iris: keep redraw comments current

iris/core/src/ui/render_state.rs

@@ -40,10 +40,8 @@ pub struct UiRenderState {
 
     old_root: Option<WidgetId>,
     resized: bool,
-    /// Widgets whose `draw` call is on the stack now. A reentrant draw would
-    /// create two retained primitive sets with one owner, so it is rejected;
-    /// completed draws are removed immediately and are instead tracked by
-    /// consuming their outstanding dirty mark.
+    /// Widgets whose `draw` call is currently on the stack. Reentrant draws
+    /// are invalid because each widget owns exactly one retained primitive set.
     draw_started: HashSet<WidgetId>,
     /// Widgets which asked from inside `draw` to be drawn on the following
     /// frame. Kept separate from `Widgets::needs_redraw` until `update_at`
@@ -266,11 +264,9 @@ impl UiRenderState {
             "a previous frame left {} widget(s) marked as mid-draw",
             self.draw_started.len(),
         );
-        // Timed unconditionally -- an `Instant::now()` pair is cheap enough
-        // not to move the `--phone` bench's frame time (checked when this
-        // was added), and gating it behind the trace toggle would leave
-        // `iris::frame` with nothing to report the one frame somebody just
-        // turned tracing on to look at.
+        // Keep timing independent of the trace toggle so the first traced
+        // frame has a duration to report. The clock reads do not measurably
+        // affect the `--phone` benchmark.
         let layout_start = Instant::now();
         let kind = if self.needs_redraw_all(root) {
             self.redraw_all(root, rsc);