Struct Font 

pub struct Font<'a> { /* private fields */ }

A parsed TrueType/OpenType font face.

The face borrows the font’s byte buffer ('a), exactly like the underlying ttf_parser::Face — keep the bytes alive for at least as long as the Font. Parsing is cheap and allocation-free; metrics and outlines are read on demand.

Glyph outline cache

Extracting a glyph’s outline from the font (the ttf-parser outline walk) is the dominant cost when the same text is redrawn — for example, once per frame. Font therefore memoizes each glyph’s outline, keyed by its GlyphId: the cached outline is stored once in font-design units and only scaled/positioned per draw. The cache uses interior mutability (RefCell), so a Font is single-threaded (not Sync) — share the loaded font bytes and create one Font per thread if you need concurrency.

Implementations

impl<'a> Font<'a>

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

Parses the first face from the bytes of a font file (.ttf/.otf).

pub fn from_collection(data: &'a [u8], index: u32) -> Result<Self, FontError>

Parses the face at index inside a font collection (.ttc). Use 0 for a plain single-face file.

pub fn units_per_em(&self) -> u16

The size of the design grid in font units — the denominator for scaling outlines and metrics to a pixel size.

pub fn ascent(&self, size: f32) -> f32

Distance from the baseline up to the font’s ascender, in pixels.

pub fn descent(&self, size: f32) -> f32

Distance from the baseline down to the font’s descender, in pixels (positive — Y grows downward in pixmap space).

pub fn line_height(&self, size: f32) -> f32

Recommended distance between successive baselines, in pixels (ascender - descender + line_gap). This is the step used for \n in Font::text_path.

pub fn advance_width(&self, ch: char, size: f32) -> f32

Horizontal advance of a single character, in pixels.

Characters with no glyph fall back to the advance of .notdef.

pub fn measure(&self, text: &str, size: f32) -> f32

Width of the widest line of text, in pixels (sum of advances per line, no kerning). \n separates lines.

pub fn glyph_path(&self, ch: char, size: f32, x: f32, y: f32) -> Option<Path>

Builds the filled outline of a single character with its baseline origin at (x, y) in pixmap coordinates, scaled to em size (pixels).

Returns None when the character has no glyph or the glyph has no contours (for example a space).

pub fn text_path(&self, text: &str, size: f32, x: f32, y: f32) -> Option<Path>

Lays a string out horizontally and returns one Path containing every glyph’s outline, ready to be filled with FillRule::NonZero — the rule TrueType/OpenType outlines are authored for.

(x, y) is the origin of the first baseline. Each \n resets the pen to x and drops the baseline by one line_height. Glyphs are advanced by their horizontal advance only (no kerning, see the module limitations). Empty glyphs such as spaces contribute no contours but still advance the pen.

Returns None if the result is empty (e.g. whitespace-only text).