Say what three retained-layout details mean

Reading this back, three things claim something they do not do.

`OnResize::Translate` is returned by `TextView::on_resize` under a
comment weighing anchored glyphs against reshaping ones, but nothing
consumes it: `try_reuse` asks only whether the answer is `Scale`, so a
widget saying `Translate` is redrawn. Say so on the variant, since the
comment beside it reads as a description of behaviour.

`depend_on_size(child, false)` and `depend_on_size(child, true)` are the
difference between a hint, which is context-free, and a size the child
produced by drawing, which carries every pixel axis the child read. That
is the subtlest rule in the file and it was spelled as a bool; give the
two cases their names.

`draw_started` is the record of what has drawn during the pass under
way, and it worked only because `redraw` removes an id before asking
about it -- nothing emptied the set, so it accumulated the id of every
widget ever drawn, including ones long gone. Empty it with the pass.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

core/src/ui/painter.rs

@@ -161,7 +161,7 @@ impl<'a> Painter<'a> {
             Some(hint) => {
                 #[cfg(feature = "layout-diagnostics")]
                 diag::bump(Counter::HintHits);
-                self.depend_on_size(id, false);
+                self.depend_on_hint(id);
                 Some(hint)
             }
             None => {
@@ -203,17 +203,22 @@ impl<'a> Painter<'a> {
         Some(size)
     }
 
-    fn depend_on_size<W: ?Sized>(&mut self, child: &StrongWidget<W>, inherit_inputs: bool) {
-        let (box_inputs, output_inputs) = match inherit_inputs {
-            true => self
+    /// Depends on a length the child gave without being drawn. A hint is
+    /// context-free, so this depends on the child but on no pixel axis.
+    fn depend_on_hint<W: ?Sized>(&mut self, child: &StrongWidget<W>) {
+        self.depend_on_size_inputs(child, [false; 2], [false; 2]);
+    }
+
+    /// Depends on a size the child produced by drawing, which carries
+    /// whatever the child read to produce it.
+    fn depend_on_drawn_size<W: ?Sized>(&mut self, child: &StrongWidget<W>) {
+        let (box_inputs, output_inputs) = self
             .state
             .active
             .get(&child.id())
             .map_or(([false; 2], [false; 2]), |active| {
                 (active.size_box_inputs, active.size_output_inputs)
-                }),
-            false => ([false; 2], [false; 2]),
-        };
+            });
         self.depend_on_size_inputs(child, box_inputs, output_inputs);
     }
 
@@ -351,7 +356,7 @@ impl<W: ?Sized> DrawResult<'_, '_, W> {
             diag::bump(Counter::SizeReads);
             diag::size_read(self.child.id(), self.painter.id, self.size);
         }
-        self.painter.depend_on_size(self.child, true);
+        self.painter.depend_on_drawn_size(self.child);
         self.size
     }
 

core/src/ui/render_state.rs

@@ -27,6 +27,9 @@ pub struct UiRenderState {
     /// content dirtiness, these may retain an answer whose observed pixel
     /// axes did not change.
     resize_marks: HashSet<WidgetId>,
+    /// What has already been drawn during the pass under way, so a widget
+    /// reached by redrawing an ancestor is not drawn again on its own
+    /// account. Emptied when the pass ends.
     draw_started: HashSet<WidgetId>,
     /// A widget's move slot, which outlives any one `ActiveData`: a redraw
     /// replaces that while its children go on pointing at the slot.
@@ -138,6 +141,7 @@ impl UiRenderState {
         self.resized = [false; 2];
         self.invalid_sizes.clear();
         self.resize_marks.clear();
+        self.draw_started.clear();
     }
 
     fn redraw_all(&mut self, root: Option<&StrongWidget>, rsc: &mut dyn UiRsc) {
@@ -574,6 +578,7 @@ impl UiRenderState {
         self.layers.clear();
         self.invalid_sizes.clear();
         self.resize_marks.clear();
+        self.draw_started.clear();
         rsc.widgets_mut().needs_redraw.clear();
         rsc.free();
     }

core/src/widget/mod.rs

@@ -21,6 +21,9 @@ pub use widgets::*;
 #[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
 pub enum OnResize {
     Scale,
+    /// Reserved: nothing reads this yet, so a widget saying it is redrawn.
+    /// Keeping an unchanged drawing in a bigger box needs the widget to say
+    /// *where* in that box it should sit, which is the alignment work.
     Translate,
     #[default]
     Redraw,