fix Draw (redraw)

core/src/ui/mod.rs

@@ -28,7 +28,7 @@ pub trait UiRsc {
     #[allow(unused_variables)]
     fn on_remove(&mut self, id: WidgetId) {}
     #[allow(unused_variables)]
-    fn on_draw(&mut self, active: &ActiveData) {}
+    fn on_draw(&mut self, active: &ActiveData, redrawn: bool) {}
     #[allow(unused_variables)]
     fn on_undraw(&mut self, active: &ActiveData) {}
 

core/src/ui/render_state.rs

@@ -81,10 +81,12 @@ impl UiRenderState {
         old_children: Option<Vec<WidgetId>>,
         rsc: &mut dyn UiRsc,
     ) {
+        let mut redrawn = old_children.is_some();
         let mut old_children = old_children.unwrap_or_default();
         if let Some(active) = self.active.get_mut(&id)
             && !rsc.widgets().needs_redraw.contains(&id)
         {
+            redrawn = true;
             // check to see if we can skip drawing first
             if active.region == region {
                 return;
@@ -149,7 +151,7 @@ impl UiRenderState {
             }
         }
 
-        rsc.on_draw(&active);
+        rsc.on_draw(&active, redrawn);
         self.active.insert(id, active);
     }