Center delimiters vertically about the axis (#1756)

5 files changed, 29 insertions, 17 deletions

diff --git a/crates/typst-library/src/math/ctx.rs b/crates/typst-library/src/math/ctx.rs
index 4a0959ab..acd60e48 100644
--- a/crates/typst-library/src/math/ctx.rs
+++ b/crates/typst-library/src/math/ctx.rs
@@ -185,8 +185,7 @@ impl<'a, 'b, 'v> MathContext<'a, 'b, 'v> {
                     glyph.into_variant()
                 };
                 // TeXbook p 155. Large operators are always vertically centered on the axis.
-                let h = variant.frame.height();
-                variant.frame.set_baseline(h / 2.0 + scaled!(self, axis_height));
+                variant.center_on_axis(self);
                 variant.into()
             } else {
                 glyph.into()
diff --git a/crates/typst-library/src/math/delimited.rs b/crates/typst-library/src/math/delimited.rs
index 99cd6c33..25ecf623 100644
--- a/crates/typst-library/src/math/delimited.rs
+++ b/crates/typst-library/src/math/delimited.rs
@@ -95,9 +95,10 @@ fn scale(
         };
 
         let short_fall = DELIM_SHORT_FALL.scaled(ctx);
-        *fragment =
-            MathFragment::Variant(glyph.stretch_vertical(ctx, height, short_fall));
+        let mut stretched = glyph.stretch_vertical(ctx, height, short_fall);
+        stretched.center_on_axis(ctx);
 
+        *fragment = MathFragment::Variant(stretched);
         if let Some(class) = apply {
             fragment.set_class(class);
         }
diff --git a/crates/typst-library/src/math/frac.rs b/crates/typst-library/src/math/frac.rs
index 0e1f78cc..cf1d38e9 100644
--- a/crates/typst-library/src/math/frac.rs
+++ b/crates/typst-library/src/math/frac.rs
@@ -122,13 +122,15 @@ fn layout(
     frame.push_frame(denom_pos, denom);
 
     if binom {
-        ctx.push(
-            GlyphFragment::new(ctx, '(', span).stretch_vertical(ctx, height, short_fall),
-        );
+        let mut left =
+            GlyphFragment::new(ctx, '(', span).stretch_vertical(ctx, height, short_fall);
+        left.center_on_axis(ctx);
+        ctx.push(left);
         ctx.push(FrameFragment::new(ctx, frame));
-        ctx.push(
-            GlyphFragment::new(ctx, ')', span).stretch_vertical(ctx, height, short_fall),
-        );
+        let mut right =
+            GlyphFragment::new(ctx, ')', span).stretch_vertical(ctx, height, short_fall);
+        right.center_on_axis(ctx);
+        ctx.push(right);
     } else {
         frame.push(
             line_pos,
diff --git a/crates/typst-library/src/math/fragment.rs b/crates/typst-library/src/math/fragment.rs
index 85fdf6a6..f4efa7f6 100644
--- a/crates/typst-library/src/math/fragment.rs
+++ b/crates/typst-library/src/math/fragment.rs
@@ -353,6 +353,15 @@ pub struct VariantFragment {
     pub limits: Limits,
 }
 
+impl VariantFragment {
+    /// Vertically adjust the fragment's frame so that it is centered
+    /// on the axis.
+    pub fn center_on_axis(&mut self, ctx: &MathContext) {
+        let h = self.frame.height();
+        self.frame.set_baseline(h / 2.0 + scaled!(ctx, axis_height));
+    }
+}
+
 impl Debug for VariantFragment {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         write!(f, "VariantFragment({:?})", self.c)
diff --git a/crates/typst-library/src/math/matrix.rs b/crates/typst-library/src/math/matrix.rs
index aaccc332..3fa53ba0 100644
--- a/crates/typst-library/src/math/matrix.rs
+++ b/crates/typst-library/src/math/matrix.rs
@@ -295,18 +295,19 @@ fn layout_delimiters(
     frame.set_baseline(height / 2.0 + axis);
 
     if let Some(left) = left {
-        ctx.push(
-            GlyphFragment::new(ctx, left, span).stretch_vertical(ctx, target, short_fall),
-        );
+        let mut left =
+            GlyphFragment::new(ctx, left, span).stretch_vertical(ctx, target, short_fall);
+        left.center_on_axis(ctx);
+        ctx.push(left);
     }
 
     ctx.push(FrameFragment::new(ctx, frame));
 
     if let Some(right) = right {
-        ctx.push(
-            GlyphFragment::new(ctx, right, span)
-                .stretch_vertical(ctx, target, short_fall),
-        );
+        let mut right = GlyphFragment::new(ctx, right, span)
+            .stretch_vertical(ctx, target, short_fall);
+        right.center_on_axis(ctx);
+        ctx.push(right);
     }
 
     Ok(())