Add hoverables (#797)

examples/lib/stories/controls/hoverables.dart

@@ -0,0 +1,34 @@
+import 'package:flame/components.dart';
+import 'package:flame/gestures.dart';
+import 'package:flutter/material.dart';
+import 'package:flame/game.dart';
+import 'package:flame/extensions.dart';
+
+class HoverableSquare extends PositionComponent with Hoverable {
+  static final Paint _white = Paint()..color = const Color(0xFFFFFFFF);
+  static final Paint _grey = Paint()..color = const Color(0xFFA5A5A5);
+
+  HoverableSquare(Vector2 position)
+      : super(position: position, size: Vector2.all(100)) {
+    anchor = Anchor.center;
+  }
+
+  @override
+  void render(Canvas canvas) {
+    super.render(canvas);
+    canvas.drawRect(size.toRect(), isHovered ? _grey : _white);
+  }
+}
+
+class HoverablesGame extends BaseGame with HasHoverableComponents, TapDetector {
+  @override
+  Future<void> onLoad() async {
+    add(HoverableSquare(Vector2(200, 500)));
+    add(HoverableSquare(Vector2(700, 300)));
+  }
+
+  @override
+  void onTapDown(TapDownInfo event) {
+    add(HoverableSquare(event.eventPosition.game));
+  }
+}