在不同位置创建的 PolygonShape

Question

我正在尝试用鼠标关节在屏幕中央创建一个多边形，非常简单。 CircleShape 效果很好。鼠标关节的行为也很奇怪，我找不到模式。所有代码都在主文件 here 中。我将代码保持在最低限度。

Vector2 vec2Median(List<Vector2> vecs) {
  var sum = Vector2(0, 0);
  for (final v in vecs) {
    sum += v;
  }
  return sum / vecs.length.toDouble();
}

void main() {
  final game = MyGame();
  runApp(GameWidget(game: game));
}

class MyGame extends Forge2DGame with MultiTouchDragDetector, HasTappables {
  MouseJoint? mouseJoint;
  static late BodyComponent grabbedBody;
  late Body groundBody;

  MyGame() : super(gravity: Vector2(0, -10.0));

  @override
  Future<void> onLoad() async {
    final boundaries = createBoundaries(this); //Adding boundries
    boundaries.forEach(add);

    groundBody = world.createBody(BodyDef());
    final center = screenToWorld(camera.viewport.effectiveSize / 2);
    final poly = Polygon([
      center + Vector2(0, 0),
      center + Vector2(0, 5),
      center + Vector2(5, 0),
      center + Vector2(5, 5)
    ], bodyType: BodyType.dynamic);
    add(poly);
    grabbedBody = poly;
  }

  @override
  bool onDragUpdate(int pointerId, DragUpdateInfo details) {
    final mouseJointDef = MouseJointDef()
      ..maxForce = 3000 * grabbedBody.body.mass * 10 //Not neccerly needed
      ..dampingRatio = 1
      ..frequencyHz = 5
      ..target.setFrom(grabbedBody.body.position)
      ..collideConnected = false //Maybe set to true
      ..bodyA = groundBody
      ..bodyB = grabbedBody.body;

    mouseJoint ??= world.createJoint(mouseJointDef) as MouseJoint;

    mouseJoint?.setTarget(details.eventPosition.game);
    return false;
  }

  @override
  bool onDragEnd(int pointerId, DragEndInfo details) {
    if (mouseJoint == null) {
      return true;
    }
    world.destroyJoint(mouseJoint!);
    mouseJoint = null;
    return false;
  }
}

abstract class TappableBodyComponent extends BodyComponent with Tappable {
  final Vector2 position;
  final BodyType bodyType;
  TappableBodyComponent(this.position, {this.bodyType = BodyType.dynamic});

  @override
  bool onTapDown(_) {
    MyGame.grabbedBody = this;
    return false;
  }

  Body tappableBCreateBody(Shape shape) {
    final fixtureDef = FixtureDef(shape)
      ..restitution = 0.8
      ..density = 1.0
      ..friction = 0.4;

    final bodyDef = BodyDef()
      // To be able to determine object in collision
      ..userData = this
      ..angularDamping = 0.8
      ..position = position
      ..type = bodyType;

    return world.createBody(bodyDef)..createFixture(fixtureDef);
  }
}

class Polygon extends TappableBodyComponent {
  final List<Vector2> vertecies;

  Polygon(this.vertecies, {BodyType bodyType = BodyType.dynamic})
      : super(vec2Median(vertecies), bodyType: bodyType);

  @override
  Body createBody() {
    final shape = PolygonShape()..set(vertecies);
    return tappableBCreateBody(shape);
  }
}

tappableBCreateBody 封装了Tappable 和body 的创建方法，Polygon 是我要创建的对象，vec2Median returns 多边形的中心（按顶点）。

非常感谢！

Answer 1

我认为您必须从顶点中删除 center 并且仅将其添加为 BodyComponent 的位置，就像您在 [=12= 的 super 调用中所做的那样] class.

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