feat: group Slingshots (#48)

* feat: removed Wall friction

* feat: included SlingShot

* feat: adjusted SlingShot size

* feat: included tests

* refactor: fixed tests

lib/game/components/board.dart

@@ -6,7 +6,6 @@ import 'package:pinball/game/game.dart';
 ///
 /// The bottom [Component]s are the [Flipper]s and the [Baseboard]s.
 /// {@endtemplate}
-// TODO(alestiago): Add [SlingShot] once provided.
 // TODO(alestiago): Consider renaming once entire Board is defined.
 class BottomGroup extends Component {
   /// {@macro bottom_group}
@@ -70,7 +69,15 @@ class _BottomGroupSide extends Component {
             Flipper.height,
           ),
     );
+    final slingShot = SlingShot(
+      side: _side,
+      position: _position +
+          Vector2(
+            (Flipper.width) * direction,
+            Flipper.height + SlingShot.size.y,
+          ),
+    );
 
-    await addAll([flipper, baseboard]);
+    await addAll([flipper, baseboard, slingShot]);
   }
 }

lib/game/components/sling_shot.dart

@@ -33,18 +33,19 @@ class SlingShot extends BodyComponent {
   /// left.
   final BoardSide _side;
 
+  /// The size of the [SlingShot] body.
+  // TODO(alestiago): Use size from PositionedBodyComponent instead,
+  // once a sprite is given.
+  static final Vector2 size = Vector2(6, 8);
+
   List<FixtureDef> _createFixtureDefs() {
     final fixtures = <FixtureDef>[];
 
-    // TODO(alestiago): Use size from PositionedBodyComponent instead,
-    // once a sprite is given.
-    final size = Vector2(10, 10);
-
     // TODO(alestiago): This magic number can be deduced by specifying the
     // angle and using polar coordinate system to place the bottom right
     // vertex.
     // Something as: y = -size.y * math.cos(angle)
-    const additionalIncrement = 2;
+    const additionalIncrement = 3;
     final triangleVertices = _side.isLeft
         ? [
             Vector2(0, 0),
@@ -78,7 +79,7 @@ class SlingShot extends BodyComponent {
       );
     // TODO(alestiago): Play with restitution value once game is bundled.
     final kickerFixtureDef = FixtureDef(kicker)
-      ..restitution = 20.0
+      ..restitution = 10.0
       ..friction = 0;
     fixtures.add(kickerFixtureDef);
 

lib/game/components/wall.dart

@@ -26,7 +26,7 @@ class Wall extends BodyComponent {
 
     final fixtureDef = FixtureDef(shape)
       ..restitution = 0.1
-      ..friction = 0.3;
+      ..friction = 0;
 
     final bodyDef = BodyDef()
       ..userData = this

test/game/components/board_test.dart

@@ -45,10 +45,10 @@ void main() {
           await game.ready();
           await game.ensureAdd(bottomGroup);
 
-          final leftFlippers = bottomGroup.findNestedChildren<Flipper>(
+          final rightFlippers = bottomGroup.findNestedChildren<Flipper>(
             condition: (flipper) => flipper.side.isRight,
           );
-          expect(leftFlippers.length, equals(1));
+          expect(rightFlippers.length, equals(1));
         },
       );
 
@@ -59,8 +59,20 @@ void main() {
           await game.ready();
           await game.ensureAdd(bottomGroup);
 
-          final leftFlippers = bottomGroup.findNestedChildren<Baseboard>();
+          final baseboards = bottomGroup.findNestedChildren<Baseboard>();
-          expect(leftFlippers.length, equals(2));
+          expect(baseboards.length, equals(2));
+        },
+      );
+
+      flameTester.test(
+        'has two SlingShots',
+        (game) async {
+          final bottomGroup = BottomGroup(position: Vector2.zero(), spacing: 0);
+          await game.ready();
+          await game.ensureAdd(bottomGroup);
+
+          final slingShots = bottomGroup.findNestedChildren<SlingShot>();
+          expect(slingShots.length, equals(2));
         },
       );
     });

test/game/components/wall_test.dart

@@ -106,7 +106,7 @@ void main() {
       );
 
       flameTester.test(
-        'has friction',
+        'has no friction',
         (game) async {
           final wall = Wall(
             start: Vector2.zero(),
@@ -115,7 +115,7 @@ void main() {
           await game.ensureAdd(wall);
 
           final fixture = wall.body.fixtures[0];
-          expect(fixture.friction, greaterThan(0));
+          expect(fixture.friction, equals(0));
         },
       );
     });