User Guide

Making OpenType Fonts
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Please, remember this key OpenType principle: OpenType layout engine
doesn’t know anything about characters! All the features that OpenType
can have are defined for glyphs. This is the process of OpenType text
processing:
0. As a source we have a sequence of characters.
1. Character codes are mapped to default glyphs using the Unicode
mapping table. In FontLab this is what you see in the Font window
when you select one of the codepages. Here we have a sequence of
characters replaced by a sequence of glyphs. No character information
is available beyond this point!
2. The source sequence of glyphs is passed to the OpenType processing
module, which then applies the font features in a pre-defined
sequence. The list of the features to apply is determined by the
application (for example, in Adobe InDesign you can explicitly select
features to apply) or operating system (e.g. the rendering of Arabic text
with an OpenType font).
3. The resulting sequence of glyphs is passed to the second stage of
feature processing which can shift the positions of glyphs. Kerning is
applied at this stage.
4. The sequence of glyphs, accompanied by the positioning information,
is passed to the rasterizer, which does the imaging of the features on
the destination device: screen or printer.