_index` : | location to store the index of the script, or `NULL`.
Returns : | `TRUE` if the script was found.

### pango_ot_info_find_language ()

    gboolean    pango_ot_info_find_language     (PangoOTInfo *info,
                                                 PangoOTTableType table_type,
                                                 guint script_index,
                                                 PangoOTTag language_tag,
                                                 guint *language_index,
                                                 guint *required_feature_index);

Finds the index of a language and its required feature index.

`info` : | a PangoOTInfo.
`table_type` : | the table type to obtain information about.
`script_index` : | the index of the script whose languages are searched.
`language_tag` : | the tag of the language to find.
`language_index` : | location to store the index of the language, or `NULL`.
`required_feature_index` : | location to store the required feature index of the language, or `NULL`.
Returns : | `TRUE` if the language was found.

### pango_ot_info_find_feature ()

    gboolean    pango_ot_info_find_feature      (PangoOTInfo *info,
                                                 PangoOTTableType table_type,
                                                 PangoOTTag feature_tag,
                                                 guint script_index,
                                                 guint language_index,
                                                 guint *feature_index);

Finds the index of a feature.

`info` : | a PangoOTInfo.
`table_type` : | the table type to obtain information about.
`feature_tag` : | the tag of the feature to find.
`script_index` : | the index of the script.
`language_index` : | the index of the language whose features are searched, or 0xffff to use the default language of the script.
`feature_index` : | location to store the index of the feature, or `NULL`.
Returns : | `TRUE` if the feature was found.

### pango_ot_info_list_scripts ()

    PangoOTTag* pango_ot_info_list_scripts      (PangoOTInfo *info,
                                                 PangoOTTableType table_type);

Obtains the list of available scripts.

`info` : | a PangoOTInfo.
`table_type` : | the table type to obtain information about.
Returns : | a newly-allocated array containing the tags of the available scripts.

### pango_ot_info_list_languages ()

    PangoOTTag* pango_ot_info_list_languages    (PangoOTInfo *info,
                                                 PangoOTTableType table_type,
                                                 guint script_index,
                                                 PangoOTTag language_tag);

Obtains the list of available languages for a given script.

`info` : | a PangoOTInfo.
`table_type` : | the table type to obtain information about.
`script_index` : | the index of the script to list languages for.
`language_tag` : | unused parameter.
Returns : | a newly-allocated array containing the tags of the available languages.

### pango_ot_info_list_features ()

    PangoOTTag* pango_ot_info_list_features     (PangoOTInfo *info,
                                                 PangoOTTableType table_type,
                                                 PangoOTTag tag,
                                                 guint script_index,
                                                 guint language_index);

Obtains the list of features for the given language of the given script.

`info` : | a PangoOTInfo.
`table_type` : | the table type to obtain information about.
`tag` : | unused parameter.
`script_index` : | the index of the script to obtain information about.
`language_index` : | the indes of the language to list features for, or 0xffff, to list features for the default language of the script.
Returns : | a newly-allocated array containing the tags of the available features.

### pango_ot_buffer_new ()

    PangoOTBuffer* pango_ot_buffer_new          (PangoFcFont *font);

`font` : |
Returns : |

### pango_ot_buffer_destroy ()

    void        pango_ot_buffer_destroy         (PangoOTBuffer *buffer);

`buffer` : |

### pango_ot_buffer_clear ()

    void        pango_ot_buffer_clear           (PangoOTBuffer *buffer);

`buffer` : |

### pango_ot_buffer_add_glyph ()

    void        pango_ot_buffer_add_glyph       (PangoOTBuffer *buffer,
                                                 guint glyph_index,
                                                 guint properties,
                                                 guint cluster);

`buffer` : |
`glyph_index` : |
`properties` : |
`cluster` : |

### pango_ot_buffer_set_rtl ()

    void        pango_ot_buffer_set_rtl         (PangoOTBuffer *buffer,
                                                 gboolean rtl);

`buffer` : |
`rtl` : |

### pango_ot_buffer_set_zero_width_marks ()

    void        pango_ot_buffer_set_zero_width_marks
                                                (PangoOTBuffer *buffer,
                                                 gboolean zero_width_marks);

Sets whether characters with a mark class should be forced to zero width. This setting is needed for proper positioning of Arabic accents, but will produce incorrect results with standard OpenType indic fonts.

`buffer` : | a PangoOTBuffer
`zero_width_marks` : | `TRUE` if characters with a mark class should be forced to zero width.

Since 1.6

### pango_ot_buffer_get_glyphs ()

    void        pango_ot_buffer_get_glyphs      (PangoOTBuffer *buffer,
                                                 PangoOTGlyph **glyphs,
                                                 int *n_glyphs);

`buffer` : |
`glyphs` : |
`n_glyphs` : |

### pango_ot_buffer_output ()

    void        pango_ot_buffer_output          (PangoOTBuffer *buffer,
                                                 PangoGlyphString *glyphs);

`buffer` : |
`glyphs` : |

### pango_ot_ruleset_new ()

    PangoOTRuleset* pango_ot_ruleset_new        (PangoOTInfo *info);

Creates a new PangoOTRuleset for the given OpenType info.

`info` : | a PangoOTInfo.
Returns : | a new PangoOTRuleset.

### pango_ot_ruleset_add_feature ()

    void        pango_ot_ruleset_add_feature    (PangoOTRuleset *ruleset,
                                                 PangoOTTableType table_type,
                                                 guint feature_index,
                                                 gulong property_bit);

Adds a feature to the ruleset. See `pango_ot_ruleset_shape()` for an explanation of `property_bit`.

`ruleset` : | a PangoOTRuleset.
`table_type` : | the table type to add a feature to.
`feature_index` : | the index of the feature to add.
`property_bit` : | the property bit to use for this feature.

### pango_ot_ruleset_substitute ()

    void        pango_ot_ruleset_substitute     (PangoOTRuleset *ruleset,
                                                 PangoOTBuffer *buffer);

`ruleset` : |
`buffer` : |

### pango_ot_ruleset_position ()

    void        pango_ot_ruleset_position       (PangoOTRuleset *ruleset,
                                                 PangoOTBuffer *buffer);

`ruleset` : |
`buffer` : |