[buildcff2vf] IndexError: list index out of range

[dy]

buildcff2vf command is failing on some particular glyph shapes. For interpolation purposes of roundness axis in wavefont, I need to have the following glyph shapes for different masters:

fontmake successfully compiles such font, but afdko errors with the following:

PS C:\projects\wavefont\masters> buildmasterotfs -d ./wavefont.designspace                                              makeotf [Note] Using features file at 'C:\projects\wavefont\masters\1_0_0.ufo\features.fea'.
makeotfexe [WARNING] <Wavefont> Negative internal leading: win.ascent + win.descent < unitsPerEm
Built release mode font 'C:\projects\wavefont\masters\1_0_0.otf' Revision 1.000
tx: --- C:/projects/wavefont/masters/1_0_0.otf
tx: (cfw) unhinted <_1>
tx: (cfw) unhinted <_1.clip>
makeotf [Note] Using features file at 'C:\projects\wavefont\masters\25_0_0.ufo\features.fea'.
makeotfexe [WARNING] <Wavefont> Negative internal leading: win.ascent + win.descent < unitsPerEm
Built release mode font 'C:\projects\wavefont\masters\25_0_0.otf' Revision 1.000
tx: --- C:/projects/wavefont/masters/25_0_0.otf
tx: (cfw) unhinted <_1>
tx: (cfw) unhinted <_1.clip>

PS C:\projects\wavefont\masters> buildcff2vf -c -k -d wavefont.designspace -o ./font/wavefont.otf                       Reading source fonts...
Checking outline compatibility in source fonts...
Traceback (most recent call last):
  File "c:\users\dfcre\appdata\local\programs\python\python39\lib\runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "c:\users\dfcre\appdata\local\programs\python\python39\lib\runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "C:\Users\dfcre\AppData\Local\Programs\Python\Python39\Scripts\buildcff2vf.exe\__main__.py", line 7, in <module>
  File "c:\users\dfcre\appdata\local\programs\python\python39\lib\site-packages\afdko\buildcff2vf.py", line 564, in main
    do_compatibility(vf, font_list, ds_data.base_idx)
  File "c:\users\dfcre\appdata\local\programs\python\python39\lib\site-packages\afdko\buildcff2vf.py", line 332, in do_compatibility
    region_charstring.draw(compat_pen)
  File "C:\Users\dfcre\AppData\Roaming\Python\Python39\site-packages\fontTools\misc\psCharStrings.py", line 982, in draw
    extractor.execute(self)
  File "C:\Users\dfcre\AppData\Roaming\Python\Python39\site-packages\fontTools\misc\psCharStrings.py", line 300, in execute
    rv = handler(index)
  File "C:\Users\dfcre\AppData\Roaming\Python\Python39\site-packages\fontTools\misc\psCharStrings.py", line 590, in op_rlineto
    self.rLineTo(point)
  File "C:\Users\dfcre\AppData\Roaming\Python\Python39\site-packages\fontTools\misc\psCharStrings.py", line 524, in rLineTo
    self.pen.lineTo(self._nextPoint(point))
  File "C:\Users\dfcre\AppData\Roaming\Python\Python39\site-packages\fontTools\pens\basePen.py", line 259, in lineTo
    self._lineTo(pt)
  File "C:\Users\dfcre\AppData\Roaming\Python\Python39\site-packages\fontTools\varLib\cff.py", line 576, in _lineTo
    self.add_point('rlineto', pt_coords)
  File "c:\users\dfcre\appdata\local\programs\python\python39\lib\site-packages\afdko\buildcff2vf.py", line 111, in add_point
    cmd = self._commands[self.pt_index]
IndexError: list index out of range

I have reproduced minimal designspace and ufo setup in the archive.

Versions:

buildcff2vf --version                                                                  2.0.2                                     
buildmasterotfs --version                                                              1.10.0

That's afdko==3.6.2a1

wavefont.zip

[josh-hadley]

@dy I believe the root of the problem is in the 1_0_0 master with the "1" ("_1") glyph (and probably 1.clip as well). It is only 1 unit wide and has all sub-1-unit fractional coordinates:

$ tx -dump -3 1_0_0.ufo
[...]
glyph[5] {_1,U+0101,
  1 width
  0 0.50 move
  0 0.78 0.22 1 0.50 1 curve
  0.50 1 line
  0.78 1 1 0.78 1 0.50 curve
  1 0.50 line
  1 0.22 0.78 0 0.50 0 curve
  0.50 0 line
  0.22 0 0 0.22 0 0.50 curve
  endchar}
[...]

In buildcff2vf, there are several steps where coordinates get rounded to integer values which would result in all of these coordinates ending up as 0 or 1 which causes failures when matching up with the 25_0_0 master coordinates.

Could you try scaling all glyphs of both masters up by, say, 10x or 100x?

[dy]

Thank you for having a look @josh-hadley, rescaling to 2048 units per em improved quality and fixed errors. I think to avoid such situations it's recommended to run some linter/validator or follow best practices.

[dy]

Rescaling doesn't seem to have helped. Here's an example of the same error with 2048 upm. All values are integers more than 1. wavefont.zip

[dy]

It has something to do with points order in glif. In the original order the first point is line, moving that first point to the end fixes the issue.

<outline>
    <contour>
-     <point x="0" y="-184" type="line"/>
      <point x="0" y="-72"/>

      <point x="92" y="20"/>
      <point x="205" y="20" type="curve" smooth="yes"/>
      <point x="205" y="20" type="line"/>
      <point x="317" y="20"/>

      <point x="410" y="-72"/>
      <point x="410" y="-184" type="curve" smooth="yes"/>
      <point x="410" y="205" type="line"/>
      <point x="410" y="92"/>

      <point x="317" y="0"/>
      <point x="205" y="0" type="curve" smooth="yes"/>
      <point x="205" y="0" type="line"/>
      <point x="92" y="0"/>

      <point x="0" y="92"/>
      <point x="0" y="205" type="curve" smooth="yes"/>
+     <point x="0" y="-184" type="line"/>
    </contour>
</outline>

[frankrolf]

Yet another old issue – this seems to have been a simple point compatibility problem.

Some tools don’t flag an off-curve start point to be incompatible with a start point on the following on-curve.

Here’s some background: https://github.com/roboDocs/ScaleFast/issues/5