fontsrv

fontsrv is a Plan 9 / Inferno-style 9P file server that provides filesystem access to scalable fonts (via FreeType), exposing them in the standard Plan 9 font + subfont format.

By default it mounts a virtual font tree at /mnt/font and posts itself as the font service.

What it serves

The exported filesystem is a two-level hierarchy:

• /mnt/font/<fontname>/
  • <size> directories for monochrome bitmaps (e.g. 13)
  • <size>a directories for anti-aliased greyscale (e.g. 13a)
    • font – a Plan 9 font file describing height/ascent and listing available subfonts
    • x000000.bit, x000100.bit, ... – subfont pages covering Unicode ranges

Sizes can be synthesized on demand: walking to (for example) 19a will generate that size if possible.

Usage

fontsrv [-m mtpt] [-s srvname]

• -m mtpt mountpoint (default: /mnt/font)
• -s srvname posted service name (default: font)

Examples

List available fonts:

% fontsrv
% ls /mnt/font/

Run acme using Monaco as fixed-width font:

% acme -F /mnt/font/Monaco/13a/font

Run sam using the same font:

% font=/mnt/font/Monaco/13a/font sam

Configuration: /sys/lib/fontsrv.map

fontsrv reads font definitions from:

• /sys/lib/fontsrv.map

The file is line-oriented. It supports either:

• path/to/fontfile.ttf
• FontName path/to/fontfile.ttf

Lines may include comments (# ...) when the # is at the start of the line or preceded by whitespace.

This repo includes an example map file at lib/fontsrv, and the top-level mkfile installs it as /sys/lib/fontsrv.map.

Build (Plan 9 mk)

This repository is set up for Plan 9's mk build system.

Key files:

• mkfile – builds the fontsrv binary and the bundled FreeType library
• libfreetype/ – vendored FreeType sources + mkfile

To build:

% mk

To install the binary, map file, and manpage:

% mk install

Installation copies:

• lib/fontsrv → /sys/lib/fontsrv.map
• man/4/fontsrv.4 → /sys/man/4/fontsrv.4

Implementation notes

• The 9P server is implemented in fontsrv.c (using lib9p), with a synthetic tree of Qids encoding:
  • which font
  • which point size
  • mono vs anti-aliased
  • which Unicode "page"
• FreeType rendering is handled in freetype.c, which:
  • discovers fonts from /sys/lib/fontsrv.map
  • lazily loads faces
  • renders glyph pages into Memsubfont objects on demand
• Subfont pages are served as .bit files named x%06x.bit, where the hex value is the start rune for that page.

Limitations

• Bitmap-only fonts are not supported (the server requires scalable faces).
• Subpixel rendering is not available.
• Hinting heuristics may not always pick the best appearance for every font/size (see the manpage).

See also

• man/4/fontsrv.4
• Plan 9 font format documentation (font(7))