fix(canvas): align rust z-order with renderer

crates/op-editor-core/src/tests_mutators.rs

@@ -238,28 +238,28 @@ fn root_ids(s: &crate::state::EditorState) -> Vec<String> {
 }
 
 #[test]
-fn reorder_selected_up_moves_to_higher_index() {
+fn reorder_selected_up_moves_toward_front_index() {
     let mut s = three_rects();
     s.set_single_selection(NodeId::new("n2"));
     assert!(s.reorder_selected(ReorderDirection::Up));
-    assert_eq!(root_ids(&s), vec!["n1", "n3", "n2"]);
+    assert_eq!(root_ids(&s), vec!["n2", "n1", "n3"]);
 }
 
 #[test]
-fn reorder_selected_down_moves_to_lower_index() {
+fn reorder_selected_down_moves_toward_back_index() {
     let mut s = three_rects();
     s.set_single_selection(NodeId::new("n2"));
     assert!(s.reorder_selected(ReorderDirection::Down));
-    assert_eq!(root_ids(&s), vec!["n2", "n1", "n3"]);
+    assert_eq!(root_ids(&s), vec!["n1", "n3", "n2"]);
 }
 
 #[test]
 fn reorder_selected_at_edges_is_noop() {
     let mut s = three_rects();
     s.set_single_selection(NodeId::new("n1"));
-    assert!(!s.reorder_selected(ReorderDirection::Down));
-    s.set_single_selection(NodeId::new("n3"));
     assert!(!s.reorder_selected(ReorderDirection::Up));
+    s.set_single_selection(NodeId::new("n3"));
+    assert!(!s.reorder_selected(ReorderDirection::Down));
 }
 
 #[test]

crates/op-editor-core/src/walkers.rs

@@ -15,10 +15,10 @@ use std::collections::HashSet;
 /// selected node swaps with in its parent's children vec.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum ReorderDirection {
-    /// Towards the front of the paint order (higher index, drawn on
-    /// top). Bound to `]`.
+    /// Towards the front of the paint order (lower index,
+    /// `children[0]` is top). Bound to `]`.
     Up,
-    /// Towards the back of the paint order (lower index, drawn
+    /// Towards the back of the paint order (higher index, drawn
     /// underneath). Bound to `[`.
     Down,
 }
@@ -193,12 +193,12 @@ pub fn reorder_in_children(
 ) -> bool {
     if let Some(idx) = children.iter().position(|n| n.id_str() == target.as_str()) {
         match direction {
-            ReorderDirection::Up if idx + 1 < children.len() => {
-                children.swap(idx, idx + 1);
+            ReorderDirection::Up if idx > 0 => {
+                children.swap(idx, idx - 1);
                 return true;
             }
-            ReorderDirection::Down if idx > 0 => {
-                children.swap(idx, idx - 1);
+            ReorderDirection::Down if idx + 1 < children.len() => {
+                children.swap(idx, idx + 1);
                 return true;
             }
             _ => return false,

crates/op-editor-ui/src/layout_scene_hit.rs

@@ -8,7 +8,7 @@
 //! reads the same resolved geometry the painter walks.
 //!
 //! Hit semantics are preserved bit-for-bit from `document/walkers.rs`:
-//! top-most-first z-order, per-node rotation inverse-transform, the
+//! top-most-first z-order (`children[0]` is frontmost), per-node rotation inverse-transform, the
 //! tighter Ellipse / Polygon / Line geometry, the locked-node
 //! body-opts-out-children-stay rule, and the hidden-subtree skip.
 
@@ -18,15 +18,15 @@ use crate::{Point2D, Rect};
 
 impl LayoutScene {
     /// Topmost node id whose geometry contains `point` (doc space)
-    /// on the active page. Walks children in reverse z-order so the
-    /// most-recently-painted node wins. `None` on dead space.
+    /// on the active page. Walks children in front-to-back z-order
+    /// (`children[0]` is frontmost). `None` on dead space.
     ///
     /// `zoom` is the live viewport zoom — it scales the Line stroke
     /// hit slack so a thin line stays clickable at any zoom.
     pub fn node_at_doc_point(&self, point: Point2D, zoom: f32) -> Option<String> {
         let zoom = zoom.max(0.0001);
         let page = self.active_page()?;
-        for child in page.children.iter().rev() {
+        for child in &page.children {
             if let Some(hit) = hit_test_walk(child, point, zoom) {
                 return Some(hit);
             }
@@ -92,7 +92,7 @@ fn hit_test_walk(node: &SceneNode, point: Point2D, zoom: f32) -> Option<String>
     } else {
         point
     };
-    for child in node.children.iter().rev() {
+    for child in &node.children {
         if let Some(hit) = hit_test_walk(child, local, zoom) {
             return Some(hit);
         }
@@ -292,22 +292,22 @@ mod tests {
     }
 
     #[test]
-    fn node_at_doc_point_picks_topmost_overlapping_node() {
+    fn node_at_doc_point_treats_first_child_as_frontmost() {
         let scene = one_page(vec![
-            leaf("under", NodeKind::Rect, Rect::xywh(0.0, 0.0, 50.0, 50.0)),
-            leaf("over", NodeKind::Rect, Rect::xywh(10.0, 10.0, 50.0, 50.0)),
+            leaf("over", NodeKind::Rect, Rect::xywh(0.0, 0.0, 50.0, 50.0)),
+            leaf("under", NodeKind::Rect, Rect::xywh(10.0, 10.0, 50.0, 50.0)),
         ]);
-        // Overlap region → the later-painted "over" wins.
+        // Overlap region -> children[0] is the top layer.
         assert_eq!(
             scene
                 .node_at_doc_point(Point2D::new(20.0, 20.0), 1.0)
                 .as_deref(),
             Some("over")
         );
-        // Only "under" covers (5, 5).
+        // Only "under" covers (55, 55).
         assert_eq!(
             scene
-                .node_at_doc_point(Point2D::new(5.0, 5.0), 1.0)
+                .node_at_doc_point(Point2D::new(55.0, 55.0), 1.0)
                 .as_deref(),
             Some("under")
         );

crates/op-editor-ui/src/widgets/canvas_viewport.rs

@@ -415,7 +415,7 @@ impl<'a> Widget for CanvasViewport<'a> {
                     rect.size.y + CULL_MARGIN * 2.0,
                 ),
             };
-            for child in &page.children {
+            for child in page.children.iter().rev() {
                 super::canvas_viewport_paint::paint_node(
                     cx,
                     child,

crates/op-editor-ui/src/widgets/canvas_viewport_paint.rs

@@ -263,7 +263,7 @@ pub fn paint_node(
             } else {
                 paint_fill_then_stroke(cx, node, world_rect, zoom, node.fill);
             }
-            for child in &node.children {
+            for child in node.children.iter().rev() {
                 paint_node(cx, child, viewport_origin, zoom, edit_caret.clone(), cull);
             }
         }
@@ -275,7 +275,7 @@ pub fn paint_node(
             node.fill,
         ),
         NodeKind::Group | NodeKind::Other(_) => {
-            for child in &node.children {
+            for child in node.children.iter().rev() {
                 paint_node(cx, child, viewport_origin, zoom, edit_caret.clone(), cull);
             }
         }