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Portable Layout Services: Context-dependent and Directional Text
Portable Layout Services:
Context-dependent and Directional Text
Copyright © 1997 The Open Group
Interface Overview
This chapter outlines the purpose of the
m_*_layout()
functions, which facilitate the transformation of the caller's data from one
form to the other.
A set of APIs to handle these transformations is defined in
Layout APIs
.
To perform their operations these APIs need descriptive information related
to the layouts (layout values of text attributes) and the peculiarities of
the characters of the text (the character classifications and mapping).
Opaque Data
The information needed to perform the transformations is encapsulated in an
opaque data type called
LayoutObject.
All locales supported by the
setlocale()
function may be associated with a LayoutObject. Applications
that use the LayoutObject functions must first initialise a
LayoutObject.
Layout values are part of the type LayoutObject. A layout value
consists of a descriptor and a data type.
The layout values are text attributes and processing indicators needed by
the layout transformation functions to relate properly to the text being
transformed.
The layout values with the data type
LayoutTextDescriptor
have two values: one for input text and one for the transformed text.
Functions
The
m_create_layout()
function initialises a LayoutObject.
When the function
m_create_layout()
is called the locale name is passed to it by an argument of type
AttrObject.
A null argument implies using the locale name of the current locale
as set by
setlocale().
The main
m_*_layout()
function is
m_transform_layout(),
which performs layout transformations, such as reordering and shaping,
on a string of text encoded in a character encoding scheme.
A similar function,
m_wtransform_layout()
is provided for text encoded in a wide-character encoding scheme.
It also provides information to the application so that it can perform
editing, shaping and character composition operations as required.
Other functions associated with the LayoutObject type are:
-
Free a LayoutObject
m_destroy_layoutm_destroy_layout()).
-
Set layout values of a LayoutObject
m_setvalues_layoutm_setvalues_layout()).
-
Get layout values of a LayoutObject
m_getvalues_layoutm_getvalues_layout()).
Descriptors and Data Types
Standard Layout Values
lists the standard layout values used by the
m_*_layout()
functions associated with a type LayoutObject.
Each layout value is specified in terms of its descriptor, data type
and whether it may be set (S) or got (G) using
m_setvalues_layout()
or
m_getvalues_layout()
respectively. For some particular national languages or regional groups and
for specific implementations, additional layout values, beyond those listed
here, may be added.
Defaults have been assigned to the layout values for the C locale,
because these locales (in the C library) are the only locales with a
consistent behaviour across implementations.
| Descriptor
| Type
| SG
|
|---|
| Orientation
| LayoutTextDescriptor
| SG
|
| Context
| LayoutTextDescriptor
| SG
|
| TypeOfText
| LayoutTextDescriptor
| SG
|
| ImplicitAlg
| LayoutTextDescriptor
| SG
|
| Swapping
| LayoutTextDescriptor
| SG
|
| Numerals
| LayoutTextDescriptor
| SG
|
| TextShaping
| LayoutTextDescriptor
| SG
|
| ActiveDirectional
| BooleanValue
| G
|
| ActiveShapeEditing
| BooleanValue
| G
|
| ShapeCharset
| char *
| SG
|
| ShapeCharsetSize
| int
| G
|
| ShapeContextSize
| LayoutEditSize
| G
|
| InOutTextDescrMask
| unsigned long
| SG
|
| InOnlyTextDescr
| unsigned long
| SG
|
| OutOnlyTextDescr
| unsigned long
| SG
|
| CheckMode
| LayoutDesc
| SG
|
| QueryValueSize
| int
| G
|
Table: Standard Layout Values
Header File <sys/layout.h>
includes descriptions of the layout values needed by the transformation
functions, and the special data structures and types used.
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