[Snippets] add otf2ttf.py using cu2qu for CFF -> TrueType conversion

See discussion at https://github.com/fonttools/fonttools/issues/802

Derived from:
https://github.com/googlei18n/cu2qu/issues/47

Snippets/otf2ttf.py

@@ -0,0 +1,91 @@
+#!/usr/bin/env python
+from __future__ import print_function, division, absolute_import
+import sys
+from fontTools.ttLib import TTFont, newTable
+from cu2qu.pens import Cu2QuPen
+from fontTools.pens.ttGlyphPen import TTGlyphPen
+from fontTools.ttx import makeOutputFileName
+import argparse
+
+
+# default approximation error, measured in UPEM
+MAX_ERR = 1.0
+
+# default 'post' table format
+POST_FORMAT = 2.0
+
+# assuming the input contours' direction is correctly set (counter-clockwise),
+# we just flip it to clockwise
+REVERSE_DIRECTION = True
+
+
+def glyphs_to_quadratic(
+        glyphs, max_err=MAX_ERR, reverse_direction=REVERSE_DIRECTION):
+    quadGlyphs = {}
+    for gname in glyphs.keys():
+        glyph = glyphs[gname]
+        ttPen = TTGlyphPen(glyphs)
+        cu2quPen = Cu2QuPen(ttPen, max_err,
+                            reverse_direction=reverse_direction)
+        glyph.draw(cu2quPen)
+        quadGlyphs[gname] = ttPen.glyph()
+    return quadGlyphs
+
+
+def otf_to_ttf(ttFont, post_format=POST_FORMAT, **kwargs):
+    assert ttFont.sfntVersion == "OTTO"
+    assert "CFF " in ttFont
+
+    glyphOrder = ttFont.getGlyphOrder()
+
+    ttFont["loca"] = newTable("loca")
+    ttFont["glyf"] = glyf = newTable("glyf")
+    glyf.glyphOrder = glyphOrder
+    glyf.glyphs = glyphs_to_quadratic(ttFont.getGlyphSet(), **kwargs)
+    del ttFont["CFF "]
+
+    ttFont["maxp"] = maxp = newTable("maxp")
+    maxp.tableVersion = 0x00010000
+    maxp.maxZones = 1
+    maxp.maxTwilightPoints = 0
+    maxp.maxStorage = 0
+    maxp.maxFunctionDefs = 0
+    maxp.maxInstructionDefs = 0
+    maxp.maxStackElements = 0
+    maxp.maxSizeOfInstructions = 0
+    maxp.maxComponentElements = max(
+        len(g.components if hasattr(g, 'components') else [])
+        for g in glyf.glyphs.values())
+
+    post = ttFont["post"]
+    post.formatType = post_format
+    post.extraNames = []
+    post.mapping = {}
+    post.glyphOrder = glyphOrder
+
+    ttFont.sfntVersion = "\000\001\000\000"
+
+
+def main(args=None):
+    parser = argparse.ArgumentParser()
+    parser.add_argument("input", metavar="INPUT")
+    parser.add_argument("-o", "--output")
+    parser.add_argument("-e", "--max-error", type=float, default=MAX_ERR)
+    parser.add_argument("--post-format", type=float, default=POST_FORMAT)
+    parser.add_argument(
+        "--keep-direction", dest='reverse_direction', action='store_false')
+    options = parser.parse_args(args)
+
+    output = options.output or makeOutputFileName(options.input,
+                                                  outputDir=None,
+                                                  extension='.ttf')
+    font = TTFont(options.input)
+    otf_to_ttf(font,
+               post_format=options.post_format,
+               max_err=options.max_error,
+               reverse_direction=options.reverse_direction)
+    font.save(output)
+
+
+if __name__ == "__main__":
+    sys.exit(main())