Add a dummy warm-up frame to the demo app to pre-cache emojis

epi/src/lib.rs

@@ -64,6 +64,14 @@ pub trait App {
     /// Optional.
     fn setup(&mut self, _ctx: &egui::CtxRef) {}
 
+    /// If `true` a warm-up call to [`Self::update`] will be issued where
+    /// `ctx.memory().everything_is_visible()` will be set to `true`.
+    ///
+    /// In this warm-up call, all paint commands will be ignored.
+    fn warm_up_enabled(&self) -> bool {
+        false
+    }
+
     /// Called once on start. Allows you to restore state.
     fn load(&mut self, _storage: &dyn Storage) {}