Adding SpriteButton

lib/widgets/sprite_button.dart

@@ -0,0 +1,77 @@
+import 'package:flutter/widgets.dart';
+import '../sprite.dart';
+import 'package:meta/meta.dart';
+
+class SpriteButton extends StatefulWidget {
+  final VoidCallback onPressed;
+  final Widget label;
+  final Sprite sprite;
+  final Sprite pressedSprite;
+  final double width;
+  final double height;
+
+  SpriteButton({
+    @required this.onPressed,
+    @required this.label,
+    @required this.sprite,
+    @required this.pressedSprite,
+
+    this.width,
+    this.height,
+  });
+
+  @override
+  State createState() => _ButtonState();
+}
+
+class _ButtonState extends State<SpriteButton> {
+  bool _pressed = false;
+
+  @override
+  Widget build(_) {
+    final width = widget.width ?? 200;
+    final height = widget.height ?? 50;
+
+    return GestureDetector(
+        onTapDown: (_) {
+          setState(() {
+            _pressed = true;
+          });
+        },
+        onTapUp: (_) {
+          setState(() {
+            _pressed = false;
+          });
+
+          widget.onPressed?.call();
+        },
+        child: Container(
+            width: width,
+            height: height,
+            child: CustomPaint(
+                painter: _ButtonPainer(_pressed ? widget.pressedSprite : widget.sprite),
+                child: Center(
+                    child: Container(
+                        padding: _pressed ? const EdgeInsets.only(top: 5) : null,
+                        child: widget.label,
+                    ),
+                ),
+            ),
+        ),
+    );
+  }
+}
+
+class _ButtonPainer extends CustomPainter {
+  final Sprite _sprite;
+
+  _ButtonPainer(this._sprite);
+
+  @override
+  bool shouldRepaint(_ButtonPainer old) => old._sprite != _sprite;
+
+  @override
+  void paint(Canvas canvas, Size size) {
+    _sprite.renderRect(canvas, Rect.fromLTWH(0, 0, size.width, size.height));
+  }
+}