go-hbsubset

Go bindings for HarfBuzz's font subsetter (hb-subset) without cgo.

This library wraps a WebAssembly build of HarfBuzz transpiled to Go using wasm2go.

Warning

These bindings are still experimental and are subject to change. They have not been tested extensively yet.

The wasm2go blob is fully reproducible and verified.

To have working IDE integration while working on the bindings, use bear -- make -C src distclean download all CXX=/path/to/wasi-sdk/bin/wasm32-wasip1-clang++ WASM_OPT=/path/to/binaryen/bin/wasm-opt to download the Harfbuzz source and generate the compile_commands.json.

Usage

To subset a single font:

import "github.com/pgaskin/go-hbsubset"

out, err := hbsubset.Subset(font, 0, &hbsubset.Options{
    Unicodes: []rune("some text"),
})

You can specify other options too:

import (
    "github.com/pgaskin/go-gfsubsets"
    "golang.org/x/text/unicode/rangetable"
)

out, err := hbsubset.Subset(data, 0, &hbsubset.Options{
    UnicodeRanges: rangetable.Merge(
        gfsubsets.Latin,
        &unicode.RangeTable{
            R16: []unicode.Range16{
                {Stride: 1, Lo: '\u2002', Hi: '\u201E'}, // spaces, smart punctuation
                {Stride: 1, Lo: '\u2022', Hi: '\u2022'}, // bullet
                {Stride: 1, Lo: '\u2026', Hi: '\u2026'}, // ellipsis
            },
        },
    ),
    PinAllAxesToDefault: true,
    AxisRanges: map[hbsubset.Tag]hbsubset.AxisRange{
        hbsubset.MakeTag("wght"): {Min: 100, Max: 900, Default: 400},
    },
    LayoutFeatures: []hbsubset.Tag{
        hbsubset.MakeTag("kern"),
        hbsubset.MakeTag("mkmk"),
        hbsubset.MakeTag("size"),
        hbsubset.MakeTag("liga"),
    },
    NameIDs: []hbsubset.NameID{
        hbsubset.NameUniqueID,
        hbsubset.NameCopyright,
        hbsubset.NameFontFamily,
        hbsubset.NameFontSubfamily,
        hbsubset.NameTypographicFamily,
        hbsubset.NameTypographicSubfamily,
        hbsubset.NameFullName,
        hbsubset.NameMacFullName,
        hbsubset.NamePostscriptName,
        hbsubset.NameManufacturer,
        hbsubset.NameDescription,
        hbsubset.NameVariationsPSPrefix,
    },
    LayoutScripts: []hbsubset.Tag{
        hbsubset.MakeTag("latn"), // latin
    },
    NameLanguages: []uint32{
        1033, // english
    },
})

You can reuse a font for multiple subsets (this also lets you access the font metadata):

face, err := hbsubset.NewFace(font, 0)
if err != nil {
    return err
}
face.Preprocess()

for _, page := range pages {
    out, err := face.Subset(&hbsubset.Options{Unicodes: page})
    // ...
}

You can use SubsetWithMapping to get the renumbered glyphs.

out, m, err := hbsubset.SubsetWithMapping(font, &hbsubset.Options{
    Unicodes: []rune("Hi"),
})

new, ok := m.NewGlyph(oldGID)

for old, new := range m.Glyphs() {
    // ...
}