91 lines
2.4 KiB
Python
91 lines
2.4 KiB
Python
"""
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Generate @font-face settings to help make the fallback font look similar
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to the non-fallback font.
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Genererated by ChatGTP 5.2-instant. Not human-modified.
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"""
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from fontTools.ttLib import TTFont
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USE_TYPO_METRICS = 1 << 7
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def get_metrics(path):
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font = TTFont(path)
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head = font["head"]
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os2 = font["OS/2"]
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hhea = font["hhea"]
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use_typo = bool(os2.fsSelection & USE_TYPO_METRICS)
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if use_typo:
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asc = os2.sTypoAscender
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desc = os2.sTypoDescender
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gap = os2.sTypoLineGap
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source = "OS/2.sTypo*"
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else:
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asc = hhea.ascent
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desc = -hhea.descent
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gap = hhea.lineGap
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source = "hhea.*"
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# x-height ALWAYS comes from OS/2
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if not hasattr(os2, "sxHeight") or os2.sxHeight <= 0:
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raise ValueError(f"{path} has no usable sxHeight")
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x_height = os2.sxHeight
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print("Source", path, source)
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return {
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"unitsPerEm": head.unitsPerEm,
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"ascender": asc,
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"descender": desc,
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"lineGap": gap,
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"xHeight": x_height,
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}
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def compute_overrides(target, fallback):
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# size-adjust: match x-height
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size_adjust = (
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(target["xHeight"] / target["unitsPerEm"]) /
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(fallback["xHeight"] / fallback["unitsPerEm"])
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)
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# overrides: force target vertical metrics
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ascent_override = target["ascender"] / target["unitsPerEm"]
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descent_override = abs(target["descender"]) / target["unitsPerEm"]
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line_gap_override = target["lineGap"] / target["unitsPerEm"]
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return {
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"size_adjust": size_adjust * 100,
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"ascent_override": ascent_override * 100,
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"descent_override": descent_override * 100,
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"line_gap_override": line_gap_override * 100,
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}
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def emit_css(family_name, local_name, values):
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return f"""
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@font-face {{
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font-family: "{family_name}";
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src: local("{local_name}");
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size-adjust: {values['size_adjust']:.2f}%;
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ascent-override: {values['ascent_override']:.2f}%;
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descent-override: {values['descent_override']:.2f}%;
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line-gap-override: {values['line_gap_override']:.2f}%;
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}}
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""".strip()
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# ---- Example usage ----
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target = get_metrics("static/fonts/gen/Lora-Regular.woff2")
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fallback = get_metrics("/System/Library/Fonts/Supplemental/Times New Roman.ttf")
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values = compute_overrides(target, fallback)
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print(emit_css(
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family_name="Lora Fallback",
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local_name="Times New Roman",
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values=values,
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))
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