Struct FontFallbackChain 

pub struct FontFallbackChain {
    primary: FontData,
    fallbacks: Vec<FontData>,
}

A font fallback chain for handling mixed-script documents.

This struct manages a primary font and a list of fallback fonts. When rendering text, it automatically selects the appropriate font for each character based on glyph coverage.

Example

let mut p = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
p.push("fonts/NotoSans-Regular.ttf");
let primary = FontData::load(&p, None).unwrap();
let mut q = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
q.push("fonts/SpaceMono-Regular.ttf");
let fallback = FontData::load(&q, None).unwrap();

let chain = FontFallbackChain::new(primary).with_fallback(fallback);

let segments = chain.segment_text("Hello 123!");
assert!(!segments.is_empty());

Fields

primary: FontData

The primary font to try first

fallbacks: Vec<FontData>

List of fallback fonts to try if primary doesn’t have a character

Implementations

impl FontFallbackChain

pub fn new(primary: FontData) -> Self

Creates a new fallback chain with the given primary font.

pub fn with_fallback(self, fallback: FontData) -> Self

Adds a fallback font to the chain.

pub fn find_font_for_char(&self, c: char) -> &FontData

Finds the best font in the chain for the given character.

Returns a reference to the first font (starting with primary) that has a glyph for this character. If no font in the chain supports the character, returns the primary font (which will render the .notdef glyph).

pub fn primary(&self) -> &FontData

Returns the primary font.

pub fn fallbacks(&self) -> &[FontData]

Returns the list of fallback fonts.

pub fn check_coverage(&self, text: &str) -> GlyphCoverage

Analyzes coverage across the entire fallback chain for the given text.

Returns statistics showing which characters are covered by any font in the chain and which are still missing.

pub fn segment_text(&self, text: &str) -> Vec<(String, &FontData)>

Segments text into chunks where each chunk uses a single font from the chain.

This analyzes the text character by character, determining which font can render each character, and groups consecutive characters using the same font into segments.

Returns

A vector of tuples (text_segment, font_data_ref) where each segment should be rendered with the corresponding font.

Example

let mut p = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
p.push("fonts/NotoSans-Regular.ttf");
let primary = FontData::load(&p, None).unwrap();
let mut q = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
q.push("fonts/SpaceMono-Regular.ttf");
let fallback = FontData::load(&q, None).unwrap();
let chain = FontFallbackChain::new(primary).with_fallback(fallback);
let segments = chain.segment_text("Hello мир!");
assert!(!segments.is_empty());

Trait Implementations

impl Clone for FontFallbackChain

fn clone(&self) -> FontFallbackChain

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for FontFallbackChain

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.