Fontforge OT Fixup

Fontforge_plugin to fix issues to generated OT font

Install

pip3 install fontforge_ot_fixup

Make sure Fontforge Python module is usable

In interactive mode of Python, run:

import fontforge

If it raises ModuleNotFoundError exception, install Fontforge first. If installed, make sure the build option set that the Python module gets also installed. If already so, Python interpreter does not recognize the module path where the required module.

export PYTHONPATH=/path/to/fontforge/python/module:$PYTHONPATH

Configuration

This plugin has configuration menu. Select File > Configure Plugins... > OT fixup utility and click Configure to open.

Configuration will be stored in ~/.config/fontforge/plugin/OT fixup utility.toml (for Linux.)

Fix post.isFixedPitch

Table: [hooks.post.isFixedPitch]
Keys: ttf and ufo
Type: bool

Enable or disable the font generation hook (see below.) Can be configured for each format, TTF (including OTF) and UFO.

Fix 'aalt' feature

Table: [hooks.GSUB.aalt]
Keys: ufo
Type: bool

Enable or disable the font generation hook (see below.) Only applicable for UFO.

Usage

In Fontforge GUI

This plugin adds following items into "Tools" menu:

• Activate smart dropout

Activate smart dropout

This appends the following bytecode into prep table:

B8h    PUSHW
01FFh  511
85h    SCANCTRL
B0h    PUSHB
04h    4
8Dh    SCANTYPE

If already appended the menu will be disabled.

Hooks

This plugin installs new/load font hook that installs font generation hook. The latter automatically fixes certain issues in exported font.

Fix post.isFixedPitch

Fontforge may export with post.isFixedPitch = 0 even for monospace fonts. This is because Fontforge requires all glyph including combining marks have the same advance width in order to export with post.isFixedPitch = 1. This is usually inappropriate.

This hook fixes the flag after normal export referring only U+0020 to U+007E.

Works when exporting TTF, OTF, or UFO.

Fix OS/2.xAvgCharWidth

For OS/2.version ≥ 3, OS/2.xAvgCharWidth is calculated from all non-zero-width glyphs. However, this causes misbehavior for CJK monospaced fonts in certain environments. Such fonts have fullwidth (zenkaku) characters as opposed to halfwidth (hankaku) ones which corresponds to any glyphs in Western fonts.

This hook fixes the average width to what calculated from only U+0020 to U+007E. This is typically the advance width of halfwidth characters.

Works when exporting TTF or OTF. Monospaced fonts only.

Fix aalt feature

Fontforge can export UFO but lacks special handling for aalt feature. This may result an invalid feature file (*.ufo/feature.fea); it is that aalt cannot contain script or language instructions.

This hook fixes aalt feature, or adds it if it does not exist. Existing lookups in aalt features will be included as aalt-only ones.

Works only when exporting UFO.

In Python script

import fontforge
import fontforge_otfixup

font = fontforge.open('path/to/font.sfd')
sdActive = fontforge_otfixup.isSmartDropoutActive(font)
fontforge_otfixup.activateSmartDropout(font)