subframe7536/maple-font · error · Exception

Font weight of `thin` must be 100

Error message

Font weight of `thin` must be 100

What it means

patch_instance post-processes a variable font's fvar instances and STAT table, assuming the weight axis covers named instances from thin (100) to extrabold (800). It raises this Exception when all_weight_map["thin"] is not exactly 100, meaning the font's minimum named weight deviates from the variable-font spec value the patching logic relies on. The name-to-weight mapping (value_to_name) would otherwise be wrong.

Source

Thrown at source/py/utils.py:455

    head.yMin = new_descender  # type: ignore
    hhea.ascent = new_ascender  # type: ignore
    hhea.descent = new_descender  # type: ignore
    os2.sTypoAscender = new_ascender  # type: ignore
    os2.sTypoDescender = new_descender  # type: ignore
    os2.usWinAscent = new_ascender  # type: ignore
    os2.usWinDescent = -new_descender  # type: ignore


def patch_instance(font: TTFont, all_weight_map: dict[str, int]):
    if all_weight_map == default_weight_map:
        print("Skip weight remapping since nothing changed.")
        return

    if "fvar" not in font or "STAT" not in font:
        return

    if all_weight_map["thin"] != 100:
        raise Exception("Font weight of `thin` must be 100")

    if all_weight_map["extrabold"] != 800:
        raise Exception("Font weight of `extrabold` must be 800")

    value_to_name = {v: k for k, v in default_weight_map.items()}

    for instance in font["fvar"].instances:  # type: ignore
        current_weight = int(instance.coordinates["wght"])
        weight_name = value_to_name.get(current_weight)
        if weight_name and weight_name in all_weight_map:
            instance.coordinates["wght"] = all_weight_map[weight_name]

    axes = font["fvar"].axes  # type: ignore
    wght_index = next((i for i, ax in enumerate(axes) if ax.axisTag == "wght"), None)
    if wght_index is None:
        return

    stat = font["STAT"].table  # type: ignore

View on GitHub (pinned to c08fda97fe)

Solutions

1. Set the thin weight back to 100 in the weight map / fvar instance coordinates configuration.
2. Verify the wght axis design space starts at 100 for the thin master/instance.
3. If a different thin weight is intentional, update patch_instance's expectation (the hardcoded 100 check) accordingly.
4. Diff your config against upstream defaults to find where the thin weight was changed.

Example fix

// before
# weight_map = {"thin": 200, ...}
// after
# weight_map = {"thin": 100, ...}  # thin must be exactly 100

def assert_thin_is_100(weight_map):
    if weight_map.get("thin") != 100:
        raise ValueError(
            f"thin weight must be 100 for variable-font patching, got {weight_map.get('thin')}"
        )

def has_valid_weight_axis(all_weight_map: dict) -> bool:
    return all_weight_map.get("thin") == 100 and all_weight_map.get("extrabold") == 800

try:
    build_variable_fonts(...)
except Exception as e:
    if "thin" in str(e) and "100" in str(e):
        print("Fix thin weight to 100 in the weight map config")
    raise

When it happens

Trigger: Calling build_variable_fonts → patch_instance when the wght axis's thin instance coordinates are not 100 — e.g. the design-space weight map was customized so thin maps to another value, or the axis range was changed.

Common situations: Editing the weight configuration (weight map / axis ranges) in the build config and setting thin to a non-100 value; regenerating the variable font with a changed wght axis minimum; a mis-merged config producing wrong instance coordinates.

Related errors

• Font weight of `extrabold` must be 800
• Invalid font source type: {type(source)}
• Invalid axe value, range: [{min_value}, {max_value}]
• line_height object must contain 'ascender' and 'descender' f
• {file_name or 'The font'} may contains glyphs that width is

AI-assisted analysis of subframe7536/maple-font@c08fda97fe (2026-08-28). Data as JSON: /api/errors/6a991b3d0196ef44. Report an issue: GitHub.