Split crates

1 files changed, 83 insertions, 0 deletions

diff --git a/library/src/layout/pad.rs b/library/src/layout/pad.rs
new file mode 100644
index 00000000..318d9f27
--- /dev/null
+++ b/library/src/layout/pad.rs
@@ -0,0 +1,83 @@
+use crate::prelude::*;
+
+/// Pad content at the sides.
+#[derive(Debug, Hash)]
+pub struct PadNode {
+    /// The amount of padding.
+    pub padding: Sides<Rel<Length>>,
+    /// The content whose sides to pad.
+    pub child: Content,
+}
+
+#[node(LayoutBlock)]
+impl PadNode {
+    fn construct(_: &mut 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(body.padded(padding))
+    }
+}
+
+impl LayoutBlock for PadNode {
+    fn layout_block(
+        &self,
+        world: Tracked<dyn World>,
+        regions: &Regions,
+        styles: StyleChain,
+    ) -> SourceResult<Vec<Frame>> {
+        // Layout child into padded regions.
+        let padding = self.padding.resolve(styles);
+        let pod = regions.map(|size| shrink(size, padding));
+        let mut frames = self.child.layout_block(world, &pod, styles)?;
+
+        for frame in &mut frames {
+            // 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(frames)
+    }
+}
+
+/// 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()))
+}