检查形状之间碰撞的设计模式

Question

我使用各种形状碰撞检测(Rectangle,Circle,Cone,Ring等)所有这些形状都从基抽象派生Shape类.我的游戏对象具有Shape类型的属性.

class GameObject
{
    (...)
    public Shape CollisionShape { get; set; }
}

在初始化过程中,我决定将为每个对象使用什么形状,例如:

GameObject person = new GameObject();
person.CollisionShape = new Circle(100); // 100 is radius

现在,当我想检查两个对象是否相交时,我使用以下类:

public class IntersectionChecker
{
   public bool Intersect(Shape a, Shape b)
   {
      Type aType = a.GetType();
      Type bType = b.GetType();

      if( aType == typeof(Rectangle) && bType == typeof(Rectangle))
          return Intersect(a as Rectangle, b as Rectangle);

      if( aType == typeof(Rectangle) && bType == typeof(Circle))
          return Intersect(a as Rectangle, b as Circle);

      // etc. etc. All combinations      
   }

   private bool Intersect(Rectangle a, Rectangle b)
   {
      // check intersection between rectangles
   }
}

所以我的代码看起来像:

IntersectionChecker ic = new IntersectionCHecker();
bool isIntersection = 
    is.Intersect(personA.CollisionShape, personB.CollisionShape);

有没有更好的方法来实现我的目标,没有在IntersectionChecker类中进行数十次'if'检查和类型检查？

编辑:

请注意,检查形状A和B之间的交点的方法可用于检查B和A之间的交点.在许多答案中(感谢您的所有想法!)建议从形状本身而不是IntersectionChecker对象调用交叉检查.我认为它会迫使我重复代码.现在我可以这样做:

  if( aType == typeof(Rectangle) && bType == typeof(Circle))
      return Intersect(a as Rectangle, b as Rectangle);

  if( aType == typeof(Circle) && bType == typeof(Rectangle))
      return Intersect(b as Rectangle, a as Circle); // same method as above

Answer 1

您可以使用访问者模式,这是一个C#示例

这将允许您简单地使用Shape.Intersect(Rectangle),Shape.Intersect(Circle),...每个派生形状实现的方法.它会阻止您以额外的方法调用为代价对类型进行任何反射.

编辑 - 这是一个示例实现,如果没有可以在Shape中使用的共享功能,那么使用接口IShape可能会更清晰,但我只是停留在一个抽象基类中.

public class GameObject
{
    private Shape _collisionShape;

    public GameObject(Shape collisionShape)
    {
        _collisionShape = collisionShape;
    }

    public bool Intersects(GameObject other)
    {
        return _collisionShape.IntersectVisit(other._collisionShape);
    }
}

public abstract class Shape
{
    public abstract bool IntersectVisit(Shape other);
    public abstract bool Intersect(Circle circle);
    public abstract bool Intersect(Rectangle circle);
}

public class Circle : Shape
{
    public override bool IntersectVisit(Shape other)
    {
        return other.Intersect(this);
    }

    public override bool Intersect(Circle circle)
    {
        Console.WriteLine("Circle intersecting Circle");
        return false; //implement circle to circle collision detection
    }

    public override bool Intersect(Rectangle rect)
    {
        Console.WriteLine("Circle intersecting Rectangle");
        return false; //implement circle to rectangle collision detection
    }
}

public class Rectangle : Shape
{
    public override bool IntersectVisit(Shape other)
    {
        return other.Intersect(this);
    }

    public override bool Intersect(Circle circle)
    {
        Console.WriteLine("Rectangle intersecting Circle");
        return true; //implement rectangle to circle collision detection
    }

    public override bool Intersect(Rectangle rect)
    {
        Console.WriteLine("Rectangle intersecting Rectangle");
        return true; //implement rectangle to rectangle collision detection
    }
}

并调用它的示例代码:

GameObject objectCircle = new GameObject(new Circle());
GameObject objectRect = new GameObject(new Rectangle());

objectCircle.Intersects(objectCircle);
objectCircle.Intersects(objectRect);
objectRect.Intersects(objectCircle);
objectRect.Intersects(objectRect);

产生输出:

Circle intersecting Circle
Rectangle intersecting Circle
Circle intersecting Rectangle
Rectangle intersecting Rectangle

Answer 2

您可以按照Shape类执行碰撞检查,向IntersectsWith(Shape other)Shape 添加方法.我也建议添加IntersectsWith(GameObject other)到您GameObject,让您保持您的CollisionShape私人.