Pad matrix cell to make matrix have a consistent height (#4153)

crates/typst/src/math/matrix.rs

@@ -22,7 +22,7 @@ use crate::visualize::{FixedStroke, Geometry, LineCap, Shape, Stroke};
 
 use super::delimiter_alignment;
 
-const DEFAULT_ROW_GAP: Em = Em::new(0.5);
+const DEFAULT_ROW_GAP: Em = Em::new(0.2);
 const DEFAULT_COL_GAP: Em = Em::new(0.5);
 const VERTICAL_PADDING: Ratio = Ratio::new(0.1);
 const DEFAULT_STROKE_THICKNESS: Em = Em::new(0.05);
@@ -441,8 +441,12 @@ fn layout_vec_body(
     for child in column {
         flat.push(ctx.layout_into_run(child, styles.chain(&denom_style))?);
     }
-
-    Ok(stack(flat, align, gap, 0, alternator))
+    // We pad ascent and descent with the ascent and descent of the paren
+    // to ensure that normal vectors are aligned with others unless they are
+    // way too big.
+    let paren =
+        GlyphFragment::new(ctx, styles.chain(&denom_style), '(', Span::detached());
+    Ok(stack(flat, align, gap, 0, alternator, Some((paren.ascent, paren.descent))))
 }
 
 /// Layout the inner contents of a matrix.
@@ -499,12 +503,18 @@ fn layout_mat_body(
     let mut cols = vec![vec![]; ncols];
 
     let denom_style = style_for_denominator(styles);
+    // We pad ascent and descent with the ascent and descent of the paren
+    // to ensure that normal matrices are aligned with others unless they are
+    // way too big.
+    let paren =
+        GlyphFragment::new(ctx, styles.chain(&denom_style), '(', Span::detached());
+
     for (row, (ascent, descent)) in rows.iter().zip(&mut heights) {
         for (cell, col) in row.iter().zip(&mut cols) {
             let cell = ctx.layout_into_run(cell, styles.chain(&denom_style))?;
 
-            ascent.set_max(cell.ascent());
-            descent.set_max(cell.descent());
+            ascent.set_max(cell.ascent().max(paren.ascent));
+            descent.set_max(cell.descent().max(paren.descent));
 
             col.push(cell);
         }

crates/typst/src/math/underover.rs

@@ -291,8 +291,14 @@ fn layout_underoverspreader(
         baseline = rows.len() - 1;
     }
 
-    let frame =
-        stack(rows, FixedAlignment::Center, gap, baseline, LeftRightAlternator::Right);
+    let frame = stack(
+        rows,
+        FixedAlignment::Center,
+        gap,
+        baseline,
+        LeftRightAlternator::Right,
+        None,
+    );
     ctx.push(FrameFragment::new(ctx, styles, frame).with_class(body_class));
 
     Ok(())
@@ -309,6 +315,7 @@ pub(super) fn stack(
     gap: Abs,
     baseline: usize,
     alternator: LeftRightAlternator,
+    minimum_ascent_descent: Option<(Abs, Abs)>,
 ) -> Frame {
     let rows: Vec<_> = rows.into_iter().flat_map(|r| r.rows()).collect();
     let AlignmentResult { points, width } = alignments(&rows);
@@ -317,20 +324,27 @@ pub(super) fn stack(
         .map(|row| row.into_line_frame(&points, alternator))
         .collect();
 
+    let padded_height = |height: Abs| {
+        height.max(minimum_ascent_descent.map_or(Abs::zero(), |(a, d)| a + d))
+    };
+
     let mut frame = Frame::soft(Size::new(
         width,
-        rows.iter().map(|row| row.height()).sum::<Abs>()
+        rows.iter().map(|row| padded_height(row.height())).sum::<Abs>()
             + rows.len().saturating_sub(1) as f64 * gap,
     ));
 
     let mut y = Abs::zero();
     for (i, row) in rows.into_iter().enumerate() {
         let x = align.position(width - row.width());
-        let pos = Point::new(x, y);
+        let ascent_padded_part = minimum_ascent_descent
+            .map_or(Abs::zero(), |(a, _)| (a - row.ascent()))
+            .max(Abs::zero());
+        let pos = Point::new(x, y + ascent_padded_part);
         if i == baseline {
-            frame.set_baseline(y + row.baseline());
+            frame.set_baseline(y + row.baseline() + ascent_padded_part);
         }
-        y += row.height() + gap;
+        y += padded_height(row.height()) + gap;
         frame.push_frame(pos, row);
     }
 

tests/suite/math/mat.typ

@@ -212,3 +212,18 @@ $ mat(delim: angle.r, 1, 2; 3, 4) $
 --- math-mat-delims-pair ---
 $ mat(delim: #(none, "["), 1, 2; 3, 4) $
 $ mat(delim: #(sym.angle.r, sym.bracket.double.r), 1, 2; 3, 4) $
+
+--- issue-1617-mat-align ---
+#set page(width: auto)
+$ mat(a, b; c, d) mat(x; y) $
+
+$ x mat(a; c) + y mat(b; d)
+  = mat(a x+b y; c x+d y) $
+
+$ mat(
+    -d_0, lambda_0, 0, 0, dots;
+    mu_1, -d_1, lambda_1, 0, dots;
+    0, mu_2, -d_2, lambda_2, dots;
+    dots.v, dots.v, dots.v, dots.v, dots.down;
+  )
+  mat(p_0; p_1; p_2; dots.v) $