A basic OpenType GSUB and GPOS layout engine written in Python.
Table of Contents
- Usage Reference
This document covers the basic usage of the compositor package. For more detailed information read the documentation strings in the source.
Some assumptions about the OpenType fonts being used are made by the package:
- The font is valid.
- The font's
cmaptable contains Platform 3 Encoding 1.
- The font does not contain
GPOSlookup types that are not supported by the GSUB or GPOS objects. If an unsupported lookup type is present, the lookup will simply be ignored. It will not raise an error.
The Font Object
from compositor import Font
font = Font(path)
- A path to an OpenType font.
glyph = font["aGlyphName"]
Returns the glyph object named
aGlyphName. This will raise a
aGlyphName is not in the font.
isThere = "aGlyphName" in font
Returns a boolean representing if
aGlyphName is in the font.
A list of all glyph names in the font.
glyphRecords = font.process(aString)
This is the most important method. It takes a string (Unicode or plain ASCII) and processes it with the features defined in the font's
GPOS tables. A list of
GlyphRecord objects will be returned.
featureTags = font.getFeatureList()
A list of all available features in GSUB and GPOS.
state = font.getFeatureState(featureTag)
Get a boolean representing if a feature is on or not. This assumes that the feature state is consistent in both the GSUB and GPOS tables. A
CompositorError will be raised if the feature is inconsistently applied. A
CompositorError will be raised if featureTag is not defined in GSUB or GPOS.
font.setFeatureState(self, featureTag, state)
Set the application state of a feature.
- The Info object for the font.
The GlyphRecord Object
- The name of the referenced glyph.
- Horizontal placement.
- Vertical placement.
- Horizontal adjustment for advance.
- Vertical adjustment for advance.
- A list of `GlyphRecords` indicating alternates for the glyph.
The Glyph Object
Draws the glyph with a FontTools pen.
- The name of the glyph.
- The glyph's index within the source font.
- The width of the glyph.
- The bounding box for the glyph. Formatted as `(xMin, yMin, xMax, yMax)`. If the glyph contains no outlines, this will return `None`.
The Info Object
Relationship to the GSUB and GPOS Specification
The Compositor GSUB and GPOS tables adhere as closely as possible to the GSUB and GPOS specification. Every effort has been made to keep terminology consistent. All known deviations from the spec are documented. (The deviations are generally trivial. For example, most the of the subtables don't implement the
Count attributes. This is done because the Python iterator provides a more convenient and faster way to deal with iteration than creating a range. Therefore, the
Count objects are not needed.)
For performance reasons, when a new font is loaded, all of the GSUB and GPOS data is extracted from the font with fontTools. The data is placed into compositor objects. These objects are then used to process text. This initial loading can be relatively expensive, but the processing speed of the objects is worth the initial expense.
To install this package, type the following in the command line:
python setup.py install