From 17f8939f8631104737b928ddeebb401134da1f6e Mon Sep 17 00:00:00 2001
From: Laurenz <laurmaedje@gmail.com>
Date: Sun, 29 Jan 2023 17:44:58 +0100
Subject: [PATCH] Fix math alignment points

---
 library/src/math/row.rs   | 16 +++++++++++++---
 library/src/math/stack.rs |  6 ++++--
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/library/src/math/row.rs b/library/src/math/row.rs
index bc0131828..f35d51c85 100644
--- a/library/src/math/row.rs
+++ b/library/src/math/row.rs
@@ -86,7 +86,7 @@ impl MathRow {
             let points = alignments(&rows);
             for (i, row) in rows.into_iter().enumerate() {
                 let size = frame.size_mut();
-                let sub = row.to_line_frame(ctx, &points);
+                let sub = row.to_line_frame(ctx, &points, Align::Center);
                 if i > 0 {
                     size.y += leading;
                 }
@@ -97,11 +97,11 @@ impl MathRow {
             }
             frame
         } else {
-            self.to_line_frame(ctx, &[])
+            self.to_line_frame(ctx, &[], Align::Center)
         }
     }
 
-    pub fn to_line_frame(self, ctx: &MathContext, points: &[Abs]) -> Frame {
+    pub fn to_line_frame(self, ctx: &MathContext, points: &[Abs], align: Align) -> Frame {
         let ascent = self.0.iter().map(MathFragment::ascent).max().unwrap_or_default();
         let descent = self.0.iter().map(MathFragment::descent).max().unwrap_or_default();
 
@@ -110,6 +110,16 @@ impl MathRow {
         let mut x = Abs::zero();
         frame.set_baseline(ascent);
 
+        if let (Some(&first), Align::Center) = (points.first(), align) {
+            let segment: Abs = self
+                .0
+                .iter()
+                .take_while(|fragment| !matches!(fragment, MathFragment::Align))
+                .map(|fragment| fragment.width())
+                .sum();
+            x = first - segment;
+        }
+
         let mut fragments = self.0.into_iter().peekable();
         let mut i = 0;
         while let Some(fragment) = fragments.next() {
diff --git a/library/src/math/stack.rs b/library/src/math/stack.rs
index c8a1252c0..ec233cd91 100644
--- a/library/src/math/stack.rs
+++ b/library/src/math/stack.rs
@@ -290,8 +290,10 @@ pub(super) fn stack(
     let mut height = rows.len().saturating_sub(1) as f64 * gap;
 
     let points = alignments(&rows);
-    let rows: Vec<_> =
-        rows.into_iter().map(|row| row.to_line_frame(ctx, &points)).collect();
+    let rows: Vec<_> = rows
+        .into_iter()
+        .map(|row| row.to_line_frame(ctx, &points, align))
+        .collect();
 
     for row in &rows {
         height += row.height();