Math root layout

library/src/math/mod.rs

@@ -48,6 +48,7 @@ pub fn define(scope: &mut Scope) {
     scope.def_func::<FracNode>("frac");
     scope.def_func::<ScriptNode>("script");
     scope.def_func::<SqrtNode>("sqrt");
+    scope.def_func::<RootNode>("root");
     scope.def_func::<VecNode>("vec");
     scope.def_func::<CasesNode>("cases");
     scope.def_func::<BoldNode>("bold");

library/src/math/root.rs

@@ -3,36 +3,171 @@ use super::*;
 /// # Square Root
 /// A square root.
 ///
-/// _Note:_ Non-square roots are not yet supported.
-///
 /// ## Example
 /// ```
 /// $ sqrt(x^2) = x = sqrt(x)^2 $
 /// ```
 ///
 /// ## Parameters
-/// - body: Content (positional, required)
+/// - radicand: Content (positional, required)
 ///   The expression to take the square root of.
 ///
 /// ## Category
 /// math
 #[func]
-#[capable(Texify)]
+#[capable(LayoutMath)]
 #[derive(Debug, Hash)]
 pub struct SqrtNode(pub Content);
 
 #[node]
 impl SqrtNode {
     fn construct(_: &Vm, args: &mut Args) -> SourceResult<Content> {
-        Ok(Self(args.expect("body")?).pack())
+        Ok(Self(args.expect("radicand")?).pack())
     }
 }
 
-impl Texify for SqrtNode {
-    fn texify(&self, t: &mut Texifier) -> SourceResult<()> {
-        t.push_str("\\sqrt{");
-        self.0.texify(t)?;
-        t.push_str("}");
-        Ok(())
+impl LayoutMath for SqrtNode {
+    fn layout_math(&self, ctx: &mut MathContext) -> SourceResult<()> {
+        layout(ctx, None, &self.0)
     }
 }
+
+/// # Root
+/// A general root.
+///
+/// ## Example
+/// ```
+/// $ radical(3, x) $
+/// ```
+///
+/// ## Parameters
+/// - index: Content (positional, required)
+///   Which root of the radicand to take.
+///
+/// - radicand: Content (positional, required)
+///   The expression to take the root of.
+///
+/// ## Category
+/// math
+#[func]
+#[capable(LayoutMath)]
+#[derive(Debug, Hash)]
+pub struct RootNode {
+    index: Content,
+    radicand: Content,
+}
+
+#[node]
+impl RootNode {
+    fn construct(_: &Vm, args: &mut Args) -> SourceResult<Content> {
+        Ok(Self {
+            index: args.expect("index")?,
+            radicand: args.expect("radicand")?,
+        }
+        .pack())
+    }
+}
+
+impl LayoutMath for RootNode {
+    fn layout_math(&self, ctx: &mut MathContext) -> SourceResult<()> {
+        layout(ctx, Some(&self.index), &self.radicand)
+    }
+}
+
+/// Layout a root.
+///
+/// https://www.w3.org/TR/mathml-core/#radicals-msqrt-mroot
+fn layout(
+    ctx: &mut MathContext,
+    mut index: Option<&Content>,
+    radicand: &Content,
+) -> SourceResult<()> {
+    let gap = scaled!(
+        ctx,
+        text: radical_vertical_gap,
+        display: radical_display_style_vertical_gap,
+    );
+    let thickness = scaled!(ctx, radical_rule_thickness);
+    let ascender = scaled!(ctx, radical_extra_ascender);
+    let kern_before = scaled!(ctx, radical_kern_before_degree);
+    let kern_after = scaled!(ctx, radical_kern_after_degree);
+    let raise = percent!(ctx, radical_degree_bottom_raise_percent);
+
+    // Layout radicand.
+    ctx.style(ctx.style.with_cramped(true));
+    let radicand = ctx.layout_frame(radicand)?;
+    ctx.unstyle();
+
+    // Layout root symbol.
+    let target = radicand.height() + thickness + gap;
+    let sqrt = precomposed(ctx, index, target)
+        .map(|frame| {
+            index = None;
+            frame
+        })
+        .unwrap_or_else(|| {
+            let glyph = GlyphFragment::new(ctx, '√');
+            glyph.stretch_vertical(ctx, target, Abs::zero()).frame
+        });
+
+    // Layout the index.
+    let mut offset = Abs::zero();
+    let index = if let Some(index) = index {
+        // Script-script style looks too small, we use Script style instead.
+        ctx.style(ctx.style.with_size(MathSize::Script));
+        let frame = ctx.layout_frame(index)?;
+        offset = kern_before + frame.width() + kern_after;
+        ctx.unstyle();
+        frame
+    } else {
+        Frame::new(Size::zero())
+    };
+
+    let width = offset + sqrt.width() + radicand.width();
+    let height = sqrt.height() + ascender;
+    let size = Size::new(width, height);
+    let remains = (sqrt.height() - radicand.height() - thickness) / 2.0;
+    let index_pos =
+        Point::new(kern_before, height - index.ascent() - raise * sqrt.height());
+    let sqrt_pos = Point::new(offset, ascender);
+    let line_pos = Point::new(offset + sqrt.width(), ascender + thickness / 2.0);
+    let line_length = radicand.width();
+    let radicand_pos =
+        Point::new(offset + sqrt.width(), ascender + thickness + gap.max(remains));
+    let baseline = radicand_pos.y + radicand.ascent();
+
+    let mut frame = Frame::new(size);
+    frame.set_baseline(baseline);
+    frame.push_frame(index_pos, index);
+    frame.push_frame(sqrt_pos, sqrt);
+    frame.push(
+        line_pos,
+        Element::Shape(
+            Geometry::Line(Point::with_x(line_length))
+                .stroked(Stroke { paint: ctx.fill, thickness }),
+        ),
+    );
+    frame.push_frame(radicand_pos, radicand);
+    ctx.push(frame);
+
+    Ok(())
+}
+
+/// Select a precomposed radical, if the font has it.
+fn precomposed(ctx: &MathContext, index: Option<&Content>, target: Abs) -> Option<Frame> {
+    let node = index?.to::<MathNode>()?.body.to::<AtomNode>()?;
+    let c = match node.0.as_str() {
+        "3" => '∛',
+        "4" => '∜',
+        _ => return None,
+    };
+
+    ctx.ttf.glyph_index(c)?;
+    let glyph = GlyphFragment::new(ctx, c);
+    let variant = glyph.stretch_vertical(ctx, target, Abs::zero()).frame;
+    if variant.height() < target {
+        return None;
+    }
+
+    Some(variant)
+}