Support viewport-relative widget sizing

src/event_loop/handlers.rs

@@ -99,6 +99,7 @@ impl<A: App> CompositorHandler for AppData<A>
 		// `App::on_resize`.
 		if matches!( focus, super::SurfaceFocus::Main )
 		{
+			self.app.on_scale_changed( new_factor as u32 );
 			self.app.on_resize( pw, ph );
 			self.dirty_caches();
 		}