Throws AssertionError: line_length 0.0 must be > 0 on OpenMoji 1F5FE

[JeppeKlitgaard]

I am trying to use nanoemoji to compile the OpenMoji set into a font, but I am running into issues with a particular SVG that triggers the assertion error: line_length 0.0 must be > 0.

I have managed to narrow it down to the 1F5FE emoji and produce the following minimal example of the fault:

example.toml

family = "An Emoji Family"
output_file = "example.picosvgz.ttf"
color_format = "picosvgz"
upem = 1024
width = 1275
ascender = 1045
descender = -275
linegap = 0
transform = "translate(0, 0)"
version_major = 1
version_minor = 0
reuse_tolerance = 0.1
ignore_reuse_error = true
keep_glyph_names = false
clip_to_viewbox = true
pretty_print = false
fea_file = "features.fea"
glyphmap_generator = "nanoemoji.write_glyphmap"
bitmap_resolution = 128
use_zopflipng = true
use_pngquant = true
pngquant_flags = "--speed 1 --skip-if-larger --quality 85-95"

[axis.wght]
name = "Weight"
default = 400

[master.regular]
style_name = "Regular"
srcs = ["1F5FE.svg",]

[master.regular.position]
wght = 400

1F5FE.svg

<svg xmlns="http://www.w3.org/2000/svg" id="emoji" viewBox="0 0 72 72">
  <defs/>
  <path fill="#92d3f5" d="M11.011,11 L61,11 A0 0 0 0 1 61,11 L61,60.767 A0.233 0.233 0 0 1 60.767,61 L11.233,61 A0.233 0.233 0 0 1 11,60.767 L11,11.011 A0.011 0.011 0 0 1 11.011,11 Z"/>
  <path fill="#d22f27" d="M54.462,47.429 L54.462,52.703 L56.529,52.703 L54.462,47.429 Z"/>
  <path fill="#d0cfce" d="M54.462,57.485 L54.462,52.703 L56.529,52.703 L54.462,57.485 Z"/>
  <path fill="#ea5a47" d="M52.394,52.703 L54.462,47.429 L54.462,52.703"/>
  <path fill="#fff" d="M52.394,52.703 L54.462,57.485 L54.462,52.703"/>
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</svg>

When run with nanoemoji example.toml it gives the following output:

I1116 10:24:05.891201 139969406056256 nanoemoji.py:639] Proceeding with 1 config(s)
I1116 10:24:05.892331 139969406056256 nanoemoji.py:602] Wrote build/example.picosvgz.toml
I1116 10:24:05.892566 139969406056256 nanoemoji.py:645] Generating build.ninja
I1116 10:24:05.895651 139969406056256 ninja.py:113] ninja -C /home/jeppe/Code/emoji_test/openmoji/color2/mwe/build
ninja: Entering directory `/home/jeppe/Code/emoji_test/openmoji/color2/mwe/build'
[6/6] /home/jeppe/Code/emoji_test/.venv/bin/python -m nanoemoji.write_font -v 0 --config...le.picosvgz.fea --glyphmap_file example.picosvgz.glyphmap --part_file parts-merged.json 
FAILED: example.picosvgz.ttf 
/home/jeppe/Code/emoji_test/.venv/bin/python -m nanoemoji.write_font -v 0 --config_file example.picosvgz.toml --fea_file example.picosvgz.fea --glyphmap_file example.picosvgz.glyphmap --part_file parts-merged.json 
I1116 10:24:08.360525 139921954416448 __init__.py:50] Pre-processing glyphs
I1116 10:24:08.361337 139921954416448 base.py:183] Running DecomposeComponentsFilter on AnEmojiFamily-Regular
I1116 10:24:08.361514 139921954416448 base.py:183] Running CubicToQuadraticFilter on AnEmojiFamily-Regular
I1116 10:24:08.361693 139921954416448 cubicToQuadratic.py:46] New spline lengths: 
I1116 10:24:08.361789 139921954416448 __init__.py:249] Building OpenType tables
Traceback (most recent call last):
  File "/home/linuxbrew/.linuxbrew/opt/python@3.10/lib/python3.10/runpy.py", line 196, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/home/linuxbrew/.linuxbrew/opt/python@3.10/lib/python3.10/runpy.py", line 86, in _run_code
    exec(code, run_globals)
  File "/home/jeppe/Code/emoji_test/.venv/lib/python3.10/site-packages/nanoemoji/write_font.py", line 838, in <module>
    app.run(main)
  File "/home/jeppe/Code/emoji_test/.venv/lib/python3.10/site-packages/absl/app.py", line 308, in run
    _run_main(main, args)
  File "/home/jeppe/Code/emoji_test/.venv/lib/python3.10/site-packages/absl/app.py", line 254, in _run_main
    sys.exit(main(argv))
  File "/home/jeppe/Code/emoji_test/.venv/lib/python3.10/site-packages/nanoemoji/write_font.py", line 831, in main
    ufo, ttfont = _generate_color_font(font_config, inputs)
  File "/home/jeppe/Code/emoji_test/.venv/lib/python3.10/site-packages/nanoemoji/write_font.py", line 772, in _generate_color_font
    _COLOR_FORMAT_GENERATORS[config.color_format].apply_ttfont(
  File "/home/jeppe/Code/emoji_test/.venv/lib/python3.10/site-packages/nanoemoji/write_font.py", line 145, in <lambda>
    lambda *args: _svg_ttfont(*args, picosvg=True, compressed=True),
  File "/home/jeppe/Code/emoji_test/.venv/lib/python3.10/site-packages/nanoemoji/write_font.py", line 672, in _svg_ttfont
    make_svg_table(config, ttfont, color_glyphs, picosvg, compressed)
  File "/home/jeppe/Code/emoji_test/.venv/lib/python3.10/site-packages/nanoemoji/svg.py", line 779, in make_svg_table
    doc_list = _picosvg_docs(config, ttfont, color_glyphs)
  File "/home/jeppe/Code/emoji_test/.venv/lib/python3.10/site-packages/nanoemoji/svg.py", line 687, in _picosvg_docs
    reuse_groups = _glyph_groups(config, color_glyphs, reuse_cache)
  File "/home/jeppe/Code/emoji_test/.venv/lib/python3.10/site-packages/nanoemoji/svg.py", line 162, in _glyph_groups
    reuse_result = reuse_cache.glyph_cache.try_reuse(
  File "/home/jeppe/Code/emoji_test/.venv/lib/python3.10/site-packages/nanoemoji/glyph_reuse.py", line 60, in try_reuse
    norm_path = normalize(SVGPath(d=path), self._normalize_tolerance).d
  File "/home/jeppe/Code/emoji_test/.venv/lib/python3.10/site-packages/picosvg/svg_reuse.py", line 261, in normalize
    _, vecy = _first_significant(_vectors(path), lambda v: v.y, tolerance)
  File "/home/jeppe/Code/emoji_test/.venv/lib/python3.10/site-packages/picosvg/svg_reuse.py", line 168, in _first_significant
    for idx, vec in enumerate(vectors):
  File "/home/jeppe/Code/emoji_test/.venv/lib/python3.10/site-packages/picosvg/svg_reuse.py", line 122, in _vectors
    y_max = _farthest(rx, ry, large_arc, abs(end_x))
  File "/home/jeppe/Code/emoji_test/.venv/lib/python3.10/site-packages/picosvg/svg_reuse.py", line 56, in _farthest
    assert line_length > 0, f"line_length {line_length} must be > 0"
AssertionError: line_length 0.0 must be > 0
picosvg/clipped/1F5FE.svg
ninja: build stopped: subcommand failed.
Traceback (most recent call last):
  File "/home/jeppe/Code/emoji_test/.venv/bin/nanoemoji", line 8, in <module>
    sys.exit(main())
  File "/home/jeppe/Code/emoji_test/.venv/lib/python3.10/site-packages/nanoemoji/nanoemoji.py", line 761, in main
    app.run(_run)
  File "/home/jeppe/Code/emoji_test/.venv/lib/python3.10/site-packages/absl/app.py", line 308, in run
    _run_main(main, args)
  File "/home/jeppe/Code/emoji_test/.venv/lib/python3.10/site-packages/absl/app.py", line 254, in _run_main
    sys.exit(main(argv))
  File "/home/jeppe/Code/emoji_test/.venv/lib/python3.10/site-packages/nanoemoji/nanoemoji.py", line 756, in _run
    maybe_run_ninja(build_file)
  File "/home/jeppe/Code/emoji_test/.venv/lib/python3.10/site-packages/nanoemoji/ninja.py", line 114, in maybe_run_ninja
    subprocess.run(ninja_cmd, check=True)
  File "/home/linuxbrew/.linuxbrew/opt/python@3.10/lib/python3.10/subprocess.py", line 526, in run
    raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command '['ninja', '-C', '/home/jeppe/Code/emoji_test/openmoji/color2/mwe/build']' returned non-zero exit status 1.

Running picosvg 1F5FE.svg doesn't lead to an error.

I don't fully understand why we need to assert that the line length must be positive. Was the intention perhaps assert that the distance was not negative? Removing the assert statement doesn't lead to any other errors.

[anthrotype]

interesting, thanks for the report. we shall take a look

[JeppeKlitgaard]

I've found an even more minimal example:

<svg xmlns="http://www.w3.org/2000/svg" id="emoji" viewBox="0 0 72 72">
  <defs/>
  <path fill="#92d3f5"
    d="
      M11.011,11
      L61,11
      A0 0 0 0 1 61,11
      L61,60.767
      Z"/>
</svg>

[anthrotype]

thanks. Whatever is happening, I believe the code simply should bail out of attempting to reuse the svg paths that we fail to normalize.

[JeppeKlitgaard]

I'm working on a quick PR that introduces a test. Would it be acceptable to fix this issue by simply converting the definite positive in the assertion to >= 0?

[anthrotype]

i'm not sure that's the right fix, but feel free to send a PR! We'll take a look

That A0 0 0 0 1 61,11 arc coming right after L61,11 look very suspicious. What does it look like when rendered? Does it even paint?

[JeppeKlitgaard]

Admittedly I know very little about SVG. The full SVG is: https://openmoji.org/library/emoji-1F5FE/

Not sure if that particular path is actually rendered though?