diff --git a/renrs-gui/src/lib.rs b/renrs-gui/src/lib.rs
index 49bf052..19c370a 100644
--- a/renrs-gui/src/lib.rs
+++ b/renrs-gui/src/lib.rs
@@ -6,12 +6,15 @@ use eframe::egui;
 use renrs::{State, Command};
 
 use sfml::{
-    graphics::{Color, RenderTarget, RenderWindow, Shape, RectangleShape},
+    graphics::{Color, RenderTarget, RenderWindow, RectangleShape, Transformable},
     system::Vector2f,
     window::{Event, mouse, Key, Style},
 };
 use egui_sfml::SfEgui;
 
+const WIDTH: f32 = 800.0;
+const HEIGHT: f32 = 600.0;
+
 pub fn run(file: PathBuf) {
     env_logger::init();
     let mut app = App::from_state(State::from_file(file));
@@ -102,7 +105,7 @@ impl App {
 
     fn run(&mut self) {
         let mut window = RenderWindow::new(
-            (800, 600),
+            (WIDTH as u32, HEIGHT as u32),
             "renrs-gui",
             Style::CLOSE,
             &Default::default(),
@@ -110,10 +113,10 @@ impl App {
         let mut sfegui = SfEgui::new(&window);
         window.set_vertical_sync_enabled(true);
 
-        let mut shape = RectangleShape::with_size(Vector2f::new(64.0, 64.0));
-        shape.set_fill_color(Color::RED);
-        shape.set_outline_color(Color::GREEN);
-        shape.set_outline_thickness(3.);
+        const SIZE: f32 = 64.0;
+        let mut velocity = Vector2f::new(4.0, 4.0);
+        let mut shape = RectangleShape::with_size(Vector2f::new(SIZE, SIZE));
+        shape.set_position(Vector2f::new(SIZE, SIZE));
 
         while window.is_open() {
             while let Some(event) = window.poll_event() {
@@ -130,7 +133,6 @@ impl App {
                     .do_frame(|ctx| {
                         egui::CentralPanel::default()
                             .frame(Frame {
-                                fill: Color32::BLACK,
                                 inner_margin: Margin::same(32.0),
                                 ..Default::default()
                             })
@@ -146,6 +148,15 @@ impl App {
                     }).unwrap();
             }
 
+            let Vector2f { x, y } = shape.position();
+            if x >= WIDTH - SIZE || x < 0.0 {
+                velocity.x *= -1.0;
+            }
+            if y >= HEIGHT - SIZE || y < 0.0 {
+                velocity.y *= -1.0;
+            }
+            shape.set_position(Vector2f::new(x + velocity.x, y + velocity.y));
+
             window.clear(Color::BLACK);
             window.draw(&shape);
             sfegui.draw(&mut window, None);