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//! Surrounding nodes with extra space.
use super::prelude::*;
/// `pad`: Pad content at the sides.
pub fn pad(_: &mut EvalContext, args: &mut Args) -> TypResult<Value> {
let all = args.find();
let left = args.named("left")?;
let top = args.named("top")?;
let right = args.named("right")?;
let bottom = args.named("bottom")?;
let body: PackedNode = args.expect("body")?;
let padding = Sides::new(
left.or(all).unwrap_or_default(),
top.or(all).unwrap_or_default(),
right.or(all).unwrap_or_default(),
bottom.or(all).unwrap_or_default(),
);
Ok(Value::block(body.padded(padding)))
}
/// A node that adds padding to its child.
#[derive(Debug, Hash)]
pub struct PadNode {
/// The amount of padding.
pub padding: Sides<Linear>,
/// The child node whose sides to pad.
pub child: PackedNode,
}
impl Layout for PadNode {
fn layout(
&self,
ctx: &mut LayoutContext,
regions: &Regions,
styles: StyleChain,
) -> Vec<Constrained<Rc<Frame>>> {
// Layout child into padded regions.
let pod = regions.map(|size| shrink(size, self.padding));
let mut frames = self.child.layout(ctx, &pod, styles);
for ((current, base), Constrained { item: frame, cts }) in
regions.iter().zip(&mut frames)
{
// Apply the padding inversely such that the grown size padded
// yields the frame's size.
let padded = grow(frame.size, self.padding);
let padding = self.padding.resolve(padded);
let offset = Point::new(padding.left, padding.top);
// Grow the frame and translate everything in the frame inwards.
let frame = Rc::make_mut(frame);
frame.size = padded;
frame.translate(offset);
// Set exact and base constraints if the child had them. Also set
// base if our padding is relative.
let is_rel = self.padding.sum_by_axis().map(Linear::is_relative);
cts.exact = current.filter(cts.exact.map_is_some());
cts.base = base.filter(is_rel | cts.base.map_is_some());
// Inflate min and max contraints by the padding.
for spec in [&mut cts.min, &mut cts.max] {
spec.as_mut()
.zip(padding.sum_by_axis())
.map(|(s, p)| s.as_mut().map(|v| *v += p));
}
}
frames
}
}
/// Shrink a size by padding relative to the size itself.
fn shrink(size: Size, padding: Sides<Linear>) -> Size {
size - padding.resolve(size).sum_by_axis()
}
/// Grow a size by padding relative to the grown size.
/// This is the inverse operation to `shrink()`.
///
/// For the horizontal axis the derivation looks as follows.
/// (Vertical axis is analogous.)
///
/// Let w be the grown target width,
/// s be given width,
/// l be the left padding,
/// r be the right padding,
/// p = l + r.
///
/// We want that: w - l.resolve(w) - r.resolve(w) = s
///
/// Thus: w - l.resolve(w) - r.resolve(w) = s
/// <=> w - p.resolve(w) = s
/// <=> w - p.rel * w - p.abs = s
/// <=> (1 - p.rel) * w = s + p.abs
/// <=> w = (s + p.abs) / (1 - p.rel)
fn grow(size: Size, padding: Sides<Linear>) -> Size {
size.zip(padding.sum_by_axis())
.map(|(s, p)| (s + p.abs).safe_div(1.0 - p.rel.get()))
}
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