Fraction layout

library/src/math/frac.rs

@@ -25,7 +25,7 @@ use super::*;
 /// ## Category
 /// math
 #[func]
-#[capable(Texify)]
+#[capable(LayoutMath)]
 #[derive(Debug, Hash)]
 pub struct FracNode {
     /// The numerator.
@@ -43,14 +43,9 @@ impl FracNode {
     }
 }
 
-impl Texify for FracNode {
-    fn texify(&self, t: &mut Texifier) -> SourceResult<()> {
-        t.push_str("\\frac{");
-        self.num.texify_unparen(t)?;
-        t.push_str("}{");
-        self.denom.texify_unparen(t)?;
-        t.push_str("}");
-        Ok(())
+impl LayoutMath for FracNode {
+    fn layout_math(&self, ctx: &mut MathContext) -> SourceResult<()> {
+        layout(ctx, &self.num, &self.denom, false)
     }
 }
 
@@ -72,7 +67,7 @@ impl Texify for FracNode {
 /// ## Category
 /// math
 #[func]
-#[capable(Texify)]
+#[capable(LayoutMath)]
 #[derive(Debug, Hash)]
 pub struct BinomNode {
     /// The upper index.
@@ -90,13 +85,83 @@ impl BinomNode {
     }
 }
 
-impl Texify for BinomNode {
-    fn texify(&self, t: &mut Texifier) -> SourceResult<()> {
-        t.push_str("\\binom{");
-        self.upper.texify(t)?;
-        t.push_str("}{");
-        self.lower.texify(t)?;
-        t.push_str("}");
-        Ok(())
+impl LayoutMath for BinomNode {
+    fn layout_math(&self, ctx: &mut MathContext) -> SourceResult<()> {
+        layout(ctx, &self.upper, &self.lower, true)
     }
 }
+
+/// Layout a fraction or binomial.
+fn layout(
+    ctx: &mut MathContext,
+    num: &Content,
+    denom: &Content,
+    binom: bool,
+) -> SourceResult<()> {
+    let axis = scaled!(ctx, axis_height);
+    let thickness = scaled!(ctx, fraction_rule_thickness);
+    let shift_up = scaled!(
+        ctx,
+        text: fraction_numerator_shift_up,
+        display: fraction_numerator_display_style_shift_up,
+    );
+    let shift_down = scaled!(
+        ctx,
+        text: fraction_denominator_shift_down,
+        display: fraction_denominator_display_style_shift_down,
+    );
+    let num_min = scaled!(
+        ctx,
+        text: fraction_numerator_gap_min,
+        display: fraction_num_display_style_gap_min,
+    );
+    let denom_min = scaled!(
+        ctx,
+        text: fraction_denominator_gap_min,
+        display: fraction_denom_display_style_gap_min,
+    );
+
+    ctx.style(ctx.style.for_numerator());
+    let num = ctx.layout_frame(num)?;
+    ctx.unstyle();
+
+    ctx.style(ctx.style.for_denominator());
+    let denom = ctx.layout_frame(denom)?;
+    ctx.unstyle();
+
+    let around = Em::new(0.1).scaled(ctx);
+    let num_gap = (shift_up - axis - num.descent()).max(num_min + thickness / 2.0);
+    let denom_gap = (shift_down + axis - denom.ascent()).max(denom_min + thickness / 2.0);
+
+    let line_width = num.width().max(denom.width());
+    let width = line_width + 2.0 * around;
+    let height = num.height() + num_gap + thickness + denom_gap + denom.height();
+    let size = Size::new(width, height);
+    let num_pos = Point::with_x((width - num.width()) / 2.0);
+    let line_pos =
+        Point::new((width - line_width) / 2.0, num.height() + num_gap + thickness / 2.0);
+    let denom_pos = Point::new((width - denom.width()) / 2.0, height - denom.height());
+    let baseline = line_pos.y + axis;
+
+    let mut frame = Frame::new(size);
+    frame.set_baseline(baseline);
+    frame.push_frame(num_pos, num);
+    frame.push_frame(denom_pos, denom);
+
+    if binom {
+        ctx.push(GlyphFragment::new(ctx, '('));
+        ctx.push(frame);
+        ctx.push(GlyphFragment::new(ctx, ')'));
+    } else {
+        frame.push(
+            line_pos,
+            Element::Shape(
+                Geometry::Line(Point::with_x(line_width))
+                    .stroked(Stroke { paint: ctx.fill, thickness }),
+            ),
+        );
+        ctx.push(frame);
+    }
+
+    Ok(())
+}

library/src/math/mod.rs

@@ -47,6 +47,7 @@ use crate::text::{families, variant, FallbackList, FontFamily, SpaceNode, Symbol
 pub fn define(scope: &mut Scope) {
     scope.def_func::<MathNode>("math");
     scope.def_func::<FracNode>("frac");
+    scope.def_func::<BinomNode>("binom");
     scope.def_func::<ScriptNode>("script");
     scope.def_func::<SqrtNode>("sqrt");
     scope.def_func::<RootNode>("root");