PDFlib 8 Windows COM/.NET Tutorial

6.3 OpenType Layout Features
Cookbook Full code samples can be found in the Cookbook topics text_output/starter_opentype and
font/opentype_feature_tester.
6.3.1 Supported OpenType Layout Features
PDFlib supports enhanced text output according to additional information in some
fonts. These font extensions are called OpenType layout features. For example, a font
may contain a liga feature which includes the information that the f, f, and i glyphs can
be combined to form a ligature. Other common examples are small caps in the smcp feature,
i.e. uppercase characters which are smaller than the regular uppercase characters,
and old-style figures in the onum feature with ascenders and descenders (as opposed to
lining figures which are all placed on the baseline). Although ligatures are a very common
OpenType feature, they are only one of many dozen possible features. An overview
of the OpenType format and OpenType feature tables can be found at
www.microsoft.com/typography/developers/opentype/default.htm
PDFlib supports the following groups of OpenType features:
> OpenType features for Western typography listed in Table 6.1; these are controlled
by the features option.
> OpenType features for Chinese, Japanese, and Korean text output listed in Table 6.7;
these are also controlled by the features option, and are discussed in more detail in
Section 6.5.4, »OpenType Layout Features for advanced CJK Text Output«, page 176.
> OpenType features for complex script shaping and vertical text output; these are automatically
evaluated subject to the shaping and script options (see Section 6.4,
»Complex Script Output«, page 164). The vert feature is controlled by the vertical font
option.
> OpenType feature tables for kerning; however, PDFlib doesn’t treat kerning as Open-
Type feature because kerning data may also be represented with other means than
OpenType feature tables. Use the readkerning font option and the kerning text option
instead to control kerning (see Section 6.2.2, »Kerning«, page 154).
More detailed descriptions of OpenType layout features can be found at
www.microsoft.com/typography/otspec/featuretags.htm
Identifying OpenType features. You can identify OpenType feature tables with the following
tools:
> The FontLab font editor is a an application for creating and editing fonts. The free
demo version (www.fontlab.com) displays and previews OpenType features
> DTL OTMaster Light (www.fonttools.org) is a free application for viewing and analyzing
fonts, including their OpenType feature tables.
> Microsoft’s free »font properties extension« 1 displays a list of OpenType features
available in a font (see Figure 6.3).
> PDFlib’s info_font( ) interface can also be used to query supported OpenType features
(see »Querying OpenType features programmatically«, page 162).
1. See www.microsoft.com/typography/TrueTypeProperty21.mspx
6.3 OpenType Layout Features 157