/usr/lib/python2.7/dist-packages/FontTools/fontTools/ttLib/tables/_g_v_a_r.py is in fonttools 3.0-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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from fontTools.misc.py23 import *
from fontTools import ttLib
from fontTools.misc import sstruct
from fontTools.misc.fixedTools import fixedToFloat, floatToFixed
from fontTools.misc.textTools import safeEval
from fontTools.ttLib import TTLibError
from . import DefaultTable
import array
import io
import sys
import struct
# Apple's documentation of 'gvar':
# https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6gvar.html
#
# FreeType2 source code for parsing 'gvar':
# http://git.savannah.gnu.org/cgit/freetype/freetype2.git/tree/src/truetype/ttgxvar.c
GVAR_HEADER_FORMAT = """
> # big endian
version: H
reserved: H
axisCount: H
sharedCoordCount: H
offsetToCoord: I
glyphCount: H
flags: H
offsetToData: I
"""
GVAR_HEADER_SIZE = sstruct.calcsize(GVAR_HEADER_FORMAT)
TUPLES_SHARE_POINT_NUMBERS = 0x8000
TUPLE_COUNT_MASK = 0x0fff
EMBEDDED_TUPLE_COORD = 0x8000
INTERMEDIATE_TUPLE = 0x4000
PRIVATE_POINT_NUMBERS = 0x2000
TUPLE_INDEX_MASK = 0x0fff
DELTAS_ARE_ZERO = 0x80
DELTAS_ARE_WORDS = 0x40
DELTA_RUN_COUNT_MASK = 0x3f
POINTS_ARE_WORDS = 0x80
POINT_RUN_COUNT_MASK = 0x7f
class table__g_v_a_r(DefaultTable.DefaultTable):
dependencies = ["fvar", "glyf"]
def compile(self, ttFont):
axisTags = [axis.axisTag for axis in ttFont["fvar"].axes]
sharedCoords = self.compileSharedCoords_(axisTags)
sharedCoordIndices = {coord:i for i, coord in enumerate(sharedCoords)}
sharedCoordSize = sum([len(c) for c in sharedCoords])
compiledGlyphs = self.compileGlyphs_(ttFont, axisTags, sharedCoordIndices)
offset = 0
offsets = []
for glyph in compiledGlyphs:
offsets.append(offset)
offset += len(glyph)
offsets.append(offset)
compiledOffsets, tableFormat = self.compileOffsets_(offsets)
header = {}
header["version"] = self.version
header["reserved"] = self.reserved
header["axisCount"] = len(axisTags)
header["sharedCoordCount"] = len(sharedCoords)
header["offsetToCoord"] = GVAR_HEADER_SIZE + len(compiledOffsets)
header["glyphCount"] = len(compiledGlyphs)
header["flags"] = tableFormat
header["offsetToData"] = header["offsetToCoord"] + sharedCoordSize
compiledHeader = sstruct.pack(GVAR_HEADER_FORMAT, header)
result = [compiledHeader, compiledOffsets]
result.extend(sharedCoords)
result.extend(compiledGlyphs)
return bytesjoin(result)
def compileSharedCoords_(self, axisTags):
coordCount = {}
for variations in self.variations.values():
for gvar in variations:
coord = gvar.compileCoord(axisTags)
coordCount[coord] = coordCount.get(coord, 0) + 1
sharedCoords = [(count, coord) for (coord, count) in coordCount.items() if count > 1]
sharedCoords.sort(reverse=True)
MAX_NUM_SHARED_COORDS = TUPLE_INDEX_MASK + 1
sharedCoords = sharedCoords[:MAX_NUM_SHARED_COORDS]
return [c[1] for c in sharedCoords] # Strip off counts.
def compileGlyphs_(self, ttFont, axisTags, sharedCoordIndices):
result = []
for glyphName in ttFont.getGlyphOrder():
glyph = ttFont["glyf"][glyphName]
numPointsInGlyph = self.getNumPoints_(glyph)
result.append(self.compileGlyph_(glyphName, numPointsInGlyph, axisTags, sharedCoordIndices))
return result
def compileGlyph_(self, glyphName, numPointsInGlyph, axisTags, sharedCoordIndices):
variations = self.variations.get(glyphName, [])
variations = [v for v in variations if v.hasImpact()]
if len(variations) == 0:
return b""
# Each glyph variation tuples modifies a set of control points. To indicate
# which exact points are getting modified, a single tuple can either refer
# to a shared set of points, or the tuple can supply its private point numbers.
# Because the impact of sharing can be positive (no need for a private point list)
# or negative (need to supply 0,0 deltas for unused points), it is not obvious
# how to determine which tuples should take their points from the shared
# pool versus have their own. Perhaps we should resort to brute force,
# and try all combinations? However, if a glyph has n variation tuples,
# we would need to try 2^n combinations (because each tuple may or may not
# be part of the shared set). How many variations tuples do glyphs have?
#
# Skia.ttf: {3: 1, 5: 11, 6: 41, 7: 62, 8: 387, 13: 1, 14: 3}
# JamRegular.ttf: {3: 13, 4: 122, 5: 1, 7: 4, 8: 1, 9: 1, 10: 1}
# BuffaloGalRegular.ttf: {1: 16, 2: 13, 4: 2, 5: 4, 6: 19, 7: 1, 8: 3, 9: 18}
# (Reading example: In Skia.ttf, 41 glyphs have 6 variation tuples).
#
# Is this even worth optimizing? If we never use a shared point list,
# the private lists will consume 112K for Skia, 5K for BuffaloGalRegular,
# and 15K for JamRegular. If we always use a shared point list,
# the shared lists will consume 16K for Skia, 3K for BuffaloGalRegular,
# and 10K for JamRegular. However, in the latter case the delta arrays
# will become larger, but I haven't yet measured by how much. From
# gut feeling (which may be wrong), the optimum is to share some but
# not all points; however, then we would need to try all combinations.
#
# For the time being, we try two variants and then pick the better one:
# (a) each tuple supplies its own private set of points;
# (b) all tuples refer to a shared set of points, which consists of
# "every control point in the glyph".
allPoints = set(range(numPointsInGlyph))
tuples = []
data = []
someTuplesSharePoints = False
for gvar in variations:
privateTuple, privateData = gvar.compile(axisTags, sharedCoordIndices, sharedPoints=None)
sharedTuple, sharedData = gvar.compile(axisTags, sharedCoordIndices, sharedPoints=allPoints)
# TODO: If we use shared points, Apple MacOS X 10.9.5 cannot display our fonts.
# This is probably a problem with our code; find the problem and fix it.
#if (len(sharedTuple) + len(sharedData)) < (len(privateTuple) + len(privateData)):
if False:
tuples.append(sharedTuple)
data.append(sharedData)
someTuplesSharePoints = True
else:
tuples.append(privateTuple)
data.append(privateData)
if someTuplesSharePoints:
data = bytechr(0) + bytesjoin(data) # 0x00 = "all points in glyph"
tupleCount = TUPLES_SHARE_POINT_NUMBERS | len(tuples)
else:
data = bytesjoin(data)
tupleCount = len(tuples)
tuples = bytesjoin(tuples)
result = struct.pack(">HH", tupleCount, 4 + len(tuples)) + tuples + data
if len(result) % 2 != 0:
result = result + b"\0" # padding
return result
def decompile(self, data, ttFont):
axisTags = [axis.axisTag for axis in ttFont["fvar"].axes]
glyphs = ttFont.getGlyphOrder()
sstruct.unpack(GVAR_HEADER_FORMAT, data[0:GVAR_HEADER_SIZE], self)
assert len(glyphs) == self.glyphCount
assert len(axisTags) == self.axisCount
offsets = self.decompileOffsets_(data[GVAR_HEADER_SIZE:], tableFormat=(self.flags & 1), glyphCount=self.glyphCount)
sharedCoords = self.decompileSharedCoords_(axisTags, data)
self.variations = {}
for i in range(self.glyphCount):
glyphName = glyphs[i]
glyph = ttFont["glyf"][glyphName]
numPointsInGlyph = self.getNumPoints_(glyph)
gvarData = data[self.offsetToData + offsets[i] : self.offsetToData + offsets[i + 1]]
self.variations[glyphName] = \
self.decompileGlyph_(numPointsInGlyph, sharedCoords, axisTags, gvarData)
def decompileSharedCoords_(self, axisTags, data):
result, _pos = GlyphVariation.decompileCoords_(axisTags, self.sharedCoordCount, data, self.offsetToCoord)
return result
@staticmethod
def decompileOffsets_(data, tableFormat, glyphCount):
if tableFormat == 0:
# Short format: array of UInt16
offsets = array.array("H")
offsetsSize = (glyphCount + 1) * 2
else:
# Long format: array of UInt32
offsets = array.array("I")
offsetsSize = (glyphCount + 1) * 4
offsets.fromstring(data[0 : offsetsSize])
if sys.byteorder != "big":
offsets.byteswap()
# In the short format, offsets need to be multiplied by 2.
# This is not documented in Apple's TrueType specification,
# but can be inferred from the FreeType implementation, and
# we could verify it with two sample GX fonts.
if tableFormat == 0:
offsets = [off * 2 for off in offsets]
return offsets
@staticmethod
def compileOffsets_(offsets):
"""Packs a list of offsets into a 'gvar' offset table.
Returns a pair (bytestring, tableFormat). Bytestring is the
packed offset table. Format indicates whether the table
uses short (tableFormat=0) or long (tableFormat=1) integers.
The returned tableFormat should get packed into the flags field
of the 'gvar' header.
"""
assert len(offsets) >= 2
for i in range(1, len(offsets)):
assert offsets[i - 1] <= offsets[i]
if max(offsets) <= 0xffff * 2:
packed = array.array("H", [n >> 1 for n in offsets])
tableFormat = 0
else:
packed = array.array("I", offsets)
tableFormat = 1
if sys.byteorder != "big":
packed.byteswap()
return (packed.tostring(), tableFormat)
def decompileGlyph_(self, numPointsInGlyph, sharedCoords, axisTags, data):
if len(data) < 4:
return []
numAxes = len(axisTags)
tuples = []
flags, offsetToData = struct.unpack(">HH", data[:4])
pos = 4
dataPos = offsetToData
if (flags & TUPLES_SHARE_POINT_NUMBERS) != 0:
sharedPoints, dataPos = GlyphVariation.decompilePoints_(numPointsInGlyph, data, dataPos)
else:
sharedPoints = []
for _ in range(flags & TUPLE_COUNT_MASK):
dataSize, flags = struct.unpack(">HH", data[pos:pos+4])
tupleSize = GlyphVariation.getTupleSize_(flags, numAxes)
tupleData = data[pos : pos + tupleSize]
pointDeltaData = data[dataPos : dataPos + dataSize]
tuples.append(self.decompileTuple_(numPointsInGlyph, sharedCoords, sharedPoints, axisTags, tupleData, pointDeltaData))
pos += tupleSize
dataPos += dataSize
return tuples
@staticmethod
def decompileTuple_(numPointsInGlyph, sharedCoords, sharedPoints, axisTags, data, tupleData):
flags = struct.unpack(">H", data[2:4])[0]
pos = 4
if (flags & EMBEDDED_TUPLE_COORD) == 0:
coord = sharedCoords[flags & TUPLE_INDEX_MASK]
else:
coord, pos = GlyphVariation.decompileCoord_(axisTags, data, pos)
if (flags & INTERMEDIATE_TUPLE) != 0:
minCoord, pos = GlyphVariation.decompileCoord_(axisTags, data, pos)
maxCoord, pos = GlyphVariation.decompileCoord_(axisTags, data, pos)
else:
minCoord, maxCoord = table__g_v_a_r.computeMinMaxCoord_(coord)
axes = {}
for axis in axisTags:
coords = minCoord[axis], coord[axis], maxCoord[axis]
if coords != (0.0, 0.0, 0.0):
axes[axis] = coords
pos = 0
if (flags & PRIVATE_POINT_NUMBERS) != 0:
points, pos = GlyphVariation.decompilePoints_(numPointsInGlyph, tupleData, pos)
else:
points = sharedPoints
deltas_x, pos = GlyphVariation.decompileDeltas_(len(points), tupleData, pos)
deltas_y, pos = GlyphVariation.decompileDeltas_(len(points), tupleData, pos)
deltas = [None] * numPointsInGlyph
for p, x, y in zip(points, deltas_x, deltas_y):
deltas[p] = (x, y)
return GlyphVariation(axes, deltas)
@staticmethod
def computeMinMaxCoord_(coord):
minCoord = {}
maxCoord = {}
for (axis, value) in coord.items():
minCoord[axis] = min(value, 0.0) # -0.3 --> -0.3; 0.7 --> 0.0
maxCoord[axis] = max(value, 0.0) # -0.3 --> 0.0; 0.7 --> 0.7
return (minCoord, maxCoord)
def toXML(self, writer, ttFont, progress=None):
writer.simpletag("version", value=self.version)
writer.newline()
writer.simpletag("reserved", value=self.reserved)
writer.newline()
axisTags = [axis.axisTag for axis in ttFont["fvar"].axes]
for glyphName in ttFont.getGlyphOrder():
variations = self.variations.get(glyphName)
if not variations:
continue
writer.begintag("glyphVariations", glyph=glyphName)
writer.newline()
for gvar in variations:
gvar.toXML(writer, axisTags)
writer.endtag("glyphVariations")
writer.newline()
def fromXML(self, name, attrs, content, ttFont):
if name == "version":
self.version = safeEval(attrs["value"])
elif name == "reserved":
self.reserved = safeEval(attrs["value"])
elif name == "glyphVariations":
if not hasattr(self, "variations"):
self.variations = {}
glyphName = attrs["glyph"]
glyph = ttFont["glyf"][glyphName]
numPointsInGlyph = self.getNumPoints_(glyph)
glyphVariations = []
for element in content:
if isinstance(element, tuple):
name, attrs, content = element
if name == "tuple":
gvar = GlyphVariation({}, [None] * numPointsInGlyph)
glyphVariations.append(gvar)
for tupleElement in content:
if isinstance(tupleElement, tuple):
tupleName, tupleAttrs, tupleContent = tupleElement
gvar.fromXML(tupleName, tupleAttrs, tupleContent)
self.variations[glyphName] = glyphVariations
@staticmethod
def getNumPoints_(glyph):
NUM_PHANTOM_POINTS = 4
if glyph.isComposite():
return len(glyph.components) + NUM_PHANTOM_POINTS
else:
# Empty glyphs (eg. space, nonmarkingreturn) have no "coordinates" attribute.
return len(getattr(glyph, "coordinates", [])) + NUM_PHANTOM_POINTS
class GlyphVariation(object):
def __init__(self, axes, coordinates):
self.axes = axes
self.coordinates = coordinates
def __repr__(self):
axes = ",".join(sorted(["%s=%s" % (name, value) for (name, value) in self.axes.items()]))
return "<GlyphVariation %s %s>" % (axes, self.coordinates)
def __eq__(self, other):
return self.coordinates == other.coordinates and self.axes == other.axes
def getUsedPoints(self):
result = set()
for i, point in enumerate(self.coordinates):
if point is not None:
result.add(i)
return result
def hasImpact(self):
"""Returns True if this GlyphVariation has any visible impact.
If the result is False, the GlyphVariation can be omitted from the font
without making any visible difference.
"""
for c in self.coordinates:
if c is not None:
return True
return False
def toXML(self, writer, axisTags):
writer.begintag("tuple")
writer.newline()
for axis in axisTags:
value = self.axes.get(axis)
if value is not None:
minValue, value, maxValue = value
defaultMinValue = min(value, 0.0) # -0.3 --> -0.3; 0.7 --> 0.0
defaultMaxValue = max(value, 0.0) # -0.3 --> 0.0; 0.7 --> 0.7
if minValue == defaultMinValue and maxValue == defaultMaxValue:
writer.simpletag("coord", axis=axis, value=value)
else:
writer.simpletag("coord", axis=axis, value=value, min=minValue, max=maxValue)
writer.newline()
wrote_any_points = False
for i, point in enumerate(self.coordinates):
if point is not None:
writer.simpletag("delta", pt=i, x=point[0], y=point[1])
writer.newline()
wrote_any_points = True
if not wrote_any_points:
writer.comment("no deltas")
writer.newline()
writer.endtag("tuple")
writer.newline()
def fromXML(self, name, attrs, _content):
if name == "coord":
axis = attrs["axis"]
value = float(attrs["value"])
defaultMinValue = min(value, 0.0) # -0.3 --> -0.3; 0.7 --> 0.0
defaultMaxValue = max(value, 0.0) # -0.3 --> 0.0; 0.7 --> 0.7
minValue = float(attrs.get("min", defaultMinValue))
maxValue = float(attrs.get("max", defaultMaxValue))
self.axes[axis] = (minValue, value, maxValue)
elif name == "delta":
point = safeEval(attrs["pt"])
x = safeEval(attrs["x"])
y = safeEval(attrs["y"])
self.coordinates[point] = (x, y)
def compile(self, axisTags, sharedCoordIndices, sharedPoints):
tupleData = []
coord = self.compileCoord(axisTags)
if coord in sharedCoordIndices:
flags = sharedCoordIndices[coord]
else:
flags = EMBEDDED_TUPLE_COORD
tupleData.append(coord)
intermediateCoord = self.compileIntermediateCoord(axisTags)
if intermediateCoord is not None:
flags |= INTERMEDIATE_TUPLE
tupleData.append(intermediateCoord)
if sharedPoints is not None:
auxData = self.compileDeltas(sharedPoints)
else:
flags |= PRIVATE_POINT_NUMBERS
points = self.getUsedPoints()
numPointsInGlyph = len(self.coordinates)
auxData = self.compilePoints(points, numPointsInGlyph) + self.compileDeltas(points)
tupleData = struct.pack('>HH', len(auxData), flags) + bytesjoin(tupleData)
return (tupleData, auxData)
def compileCoord(self, axisTags):
result = []
for axis in axisTags:
_minValue, value, _maxValue = self.axes.get(axis, (0.0, 0.0, 0.0))
result.append(struct.pack(">h", floatToFixed(value, 14)))
return bytesjoin(result)
def compileIntermediateCoord(self, axisTags):
needed = False
for axis in axisTags:
minValue, value, maxValue = self.axes.get(axis, (0.0, 0.0, 0.0))
defaultMinValue = min(value, 0.0) # -0.3 --> -0.3; 0.7 --> 0.0
defaultMaxValue = max(value, 0.0) # -0.3 --> 0.0; 0.7 --> 0.7
if (minValue != defaultMinValue) or (maxValue != defaultMaxValue):
needed = True
break
if not needed:
return None
minCoords = []
maxCoords = []
for axis in axisTags:
minValue, value, maxValue = self.axes.get(axis, (0.0, 0.0, 0.0))
minCoords.append(struct.pack(">h", floatToFixed(minValue, 14)))
maxCoords.append(struct.pack(">h", floatToFixed(maxValue, 14)))
return bytesjoin(minCoords + maxCoords)
@staticmethod
def decompileCoord_(axisTags, data, offset):
coord = {}
pos = offset
for axis in axisTags:
coord[axis] = fixedToFloat(struct.unpack(">h", data[pos:pos+2])[0], 14)
pos += 2
return coord, pos
@staticmethod
def decompileCoords_(axisTags, numCoords, data, offset):
result = []
pos = offset
for _ in range(numCoords):
coord, pos = GlyphVariation.decompileCoord_(axisTags, data, pos)
result.append(coord)
return result, pos
@staticmethod
def compilePoints(points, numPointsInGlyph):
# If the set consists of all points in the glyph, it gets encoded with
# a special encoding: a single zero byte.
if len(points) == numPointsInGlyph:
return b"\0"
# In the 'gvar' table, the packing of point numbers is a little surprising.
# It consists of multiple runs, each being a delta-encoded list of integers.
# For example, the point set {17, 18, 19, 20, 21, 22, 23} gets encoded as
# [6, 17, 1, 1, 1, 1, 1, 1]. The first value (6) is the run length minus 1.
# There are two types of runs, with values being either 8 or 16 bit unsigned
# integers.
points = list(points)
points.sort()
numPoints = len(points)
# The binary representation starts with the total number of points in the set,
# encoded into one or two bytes depending on the value.
if numPoints < 0x80:
result = [bytechr(numPoints)]
else:
result = [bytechr((numPoints >> 8) | 0x80) + bytechr(numPoints & 0xff)]
MAX_RUN_LENGTH = 127
pos = 0
while pos < numPoints:
run = io.BytesIO()
runLength = 0
lastValue = 0
useByteEncoding = (points[pos] <= 0xff)
while pos < numPoints and runLength <= MAX_RUN_LENGTH:
curValue = points[pos]
delta = curValue - lastValue
if useByteEncoding and delta > 0xff:
# we need to start a new run (which will not use byte encoding)
break
if useByteEncoding:
run.write(bytechr(delta))
else:
run.write(bytechr(delta >> 8))
run.write(bytechr(delta & 0xff))
lastValue = curValue
pos += 1
runLength += 1
if useByteEncoding:
runHeader = bytechr(runLength - 1)
else:
runHeader = bytechr((runLength - 1) | POINTS_ARE_WORDS)
result.append(runHeader)
result.append(run.getvalue())
return bytesjoin(result)
@staticmethod
def decompilePoints_(numPointsInGlyph, data, offset):
"""(numPointsInGlyph, data, offset) --> ([point1, point2, ...], newOffset)"""
pos = offset
numPointsInData = byteord(data[pos])
pos += 1
if (numPointsInData & POINTS_ARE_WORDS) != 0:
numPointsInData = (numPointsInData & POINT_RUN_COUNT_MASK) << 8 | byteord(data[pos])
pos += 1
if numPointsInData == 0:
return (range(numPointsInGlyph), pos)
result = []
while len(result) < numPointsInData:
runHeader = byteord(data[pos])
pos += 1
numPointsInRun = (runHeader & POINT_RUN_COUNT_MASK) + 1
point = 0
if (runHeader & POINTS_ARE_WORDS) == 0:
for _ in range(numPointsInRun):
point += byteord(data[pos])
pos += 1
result.append(point)
else:
for _ in range(numPointsInRun):
point += struct.unpack(">H", data[pos:pos+2])[0]
pos += 2
result.append(point)
if max(result) >= numPointsInGlyph:
raise TTLibError("malformed 'gvar' table")
return (result, pos)
def compileDeltas(self, points):
deltaX = []
deltaY = []
for p in sorted(list(points)):
c = self.coordinates[p]
if c is not None:
deltaX.append(c[0])
deltaY.append(c[1])
return self.compileDeltaValues_(deltaX) + self.compileDeltaValues_(deltaY)
@staticmethod
def compileDeltaValues_(deltas):
"""[value1, value2, value3, ...] --> bytestring
Emits a sequence of runs. Each run starts with a
byte-sized header whose 6 least significant bits
(header & 0x3F) indicate how many values are encoded
in this run. The stored length is the actual length
minus one; run lengths are thus in the range [1..64].
If the header byte has its most significant bit (0x80)
set, all values in this run are zero, and no data
follows. Otherwise, the header byte is followed by
((header & 0x3F) + 1) signed values. If (header &
0x40) is clear, the delta values are stored as signed
bytes; if (header & 0x40) is set, the delta values are
signed 16-bit integers.
""" # Explaining the format because the 'gvar' spec is hard to understand.
stream = io.BytesIO()
pos = 0
while pos < len(deltas):
value = deltas[pos]
if value == 0:
pos = GlyphVariation.encodeDeltaRunAsZeroes_(deltas, pos, stream)
elif value >= -128 and value <= 127:
pos = GlyphVariation.encodeDeltaRunAsBytes_(deltas, pos, stream)
else:
pos = GlyphVariation.encodeDeltaRunAsWords_(deltas, pos, stream)
return stream.getvalue()
@staticmethod
def encodeDeltaRunAsZeroes_(deltas, offset, stream):
runLength = 0
pos = offset
numDeltas = len(deltas)
while pos < numDeltas and runLength < 64 and deltas[pos] == 0:
pos += 1
runLength += 1
assert runLength >= 1 and runLength <= 64
stream.write(bytechr(DELTAS_ARE_ZERO | (runLength - 1)))
return pos
@staticmethod
def encodeDeltaRunAsBytes_(deltas, offset, stream):
runLength = 0
pos = offset
numDeltas = len(deltas)
while pos < numDeltas and runLength < 64:
value = deltas[pos]
if value < -128 or value > 127:
break
# Within a byte-encoded run of deltas, a single zero
# is best stored literally as 0x00 value. However,
# if are two or more zeroes in a sequence, it is
# better to start a new run. For example, the sequence
# of deltas [15, 15, 0, 15, 15] becomes 6 bytes
# (04 0F 0F 00 0F 0F) when storing the zero value
# literally, but 7 bytes (01 0F 0F 80 01 0F 0F)
# when starting a new run.
if value == 0 and pos+1 < numDeltas and deltas[pos+1] == 0:
break
pos += 1
runLength += 1
assert runLength >= 1 and runLength <= 64
stream.write(bytechr(runLength - 1))
for i in range(offset, pos):
stream.write(struct.pack('b', deltas[i]))
return pos
@staticmethod
def encodeDeltaRunAsWords_(deltas, offset, stream):
runLength = 0
pos = offset
numDeltas = len(deltas)
while pos < numDeltas and runLength < 64:
value = deltas[pos]
# Within a word-encoded run of deltas, it is easiest
# to start a new run (with a different encoding)
# whenever we encounter a zero value. For example,
# the sequence [0x6666, 0, 0x7777] needs 7 bytes when
# storing the zero literally (42 66 66 00 00 77 77),
# and equally 7 bytes when starting a new run
# (40 66 66 80 40 77 77).
if value == 0:
break
# Within a word-encoded run of deltas, a single value
# in the range (-128..127) should be encoded literally
# because it is more compact. For example, the sequence
# [0x6666, 2, 0x7777] becomes 7 bytes when storing
# the value literally (42 66 66 00 02 77 77), but 8 bytes
# when starting a new run (40 66 66 00 02 40 77 77).
isByteEncodable = lambda value: value >= -128 and value <= 127
if isByteEncodable(value) and pos+1 < numDeltas and isByteEncodable(deltas[pos+1]):
break
pos += 1
runLength += 1
assert runLength >= 1 and runLength <= 64
stream.write(bytechr(DELTAS_ARE_WORDS | (runLength - 1)))
for i in range(offset, pos):
stream.write(struct.pack('>h', deltas[i]))
return pos
@staticmethod
def decompileDeltas_(numDeltas, data, offset):
"""(numDeltas, data, offset) --> ([delta, delta, ...], newOffset)"""
result = []
pos = offset
while len(result) < numDeltas:
runHeader = byteord(data[pos])
pos += 1
numDeltasInRun = (runHeader & DELTA_RUN_COUNT_MASK) + 1
if (runHeader & DELTAS_ARE_ZERO) != 0:
result.extend([0] * numDeltasInRun)
elif (runHeader & DELTAS_ARE_WORDS) != 0:
for _ in range(numDeltasInRun):
result.append(struct.unpack(">h", data[pos:pos+2])[0])
pos += 2
else:
for _ in range(numDeltasInRun):
result.append(struct.unpack(">b", data[pos:pos+1])[0])
pos += 1
assert len(result) == numDeltas
return (result, pos)
@staticmethod
def getTupleSize_(flags, axisCount):
size = 4
if (flags & EMBEDDED_TUPLE_COORD) != 0:
size += axisCount * 2
if (flags & INTERMEDIATE_TUPLE) != 0:
size += axisCount * 4
return size
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