scribe

First-class text rendering in pure Common Lisp. Clean-room — no FFI, no FreeType, no HarfBuzz, no Cairo. A scribe writes letterforms by hand.

scribe takes font bytes and a string and produces correctly shaped, antialiased, gamma-correct pixels — the whole pipeline, from wOF2/sfnt parsing through OpenType shaping to an analytic rasterizer — implemented from scratch. It is the text engine for weft (a pure-CL web engine) but stands alone. The bar is not "draws glyphs"; it is matching the reference implementations byte-for-byte.

What works

Stage	Coverage
Containers	sfnt (.ttf/.otf), WOFF, WOFF2 (glyf-transform reversal)
Outlines	TrueType glyf (quadratic), CFF/CFF2 (cubic Type2 charstrings + flex), composite glyphs
Variable fonts	fvar axes, avar remap, gvar deltas, HVAR advance variations
Shaping (GSUB)	single, multiple, ligature, contextual + chaining-context (calt/ccmp)
Shaping (GPOS)	single, pair (kerning), mark-to-base/mark/ligature (accents)
	+ GDEF classes & lookupFlag mark filtering, extension lookups
Rasterizer	analytic signed-area coverage (not supersampling), quad + cubic
Compositing	gamma-correct linear-light blend, subpixel positioning, stem-darkening knob

Everything is verified against the reference implementations — and matches them:

• Rasterization — coverage matches FreeType (ink within 0.5%; visually identical). Measured against Apple's own baked text, scribe's AA profile is the same: grayscale, geometric, ~1px edges, no subpixel (the Safari/Retina recipe).
• Shaping — byte-identical to HarfBuzz across the corpus (kerning, ligatures, contextual/calt, small-caps, accents): 330/330 + 170/170 glyph positions, gid streams exact.
• Variable fonts — advance & outline deltas match the fontTools instancer exactly (e.g. New York H = 1446 / 1662 / 1735 at default / opsz12 / wght1000).
• WOFF/WOFF2 — reconstructed outlines are identical to the originals (WOFF1 3369/3369, WOFF2-glyf 3369/3369 simple+composite, WOFF2-CFF 11/11).

Quick start

(asdf:load-system "scribe")

(let* ((font  (scribe:open-font (alexandria:read-file-into-byte-vector "Font.ttf")))
       (glyphs (scribe:shape-run font "Hard waffle —fi"        ; cmap + GSUB + GPOS
                                 :features '(:liga :kern :calt))))
  ;; glyphs: a vector of positioned glyph-pos (gid + advances/offsets, font units)
  (loop for g across glyphs
        do (multiple-value-bind (coverage w h left top)
               (scribe:rasterize-glyph font (scribe::glyph-pos-gid g) 48)
             ;; coverage: (simple-array double-float) of w*h in [0,1]
             (scribe:blend-coverage canvas x y cov '(0 0 0)))))   ; gamma-correct

open-font transparently accepts .ttf, .otf, .woff, and .woff2. See demo/ for runnable specimens (gamma-demo, text-demo, cff-demo, shape-demo, var-demo, hidpi-demo) — each writes a PNG to /tmp.

Building

git clone --recursive https://github.com/modus-lisp/scribe.git
cd scribe
sh inspect/run-all.sh        # the offline gate suite (no Python needed)

--recursive pulls the one dependency, brotli-pure (a from-scratch Common Lisp Brotli codec), needed only for WOFF2. WOFF1 and the rest use scribe's own from-scratch DEFLATE (src/deflate.lisp).

Design

• No hinting, no subpixel — both are deliberate. Hinting's grid-snap creates the jagged look; subpixel AA is panel-dependent and can't be baked into a portable image (Apple dropped it in 2018). scribe bets on grayscale analytic AA
  • stem darkening + rendering at the device's native DPI — the modern, display-independent path.
• Differential everything — every layer is gated against a reference (FreeType for coverage, HarfBuzz for shaping, the fontTools instancer for variations), the same discipline as brotli-pure/zstd-pure. References live only in the test harness (inspect/), never in scribe. The vendored oracle vectors let the gates run offline.

Layout

src/    blend (compositing+canvas+PNG) · font (sfnt) · tables/ · cmap · cff ·
        var (fvar/avar/gvar/HVAR) · glyf · raster · otl (GSUB/GPOS) · woff · deflate
inspect/  the gate suite + vendored oracle vectors + redistributable test fonts
demo/   runnable specimens
tools/  dmg-fonts (pure-CL Apple-font extractor), reusable deflate

Status & license

Research / educational; not audited. MIT (LICENSE). Test-corpus fonts are vendored under their own licenses — see inspect/corpus/FONT-LICENSES.md.