Struct Font 

pub struct Font { /* private fields */ }

A loaded font, ready for shaping and rasterization.

Constructed from raw TTF/OTF bytes via Font::from_bytes. The data is reference-counted so fonts can be cheaply shared and saved across frames.

An optional fallback font can be chained via Font::with_fallback; when a glyph is missing from the primary font (glyph_id == 0 after shaping), the fallback is consulted for both the glyph outline and advance width.

Implementations

impl Font

pub fn from_bytes(data: Vec<u8>) -> Result<Self, &'static str>

Parse a font from raw TTF/OTF bytes.

Returns Err if the data is not a valid font.

pub fn from_slice(data: &[u8]) -> Result<Self, &'static str>

Parse a font from a borrowed byte slice (data is copied).

pub fn with_fallback(self, fallback: Arc<Font>) -> Self

Chain a fallback font consulted when this font lacks a glyph.

Returns self so it can be used as a builder method:

let font = Font::from_slice(MAIN_BYTES)?.with_fallback(Arc::new(emoji_font));

pub fn units_per_em(&self) -> u16

pub fn ascender_px(&self, size: f64) -> f64

Ascender height in pixels at the given font size.

pub fn descender_px(&self, size: f64) -> f64

Descender depth in pixels at the given font size (positive value).

pub fn line_height_px(&self, size: f64) -> f64

Recommended line height in pixels at the given font size.

pub fn glyph_visual_bounds(&self, glyph: char, size: f64) -> Option<(f64, f64)>

Actual vertical extent of a single glyph in pixels (Y-up), relative to the baseline. Returns (y_min, y_max) where y_min is how far the glyph dips below the baseline (negative for descenders, near zero for upright glyphs) and y_max is how far it rises above.

Use this for visually centring an icon glyph in a button — ascender_px/descender_px describe the FONT’s worst-case extents and are too generous for most icon fonts (Font Awesome glyphs sit in a sub-rectangle of the design space, so centring by the font metric leaves them noticeably high). Returns None when the glyph has no outline (e.g. a space) or isn’t in the font.

pub fn characters(&self) -> BTreeSet<char>

Enumerate every character this font can actually render.

Walks the cmap table’s Unicode subtables, keeping only code points that resolve to a real (non-.notdef) glyph, then recurses into the fallback chain so the set reflects everything the whole font stack can draw — Font Awesome / emoji glyphs that live in a fallback are included, matching how the text renderer resolves them at shape time.

Returns a sorted, de-duplicated BTreeSet<char>. This backs the Font Book demo’s glyph grid and its “supports N characters” count, replacing the previous hard-coded glyph list.