Start varLib, for gvar-style font variations

Right now, just reinventing some concepts form MutatorMath.objects
in a more compact (and more correct?) way.

Lib/fontTools/varLib/__init__.py

@@ -0,0 +1,73 @@
+"""Module for dealing with 'gvar'-style font variations,
+also known as run-time interpolation."""
+
+from __future__ import print_function, division, absolute_import
+from __future__ import unicode_literals
+from fontTools.misc.py23 import *
+
+
+def getMasterLocationsSortKeyFunc(locations, axisOrder=[]):
+	assert {} in locations, "Base master not found."
+	axisPoints = {}
+	for loc in locations:
+		if len(loc) != 1:
+			continue
+		axis = next(iter(loc))
+		value = loc[axis]
+		if axis not in axisPoints:
+			axisPoints[axis] = {0}
+		assert value not in axisPoints[axis]
+		axisPoints[axis].add(value)
+
+	def getKey(axisPoints, axisOrder):
+		def sign(v):
+			return -1 if v < 0 else +1 if v > 0 else 0
+		def key(loc):
+			rank = len(loc)
+			onPointAxes = [axis for axis,value in loc.items() if value in axisPoints[axis]]
+			orderedAxes = [axis for axis in axisOrder if axis in loc]
+			orderedAxes.extend([axis for axis in sorted(loc.keys()) if axis not in axisOrder])
+			return (
+				rank, # First, order by increasing rank
+				-len(onPointAxes), # Next, by decreasing number of onPoint axes
+				tuple(axisOrder.index(axis) if axis in axisOrder else 0x10000 for axis in orderedAxes), # Next, by known axes
+				tuple(orderedAxes), # Next, by all axes
+				tuple(sign(loc[axis]) for axis in orderedAxes), # Next, by signs of axis values
+				tuple(abs(loc[axis]) for axis in orderedAxes), # Next, by absolute value of axis values
+			)
+		return key
+
+	return getKey(axisPoints, axisOrder)
+
+
+def sortMasterLocations(locations, axisOrder=[]):
+	"""
+	Sort masters.
+	Locations must be in normalized space.  Ie. base master
+	is at origin (0).
+	"""
+
+	return sorted(locations, key=getMasterLocationsSortKeyFunc(locations, axisOrder=axisOrder))
+
+locations = [
+{'wght':100},
+{'wght':-100},
+{'wght':-180},
+{'wdth':+.3},
+{'wght':+120,'wdth':.3},
+{'wght':+120,'wdth':.2},
+{'wght':+180,'wdth':.3},
+{'wght':+180},
+{},
+]
+from pprint import pprint
+assert sortMasterLocations(locations, axisOrder=['wght']) == \
+[{},
+ {u'wght': -100},
+ {u'wght': -180},
+ {u'wght': 100},
+ {u'wght': 180},
+ {u'wdth': 0.3},
+ {u'wdth': 0.3, u'wght': 180},
+ {u'wdth': 0.3, u'wght': 120},
+ {u'wdth': 0.2, u'wght': 120}]