Keep the redraw invariant concise

core/src/ui/render_state.rs

@@ -52,7 +52,7 @@ impl UiRenderState {
             );
         }
         let root = root.into();
-        if self.needs_redraw_all(root) {
+        if self.needs_full_redraw(root) {
             self.redraw_all(root, rsc);
             self.old_root = root.map(|r| r.id());
             self.resized = false;
@@ -218,15 +218,8 @@ impl UiRenderState {
         root.into().map(|r| r.id()) != self.old_root
     }
 
-    /// What `update` will redraw everything for. Named and shared with
-    /// `needs_redraw` rather than written out twice, because the two must
-    /// agree: `needs_redraw` is what asks for the frame that `update` would
-    /// draw, so a condition in one and not the other is a frame nobody
-    /// requests and a stale window. `resized` was missing from `needs_redraw`,
-    /// which is latent on Wayland only because winit asks for a redraw after a
-    /// resize by itself -- a resize changes neither the root nor any widget,
-    /// so nothing else here would have asked.
-    fn needs_redraw_all<'a>(&self, root: impl Into<Option<&'a StrongWidget>>) -> bool {
+    // Scheduling and drawing must use the same full-redraw predicate.
+    fn needs_full_redraw<'a>(&self, root: impl Into<Option<&'a StrongWidget>>) -> bool {
         self.root_changed(root) || self.resized
     }
 
@@ -235,7 +228,7 @@ impl UiRenderState {
         root: impl Into<Option<&'a StrongWidget>>,
         widgets: &Widgets,
     ) -> bool {
-        self.needs_redraw_all(root) || widgets.has_updates()
+        self.needs_full_redraw(root) || widgets.has_updates()
     }
 
     pub fn active_widgets(&self) -> usize {