Under- and overbraces

library/src/math/braced.rs

@@ -0,0 +1,123 @@
+use super::*;
+
+const BRACED_GAP: Em = Em::new(0.3);
+
+/// # Underbrace
+/// A horizontal brace under content, with an optional annotation below.
+///
+/// ## Example
+/// ```
+/// $ underbrace(1 + 2 + ... + 5, "numbers") $
+/// ```
+///
+/// ## Parameters
+/// - body: Content (positional, required)
+///   The content above the brace.
+///
+/// - annotation: Content (positional)
+///   The optional content below the brace.
+///
+/// ## Category
+/// math
+#[func]
+#[capable(LayoutMath)]
+#[derive(Debug, Hash)]
+pub struct UnderbraceNode {
+    /// The content above the brace.
+    pub body: Content,
+    /// The optional content below the brace.
+    pub annotation: Option<Content>,
+}
+
+#[node]
+impl UnderbraceNode {
+    fn construct(_: &Vm, args: &mut Args) -> SourceResult<Content> {
+        let body = args.expect("body")?;
+        let annotation = args.eat()?;
+        Ok(Self { body, annotation }.pack())
+    }
+}
+
+impl LayoutMath for UnderbraceNode {
+    fn layout_math(&self, ctx: &mut MathContext) -> SourceResult<()> {
+        let gap = BRACED_GAP.scaled(ctx);
+        let body = ctx.layout_row(&self.body)?;
+        let glyph = GlyphFragment::new(ctx, '⏟');
+        let brace = glyph.stretch_horizontal(ctx, body.width(), Abs::zero());
+
+        let mut rows = vec![body, brace.into()];
+        ctx.style(ctx.style.for_subscript());
+        rows.extend(
+            self.annotation
+                .as_ref()
+                .map(|annotation| ctx.layout_row(annotation))
+                .transpose()?,
+        );
+        ctx.unstyle();
+        ctx.push(stack(ctx, rows, Align::Center, gap, 0));
+
+        Ok(())
+    }
+}
+
+/// # Overbrace
+/// A horizontal brace over content, with an optional annotation above.
+///
+/// ## Example
+/// ```
+/// $ overbrace(1 + 2 + ... + 5, "numbers") $
+/// ```
+///
+/// ## Parameters
+/// - body: Content (positional, required)
+///   The content below the brace.
+///
+/// - annotation: Content (positional)
+///   The optional content above the brace.
+///
+/// ## Category
+/// math
+#[func]
+#[capable(LayoutMath)]
+#[derive(Debug, Hash)]
+pub struct OverbraceNode {
+    /// The content below the brace.
+    pub body: Content,
+    /// The optional content above the brace.
+    pub annotation: Option<Content>,
+}
+
+#[node]
+impl OverbraceNode {
+    fn construct(_: &Vm, args: &mut Args) -> SourceResult<Content> {
+        let body = args.expect("body")?;
+        let annotation = args.eat()?;
+        Ok(Self { body, annotation }.pack())
+    }
+}
+
+impl LayoutMath for OverbraceNode {
+    fn layout_math(&self, ctx: &mut MathContext) -> SourceResult<()> {
+        let gap = BRACED_GAP.scaled(ctx);
+        let body = ctx.layout_row(&self.body)?;
+        let glyph = GlyphFragment::new(ctx, '⏞');
+        let brace = glyph.stretch_horizontal(ctx, body.width(), Abs::zero());
+
+        let mut rows = vec![];
+        ctx.style(ctx.style.for_superscript());
+        rows.extend(
+            self.annotation
+                .as_ref()
+                .map(|annotation| ctx.layout_row(annotation))
+                .transpose()?,
+        );
+        ctx.unstyle();
+        rows.push(brace.into());
+        rows.push(body);
+
+        let last = rows.len() - 1;
+        ctx.push(stack(ctx, rows, Align::Center, gap, last));
+
+        Ok(())
+    }
+}

library/src/math/mod.rs

@@ -5,6 +5,7 @@ mod ctx;
 mod accent;
 mod align;
 mod atom;
+mod braced;
 mod frac;
 mod group;
 mod matrix;
@@ -55,6 +56,8 @@ pub fn define(scope: &mut Scope) {
     scope.def_func::<RootNode>("root");
     scope.def_func::<VecNode>("vec");
     scope.def_func::<CasesNode>("cases");
+    scope.def_func::<UnderbraceNode>("underbrace");
+    scope.def_func::<OverbraceNode>("overbrace");
     scope.def_func::<BoldNode>("bold");
     scope.def_func::<ItalicNode>("italic");
     scope.def_func::<SerifNode>("serif");