typst/src/library/sized.rs

use super::prelude::*;

/// `box`: Size content and place it into a paragraph.
pub fn box_(_: &mut EvalContext, args: &mut Args) -> TypResult<Value> {
    let width = args.named("width")?;
    let height = args.named("height")?;
    let body: Node = args.find().unwrap_or_default();
    Ok(Value::inline(
        body.into_block().sized(Spec::new(width, height)),
    ))
}

/// `block`: Place content into the flow.
pub fn block(_: &mut EvalContext, args: &mut Args) -> TypResult<Value> {
    let body: Node = args.find().unwrap_or_default();
    Ok(Value::block(body.into_block()))
}

/// A node that sizes its child.
#[derive(Debug, Hash)]
pub struct SizedNode {
    /// How to size the node horizontally and vertically.
    pub sizing: Spec<Option<Linear>>,
    /// The node to be sized.
    pub child: PackedNode,
}

impl Layout for SizedNode {
    fn layout(
        &self,
        ctx: &mut LayoutContext,
        regions: &Regions,
    ) -> Vec<Constrained<Rc<Frame>>> {
        let is_auto = self.sizing.map_is_none();
        let is_rel = self.sizing.map(|s| s.map_or(false, Linear::is_relative));

        // The "pod" is the region into which the child will be layouted.
        let pod = {
            // Resolve the sizing to a concrete size.
            let size = self
                .sizing
                .zip(regions.base)
                .map(|(s, b)| s.map(|v| v.resolve(b)))
                .unwrap_or(regions.current);

            // Select the appropriate base and expansion for the child depending
            // on whether it is automatically or linearly sized.
            let base = is_auto.select(regions.base, size);
            let expand = regions.expand | !is_auto;

            Regions::one(size, base, expand)
        };

        let mut frames = self.child.layout(ctx, &pod);
        let Constrained { item: frame, cts } = &mut frames[0];

        // Ensure frame size matches regions size if expansion is on.
        let target = regions.expand.select(regions.current, frame.size);
        Rc::make_mut(frame).resize(target, Align::LEFT_TOP);

        // Set base & exact constraints if the child is automatically sized
        // since we don't know what the child might have done. Also set base if
        // our sizing is relative.
        *cts = Constraints::new(regions.expand);
        cts.exact = regions.current.filter(regions.expand | is_auto);
        cts.base = regions.base.filter(is_rel | is_auto);

        frames
    }
}