vfont2(5)

📦 version 1.1.3, in nixpkgs unstable, ubuntu stonking

✨ vfont2 — the variable-size font format ✨

okay bestie, so this is a page from the PSF Tools manual — it's vfont2(5), the fifth-section one (that's "file formats", for the uninitiated 💅) — and she's here to explain a font file layout. strap in, it's giving very much "binary structures but make it cute" 🎀

🌸 NAME 🌸

vfont2 — variable-size font format

🦋 SYNOPSIS 🦋

/usr/lib/vfont/∗

💖 DESCRIPTION 💖

so vfont2 is lowkey an attempted glow-up of the original vfont(5) file format — like, the original was cute but she had limitations, and this one is here to fix them: supporting more than 256 characters, larger characters, and Unicode. icon behavior, honestly 👑

the header looks like this, no cap:

#define VFONT2_MAGIC0 0x27
#define VFONT2_MAGIC1 0x5b
#define VFONT2_MAGIC2 0xA4
#define VFONT2_MAGIC3 0x68

/* bits used in flags */
#define VFONT2_HAS_UNICODE_TABLE 0x01

/* max version recognized so far */
#define VFONT2_MAXVERSION 0

/* UTF8 separators */
#define VFONT2_SEPARATOR  0xFF
#define VFONT2_STARTSEQ   0xFE

struct vfont2_header {
        unsigned char magic[4];
        unsigned int version;
        unsigned int headersize;    /* offset of dispatch table */
        unsigned int flags;
        unsigned int length;        /* number of glyphs */
        unsigned int bitmap_size;   /* total number of bytes for bitmaps */
        unsigned int max_height;    /* max size of a character bitmap */
     unsigned int max_width;
};

compared to an original vfont file, the "unused" xtend field has no counterpart here — she said "not me, don't know her" 🙈. and like, if somebody ever needed to extend the header, it would be straightforward: just bump up headersize and drop the extra field(s) in. easy.

🌈 the dispatch table 🌈

at offset headersize in the file you'll find the dispatch table (iykyk, the main character ✨). it has length entries, and each one is 18 bytes long:

struct vfont2_dispatch {
     unsigned int addr;      /* offset of glyph from start of bitmaps */
     unsigned int size;          /* number of bytes (0 if no glyph) */
     signed short up;        /* number of rows above baseline point */
     signed short down;      /* number of rows below baseline point */
     signed short left;      /* number of columns left of baseline point */
     signed short right;     /* number of columns right of baseline point */
     signed short width;         /* logical width, used by troff */
};

the number of lines present in the bitmap is up + down. and similarly, the number of columns is left + right. math is mathing 🧮

okay so here's the tea: as long as the total height and width stay positive, any of up, down, left or right can be negative 💀. and that just means the baseline point is outside the character bitmap. it's giving "off-grid" and we respect it.

the logical width gets used when rendering the characters — it's literally the number of pixels between one character's baseline point and the next. spacing queen 📏

🫶 the bitmaps 🫶

the bitmaps come immediately after the dispatch table. for each character there are up + down rows, and each of those rows is (( left + right ) + 7) / 8 bytes. periodt.

if a Unicode table is present, it will immediately follow the bitmaps. it's in the same format as PSF2, which goes a lil something like:

<unicodedescription> := <uc>*<seq>*<term>
<seq> := <ss><uc><uc>*
<ss> := 0xFE
<term> := 0xFF

where <uc> is a Unicode value coded in UTF-8, and the * means "zero or more occurrences of the thing before me". standard asterisk behavior 💅

the leading <uc>* part gives you the Unicode symbols that are all represented by this font position. and then the following sequences are sequences of Unicode symbols — probably a symbol together with combining accents, bestie — that are also represented by this font position. so many aliases, so iconic 👑

for example!! at the font position for a capital A-ring glyph, the Unicode sequence may be:

c3 85 e2 84 ab fe 41 cc 8a ff

the first six bytes correspond to two Unicode characters (U+00C5 LATIN CAPITAL LETTER A WITH RING ABOVE and U+212B ANGSTROM SIGN). then 0xfe acts as a separator, and the next three bytes correspond to the two Unicode characters U+0041 LATIN CAPITAL LETTER A and U+030A COMBINING RING ABOVE. truly a serve 🌟

⭐ SEE ALSO ⭐

👑 AUTHOR 👑

John Elliott <seasip.webmaster@gmail.com>.

k that's the whole page bestie, go forth and read some font binaries 🦋

Version 1.1.3 — 22 January, 2021 💖 mwah, that's the whole vibe, thanks for coming to my ted talk ✨🎀🫶

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