pi-imgen/docs/typst-verified.md

Typst behaviour — verified empirically

Everything here was tested against the real binary (typst 0.15.1, 9dfd3a08), not inferred from documentation. Re-run these checks if the pinned Typst version changes.

Confirmed

Claim	Result
--format / --ppi / --input / --font-path / --ignore-system-fonts / --pdf-standard / --root / --pages all exist	✅ present in typst compile --help
#set page(bleed: 3mm) emits a real PDF TrimBox	✅ /TrimBox [8.503937 8.503906 850.3937 1199.0552]
A3 trim geometry is exact	✅ TrimBox = 841.89 pt = 297.0 mm; MediaBox 858.9×1207.6 pt = 303×426 mm
json(sys.inputs.specfile) reads the spec as data	✅
context measure() bisection auto-fit	✅ compiles and fits
gradient.linear(...) for scrims	✅
Italian accents and « »	✅ à è é ì ò ù render correctly
Variable-font axes at render time	✅ text(variations: (wdth: 62, wght: 700)) with Archivo[wdth,wght].ttf

The variable-axis result matters: it means the auto-fit routine can narrow a long Italian title on the wdth axis before falling back to shrinking it, which preserves a poster's optical weight. That strategy is viable, not theoretical.

⚠️ Corrections to earlier assumptions

1. PNG export renders the TRIM page, not the bleed page.

typst compile poster.typ out.png --format png --ppi 300
  -> 3508x4961 px   (A3 trim @300dpi)
  NOT 3579x5032 px  (A3 + 3mm bleed @300dpi)

So: PDF carries the bleed and the TrimBox; PNG comes out already trimmed. This is convenient rather than a problem — screen/social output wants the trimmed image, and the print path uses the PDF anyway — but the renderer must not assume the two are the same size, and must not try to obtain a bleed area as PNG.

2. Output is byte-reproducible without SOURCE_DATE_EPOCH.

Two compiles a second apart produced byte-identical PDFs with and without the env var, because #set document(date: none) already removes the only nondeterministic field. Keep setting SOURCE_DATE_EPOCH=0 anyway — it costs nothing and protects against any future field that does read the clock — but the load-bearing directive is #set document(date: none) in every template. Golden-file tests are therefore sound.

Reproducing

typst compile probe.typ probe.pdf --input specfile=spec.json --root .
python3 -c "import re;d=open('probe.pdf','rb').read();print(re.search(rb'/TrimBox\s*\[([^\]]*)\]',d).group(1))"