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# Copyright 2015 Google Inc. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from feaTools import parser
from feaTools.writers.baseWriter import AbstractFeatureWriter
class KernFeatureWriter(AbstractFeatureWriter):
"""Generates a kerning feature based on glyph class definitions.
Uses the kerning rules contained in an RFont's kerning attribute, as well as
glyph classes from parsed OTF text. Class-based rules are set based on the
existing rules for their key glyphs.
"""
def __init__(self, font):
self.kerning = font.kerning
self.leftClasses = []
self.rightClasses = []
self.classSizes = {}
def write(self, linesep="\n"):
"""Write kern feature."""
# maintain collections of different rule types
leftClassKerning, rightClassKerning, classPairKerning = {}, {}, {}
for leftName, leftContents in self.leftClasses:
leftKey = leftContents[0]
# collect rules with two classes
for rightName, rightContents in self.rightClasses:
rightKey = rightContents[0]
pair = leftKey, rightKey
kerningVal = self.kerning[pair]
if kerningVal is None:
continue
classPairKerning[leftName, rightName] = kerningVal
self.kerning.remove(pair)
# collect rules with left class and right glyph
for pair, kerningVal in self.kerning.getLeft(leftKey):
leftClassKerning[leftName, pair[1]] = kerningVal
self.kerning.remove(pair)
# collect rules with left glyph and right class
for rightName, rightContents in self.rightClasses:
rightKey = rightContents[0]
for pair, kerningVal in self.kerning.getRight(rightKey):
rightClassKerning[pair[0], rightName] = kerningVal
self.kerning.remove(pair)
# write the feature
self.ruleCount = 0
lines = ["feature kern {"]
lines.append(self._writeKerning(self.kerning, linesep))
lines.append(self._writeKerning(leftClassKerning, linesep, True))
lines.append(self._writeKerning(rightClassKerning, linesep, True))
lines.append(self._writeKerning(classPairKerning, linesep))
lines.append("} kern;")
return linesep.join(lines)
def _writeKerning(self, kerning, linesep, enum=False):
"""Write kerning rules for a mapping of pairs to values."""
lines = []
enum = "enum " if enum else ""
pairs = kerning.items()
pairs.sort()
for (left, right), val in pairs:
if enum:
rulesAdded = (self.classSizes.get(left, 1) *
self.classSizes.get(right, 1))
else:
rulesAdded = 1
self.ruleCount += rulesAdded
if self.ruleCount > 1024:
lines.append(" subtable;")
self.ruleCount = rulesAdded
lines.append(" %spos %s %s %d;" % (enum, left, right, val))
return linesep.join(lines)
def classDefinition(self, name, contents):
"""Store a class definition as either a left- or right-hand class."""
if not name.startswith("@_"):
return
info = (name, contents)
if name.endswith("_L"):
self.leftClasses.append(info)
elif name.endswith("_R"):
self.rightClasses.append(info)
self.classSizes[name] = len(contents)
def makeKernFeature(font, text):
"""Add a kern feature to the font, using a KernFeatureWriter."""
writer = KernFeatureWriter(font)
parser.parseFeatures(writer, text)
font.features.text += writer.write()
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