Representing Scripts on the Macintosh
- Using the Script Manager
- Checking and Modifying Script Manager Global and Local Variables
- Accepting Implicit Script Codes
- Verbs for GetScript and SetScript
- Verbs for GetEnvirons and SetEnvirons
Worldwide system software makes it possible to represent many scripts and
languages on the Macintosh. The Macintosh Script Management System extends
the Macintosh computer's text-manipulation capabilities beyond Roman
scripts. Character representation and the keyboard are the first components to
be considered when attempting to represent any script on a Macintosh
computer.
Character Set Encoding
Character set encoding refers to the numeric codes that represent the
characters of a script in memory. The character set encoding for a script
determines the behavior of many of the features of the script, including
sorting and composition rules for drawing and measuring. Therefore, the
character set encoding is fixed; it cannot be changed without significant
con sequences. For example, features such as sorting depend on the fact that the
coding does not change.
Most scripts fit within the limits set by the size of a byte, with up to 256
distinct characters. Scripts with ideographic characters, such as Chinese,
Japanese, and Korean, need more than 256 distinct characters.A variety of
solutions have been implemented for scripts that require 2-byte codes for
computer storage in addition to or in place of the 1-byte codes that are
permits your application to run without knowing whether 1-byte or 2-byte
codes are being used, as long as it has been written to allow the possibility of
2-byte codes.
Warning: Typically, ideographic scripts use a mixture of
single-byte and double-byte encodings to represent characters;
therefore, you cannot use the terms byte and character
inter changeably.
Note: Currently, every different character set encoding does not
have a different script code. For example, the Symbol font is in the
Roman range but has a different character assignment. Before system
software version 7.0, the traditional and simplified Chinese systems
used different character codings, but had the same script code (2).
With system software version 6.0.5, these systems have been assigned
separate script codes: (2) and smSimpChinese (25).
Character Input
Character input is often more complicated than simply providing a keyboard
layout. Ideographic scripts such as Japanese cannot simply use a larger
keyboard or multiple dead keys for effective input. The sheer number of
characters demands a more complex solution, such as providing ways to
transcribe phonetic text into ideographic text. Most ideographic script
systems provide for the complex parsing of phonetic sequences and character
clusters.
Composition Rules
Each script system contains composition rules that determine the behavior
(that is, the visual appearance) of text when it is drawn, measured, or edited.
These intricate rules also provide for other features of the script, such as
determining when a sequence of characters forms a word or whether a byte is a
single character or part of a double-byte character.
Text Manipulation
With a flexible operating system, most script features are implemented
transparently. Usually, your application does not need to know that its dialog
boxes can accept Japanese text. However, if your application depends more
heavily on features of the language, you need access to information that varies
with the script.
For example, to perform word selection and word wrap (the automatic
continuation of text from the end of one line to the beginning of the next
without breaking in the middle of a word), your application may need routines
to determine the boundaries of words in the script. In Roman scripts, you can
determine word boundaries fairly easily: spaces delimit words that are not
otherwise delimited (for example, by punctuation). Other scripts, such as
Japanese and Thai, do not use characters such as spaces to delimit words. Word
boundaries are not well defined, and native writers of the language may not
agree on where particular word boundaries occur.
Because of differences in the treatment of uppercase and lowercase characters
and diacritical marks, your application may need routines and tables to
perform case conversion and, when sorting is to be done, to strip diacritical
marks. The Macintosh Script Management System supplies such routines; they
Worldwide Development: Guide to System Software.
In addition, your application may require routines to determine whether a
byte represents a single character or is part of a double-byte character, or to
highlight bidirectional text (for example, Arabic mixed with English). To
allow applications to function independently of scripts, the Macintosh Script
Management System provides such routines; they are described briefly in
Worldwide Development: Guide to System Software.
Text Rendering
The process of displaying characters that are stored in memory is called text
rendering. Backing-store order refers to the order in which character
codes are stored in memory. In general, characters for a given script are
stored in writing order, that is, the order in which someone would set the
characters down on paper. This may be different from the display order,
that is, the left-to-right order in which characters are drawn on a device by
characters appear on the screen so that the glyph corresponding to the first
character in the string actually appears on the right of the string (see the
Figure below). In another example, when diacritical marks are stored as
separate overlapping characters, they are typically stored after the base
character. Writing order is very similar to phonetic order, that is, the
order in which the characters are pronounced, but the two differ in certain
circumstances. In some cases, the phonetic order is not well defined, as with
diacritical characters.
Backing-store and display order