diff --git a/README.md b/README.md
new file mode 100644
index 0000000..1eb6ba2
--- /dev/null
+++ b/README.md
@@ -0,0 +1,10 @@
+## Build `ENGINE`
+
+```sh
+# install rollup
+npm install --global rollup
+
+# compile engine
+cd src/js/
+rollup main.js --file engine.js --format es
+```
diff --git a/src/js/.gitignore b/src/js/.gitignore
index 444fa09..1eb9afd 100644
--- a/src/js/.gitignore
+++ b/src/js/.gitignore
@@ -1 +1,2 @@
 game.js*
+engine.js
diff --git a/src/js/app.js b/src/js/main.js
similarity index 89%
rename from src/js/app.js
rename to src/js/main.js
index 5f8bba1..6fb27c2 100644
--- a/src/js/app.js
+++ b/src/js/main.js
@@ -1,6 +1,7 @@
-import { Scene } from './scene.js';
 import { Settings } from './settings.js';
 import { Pointer } from './pointer.js';
+import { Scene, SceneLayer } from './scene.js';
+import { Rect, StrokeRect, Sprite, TiledSprite } from './objects.js';
 
 export class App {
   #version;
@@ -66,3 +67,5 @@ export class App {
     requestAnimationFrame(this.run);
   };
 }
+
+export { Scene, SceneLayer, Rect, StrokeRect, Sprite, TiledSprite };