Function find_best_match

objdiff-gui/src/fonts/matching.rs:22–146

This follows CSS Fonts Level 3 § 5.2 [1]. https://drafts.csswg.org/css-fonts-3/#font-style-matching

(
    candidates: &[Properties],
    query: &Properties,
)

///
/// https://drafts.csswg.org/css-fonts-3/#font-style-matching
pub fn find_best_match(
    candidates: &[Properties],
    query: &Properties,
) -> Result<usize, SelectionError> {
    // Step 4.
    let mut matching_set: Vec<usize> = (0..candidates.len()).collect();
    if matching_set.is_empty() {
        return Err(SelectionError::NotFound);
    }

    // Step 4a (`font-stretch`).
    let matching_stretch = if matching_set
        .iter()
        .any(|&index| candidates[index].stretch == query.stretch)
    {
        // Exact match.
        query.stretch
    } else if query.stretch <= Stretch::NORMAL {
        // Closest width, first checking narrower values and then wider values.
        match matching_set
            .iter()
            .filter(|&&index| candidates[index].stretch < query.stretch)
            .min_by_key(|&&index| FloatOrd(query.stretch.0 - candidates[index].stretch.0))
        {
            Some(&matching_index) => candidates[matching_index].stretch,
            None => {
                let matching_index = *matching_set
                    .iter()
                    .min_by_key(|&&index| FloatOrd(candidates[index].stretch.0 - query.stretch.0))
                    .unwrap();
                candidates[matching_index].stretch
            }
        }
    } else {
        // Closest width, first checking wider values and then narrower values.
        match matching_set
            .iter()
            .filter(|&&index| candidates[index].stretch > query.stretch)
            .min_by_key(|&&index| FloatOrd(candidates[index].stretch.0 - query.stretch.0))
        {
            Some(&matching_index) => candidates[matching_index].stretch,
            None => {
                let matching_index = *matching_set
                    .iter()
                    .min_by_key(|&&index| FloatOrd(query.stretch.0 - candidates[index].stretch.0))
                    .unwrap();
                candidates[matching_index].stretch
            }
        }
    };
    matching_set.retain(|&index| candidates[index].stretch == matching_stretch);

    // Step 4b (`font-style`).
    let style_preference = match query.style {
        Style::Italic => [Style::Italic, Style::Oblique, Style::Normal],
        Style::Oblique => [Style::Oblique, Style::Italic, Style::Normal],
        Style::Normal => [Style::Normal, Style::Oblique, Style::Italic],
    };