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use super::*;
/// A node that adds padding to its child.
#[derive(Debug, Clone, PartialEq)]
pub struct PadNode {
/// The amount of padding.
pub padding: Sides<Linear>,
/// The child node whose sides to pad.
pub child: Node,
}
impl Layout for PadNode {
fn layout(&self, ctx: &mut LayoutContext, areas: &Areas) -> Fragment {
let areas = shrink(areas, self.padding);
let mut fragment = self.child.layout(ctx, &areas);
for frame in fragment.frames_mut() {
pad(frame, self.padding);
}
fragment
}
}
impl From<PadNode> for AnyNode {
fn from(pad: PadNode) -> Self {
Self::new(pad)
}
}
/// Shrink all areas by the padding.
fn shrink(areas: &Areas, padding: Sides<Linear>) -> Areas {
areas.map(|size| size - padding.resolve(size).size())
}
/// Pad the frame and move all elements inwards.
fn pad(frame: &mut Frame, padding: Sides<Linear>) {
let padded = solve(padding, frame.size);
let padding = padding.resolve(padded);
let origin = Point::new(padding.left, padding.top);
frame.size = padded;
for (point, _) in &mut frame.elements {
*point += origin;
}
}
/// Solve for the size `padded` that satisfies (approximately):
/// `padded - padding.resolve(padded).size() == size`
fn solve(padding: Sides<Linear>, size: Size) -> Size {
fn solve_axis(length: Length, padding: Linear) -> Length {
(length + padding.abs) / (1.0 - padding.rel.get())
}
Size::new(
solve_axis(size.width, padding.left + padding.right),
solve_axis(size.height, padding.top + padding.bottom),
)
}
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