Adding FlameSpriteWidget

lib/widgets/flame_sprite_widget.dart

@@ -0,0 +1,56 @@
+import 'package:flutter/widgets.dart';
+import 'package:meta/meta.dart';
+import '../sprite.dart';
+
+import 'dart:math';
+
+class FlameSpriteWidget extends StatelessWidget {
+  final Sprite sprite;
+  final bool center;
+
+  FlameSpriteWidget({
+    @required this.sprite,
+    this.center = false,
+  }) : assert(sprite.loaded(), 'Sprite must be loaded');
+
+  @override
+  Widget build(_) {
+    return Container(
+      child: CustomPaint(painter: _FlameSpritePainer(sprite, center)),
+    );
+  }
+}
+
+class _FlameSpritePainer extends CustomPainter {
+  final Sprite _sprite;
+  final bool _center;
+
+  _FlameSpritePainer(this._sprite, this._center);
+
+  @override
+  bool shouldRepaint(_FlameSpritePainer old) => old._sprite != _sprite;
+
+  @override
+  void paint(Canvas canvas, Size size) {
+    final widthRate = size.width / _sprite.size.x;
+    final heightRate = size.height / _sprite.size.y;
+
+    final rate = min(widthRate, heightRate);
+
+    final rect = Rect.fromLTWH(
+      0,
+      0,
+      _sprite.size.x * rate,
+      _sprite.size.y * rate,
+    );
+
+    if (_center) {
+      canvas.translate(
+        size.width / 2 - rect.width / 2,
+        size.height / 2 - rect.height / 2,
+      );
+    }
+
+    _sprite.renderRect(canvas, rect);
+  }
+}