opentype.sgml

Pango is a library for layout and rendering of text, with an emphasis on internationalization. Pang

<!-- ##### SECTION Title ##### -->
OpenType Font Handling

<!-- ##### SECTION Short_Description ##### -->
Obtaining information from OpenType tables

<!-- ##### SECTION Long_Description ##### -->
<para>
Functions and macros in this section are used to implement the OpenType Layout
features and algorithms.  These are mostly useful when writing Fontconfig-based
shaping engines
</para>

<!-- ##### SECTION See_Also ##### -->
<para>

</para>

<!-- ##### SECTION Stability_Level ##### -->
Unstable

<!-- ##### TYPEDEF PangoOTTag ##### -->
<para>
The <type>PangoOTTag</type> typedef is used to represent TrueType and OpenType
four letter tags inside Pango. Use PANGO_OT_TAG_MAKE()
or PANGO_OT_TAG_MAKE_FROM_STRING() macros to create <type>PangoOTTag</type>s manually.
</para>


<!-- ##### STRUCT PangoOTInfo ##### -->
<para>
The #PangoOTInfo struct contains the various 
tables associated with an OpenType font. It contains only private fields and
should only be accessed via the <function>pango_ot_info_*</function> functions
which are documented below. To obtain a #PangoOTInfo,
use pango_ot_info_new().
</para>


<!-- ##### STRUCT PangoOTBuffer ##### -->
<para>
The #PangoOTBuffer structure is used to store strings of glyphs associated
with a #PangoFcFont, suitable for OpenType layout processing.  It contains
only private fields and should only be accessed via the
<function>pango_ot_buffer_*</function> functions which are documented below.
To obtain a #PangoOTBuffer, use pango_ot_buffer_new().
</para>


<!-- ##### STRUCT PangoOTGlyph ##### -->
<para>
The #PangoOTGlyph structure represents a single glyph together with
information used for OpenType layout processing of the glyph.
It contains the following fields.
</para>

@glyph: the glyph itself.
@properties: the properties value, identifying which features should be
	     applied on this glyph.  See pango_ruleset_add_feature().
@cluster: the cluster that this glyph belongs to.
@component: a component value, set by the OpenType layout engine.
@ligID: a ligature index value, set by the OpenType layout engine.
@property_cache: for internal use.

<!-- ##### STRUCT PangoOTRuleset ##### -->
<para>
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 added
to it with pango_ot_ruleset_add_feature(), then it is
applied to a #PangoGlyphString with pango_ot_ruleset_shape().
</para>


<!-- ##### STRUCT PangoOTRulesetDescription ##### -->
<para>
The #PangoOTRuleset structure holds all the information needed
to build a complete #PangoOTRuleset from an OpenType font.
The main use of this struct is to act as the key for a per-font
hash of rulesets.  The user populates a ruleset description and
gets the ruleset using pango_ot_ruleset_get_for_description()
or create a new one using pango_ot_ruleset_new_from_description().
</para>

@script: a #PangoScript.
@language: a #PangoLanguage.
@static_gsub_features: static map of GSUB features, or %NULL.
@n_static_gsub_features: length of @static_gsub_features, or 0.
@static_gpos_features: static map of GPOS features, or %NULL.
@n_static_gpos_features: length of @static_gpos_features, or 0.
@other_features: map of extra features to add to both GSUB and GPOS, or %NULL.
                 Unlike the static maps, this pointer need not live beyond
		 the life of function calls taking this struct.
@n_other_features: length of @other_features, or 0.
@Since: 1.18

<!-- ##### ENUM PangoOTTableType ##### -->
<para>
The <type>PangoOTTableType</type> enumeration values are used to
identify the various OpenType tables in the
<function>pango_ot_info_*</function> functions.
</para>

@PANGO_OT_TABLE_GSUB: The GSUB table.
@PANGO_OT_TABLE_GPOS: The GPOS table.

<!-- ##### STRUCT PangoOTFeatureMap ##### -->
<para>
The <type>PangoOTFeatureMap</type> typedef is used to represent an OpenType
feature with the property bit associated with it.  The feature tag is
represented as a char array instead of a #PangoOTTag for convenience.
</para>

@feature_name: feature tag in represented as four-letter ASCII string.
@property_bit: the property bit to use for this feature.  See
	       pango_ot_ruleset_add_feature() for details.
@Since: 1.18

<!-- ##### MACRO PANGO_OT_TAG_MAKE ##### -->
<para>
Creates a #PangoOTTag from four characters.  This is similar and
compatible with the <function>FT_MAKE_TAG()</function> macro from
FreeType.
</para>

@c1: First character.
@c2: Second character.
@c3: Third character.
@c4: Fourth character.


<!-- ##### MACRO PANGO_OT_TAG_MAKE_FROM_STRING ##### -->
<para>
Creates a #PangoOTTag from a string. The string should be at least
four characters long (pad with space characters if needed), and need
not be nul-terminated.  This is a convenience wrapper around
PANGO_OT_TAG_MAKE(), but cannot be used in certain situations, for
example, as a switch expression, as it dereferences pointers.
</para>

@s: The string representation of the tag.


<!-- ##### MACRO PANGO_OT_ALL_GLYPHS ##### -->
<para>
This is used as the property bit in pango_ot_ruleset_add_feature() when a
feature should be applied to all glyphs.
</para>

@Since: 1.16


<!-- ##### MACRO PANGO_OT_NO_FEATURE ##### -->
<para>
This is used as a feature index that represent no feature, that is, should be
skipped.  It may be returned as feature index by pango_ot_info_find_feature()
if the feature is not found, and pango_ot_rulset_add_feature() function
automatically skips this value, so no special handling is required by the
user.
</para>

@Since: 1.18


<!-- ##### MACRO PANGO_OT_NO_SCRIPT ##### -->
<para>
This is used as a script index that represent no script, that is, when the
requested script was not found, and a default ('DFLT') script was not found
either.  It may be returned as script index by pango_ot_info_find_script()
if the script or a default script are not found, all other functions
taking a script index essentially return if the input script index is
this value, so no special handling is required by the user.
</para>

@Since: 1.18


<!-- ##### MACRO PANGO_OT_DEFAULT_LANGUAGE ##### -->
<para>
This is used as the language index in pango_ot_info_find_feature() when
the default language system of the script is desired.

It is also returned by pango_ot_info_find_language() if the requested language
is not found, or the requested language tag was PANGO_OT_TAG_DEFAULT_LANGUAGE.
The end result is that one can always call pango_ot_tag_from_language()
followed by pango_ot_info_find_language() and pass the result to
pango_ot_info_find_feature() without having to worry about falling back to
default language system explicitly.
</para>

@Since: 1.16


<!-- ##### MACRO PANGO_OT_TAG_DEFAULT_LANGUAGE ##### -->
<para>
This is a #PangoOTTag representing a special language tag 'dflt'.  It is
returned as language tag by pango_ot_tag_from_language() if the requested
language is not found.  It is safe to pass this value to
pango_ot_info_find_language() as that function falls back to returning default
language-system if the requested language tag is not found.
</para>

@Since: 1.18


<!-- ##### MACRO PANGO_OT_TAG_DEFAULT_SCRIPT ##### -->
<para>
This is a #PangoOTTag representing the special script tag 'DFLT'.  It is
returned as script tag by pango_ot_tag_from_script() if the requested script
is not found.
</para>

@Since: 1.18


<!-- ##### FUNCTION pango_ot_info_get ##### -->
<para>

</para>

@face: 
@Returns: 


<!-- ##### FUNCTION pango_ot_info_find_script ##### -->
<para>

</para>

@info: 
@table_type: 
@script_tag: 
@script_index: 
@Returns: 


<!-- ##### FUNCTION pango_ot_info_find_language ##### -->
<para>

</para>

@info: 
@table_type: 
@script_index: 
@language_tag: 
@language_index: 
@required_feature_index: 
@Returns: 


<!-- ##### FUNCTION pango_ot_info_find_feature ##### -->
<para>

</para>

@info: 
@table_type: 
@feature_tag: 
@script_index: 
@language_index: 
@feature_index: 
@Returns: 


<!-- ##### FUNCTION pango_ot_info_list_scripts ##### -->
<para>

</para>

@info: 
@table_type: 
@Returns: 


<!-- ##### FUNCTION pango_ot_info_list_languages ##### -->
<para>

</para>

@info: 
@table_type: 
@script_index: 
@language_tag: 
@Returns: 


<!-- ##### FUNCTION pango_ot_info_list_features ##### -->
<para>

</para>

@info: 
@table_type: 
@tag: 
@script_index: 
@language_index: 
@Returns: 


<!-- ##### FUNCTION pango_ot_buffer_new ##### -->
<para>

</para>

@font: 
@Returns: 


<!-- ##### FUNCTION pango_ot_buffer_destroy ##### -->
<para>

</para>

@buffer: 


<!-- ##### FUNCTION pango_ot_buffer_clear ##### -->
<para>

</para>

@buffer: 


<!-- ##### FUNCTION pango_ot_buffer_add_glyph ##### -->
<para>

</para>

@buffer: 
@glyph: 
@properties: 
@cluster: 


<!-- ##### FUNCTION pango_ot_buffer_set_rtl ##### -->
<para>

</para>

@buffer: 
@rtl: 


<!-- ##### FUNCTION pango_ot_buffer_set_zero_width_marks ##### -->
<para>

</para>

@buffer: 
@zero_width_marks: 


<!-- ##### FUNCTION pango_ot_buffer_get_glyphs ##### -->
<para>

</para>

@buffer: 
@glyphs: 
@n_glyphs: 


<!-- ##### FUNCTION pango_ot_buffer_output ##### -->
<para>

</para>

@buffer: 
@glyphs: 


<!-- ##### FUNCTION pango_ot_ruleset_get_for_description ##### -->
<para>

</para>

@info: 
@desc: 
@Returns: 


<!-- ##### FUNCTION pango_ot_ruleset_new ##### -->
<para>

</para>

@info: 
@Returns: 


<!-- ##### FUNCTION pango_ot_ruleset_new_for ##### -->
<para>

</para>

@info: 
@script: 
@language: 
@Returns: 


<!-- ##### FUNCTION pango_ot_ruleset_new_from_description ##### -->
<para>

</para>

@info: 
@desc: 
@Returns: 


<!-- ##### FUNCTION pango_ot_ruleset_add_feature ##### -->
<para>

</para>

@ruleset: 
@table_type: 
@feature_index: 
@property_bit: 


<!-- ##### FUNCTION pango_ot_ruleset_maybe_add_feature ##### -->
<para>

</para>

@ruleset: 
@table_type: 
@feature_tag: 
@property_bit: 
@Returns: 


<!-- ##### FUNCTION pango_ot_ruleset_maybe_add_features ##### -->
<para>

</para>

@ruleset: 
@table_type: 
@features: 
@n_features: 
@Returns: 


<!-- ##### FUNCTION pango_ot_ruleset_get_feature_count ##### -->
<para>

</para>

@ruleset: 
@n_gsub_features: 
@n_gpos_features: 
@Returns: 


<!-- ##### FUNCTION pango_ot_ruleset_substitute ##### -->
<para>

</para>

@ruleset: 
@buffer: 


<!-- ##### FUNCTION pango_ot_ruleset_position ##### -->
<para>

</para>

@ruleset: 
@buffer: 


<!-- ##### FUNCTION pango_ot_ruleset_description_copy ##### -->
<para>

</para>

@desc: 
@Returns: 


<!-- ##### FUNCTION pango_ot_ruleset_description_equal ##### -->
<para>

</para>

@desc1: 
@desc2: 
@Returns: 


<!-- ##### FUNCTION pango_ot_ruleset_description_free ##### -->
<para>

</para>

@desc: 


<!-- ##### FUNCTION pango_ot_ruleset_description_hash ##### -->
<para>

</para>

@desc: 
@Returns: 


<!-- ##### FUNCTION pango_ot_tag_from_language ##### -->
<para>

</para>

@language: 
@Returns: 


<!-- ##### FUNCTION pango_ot_tag_from_script ##### -->
<para>

</para>

@script: 
@Returns: 


<!-- ##### FUNCTION pango_ot_tag_to_language ##### -->
<para>

</para>

@language_tag: 
@Returns: 


<!-- ##### FUNCTION pango_ot_tag_to_script ##### -->
<para>

</para>

@script_tag: 
@Returns: