diff --git a/core/src/layout_diagnostics.rs b/core/src/layout_diagnostics.rs
index f986803..bd52660 100644
--- a/core/src/layout_diagnostics.rs
+++ b/core/src/layout_diagnostics.rs
@@ -45,7 +45,7 @@ pub(crate) enum Counter {
     ResizeChecks,
     ResizeCheckChildren,
     QueuePops,
-    DepthSteps,
+    DepthReads,
     EagerReaderRedraws,
     LocalRedraws,
     SizeChanges,
@@ -82,7 +82,7 @@ impl Counter {
         "resize checks",
         "resize children checked",
         "redraw queue pops",
-        "depth steps",
+        "depth reads",
         "eager reader redraws",
         "local redraws",
         "size changes",
diff --git a/core/src/ui/active.rs b/core/src/ui/active.rs
index df61ef0..a984207 100644
--- a/core/src/ui/active.rs
+++ b/core/src/ui/active.rs
@@ -14,6 +14,10 @@ pub struct ActiveData {
     /// has since changed is a different number of pixels.
     pub px: Vec2,
     pub parent: Option<WidgetId>,
+    /// How far down the tree it was drawn, the root being 1. Carried down a
+    /// draw rather than worked out by walking up, so it is right for every
+    /// widget a frame visits and cannot drift while one is being drawn.
+    pub depth: usize,
     pub textures: Vec<TextureHandle>,
     pub primitives: Vec<PrimitiveHandle>,
     pub children: Vec<WidgetId>,
diff --git a/core/src/ui/painter.rs b/core/src/ui/painter.rs
index 24c5a00..5a403ff 100644
--- a/core/src/ui/painter.rs
+++ b/core/src/ui/painter.rs
@@ -31,6 +31,7 @@ pub struct Painter<'a> {
     /// its parent placed it, otherwise the nearest ancestor that has one.
     pub(super) move_idx: MoveIdx,
     pub layer: usize,
+    pub(super) depth: usize,
     pub(super) id: WidgetId,
 }
 
@@ -134,6 +135,7 @@ impl<'a> Painter<'a> {
             id.id(),
             region,
             Some(self.id),
+            self.depth + 1,
             self.move_idx,
             slotted,
             self.mask,
diff --git a/core/src/ui/render_state.rs b/core/src/ui/render_state.rs
index 376216c..1dc40b7 100644
--- a/core/src/ui/render_state.rs
+++ b/core/src/ui/render_state.rs
@@ -155,6 +155,7 @@ impl UiRenderState {
                 id.id(),
                 UiRegion::FULL,
                 None,
+                1,
                 MoveIdx::NONE,
                 false,
                 MaskIdx::NONE,
@@ -172,6 +173,7 @@ impl UiRenderState {
         id: WidgetId,
         region: UiRegion,
         parent: Option<WidgetId>,
+        depth: usize,
         parent_move: MoveIdx,
         slotted: bool,
         mask: MaskIdx,
@@ -185,7 +187,7 @@ impl UiRenderState {
         }
         let mut old_children = old_children.unwrap_or_default();
         if self.active.contains_key(&id) {
-            if let Some(size) = self.try_reuse(id, region, parent_move, rsc) {
+            if let Some(size) = self.try_reuse(id, region, depth, parent_move, rsc) {
                 return size;
             }
             // if not, then maintain resize and track old children to remove unneeded
@@ -217,6 +219,7 @@ impl UiRenderState {
             primitives: Vec::new(),
             children: Vec::new(),
             size_deps: Vec::new(),
+            depth,
             size_box_inputs: [false; 2],
             size_output_inputs: [false; 2],
             reads_output: [false; 2],
@@ -249,6 +252,7 @@ impl UiRenderState {
             reads_output,
             move_idx,
             layer,
+            depth: _,
             id,
         } = painter;
 
@@ -265,6 +269,7 @@ impl UiRenderState {
             size,
             px,
             parent,
+            depth,
             textures,
             primitives,
             children,
@@ -383,6 +388,7 @@ impl UiRenderState {
         &mut self,
         id: WidgetId,
         region: UiRegion,
+        depth: usize,
         parent_move: MoveIdx,
         rsc: &mut dyn UiRsc,
     ) -> Option<Size> {
@@ -429,6 +435,7 @@ impl UiRenderState {
                 diag::bump(Counter::ReuseExact);
                 diag::reuse(id, ReuseOutcome::Exact);
             }
+            self.keep_depth(id, depth);
             return Some(size);
         }
         // Only a placed widget can be given a different box without drawing
@@ -469,6 +476,7 @@ impl UiRenderState {
             }
         }
         self.moves.set(slot, region);
+        self.keep_depth(id, depth);
         let active = self.active.get_mut(&id).unwrap();
         active.region = region;
         #[cfg(feature = "layout-diagnostics")]
@@ -614,12 +622,32 @@ impl UiRenderState {
         rsc.free();
     }
 
+    /// Keeps a reused widget's depth current, since being reused is being
+    /// visited: only a subtree nobody looked at can hold a stale one.
+    fn keep_depth(&mut self, id: WidgetId, depth: usize) {
+        if let Some(active) = self.active.get_mut(&id) {
+            active.depth = depth;
+        }
+    }
+
     fn depth(&self, id: WidgetId) -> usize {
+        #[cfg(feature = "layout-diagnostics")]
+        diag::bump(Counter::DepthReads);
+        let depth = self.active.get(&id).map_or(1, |active| active.depth);
+        debug_assert_eq!(
+            depth,
+            self.walked_depth(id),
+            "a widget's kept depth is not the one its ancestry says"
+        );
+        depth
+    }
+
+    /// What the kept depth is checked against, and the only thing that reads
+    /// the ancestry to find one.
+    fn walked_depth(&self, id: WidgetId) -> usize {
         let mut depth = 0;
         let mut at = Some(id);
         while let Some(id) = at {
-            #[cfg(feature = "layout-diagnostics")]
-            diag::bump(Counter::DepthSteps);
             at = self.active.get(&id).and_then(|active| active.parent);
             depth += 1;
         }
@@ -714,6 +742,7 @@ impl UiRenderState {
             id,
             active.region,
             active.parent,
+            active.depth,
             active.parent_move,
             active.move_idx != active.parent_move,
             active.mask,