woff2: add support for hmtx transformation
no tests yet fixup
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Cosimo Lupo
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0162446f4c
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deaeb909a7
@ -98,6 +98,8 @@ class WOFF2Reader(SFNTReader):
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data = self._reconstructGlyf(rawData, padding)
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elif tag == 'loca':
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data = self._reconstructLoca()
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elif tag == 'hmtx':
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data = self._reconstructHmtx(rawData)
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else:
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raise TTLibError("transform for table '%s' is unknown" % tag)
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return data
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@ -128,6 +130,34 @@ class WOFF2Reader(SFNTReader):
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% (self.tables['loca'].origLength, len(data)))
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return data
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def _reconstructHmtx(self, data):
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""" Return reconstructed hmtx table data. """
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# Before reconstructing 'hmtx' table we need to parse other tables:
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# 'glyf' is required for reconstructing the sidebearings from the glyphs'
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# bounding box; 'hhea' is needed for the numberOfHMetrics field.
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if "glyf" in self.flavorData.transformedTables:
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# transformed 'glyf' table is self-contained, thus 'loca' not needed
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tableDependencies = ("maxp", "hhea", "glyf")
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else:
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# decompiling untransformed 'glyf' requires 'loca', which requires 'head'
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tableDependencies = ("maxp", "head", "hhea", "loca", "glyf")
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for tag in tableDependencies:
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self._decompileTable(tag)
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hmtxTable = self.ttFont["hmtx"] = WOFF2HmtxTable()
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hmtxTable.reconstruct(data, self.ttFont)
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data = hmtxTable.compile(self.ttFont)
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return data
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def _decompileTable(self, tag):
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"""Decompile table data and store it inside self.ttFont."""
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data = self[tag]
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if self.ttFont.isLoaded(tag):
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return self.ttFont[tag]
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tableClass = getTableClass(tag)
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table = tableClass(tag)
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self.ttFont.tables[tag] = table
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table.decompile(data, self.ttFont)
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class WOFF2Writer(SFNTWriter):
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@ -257,6 +287,8 @@ class WOFF2Writer(SFNTWriter):
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tableClass = WOFF2LocaTable
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elif tag == 'glyf':
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tableClass = WOFF2GlyfTable
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elif tag == 'hmtx':
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tableClass = WOFF2HmtxTable
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else:
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tableClass = getTableClass(tag)
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table = tableClass(tag)
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@ -286,19 +318,13 @@ class WOFF2Writer(SFNTWriter):
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def _transformTables(self):
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"""Return transformed font data."""
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transformedTables = self.flavorData.transformedTables
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if (
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"glyf" in transformedTables and "loca" not in transformedTables
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or "loca" in transformedTables and "glyf" not in transformedTables
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):
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raise ValueError(
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"'glyf' and 'loca' must be transformed (or not) together"
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)
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for tag, entry in self.tables.items():
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data = None
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if tag in transformedTables:
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data = self.transformTable(tag)
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if data is not None:
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entry.transformed = True
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else:
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if data is None:
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# pass-through the table data without transformation
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data = entry.data
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entry.transformed = False
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@ -310,7 +336,9 @@ class WOFF2Writer(SFNTWriter):
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return fontData
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def transformTable(self, tag):
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"""Return transformed table data."""
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"""Return transformed table data, or None if some pre-conditions aren't
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met -- in which case, the non-transformed table data will be used.
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"""
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if tag == "loca":
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data = b""
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elif tag == "glyf":
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@ -318,6 +346,13 @@ class WOFF2Writer(SFNTWriter):
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self._decompileTable(tag)
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glyfTable = self.ttFont['glyf']
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data = glyfTable.transform(self.ttFont)
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elif tag == "hmtx":
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if "glyf" not in self.tables:
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return
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for tag in ("maxp", "head", "hhea", "loca", "glyf", "hmtx"):
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self._decompileTable(tag)
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hmtxTable = self.ttFont["hmtx"]
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data = hmtxTable.transform(self.ttFont) # can be None
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else:
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raise TTLibError("Transform for table '%s' is unknown" % tag)
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return data
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@ -931,6 +966,164 @@ class WOFF2GlyfTable(getTableClass('glyf')):
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self.glyphStream += triplets.tostring()
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class WOFF2HmtxTable(getTableClass("hmtx")):
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def __init__(self, tag=None):
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self.tableTag = Tag(tag or 'hmtx')
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def reconstruct(self, data, ttFont):
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flags, = struct.unpack(">B", data[:1])
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data = data[1:]
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if flags & 0b11111100 != 0:
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raise TTLibError("Bits 2-7 of '%s' flags are reserved" % self.tableTag)
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# When bit 0 is _not_ set, the lsb[] array is present
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hasLsbArray = flags & 1 == 0
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# When bit 1 is _not_ set, the leftSideBearing[] array is present
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hasLeftSideBearingArray = flags & 2 == 0
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if hasLsbArray and hasLeftSideBearingArray:
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raise TTLibError(
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"either bits 0 or 1 (or both) must set in transformed '%s' flags"
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% self.tableTag
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)
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glyfTable = ttFont["glyf"]
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headerTable = ttFont["hhea"]
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glyphOrder = glyfTable.glyphOrder
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numGlyphs = len(glyphOrder)
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numberOfHMetrics = min(int(headerTable.numberOfHMetrics), numGlyphs)
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assert len(data) >= 2 * numberOfHMetrics
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advanceWidthArray = array.array("H", data[:2 * numberOfHMetrics])
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if sys.byteorder != "big":
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advanceWidthArray.byteswap()
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data = data[2 * numberOfHMetrics:]
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if hasLsbArray:
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assert len(data) >= 2 * numberOfHMetrics
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lsbArray = array.array("h", data[:2 * numberOfHMetrics])
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if sys.byteorder != "big":
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lsbArray.byteswap()
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data = data[2 * numberOfHMetrics:]
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else:
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# compute (proportional) glyphs' lsb from their xMin
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lsbArray = array.array("h")
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for i, glyphName in enumerate(glyphOrder):
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if i >= numberOfHMetrics:
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break
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glyph = glyfTable[glyphName]
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xMin = getattr(glyph, "xMin", 0)
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lsbArray.append(xMin)
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numberOfSideBearings = numGlyphs - numberOfHMetrics
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if hasLeftSideBearingArray:
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assert len(data) >= 2 * numberOfSideBearings
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leftSideBearingArray = array.array("h", data[:2 * numberOfSideBearings])
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if sys.byteorder != "big":
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leftSideBearingArray.byteswap()
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data = data[2 * numberOfSideBearings:]
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else:
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# compute (monospaced) glyphs' leftSideBearing from their xMin
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leftSideBearingArray = array.array("h")
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for i, glyphName in enumerate(glyphOrder):
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if i < numberOfHMetrics:
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continue
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glyph = glyfTable[glyphName]
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xMin = getattr(glyph, "xMin", 0)
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leftSideBearingArray.append(xMin)
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if data:
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raise TTLibError("too much '%s' table data" % self.tableTag)
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self.metrics = {}
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for i in range(numberOfHMetrics):
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glyphName = glyphOrder[i]
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advanceWidth, lsb = advanceWidthArray[i], lsbArray[i]
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self.metrics[glyphName] = (advanceWidth, lsb)
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lastAdvance = advanceWidthArray[-1]
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for i in range(numberOfSideBearings):
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glyphName = glyphOrder[i + numberOfHMetrics]
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self.metrics[glyphName] = (lastAdvance, leftSideBearingArray[i])
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def transform(self, ttFont):
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glyphOrder = ttFont.getGlyphOrder()
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glyf = ttFont["glyf"]
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hhea = ttFont["hhea"]
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numberOfHMetrics = hhea.numberOfHMetrics
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# check if any of the proportional glyphs has left sidebearings that
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# differ from their xMin bounding box values.
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hasLsbArray = False
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for i in range(numberOfHMetrics):
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glyphName = glyphOrder[i]
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lsb = self.metrics[glyphName][1]
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if lsb != getattr(glyf[glyphName], "xMin", 0):
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hasLsbArray = True
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break
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# do the same for the monospaced glyphs (if any) at the end of hmtx table
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hasLeftSideBearingArray = False
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for i in range(numberOfHMetrics, len(glyphOrder)):
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glyphName = glyphOrder[i]
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lsb = self.metrics[glyphName][1]
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if lsb != getattr(glyf[glyphName], "xMin", 0):
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hasLeftSideBearingArray = True
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break
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# if we need to encode both sidebearings arrays, then no transformation is
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# applicable, and we must use the untransformed hmtx data
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if hasLsbArray and hasLeftSideBearingArray:
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return
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# set bit 0 and 1 when the respective arrays are _not_ present
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flags = 0
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if not hasLsbArray:
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flags |= 1 << 0
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if not hasLeftSideBearingArray:
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flags |= 1 << 1
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data = struct.pack(">B", flags)
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advanceWidthArray = array.array(
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"H",
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[
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self.metrics[glyphName][0]
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for i, glyphName in enumerate(glyphOrder)
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if i < numberOfHMetrics
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]
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)
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if sys.byteorder != "big":
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advanceWidthArray.byteswap()
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data += advanceWidthArray.tostring()
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if hasLsbArray:
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lsbArray = array.array(
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"h",
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[
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self.metrics[glyphName][1]
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for i, glyphName in enumerate(glyphOrder)
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if i < numberOfHMetrics
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]
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)
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if sys.byteorder != "big":
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lsbArray.byteswap()
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data += lsbArray.tostring()
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if hasLeftSideBearingArray:
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leftSideBearingArray = array.array(
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"h",
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[
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self.metrics[glyphOrder[i]][1]
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for i in range(numberOfHMetrics, len(glyphOrder))
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]
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)
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if sys.byteorder != "big":
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leftSideBearingArray.byteswap()
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data += leftSideBearingArray.tostring()
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return data
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class WOFF2FlavorData(WOFFFlavorData):
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Flavor = 'woff2'
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@ -948,8 +1141,17 @@ class WOFF2FlavorData(WOFFFlavorData):
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raise TypeError(
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"'reader' and 'transformedTables' arguments are mutually exclusive"
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)
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if transformedTables is None:
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transformedTables = woff2TransformedTableTags
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else:
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if (
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"glyf" in transformedTables and "loca" not in transformedTables
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or "loca" in transformedTables and "glyf" not in transformedTables
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):
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raise ValueError(
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"'glyf' and 'loca' must be transformed (or not) together"
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)
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self.majorVersion = None
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self.minorVersion = None
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