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use crate::prelude::*;
/// # Padding
/// Add spacing around content.
///
/// The `pad` function adds spacing around content. The spacing can be specified
/// for each side individually, or for all sides at once by specifying a
/// positional argument.
///
/// ## Example
/// ```example
/// #set align(center)
///
/// #pad(x: 16pt, image("typing.jpg"))
/// _Typing speeds can be
/// measured in words per minute._
/// ```
///
/// ## Parameters
/// - body: `Content` (positional, required)
/// The content to pad at the sides.
///
/// - left: `Rel<Length>` (named)
/// The padding at the left side.
///
/// - right: `Rel<Length>` (named)
/// The padding at the right side.
///
/// - top: `Rel<Length>` (named)
/// The padding at the top side.
///
/// - bottom: `Rel<Length>` (named)
/// The padding at the bottom side.
///
/// - x: `Rel<Length>` (named)
/// The horizontal padding. Both `left` and `right` take precedence over this.
///
/// - y: `Rel<Length>` (named)
/// The vertical padding. Both `top` and `bottom` take precedence over this.
///
/// - rest: `Rel<Length>` (named)
/// The padding for all sides. All other parameters take precedence over this.
///
/// ## Category
/// layout
#[func]
#[capable(Layout)]
#[derive(Debug, Hash)]
pub struct PadNode {
/// The amount of padding.
pub padding: Sides<Rel<Length>>,
/// The content whose sides to pad.
pub body: Content,
}
#[node]
impl PadNode {
fn construct(_: &Vm, args: &mut Args) -> SourceResult<Content> {
let all = args.named("rest")?.or(args.find()?);
let x = args.named("x")?;
let y = args.named("y")?;
let left = args.named("left")?.or(x).or(all).unwrap_or_default();
let top = args.named("top")?.or(y).or(all).unwrap_or_default();
let right = args.named("right")?.or(x).or(all).unwrap_or_default();
let bottom = args.named("bottom")?.or(y).or(all).unwrap_or_default();
let body = args.expect::<Content>("body")?;
let padding = Sides::new(left, top, right, bottom);
Ok(Self { padding, body }.pack())
}
}
impl Layout for PadNode {
fn layout(
&self,
vt: &mut Vt,
styles: StyleChain,
regions: Regions,
) -> SourceResult<Fragment> {
let mut backlog = vec![];
// Layout child into padded regions.
let padding = self.padding.resolve(styles);
let pod = regions.map(&mut backlog, |size| shrink(size, padding));
let mut fragment = self.body.layout(vt, styles, pod)?;
for frame in &mut fragment {
// Apply the padding inversely such that the grown size padded
// yields the frame's size.
let padded = grow(frame.size(), padding);
let padding = padding.relative_to(padded);
let offset = Point::new(padding.left, padding.top);
// Grow the frame and translate everything in the frame inwards.
frame.set_size(padded);
frame.translate(offset);
}
Ok(fragment)
}
}
/// Shrink a size by padding relative to the size itself.
fn shrink(size: Size, padding: Sides<Rel<Abs>>) -> Size {
size - padding.relative_to(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 the 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<Rel<Abs>>) -> Size {
size.zip(padding.sum_by_axis())
.map(|(s, p)| (s + p.abs).safe_div(1.0 - p.rel.get()))
}
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