typst/library/src/math/delimited.rs

use super::*;

/// How much less high scaled delimiters can be than what they wrap.
pub(super) const DELIM_SHORT_FALL: Em = Em::new(0.1);

/// Scales delimiters.
///
/// While matched delimiters scale by default, this can be used to scale
/// unmatched delimiters and to control the delimiter scaling more precisely.
///
/// ## Example
/// ```example
/// $ lr(]a, b/2]) $
/// $ lr(]sum_(x=1)^n] x, size: #50%) $
/// ```
///
/// Display: Left/Right
/// Category: math
#[element(LayoutMath)]
pub struct LrElem {
    /// The size of the brackets, relative to the height of the wrapped content.
    ///
    /// Defaults to `{100%}`.
    pub size: Smart<Rel<Length>>,

    /// The delimited content, including the delimiters.
    #[required]
    #[parse(
        let mut body = Content::empty();
        for (i, arg) in args.all::<Content>()?.into_iter().enumerate() {
            if i > 0 {
                body += TextElem::packed(',');
            }
            body += arg;
        }
        body
    )]
    pub body: Content,
}

impl LayoutMath for LrElem {
    fn layout_math(&self, ctx: &mut MathContext) -> SourceResult<()> {
        let mut body = self.body();
        if let Some(elem) = body.to::<LrElem>() {
            if elem.size(ctx.styles()).is_auto() {
                body = elem.body();
            }
        }

        let mut fragments = ctx.layout_fragments(&body)?;
        let axis = scaled!(ctx, axis_height);
        let max_extent = fragments
            .iter()
            .map(|fragment| (fragment.ascent() - axis).max(fragment.descent() + axis))
            .max()
            .unwrap_or_default();

        let height = self
            .size(ctx.styles())
            .unwrap_or(Rel::one())
            .resolve(ctx.styles())
            .relative_to(2.0 * max_extent);

        match fragments.as_mut_slice() {
            [one] => scale(ctx, one, height, None),
            [first, .., last] => {
                scale(ctx, first, height, Some(MathClass::Opening));
                scale(ctx, last, height, Some(MathClass::Closing));
            }
            _ => {}
        }

        ctx.extend(fragments);

        Ok(())
    }
}

/// Scale a math fragment to a height.
fn scale(
    ctx: &mut MathContext,
    fragment: &mut MathFragment,
    height: Abs,
    apply: Option<MathClass>,
) {
    if matches!(
        fragment.class(),
        Some(MathClass::Opening | MathClass::Closing | MathClass::Fence)
    ) {
        let glyph = match fragment {
            MathFragment::Glyph(glyph) => glyph.clone(),
            MathFragment::Variant(variant) => {
                GlyphFragment::new(ctx, variant.c, variant.span)
            }
            _ => return,
        };

        let short_fall = DELIM_SHORT_FALL.scaled(ctx);
        *fragment =
            MathFragment::Variant(glyph.stretch_vertical(ctx, height, short_fall));

        if let Some(class) = apply {
            fragment.set_class(class);
        }
    }
}

/// Floor an expression.
///
/// ## Example
/// ```example
/// $ floor(x/2) $
/// ```
///
/// Display: Floor
/// Category: math
/// Returns: content
#[func]
pub fn floor(
    /// The expression to floor.
    body: Content,
) -> Value {
    delimited(body, '⌊', '⌋')
}

/// Ceil an expression.
///
/// ## Example
/// ```example
/// $ ceil(x/2) $
/// ```
///
/// Display: Ceil
/// Category: math
/// Returns: content
#[func]
pub fn ceil(
    /// The expression to ceil.
    body: Content,
) -> Value {
    delimited(body, '⌈', '⌉')
}

/// Round an expression.
///
/// ## Example
/// ```example
/// $ round(x/2) $
/// ```
///
/// Display: Round
/// Category: math
/// Returns: content
#[func]
pub fn round(
    /// The expression to round.
    body: Content,
) -> Value {
    delimited(body, '⌊', '⌉')
}

/// Take the absolute value of an expression.
///
/// ## Example
/// ```example
/// $ abs(x/2) $
/// ```
///
///
/// Display: Abs
/// Category: math
/// Returns: content
#[func]
pub fn abs(
    /// The expression to take the absolute value of.
    body: Content,
) -> Value {
    delimited(body, '|', '|')
}

/// Take the norm of an expression.
///
/// ## Example
/// ```example
/// $ norm(x/2) $
/// ```
///
/// Display: Norm
/// Category: math
/// Returns: content
#[func]
pub fn norm(
    /// The expression to take the norm of.
    body: Content,
) -> Value {
    delimited(body, '‖', '‖')
}

fn delimited(body: Content, left: char, right: char) -> Value {
    LrElem::new(Content::sequence([
        TextElem::packed(left),
        body,
        TextElem::packed(right),
    ]))
    .pack()
    .into()
}