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CFont: A font component. This is a rendering-specific entity
which is paired with a glyph index to uniquely indentify
a glyph. Each abstract Font maps to one or more CFonts;
the method for obtaining CFonts from Fonts is also
rendering system specific.
Cluster: A cluster is a small portion of text that is rendered
as typographically intertwined glyphs.
A number of properties are associated with clusters
and cluster boundaries.
1) Clusters are the smallest unit of text that is guaranteed to
progress in reading order. Within a cluster, reordering
of glyphs may occur.
2) At the boundaries of clusters, character boundaries
and glyph boundaries are guaranteed to coincide.
3) There will be a cursor position between every two clusters.
There may not be a cursor position at some positions
inside a cluster.
4) The cluster boundary is the only place where information
about the correspondence between character position
and screen position is conveyed from the shape-engine
to the layers above.
Engine: A script-specific object that is responsible for
converting Unicode text into glyphs or resolving
the properties of the text. Engines may be
rendering-system specific or independent of rendering
system.
Font: An abstract font. The method in which a font is
created is dependent on the rendering system.
Item: An item is a portion of text in a single script, handled
by a single shaping engine, and with a single directional
level. g_script_itemize() returns a list of items.
Module: A dynamically loaded shared object containing one
or more Engines.
Range: A subportion of an item. You pass a range into
g_script_shape() by passing in the analysis structure
for the item and some subportion of the text.
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