#1197: Make Compound Path cuts holes where paths overlap

Make Compound Path kept each path's direction under the non-zero fill
rule, so a shape drawn inside or across another, running the same way,
left the overlap filled instead of making a hole. The paths in front of
the backmost one now run against it, so where they overlap it they cut
holes, as users expect from a compound path.

crates/engine/src/cmd/object.rs

@@ -652,11 +652,19 @@ fn compound_make(s: &mut Session, _: &Value) -> Result<Value> {
             d.remove(*id)?;
         }
         let ch = d.node_mut(cid).and_then(|n| n.children_mut()).ok_or(EngineError::NoNode(cid))?;
-        for mut p in paths {
+        // The paths in front run against the backmost one, so where they overlap it they cut holes
+        // under the non-zero fill rule (#1197).
+        let direction = |n: &Node| n.path_data().and_then(|pd| pd.subpaths.first()).map_or(0.0, |sp| sp.signed_area().signum());
+        let back = paths.first().map_or(0.0, |p| direction(p));
+        for (i, mut p) in paths.into_iter().enumerate() {
             let pn = Arc::make_mut(&mut p);
             pn.appearance = Appearance::default();
-            if let NodeKind::Path { live, .. } = &mut pn.kind {
+            let flip = i > 0 && back != 0.0 && direction(pn) == back;
+            if let NodeKind::Path { path, live, .. } = &mut pn.kind {
                 *live = None;
+                if flip {
+                    path.reverse();
+                }
             }
             ch.push(p);
         }

crates/engine/src/tests.rs

@@ -1699,3 +1699,19 @@ fn file_list_lists_a_folder_within_the_read_root() {
     assert!(s.execute("file.list", &json!({})).is_err());
     let _ = std::fs::remove_dir_all(base);
 }
+
+/// #1197: Make Compound Path cuts holes where the paths in front overlap the backmost one, also
+/// when they were drawn running the same way.
+#[test]
+fn a_compound_path_has_holes_where_its_paths_overlap() {
+    let mut s = session();
+    let square = rect(&mut s, 0.0, 0.0, 100.0, 100.0);
+    let diamond = NodeId(s.execute("path.create", &json!({"d": "M50 -20 L120 50 L50 120 L-20 50 Z"})).unwrap()["id"].as_u64().unwrap());
+    s.execute("select.set", &json!({"ids": [square.0, diamond.0]})).unwrap();
+    let c = NodeId(s.execute("object.compoundPath.make", &json!({})).unwrap()["id"].as_u64().unwrap());
+    let hit =
+        |x: f64, y: f64| vectorcraft_doc::hit::hit_test(&s.doc().unwrap().doc, Point::new(x, y), Default::default()).map(|h| h.top_object(None));
+    assert_eq!(hit(50.0, 50.0), None, "the overlap is a hole");
+    assert_eq!(hit(3.0, 3.0), Some(c), "the square's corner is filled");
+    assert_eq!(hit(110.0, 50.0), Some(c), "the diamond's point outside the square is filled");
+}