gpforge

A bitmap font editor for gfxprim.

Supported formats

• Export to BDF
• Export to gfxprim C compiled-in font

A native font is a directory of text files — family metadata, and one file per style variant that stores only what it changes. The format is described in FONT_FORMAT.md.

Design choices

Four variants, one drawing. mono, regular, bold-mono and bold are one family: each is a diff against its parent, bold is derived by emboldening, and a glyph is drawn once and reused by every variant that does not need its own. The strip under the canvas shows all four live, and clicking one switches to it.

Editing. Pixels with the mouse or the keyboard, shift and flip, the advance and both bearings on spin buttons. A glyph can be started as a copy of another, ¿ is ? pasted and flipped both ways. The canvas shows the baseline, the ascent and descent, the origin and the advance, because a bitmap glyph is metrics as much as ink. Editing an inherited glyph creates the overlay; v deletes it again and the glyph goes back to what the lattice derives.

Undo is one journal for the whole family, one entry per stroke or command, and a command that touches many glyphs is taken back in one go.

Glyph table paged by unicode block, with the coverage of each block, the codepoint over every cell, and the character as another font draws it for comparison. Blocks the font has no glyphs in yet can be declared so an empty font remembers what it is aiming at.

Accented letters are drawings, not compositions. A strip shows every accented form of the letter being edited; ticking update copies each edit into all of them, and clicking an empty slot draws that letter once from the base and the accent. Selecting a combining mark instead lists the letters that wear it, composed with the mark as it is being drawn.

Preview through gfxprim itself — the variant is compiled into a real gp_font_face, so what is on the screen is what an application will render. A sample per unicode block, the selected glyph between reference glyphs for judging spacing, and a line to type whatever you want to look at. Check boxes draw the font's underline, strikethrough and overline over it, each at the size its line is drawn at.

Lint for what cannot be seen one glyph at a time: ink outside a monospace cell, an advance that does not match the variant, an accent above the ascent, an x-height letter that does not reach the x-height. One key walks to the next finding, wrapping, recomputed every time.

Font properties in one dialog: the family name, the line box, em, x-height, cap height, digit width and the three rules. The metrics the importer measures can be measured again off the variant being edited, and the whole change is one undo. With no font open the same dialog starts a new one.

Import and export. BDF in (including iso8859-2 fonts, mapped to unicode), and out to BDF again or to a gfxprim C compiled-in font.

Build

make                  # gpforge and gpforge-cli
make test             # the unit tests and the corpus round trips
make lint             # the checks over the corpus
make install          # binaries, the layout and the desktop entry

make install honours DESTDIR, and gpforge.spec builds an RPM from it. The editor reads its layout from /etc/gp_apps/gpforge/layout.json, or from ./layout.json when run from the source tree.

The corpus tests run over the terminal bitmap fonts, expected in ../fonts (override with FONTS=), and skip when it is not there.

Run

gpforge font.bdf        # a BDF, imported
gpforge font-dir/       # a font directory
gpforge                 # nothing open, use open or new

On the canvas:

mouse	toggle a pixel, drag to continue
space	toggle the pixel under the cursor
arrows	move the pixel cursor, with alt by five
shift+arrows	shift the ink, which is a bearing edit

On the glyph table:

click	select a glyph
arrows	move the selection
wheel, PgUp / PgDn	a page of the block

On the accented letters strip:

click	select it, or draw it when the slot is empty
wheel	scroll the list by a cell

Anywhere:

[ ]	advance
x y	flip horizontally / vertically
Del	clear the glyph
v	revert to inherited / derived
l	next lint finding
Ctrl+C / Ctrl+V	copy the glyph / paste it over the selected one
Ctrl+Z / Ctrl+Shift+Z	undo / redo
Ctrl+O / N / S	open / new / save
Ctrl+P	font properties
Ctrl+Q	quit

The variant is the strip under the canvas, and the block is the spin button over the table with the codepoint field beside it — both are clicked, not typed at.

Command line

gpforge-cli import <font.bdf> <dir>                 # BDF -> a font directory
gpforge-cli write  <dir> <out-dir>                  # rewrite a directory
gpforge-cli dump   <font.bdf|dir>                   # the model, as text
gpforge-cli face   <font.bdf|dir> <variant>         # one resolved face
gpforge-cli lint   <font.bdf|dir>                   # the checks
gpforge-cli c      <font.bdf|dir> <id> <name>       # a gfxprim C font
gpforge-cli bdf    <font.bdf|dir> <variant>         # one variant as BDF

face is the quickest way to see what the variant lattice actually produces: every glyph with its provenance, its metrics and its ink.

Licence

GPL-2.0-or-later.