Compose: vertical justification looks up each wrap's anchored object once

The object anchored at each story byte is indexed once per column, and each wrap's object is found once, not once for every line.

crates/compose/src/lib.rs

@@ -5691,14 +5691,20 @@ fn wrap_rooms(ft: &FrameText, f: &FrameSpec, c: u32, spanned: bool, anchors: &[u
     };
     let in_col = |k: u32| spanned || k == c;
     let justify = f.opts.vertical_justification == VerticalJustification::Justify;
+    // The object whose mark is at each story byte, placed on one of these lines (the first one
+    // listed).
+    let mut by_anchor = HashMap::new();
+    for o in ft.objects.iter().filter(|o| ft.lines.get(o.line).is_some_and(|l| in_col(l.column))) {
+        if let Some(&a) = anchors.get(o.index) {
+            by_anchor.entry(a).or_insert(o);
+        }
+    }
     // An own-story anchored object whose anchor is on one of these lines and whose position
     // follows its line moves with the text: the index in `ft.lines` of its anchor's line, and how
     // much lower that line was when the wrap was taken (an earlier pass placed the object after
     // moving the lines).
     let moves_with_text = |e: &Exclusion| -> Option<(usize, f64)> {
-        let a = e.after?;
-        // The object whose mark is the anchor, placed on one of these lines.
-        let o = ft.objects.iter().find(|o| anchors.get(o.index) == Some(&a) && ft.lines.get(o.line).is_some_and(|l| in_col(l.column)))?;
+        let o = *by_anchor.get(&e.after?)?;
         let follows = match &o.object.position {
             designcraft_doc::AnchorPosition::Inline { .. } | designcraft_doc::AnchorPosition::AboveLine { .. } => true,
             // Kept within the column, it can stop at the column's edge instead of following.
@@ -5709,6 +5715,8 @@ fn wrap_rooms(ft: &FrameText, f: &FrameSpec, c: u32, spanned: bool, anchors: &[u
         let now = ft.lines.get(o.line).map_or(0.0, |l| l.baseline);
         follows.then(|| (o.line, e.anchor_baseline.map_or(0.0, |b| b - now)))
     };
+    // Each wrap's object is looked up once, not for every line.
+    let moving: Vec<Option<(usize, f64)>> = f.exclusions.iter().map(moves_with_text).collect();
     // Justify keeps the first row (its segments and a table on them) in place, so wraps under it
     // set no limit.
     let first = ft.lines.iter().find(|l| in_col(l.column)).map(|l| l.baseline);
@@ -5734,8 +5742,7 @@ fn wrap_rooms(ft: &FrameText, f: &FrameSpec, c: u32, spanned: bool, anchors: &[u
         let col = ft.columns.get(k as usize).copied().unwrap_or(f.area);
         let col = Rect { x0: col.x0.min(x0), x1: col.x1.max(x1), ..col };
         let meets = |(a, b): (f64, f64)| a < x1 - EPS && b > x0 + EPS;
-        for e in f.exclusions.iter().filter(|e| e.wraps_line(start)) {
-            let anchor = moves_with_text(e);
+        for (e, &anchor) in f.exclusions.iter().zip(&moving).filter(|(e, _)| e.wraps_line(start)) {
             if anchor.is_some() && !justify {
                 continue;
             }