Move files to src and comply with the dart package layout convention (#621)

* 👌 Use `Offset` type directly in `JoystickAction.update` calculations (#631)

* Move files to src and comply with the dart package layout convention

* Fixing widgets example

Co-authored-by: Serge Matveenko <lig@countzero.co>
Co-authored-by: Erick Zanardo <erickzanardoo@gmail.com>

lib/src/sprite.dart

@@ -0,0 +1,79 @@
+import 'dart:ui';
+
+import 'anchor.dart';
+import 'extensions/offset.dart';
+import 'extensions/vector2.dart';
+import 'flame.dart';
+import 'palette.dart';
+import 'assets/images.dart';
+
+class Sprite {
+  Paint paint = BasicPalette.white.paint;
+  Image image;
+  Rect src = Rect.zero;
+
+  Sprite(
+    this.image, {
+    Vector2 srcPosition,
+    Vector2 srcSize,
+  }) : assert(image != null, "image can't be null") {
+    this.srcSize = srcSize;
+    this.srcPosition = srcPosition;
+  }
+
+  /// Takes a path of an image, a [srcPosition] and [srcSize] and loads the sprite animation
+  /// When the [images] is omitted, the global [Flame.images] is used
+  static Future<Sprite> load(
+    String src, {
+    Vector2 srcPosition,
+    Vector2 srcSize,
+    Images images,
+  }) async {
+    final _images = images ?? Flame.images;
+    final image = await _images.load(src);
+    return Sprite(image, srcPosition: srcPosition, srcSize: srcSize);
+  }
+
+  double get _imageWidth => image.width.toDouble();
+
+  double get _imageHeight => image.height.toDouble();
+
+  Vector2 get originalSize => Vector2(_imageWidth, _imageHeight);
+
+  Vector2 get srcSize => Vector2(src.width, src.height);
+
+  set srcSize(Vector2 size) {
+    size ??= Vector2Extension.fromInts(image.width, image.height);
+    src = srcPosition.toPositionedRect(size);
+  }
+
+  Vector2 get srcPosition => src.topLeft.toVector2();
+
+  set srcPosition(Vector2 position) {
+    src = (position ?? Vector2.zero()).toPositionedRect(srcSize);
+  }
+
+  /// Renders this sprite onto the canvas.
+  ///
+  /// * position: x,y coordinates where it will be drawn; default to origin.
+  /// * size: width/height dimensions; it can be bigger or smaller than the original size -- but it defaults to the original texture size.
+  /// * overridePaint: paint to use. You can also change the paint on your Sprite instance. Default is white.
+  /// * anchor: where in the sprite the x/y coordinates refer to; defaults to topLeft.
+  void render(
+    Canvas canvas, {
+    Vector2 position,
+    Vector2 size,
+    Anchor anchor = Anchor.topLeft,
+    Paint overridePaint,
+  }) {
+    final drawPosition = position ?? Vector2.zero();
+    final drawSize = size ?? srcSize;
+
+    final delta = anchor.toVector2..multiply(drawSize);
+    final drawRect = (drawPosition + delta).toPositionedRect(drawSize);
+
+    final drawPaint = overridePaint ?? paint;
+
+    canvas.drawImageRect(image, src, drawRect, drawPaint);
+  }
+}