_qcurveto_to_svg fails with specific paths

[sakiodre]

While using nanoemoji to build a font, I encountered a case where nanoemoji.write_part_file fails with this error:

  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "C:\dev\Python311\Lib\site-packages\nanoemoji\write_part_file.py", line 54, in <module>
    app.run(main)
  File "C:\dev\Python311\Lib\site-packages\absl\app.py", line 308, in run
    _run_main(main, args)
  File "C:\dev\Python311\Lib\site-packages\absl\app.py", line 254, in _run_main
    sys.exit(main(argv))
             ^^^^^^^^^^
  File "C:\dev\Python311\Lib\site-packages\nanoemoji\write_part_file.py", line 42, in main
    parts.add(svg)
  File "C:\dev\Python311\Lib\site-packages\nanoemoji\parts.py", line 168, in add
    self._add(as_shape(shape))
  File "C:\dev\Python311\Lib\site-packages\nanoemoji\parts.py", line 143, in _add
    norm = self.normalize(shape)
           ^^^^^^^^^^^^^^^^^^^^^
  File "C:\dev\Python311\Lib\site-packages\nanoemoji\parts.py", line 128, in normalize
    SVGPath(d=path).apply_transform(Affine2D.identity()),
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\dev\Python311\Lib\site-packages\picosvg\svg_types.py", line 275, in apply_transform
    return target.update_path(cmds, inplace=True)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\dev\Python311\Lib\site-packages\picosvg\svg_types.py", line 696, in update_path
    for cmd, args in svg_cmds:
  File "C:\dev\Python311\Lib\site-packages\picosvg\svg_pathops.py", line 101, in svg_commands
    for svg_cmd, svg_args in _SKIA_CMD_TO_SVG_CMD[cmd](points):
  File "C:\dev\Python311\Lib\site-packages\picosvg\svg_pathops.py", line 55, in _qcurveto_to_svg
    yield ("Q", control_pt + end_pt)
                ~~~~~~~~~~~^~~~~~~~
TypeError: can only concatenate tuple (not "NoneType") to tuple

When debugging, the last point is None:

Minimal reproducible svg file:

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16">
  <defs/>
  <path fill="#e3e3e3" d="M8.805,4.1 Q8.805,2.146 8.055,2.146 Q7.255,2.146 7.255,4.158 Q7.255,6.053 8.04,6.058 Q8.8,6.056 8.805,4.1 Z"/>
</svg>

Command:

python.exe -m nanoemoji.write_part_file -v 0 --reuse_tolerance 0.1 --wh 1200 --output_file parts.json ee49.svg

Minimal reproducible code using picosvg:

from picosvg.svg_types import SVGPath
from picosvg.svg_transform import Affine2D

path = "M0.117,0.055 Q0.117,0.029 0.107,0.029 Q0.097,0.029 0.097,0.055 Q0.097,0.081 0.107,0.081 Q0.117,0.081 0.117,0.055 Z"
SVGPath(d=path).apply_transform(Affine2D.identity())

This only occurs when the viewbox size is 16x16, the SVG renders fine in all browsers and editors, is this a bug or I'm just misusing it?

Edit:
After some debugging, it looks like the root problem is in the skia_path:

path = "M0.117,0.055 Q0.117,0.029 0.107,0.029 Q0.097,0.029 0.097,0.055 Q0.097,0.081 0.107,0.081 Q0.117,0.081 0.117,0.055 Z"
svg_path = SVGPath(d=path)
svg_cmds = svg_path.as_cmd_seq()
skia = skia_path(svg_cmds, fill_rule="nonzero")

for cmd, points in skia.segments:
    print(cmd, points)

Output (has None in points):

qCurveTo ((0.11699999868869781, 0.028999999165534973), (0.09700000286102295, 0.028999999165534973), (0.09700000286102295, 0.08100000023841858), (0.11699999868869781, 0.08100000023841858), None)
closePath ()

It looks like there's a problem in the method close of pathops._pathops.Path class, here is the full log of each iteration of the commands, notice in the last command "Z", it makes the last point in segments None:

Command M (0.117, 0.055)
  moveTo ((0.11699999868869781, 0.054999999701976776),)
  endPath ()

Command Q (0.117, 0.029, 0.107, 0.029)
  moveTo ((0.11699999868869781, 0.054999999701976776),)
  qCurveTo ((0.11699999868869781, 0.028999999165534973), (0.10700000077486038, 0.028999999165534973))
  endPath ()

Command Q (0.097, 0.029, 0.097, 0.055)
  moveTo ((0.11699999868869781, 0.054999999701976776),)
  qCurveTo ((0.11699999868869781, 0.028999999165534973), (0.09700000286102295, 0.028999999165534973), (0.09700000286102295, 0.054999999701976776))
  endPath ()

Command Q (0.097, 0.081, 0.107, 0.081)
  moveTo ((0.11699999868869781, 0.054999999701976776),)
  qCurveTo ((0.11699999868869781, 0.028999999165534973), (0.09700000286102295, 0.028999999165534973), (0.09700000286102295, 0.08100000023841858), (0.10700000077486038, 0.08100000023841858))
  endPath ()

Command Q (0.117, 0.081, 0.117, 0.055)
  moveTo ((0.11699999868869781, 0.054999999701976776),)
  qCurveTo ((0.11699999868869781, 0.028999999165534973), (0.09700000286102295, 0.028999999165534973), (0.09700000286102295, 0.08100000023841858), (0.11699999868869781, 0.08100000023841858), (0.11699999868869781, 0.054999999701976776))
  endPath ()

Command Z ()
  qCurveTo ((0.11699999868869781, 0.028999999165534973), (0.09700000286102295, 0.028999999165534973), (0.09700000286102295, 0.08100000023841858), (0.11699999868869781, 0.08100000023841858), None)
  closePath ()

[sakiodre]

As a workaround, add a check if end_pt is None works just fine, I'm not sure if this is the proper way to handle this:

def _qcurveto_to_svg(points) -> SVGCommandGen:
    for control_pt, end_pt in pathops.decompose_quadratic_segment(points):
+        if end_pt is None: continue
        yield ("Q", control_pt + end_pt)

[anthrotype]

thanks for the details bug report, yes this is a know issue introduced by latest skia-pathops 0.8, see googlefonts/nanoemoji#455.
You can temporarily workaround by pinning skia-pathops version to the one immediately preceding (e.g. pip install skia-pathops==0.7.4).
It's not a bug, but just haven't had the time to update picosvg to take the new feature into account.

[anthrotype]

add a check if end_pt is None

no that would not be the correct fix, I'm afraid. Please pin the version for now, I will fix it soonish

[sakiodre]

Thank you, i just tested and it works with the 0.7.4 version