pdfrum-font

Font dictionaries and the glyph pipeline (ISO 32000-1 §9): Type 1, TrueType, Type 0 composite, Type 3 procedure and CID fonts; simple and /Differences encodings, CMaps, /ToUnicode, the base-14 substitutes, and the widths ladder.

use pdfrum_common::{Diagnostics, Limits};
use pdfrum_font::{FontCache, load};
use pdfrum_object::NoResolve;

# fn demo(dict: &pdfrum_object::Dict) {
let Some(font) = load(
    dict,
    &NoResolve,
    &FontCache::default(),
    &Limits::default(),
    &mut Diagnostics::default(),
) else {
    return;
};
for item in font.decode(b"Hello") {
    let _ = (item.code, item.gid, item.width, &item.unicode);
}
# }

Which glyph a byte selects, what character it stands for, and how wide it is are three different ladders, and a font can answer any one of them without the others. The glyph comes from the encoding and the font program; the character comes from /ToUnicode, then the encoding's glyph names, then a CID-to-Unicode table; the width comes from /Widths or /W, then the program's own metrics, then a default. A file routinely disagrees with itself across the three — text that draws correctly but copies as mojibake is exactly that disagreement. [Font::decode] answers all three at once, per code, so a caller never has to re-derive one from another.

A simple font always constructs. Only Type0 can fail to [load], because only it depends on a CMap that may be unresolvable; everything else falls back — a missing program becomes a base-14 substitute, a missing width becomes the default — because a page with an unloadable font still has to draw. [FontCache] is shared across pages, since a document's fonts are per-document and re-parsing an embedded program per page is the difference between a fast and a slow render.

Feature system-fonts adds host font fallback via fontdb; it is not available on wasm32, where the bundled base-14 faces carry the text.

Part of pdfrum. #![forbid(unsafe_code)].

MIT OR Apache-2.0