1 files changed, 102 insertions, 0 deletions
diff --git a/scripts/lib/fontbuild/kerning.py b/scripts/lib/fontbuild/kerning.py
new file mode 100644
index 0000000..4e6e47e
--- /dev/null
+++ b/scripts/lib/fontbuild/kerning.py
@@ -0,0 +1,102 @@
+# 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 = []
+
+    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
+                if not self.kerning.has_key(pair):
+                    continue
+                classPairKerning[leftName, rightName] = self.kerning[pair]
+                self.kerning.remove(pair)
+
+            # collect rules with left class and right glyph
+            for pair, val in self.kerning.getLeft(leftKey):
+                if pair == ('O', 'A.smcp'): print pair, val
+                leftClassKerning[leftName, pair[1]] = self.kerning[pair]
+                self.kerning.remove(pair)
+
+        # collect rules with left glyph and right class
+        for rightName, rightContents in self.rightClasses:
+            rightKey = rightContents[0]
+            for pair, val in self.kerning.getRight(rightKey):
+                rightClassKerning[pair[0], rightName] = self.kerning[pair]
+                self.kerning.remove(pair)
+
+        # write the feature
+        lines = ["feature kern {"]
+        lines.append(self._writeKerning(self.kerning, linesep))
+        lines.append(self._writeKerning(leftClassKerning, linesep, True))
+        lines.append("    subtable;")
+        lines.append(self._writeKerning(rightClassKerning, linesep, True))
+        lines.append("    subtable;")
+        lines.append(self._writeKerning(classPairKerning, linesep))
+        lines.append("} kern;")
+        return linesep.join(lines)
+
+    def _writeKerning(self, kerning, linesep, enum=""):
+        """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:
+            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)
+
+
+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()