moli/scripts/generate-layout-test-font.py

# /// script
# requires-python = ">=3.11"
# dependencies = [
#   "brotli==1.1.0",
#   "fonttools==4.59.0",
# ]
# ///
"""Generate the deterministic fixed fonts used by Phase 3 layout tests."""

import hashlib
import os
from pathlib import Path

from fontTools.fontBuilder import FontBuilder
from fontTools.pens.ttGlyphPen import TTGlyphPen
from fontTools.subset import Options, Subsetter
from fontTools.ttLib import TTFont


ROOT = Path(__file__).resolve().parents[1]
FIXTURES = ROOT / "moli-layout" / "tests" / "fixtures"
TTF_PATH = FIXTURES / "moli-ahem.ttf"
HEBREW_EMOJI_PATH = FIXTURES / "moli-hebrew-emoji.ttf"
CJK_PATH = FIXTURES / "moli-cjk.ttf"
DEJAVU_SOURCE = Path(
    os.environ.get(
        "MOLI_DEJAVU_FONT_SOURCE",
        "/usr/share/fonts/truetype/dejavu/DejaVuSans.ttf",
    )
)
DROID_CJK_SOURCE = Path(
    os.environ.get(
        "MOLI_DROID_CJK_FONT_SOURCE",
        "/usr/share/fonts/truetype/droid/DroidSansFallbackFull.ttf",
    )
)
DEJAVU_SOURCE_SHA256 = "57f73e11f51999432bf7ab22ce55b6f945d5eca1bf824404cfa9ec2e3718c84e"
DROID_CJK_SOURCE_SHA256 = "acb6440a713d880a13a21b468ba7cd43f5a2b2934972e51be791c880730777b8"
# OpenType stores seconds since 1904-01-01. This value is Unix epoch and avoids
# FontTools treating a deliberately deterministic zero as a Unix timestamp.
OPEN_TYPE_UNIX_EPOCH = 2_082_844_800


def empty_glyph():
    pen = TTGlyphPen(None)
    return pen.glyph()


def box_glyph():
    pen = TTGlyphPen(None)
    pen.moveTo((0, 0))
    pen.lineTo((600, 0))
    pen.lineTo((600, 800))
    pen.lineTo((0, 800))
    pen.closePath()
    return pen.glyph()


def build_ttf() -> None:
    builder = FontBuilder(1000, isTTF=True)
    codepoints = list(range(0x21, 0x7F))
    codepoints += [0x00A0, 0x00DF]
    glyph_names = {
        codepoint: (
            f"uni{codepoint:04X}" if codepoint <= 0xFFFF else f"u{codepoint:05X}"
        )
        for codepoint in codepoints
    }
    glyph_order = [".notdef", "space", *glyph_names.values()]
    builder.setupGlyphOrder(glyph_order)

    # Keep glyph identities distinct so source/glyph assertions can distinguish
    # transformed characters without depending on a platform font.
    cmap = dict(glyph_names)
    cmap[0x20] = "space"
    builder.setupCharacterMap(cmap)

    glyphs = {name: box_glyph() for name in glyph_names.values()}
    glyphs.update({".notdef": box_glyph(), "space": empty_glyph()})
    builder.setupGlyf(glyphs)
    builder.setupHorizontalMetrics({glyph: (600, 0) for glyph in glyph_order})
    builder.setupHorizontalHeader(ascent=800, descent=-200, lineGap=0)
    builder.setupNameTable(
        {
            "familyName": "Moli Ahem",
            "styleName": "Regular",
            "uniqueFontIdentifier": "Moli Ahem Regular 1.0",
            "fullName": "Moli Ahem Regular",
            "psName": "MoliAhem-Regular",
            "version": "Version 1.000",
        }
    )
    builder.setupOS2(
        sTypoAscender=800,
        sTypoDescender=-200,
        sTypoLineGap=0,
        usWinAscent=800,
        usWinDescent=200,
        sxHeight=800,
        sCapHeight=800,
        fsSelection=1 << 6,
    )
    builder.setupPost()
    builder.setupMaxp()
    builder.setupHead(created=OPEN_TYPE_UNIX_EPOCH, modified=OPEN_TYPE_UNIX_EPOCH)
    builder.save(TTF_PATH)


def verify_source(source: Path, expected_sha256: str) -> None:
    if not source.is_file():
        raise SystemExit(f"required fixed-font source does not exist: {source}")
    actual_sha256 = hashlib.sha256(source.read_bytes()).hexdigest()
    if actual_sha256 != expected_sha256:
        raise SystemExit(
            f"fixed-font source hash mismatch for {source}: "
            f"expected {expected_sha256}, got {actual_sha256}"
        )


def subset_font(source: Path, output: Path, codepoints: list[int]) -> None:
    font = TTFont(source, recalcTimestamp=False)
    options = Options()
    options.recalc_timestamp = False
    options.retain_gids = False
    options.name_IDs = [0, 1, 2, 3, 4, 5, 6, 13, 14]
    subsetter = Subsetter(options=options)
    subsetter.populate(unicodes=codepoints)
    subsetter.subset(font)
    font["head"].created = OPEN_TYPE_UNIX_EPOCH
    font["head"].modified = OPEN_TYPE_UNIX_EPOCH
    font.save(output, reorderTables=False)


def convert(flavor: str) -> None:
    font = TTFont(TTF_PATH, recalcTimestamp=False)
    font.flavor = flavor
    font.save(FIXTURES / f"moli-ahem.{flavor}", reorderTables=False)


def main() -> None:
    FIXTURES.mkdir(parents=True, exist_ok=True)
    verify_source(DEJAVU_SOURCE, DEJAVU_SOURCE_SHA256)
    verify_source(DROID_CJK_SOURCE, DROID_CJK_SOURCE_SHA256)
    build_ttf()
    convert("woff")
    convert("woff2")
    subset_font(DEJAVU_SOURCE, HEBREW_EMOJI_PATH, [0x20, 0x05D0, 0x05D1, 0x1F600])
    subset_font(DROID_CJK_SOURCE, CJK_PATH, [0x20, 0x4E2D, 0x6587])


if __name__ == "__main__":
    main()