#1010: keep a parented camera's or light's Point of Interest in place

Parenting a camera or light (layer.setParent, compensate on) now re-expresses its Position and
Point of Interest in the new parent's space, like the other 3D layers. The 3D loop in parent_fixes
skipped cameras and lights, so their positions stayed in the old space and the camera moved by the
null's offset. Orientation is still left as authored; a later commit re-expresses it.

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>

crates/engine/src/commands/layer.rs

@@ -591,7 +591,8 @@ pub(crate) struct ParentFix {
     rotation: f64,
     /// Multiply Scale.
     scale: [f64; 2],
-    /// 3D AV layers retain their world-space anchor, including Z.
+    /// 3D AV layers retain their world-space anchor, including Z. Cameras and lights also
+    /// re-express their Point of Interest.
     position_3d: Option<effectcraft_geom::Mat4>,
     /// A uniform relative parent transform can preserve static Orientation and Scale.
     pose_3d: Option<([f64; 3], f64)>,
@@ -626,7 +627,8 @@ impl ParentFix {
                     }
                 }
             }
-            if let Some(pr) = tr.get_mut("position") {
+            // Position and a camera's or light's Point of Interest are both points in the parent's space.
+            let map_point = |pr: &mut effectcraft_project::Property| {
                 pr.value = map_position(&pr.value);
                 for key in &mut pr.keys {
                     key.value = map_position(&key.value);
@@ -646,6 +648,12 @@ impl ParentFix {
                         }
                     }
                 }
+            };
+            if let Some(pr) = tr.get_mut("position") {
+                map_point(pr);
+            }
+            if let Some(pr) = tr.get_mut("poi") {
+                map_point(pr);
             }
             if let Some((orientation, factor)) = self.pose_3d {
                 if let Some(pr) = tr.get_mut("orientation") {
@@ -793,7 +801,7 @@ pub(crate) fn parent_fixes(s: &Session, cid: ItemId, ids: &[LayerId], parent: Op
         })
     };
     if let Some(inv) = space_3d(parent).inverse().filter(|m| m.0.iter().flatten().all(|v| v.is_finite())) {
-        for layer in comp.layers.iter().filter(|l| ids.contains(&l.id) && l.is_3d() && !l.is_camera() && !l.is_light() && l.parent != parent) {
+        for layer in comp.layers.iter().filter(|l| ids.contains(&l.id) && l.is_3d() && l.parent != parent) {
             let m = inv * space_3d(layer.parent);
             if m.0.iter().flatten().all(|v| v.is_finite()) {
                 let pose_3d = layer.transform().and_then(|tr| {

crates/engine/src/tests_rig3d.rs

@@ -207,6 +207,29 @@ fn control_light_with_camera_follows_and_releases() {
     assert!(s.execute("light.controlWithCamera", json!({"layers": [cam]})).is_err());
 }
 
+/// Parenting keeps a camera where it is (After Effects' Parent & Link): Position and Point of
+/// Interest are re-expressed in the null's space, so the frame does not move.
+#[test]
+fn parented_camera_keeps_its_frame_under_an_offset_null() {
+    let mut s = session();
+    let cam = camera(&mut s);
+    let (eye0, f0) = frame(&s, cam);
+    let nul = s.execute("layer.newNull", json!({})).unwrap()["layer"].as_u64().unwrap();
+    s.execute("prop.set", json!({"layer": nul, "path": "transform/position", "value": [100, 60, 0]})).unwrap();
+    s.execute("layer.setParent", json!({"layers": [cam], "parent": nul})).unwrap();
+    let (eye1, f1) = frame(&s, cam);
+    assert!((eye1 - eye0).length() < 1e-6 && (f1 - f0).length() < 1e-6, "{eye0:?} {eye1:?}");
+    // The null's origin is Position minus its default anchor (50, 50): (50, 10) in the comp.
+    let c = layer_in(&s, cid(&s), cam);
+    assert!(close3(v3(&c, "transform/position"), [270.0, 170.0, -800.0], 1e-6), "{:?}", v3(&c, "transform/position"));
+    assert!(close3(v3(&c, "transform/poi"), [270.0, 170.0, 0.0], 1e-6), "{:?}", v3(&c, "transform/poi"));
+    // Moving the null carries the camera and keeps its aim.
+    s.execute("prop.set", json!({"layer": nul, "path": "transform/position", "value": [140, 90, 0]})).unwrap();
+    let (eye2, f2) = frame(&s, cam);
+    assert!((eye2 - (eye0 + vec3(40.0, 30.0, 0.0))).length() < 1e-6, "{eye2:?}");
+    assert!((f2 - f0).length() < 1e-6, "{f2:?}");
+}
+
 // ---------------------------------------------------------------- from 3D model
 
 struct DiskModels;