feat: implemented Flipper

lib/game/components/flipper.dart

@@ -0,0 +1,161 @@
+import 'dart:async';
+import 'dart:math' as math;
+
+import 'package:flame_forge2d/flame_forge2d.dart';
+import 'package:flutter/material.dart';
+import 'package:pinball/game/game.dart';
+
+/// {@template flipper}
+/// A bat, typically found in pairs at the bottom of the board.
+///
+/// [Flipper] can be controlled by the player in an arc motion.
+/// {@endtemplate flipper}
+class Flipper extends BodyComponent {
+  /// {@macro flipper}
+  Flipper({
+    required Vector2 position,
+    bool isMirrored = false,
+  })  : _position = position,
+        _isMirrored = isMirrored,
+        _speed = calculateRequiredSpeed() {
+    // TODO(alestiago): Use sprite instead of color when provided.
+    paint = Paint()
+      ..color = const Color(0xFF00FF00)
+      ..style = PaintingStyle.fill;
+  }
+
+  static final size = Vector2(12, 2.8);
+
+  /// The total duration of a full flipper's arc motion.
+  ///
+  /// A full flipper's arc motion is from the lowest position (resting point) to
+  /// the highest position.
+  static const _sweepingAnimationDuration = Duration(milliseconds: 250);
+
+  static double calculateRequiredSpeed() {
+    // TODO(alestiago): Modify to be mathematically correct.
+    final sweepingDistance = math.sqrt(2 * math.pow(size.x, 2));
+    final seconds = _sweepingAnimationDuration.inMicroseconds /
+        Duration.microsecondsPerSecond;
+    return sweepingDistance / seconds;
+  }
+
+  /// The speed required to move the [Flipper] to its heighst position, while
+  /// respecting the [_sweepingAnimationDuration].
+  ///
+  /// The speed value is proportional to the time it takes to move the flipper
+  /// to its highest position.
+  final double _speed;
+
+  /// The initial position of the [Flipper] body.
+  final Vector2 _position;
+
+  /// Whether the [Flipper] is mirrored.
+  ///
+  /// A mirrored [Flipper] is one positioned at the right of the borad.
+  final bool _isMirrored;
+
+  /// Applies downard linear velocity to the [Flipper] to move it up.
+  void moveDown() {
+    body.linearVelocity = Vector2(0, -_speed);
+  }
+
+  /// Applies upward linear velocity to the [Flipper] to move it up.
+  void moveUp() {
+    body.linearVelocity = Vector2(0, _speed);
+  }
+
+  // TODO(erickzanardo): Remove this once the issue is solved:
+  // https://github.com/flame-engine/flame/issues/1417
+  final Completer hasMounted = Completer<void>();
+
+  List<FixtureDef> _createFixtureDefs() {
+    final fixtures = <FixtureDef>[];
+
+    final bigRadius = size.y / 2;
+    final bigCircleShape = CircleShape()
+      ..radius = bigRadius
+      ..position.setValues(
+        _isMirrored ? size.x - bigRadius : bigRadius,
+        -bigRadius,
+      );
+    final bigCircleFixtureDef = FixtureDef(bigCircleShape);
+    fixtures.add(bigCircleFixtureDef);
+
+    final smallRadius = bigRadius / 2;
+    final smallCircleShape = CircleShape()
+      ..radius = smallRadius
+      ..position.setValues(
+        _isMirrored ? smallRadius : size.x - smallRadius,
+        -2 * smallRadius,
+      );
+    final smallCircleFixtureDef = FixtureDef(smallCircleShape);
+    fixtures.add(smallCircleFixtureDef);
+
+    final inclineSpace = (size.y - (2 * smallRadius)) / 2;
+    final trapeziumVertices = _isMirrored
+        ? [
+            Vector2(smallRadius, -inclineSpace),
+            Vector2(size.x - bigRadius, 0),
+            Vector2(size.x - bigRadius, -size.y),
+            Vector2(smallRadius, -size.y + inclineSpace),
+          ]
+        : [
+            Vector2(bigCircleShape.radius, 0),
+            Vector2(size.x - smallCircleShape.radius, -inclineSpace),
+            Vector2(size.x - smallCircleShape.radius, -size.y + inclineSpace),
+            Vector2(bigCircleShape.radius, -size.y),
+          ];
+    final trapezium = PolygonShape()..set(trapeziumVertices);
+    final trapeziumFixtureDef = FixtureDef(trapezium)
+      ..density = 50.0
+      ..friction = .1;
+    fixtures.add(trapeziumFixtureDef);
+
+    return fixtures;
+  }
+
+  @override
+  Body createBody() {
+    final bodyDef = BodyDef()
+      ..gravityScale = 0
+      ..type = BodyType.dynamic
+      ..position = _position;
+
+    final body = world.createBody(bodyDef);
+    _createFixtureDefs().forEach(body.createFixture);
+
+    return body;
+  }
+
+  @override
+  void onMount() {
+    super.onMount();
+    hasMounted.complete();
+  }
+}
+
+/// {@template flipper_anchor_revolute_joint_def}
+/// Hinges one end of [Flipper] to an [Anchor] to achieve an arc motion.
+/// {@endtemplate}
+class FlipperAnchorRevoluteJointDef extends RevoluteJointDef {
+  /// {@macro flipper_anchor_revolute_joint_def}
+  FlipperAnchorRevoluteJointDef({
+    required Flipper flipper,
+    required Anchor anchor,
+    bool isMirrored = false,
+  }) {
+    initialize(
+      flipper.body,
+      anchor.body,
+      anchor.body.position,
+    );
+    enableLimit = true;
+    final angle = isMirrored ? -_sweepingAngle : _sweepingAngle;
+    lowerAngle = angle;
+    upperAngle = angle;
+  }
+
+  /// The total angle of the arc motion.
+  static const _sweepingAngle = math.pi / 7;
+}