PDFlib 8 Windows COM/.NET Tutorial

6.4 Complex Script Output
Cookbook A full code sample can be found in the Cookbook topic complex_scripts/starter_shaping.
6.4.1 Complex Scripts
The Latin script basically places one character after the other in left-to-right order. Other
writing systems have additional requirements for correct text output. We refer to
such writing systems as complex scripts. PDFlib performs text processing for complex
scripts for a variety of scripts including those listed in Table 6.2.
In this section we will discuss shaping for complex scripts in more detail. While most
Western languages can be written by simply placing one character after the other from
left to right, some writing systems (scripts) require additional processing:
> The Arabic and Hebrew scripts place text from right to left. Mixed text (e.g. Arabic
with a Latin insert) contains both right-to-left and left-to-right segments. These segments
must be reordered, which is referred to as the Bidi (bidirectional) problem.
> Some scripts, especially Arabic, use different character shapes depending on the position
of the character (isolated, beginning/middle/end of a word).
> Mandatory ligatures replace sequences of characters.
> The position of glyphs must be adjusted horizontally and vertically.
> Indic scripts require reordering of some characters, i.e. characters may change their
position in the text.
> Special word break and justification rules apply to some scripts.
Scripts which require one or more of these processing steps are called complex scripts.
The process of preparing incoming logical text for proper presentation is called shaping
(this term also includes reordering and Bidi processing). The user always supplies text
in unshaped form and in logical order, while PDFlib performs the necessary shaping before
producing PDF output.
Complex script shaping can be enabled with the shaping text option, which in turn
requires the script option and optionally allows the language option. The following option
list enables Arabic shaping (and Bidi processing):
shaping script=arab
Caveats. Note the following when working with complex script shaping:
> PDFlib does not automatically set the shaping and script options, but expects them to
be supplied by the user.
> Script-specific shaping (options shaping, script, language) will only be applied to
glyphs within the same font, but not across glyphs from different fonts. If fallback
fonts are used, shaping will only be applied within text runs which contain text in
the same (master or fallback) font.
> Since shaping may reorder characters in the text, care must be taken regarding attribute
changes within a word. For example, if you use inline options in Textflow to
colorize the second character in a word – what should happen when shaping swaps
the first and second characters? For this reason, formatting changes should only be
applied at word boundaries, but not within words.
6.4 Complex Script Output 163