hint-bake

Bake a font's TrueType hinting into its outlines for one size.

Some renderers ignore TrueType hints entirely (e.g. macOS Core Text), so a well-hinted font can look blurry or off-shape there. This script runs the font's real native hints in FreeType at your target size and writes the grid-fitted outlines back into a new font, which then renders the same shapes anywhere -- no hinter required.

Works with any TrueType-flavored font (glyf table). Best with fonts that carry hint bytecode (cvt/fpgm); without it the script warns and the output equals the unhinted shapes.

Motivation

Fonts like Microsoft's Consolas were hinted for Windows ClearType, but macOS Core Text ignores those hints, so the same font looks off-shape there. This freezes the ClearType shapes into plain outlines so your programming font keeps its hinted forms on a Mac (same shapes, not pixel-crisp -- macOS still smooths in grayscale).

Requirements

pip install fonttools freetype-py

Only --thin needs more: FontForge (e.g. brew install fontforge).

Usage

python3 hint_bake.py INPUT.ttf --pt 20.5 --dpi 72 --thin 35
python3 hint_bake.py INPUT.ttf --pt 12 --dpi 96 --thin 0 --output Out.ttf

• --pt: target point size, fractions allowed (required).
• --dpi: target resolution, default 72 (macOS: 1pt = 1px). Use 96 for Windows sizes, e.g. 21pt @ 96dpi = 28px.
• --thin: stem thinning in font units, default 0 (off). 20-35 suits ~20px text (1px ~= upm / px units). Requires FontForge.
• --interp: hinter version: 40 = DirectWrite (default), 35 = GDI classic.
• --mode: hinting target: normal (default), light, mono, lcd.
• --family: new family name (default: <orig> Baked <pt>pt).
• --output: output path (default: <input>-<pt>pt-<dpi>dpi-baked.ttf).

How it works

1. Sets the FreeType char size from --pt/--dpi (fractional sizes supported).
2. Loads every glyph with the font's native hinter and reads back the fitted outline + advance.
3. Rescales from pixels to the font's units-per-em and rewrites glyf/hmtx.
4. Strips the now-redundant hint bytecode (fpgm, prep, cvt, hdmx, VDMX, LTSH) and the DSIG signature, sets gasp to grayscale without gridfitting, and renames the family so the bake installs side-by-side with the original.
5. With --thin, erodes stems via FontForge changeWeight; advances are untouched, so monospace stays monospace.

Note: TrueType hints snap to integer pixels-per-em, so e.g. 20.5pt @ 72dpi is hinted at 21ppem and scaled -- the script reports the rounded ppem.

License note

Bring your own font file: the script only transforms it locally. Do not redistribute the output unless the input font's license allows derivatives (many commercial fonts, e.g. Microsoft's, prohibit this -- use such bakes for yourself and share the script instead).

Related: fonttools-opentype-hinting-freezer does integer-ppem freezing as a maintained package; this script adds fractional pt/dpi sizing, stem thinning, and side-by-side renaming.