SVG: centred and right-aligned type on a path keeps its place

Squashed from #5977 onto main.

contributors/people.toml

@@ -208,7 +208,7 @@ sync_github_name = true
 [people.sadkotheguest]
 real_name = "Alexander Buraga"
 display_name = "Alexander Buraga"
-sync_github_name = false
+sync_github_name = false
 
 [people.adikshan11]
 real_name = "Adithya Shankaran"
@@ -216,3 +216,7 @@ sync_github_name = true
 
 [people.slafebre]
 real_name = "Sven Lafebre"
+
+[people.kylekanouse]
+real_name = "Kyle Kanouse"
+sync_github_name = true

crates/svg/src/export/text.rs

@@ -519,14 +519,24 @@ impl Writer<'_> {
         let space = (lay.bounds, self.xf * t.xf);
         let base = self.char_props(&t.first_style(), space);
         let mut props = base.clone();
-        match t.para_at(0).justify {
-            Justify::Center | Justify::JustifyCenter => props.push(("text-anchor", "middle".into())),
-            Justify::Right | Justify::JustifyRight => props.push(("text-anchor", "end".into())),
-            _ => {}
-        }
+        let (from, to) = t.kind.path_span().unwrap_or((start, 1.0));
+        // The anchor sits where the layout aligns the line within its span.
+        let at = match t.para_at(0).justify {
+            Justify::Center | Justify::JustifyCenter => {
+                props.push(("text-anchor", "middle".into()));
+                (from + to) / 2.0
+            }
+            Justify::Right | Justify::JustifyRight => {
+                props.push(("text-anchor", "end".into()));
+                to
+            }
+            _ => from,
+        };
+        // A closed path's span runs past its start point; `startOffset` can't, so wrap it.
+        let at = if at > 1.0 { at - 1.0 } else { at };
         props.extend(css::transparency(n));
         let a = self.attrs(&props);
-        let offset = fmt_num(start * 100.0, 3);
+        let offset = fmt_num(at * 100.0, 3);
         let mut s = format!("<text{id} xml:space=\"preserve\"{a}><textPath xlink:href=\"#{pid}\" startOffset=\"{offset}%\">");
         for run in &t.runs {
             let mut diff = run_diff(&base, self.char_props(&run.style, space));

crates/svg/tests/it/roundtrip.rs

@@ -444,6 +444,40 @@ fn text_on_path_roundtrip() {
     assert!(close_rect(doc_path, PathData::from_bezpath(&curve).bounds().unwrap(), 0.01), "{doc_path:?}");
 }
 
+/// Centred and right-aligned type on a path anchors where the layout aligns it: the middle or the
+/// end of its span, wrapped on a closed path. It reads back drawn where it was.
+#[test]
+fn aligned_text_on_path_anchors_within_its_span() {
+    use vectorcraft_doc::Justify;
+    use vectorcraft_geom::Shape;
+    let mut curve = vectorcraft_geom::BezPath::new();
+    curve.move_to((20.0, 150.0));
+    curve.curve_to((60.0, 40.0), (140.0, 40.0), (180.0, 150.0));
+    let circle = vectorcraft_geom::kurbo::Circle::new((100.0, 100.0), 60.0).to_path(0.01);
+    let drawn = |t: &TextObject| t.xf.transform_rect_bbox(vectorcraft_text::layout(vectorcraft_text::FontDb::global(), t).bounds);
+    for (path, start, justify, offset) in [
+        (&curve, 0.25, Justify::Center, "62.5%"),
+        (&curve, 0.25, Justify::Right, "100%"),
+        (&curve, 0.25, Justify::Left, "25%"),
+        (&circle, 0.7, Justify::Center, "20%"),
+    ] {
+        let mut d = Document::new(200.0, 200.0);
+        let mut t = TextObject::point(Point::ZERO, "Aligned", CharStyle { size: 14.0, ..CharStyle::default() });
+        t.kind = TextKind::OnPath { path: PathData::from_bezpath(path), start, end: None };
+        t.para.justify = justify;
+        let before = drawn(&t);
+        let id = d.alloc_id();
+        let d = doc_with(vec![Node::new(id, NodeKind::Text(Box::new(t)))]);
+        let svg = export(&d, &ExportOptions::default());
+        assert!(svg.contains(&format!("startOffset=\"{offset}\"")), "{justify:?} at {start}: {svg}");
+        if path == &curve {
+            let r = import(&svg).unwrap();
+            let NodeKind::Text(t) = &art(&r)[0].kind else { panic!() };
+            assert!(close_rect(drawn(t), before, 0.5), "{justify:?}: {:?} {before:?}", drawn(t));
+        }
+    }
+}
+
 /// An end bracket, Align to Path or Spacing, which `<textPath>` can't express, keep their look as
 /// outlines (#429).
 #[test]