Fix loupe example not requesting redraws

Closes #3153.

Author: hecrj

examples/loupe/src/main.rs

@@ -47,11 +47,12 @@ impl Loupe {
 
 mod loupe {
     use iced::advanced::Renderer as _;
+    use iced::advanced::Shell;
     use iced::advanced::layout::{self, Layout};
     use iced::advanced::renderer;
     use iced::advanced::widget::{self, Widget};
     use iced::mouse;
-    use iced::{Color, Element, Length, Rectangle, Renderer, Size, Theme, Transformation};
+    use iced::{Color, Element, Event, Length, Rectangle, Renderer, Size, Theme, Transformation};
 
     pub fn loupe<'a, Message>(
         zoom: f32,
@@ -101,6 +102,21 @@ mod loupe {
             self.content.as_widget_mut().layout(tree, renderer, limits)
         }
 
+        fn update(
+            &mut self,
+            _tree: &mut widget::Tree,
+            _event: &Event,
+            layout: Layout<'_>,
+            cursor: mouse::Cursor,
+            _renderer: &Renderer,
+            shell: &mut Shell<'_, Message>,
+            _viewport: &Rectangle,
+        ) {
+            if cursor.is_over(layout.bounds().expand(10)) {
+                shell.request_redraw();
+            }
+        }
+
         fn draw(
             &self,
             tree: &widget::Tree,