Trait FontRef

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pub trait FontRef: Send + Sync {
    // Required methods
    fn data(&self) -> &[u8] ⓘ;
    fn units_per_em(&self) -> u16;
    fn glyph_id(&self, ch: char) -> Option<GlyphId>;
    fn advance_width(&self, glyph_id: GlyphId) -> f32;

    // Provided methods
    fn data_shared(&self) -> Option<Arc<dyn AsRef<[u8]> + Send + Sync>> { ... }
    fn metrics(&self) -> Option<FontMetrics> { ... }
    fn glyph_count(&self) -> Option<u32> { ... }
    fn variation_axes(&self) -> Option<Vec<VariationAxis>> { ... }
    fn is_variable(&self) -> bool { ... }
}

Expand description

Your key to unlocking font secrets

Every font format speaks the same language through this trait. TTF, OTF, WOFF - they all expose their data and metrics the same way.

struct MyFont {
    data: Vec<u8>,
    // ... your internal state
}

impl FontRef for MyFont {
    fn data(&self) -> &[u8] {
        &self.data
    }

    fn units_per_em(&self) -> u16 {
        1000 // Common for Type 1 fonts
    }

    fn glyph_id(&self, ch: char) -> Option<GlyphId> {
        // Turn Unicode into font-specific glyph IDs
        Some(42)
    }

    fn advance_width(&self, glyph_id: GlyphId) -> f32 {
        // How far to move after this glyph
        500.0
    }
}

Required Methods§

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fn data(&self) -> &[u8] ⓘ

Raw font bytes as they live in the file

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fn units_per_em(&self) -> u16

The font’s internal coordinate system scale

Used to convert between font units and rendered pixels. Type 1 fonts use 1000, TrueType often uses 2048.

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fn glyph_id(&self, ch: char) -> Option<GlyphId>

Find the glyph that represents this character

Returns None when the font doesn’t contain this character.

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fn advance_width(&self, glyph_id: GlyphId) -> f32

How wide this glyph stands in font units

This spacing determines how glyphs sit next to each other.

Provided Methods§

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fn data_shared(&self) -> Option<Arc<dyn AsRef<[u8]> + Send + Sync>>

Optional shared font bytes for zero-copy downstream consumption.

Implementations that store their bytes in an Arc SHOULD override this to avoid per-call allocations/copies in downstream libraries that require shared ownership.

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fn metrics(&self) -> Option<FontMetrics>

Optional font-wide metrics in font units (ascent/descent/line gap).

Backends that can parse OpenType tables SHOULD provide this to allow consumers to make baseline/layout decisions without depending on a specific font parser.

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