All of it.

chess/src/chess/Game.java

@@ -1,6 +1,12 @@
 package chess;
 
-class Game {
+import javalib.impworld.*;
+
+class Game extends World {
     Actor white;
     Actor black;
+
+    public WorldScene makeScene() { return new WorldScene(0, 0); }
+
+    void run() { this.bigBang(0, 0, 0.01); }
 }