帮忙解决设计问题
这是我的问题。
我正在使用一个名为 Box2D 的物理库。我可以连接一个监听器，它会在两个灯具发生碰撞时告诉我。
本质上，Box2D 的工作方式是创建 b2Bodies。因此，我只知道碰撞的fixture属于哪个b2Body。在我的游戏中，我有一个实体，并且从中我有一个 PhicsEntity。一个PhysicsEntity持有一个指向b2Body的指针。它还有一个来自 Entity 的 sendMessage 方法。问题是，如何从 b2Body 向PhysicsEntity 发送碰撞消息。我想做的是将 b2Body 的 userData void* 设置为其对应的PhysicsEntity。不过，必须强制转换 void* 来执行此操作似乎非常错误。
有没有更好的方法可以让我快速了解与 b2Body 关联的物理实体，而无需进行强制转换或查找？
谢谢
Here is my problem.
I'm using a physics library called Box2D. I'm able to hook up a listener that will tell me when 2 fixtures collide.
Essentially the way Box2D works is by creating b2Bodies. Therefore, I only know which b2Body the fixture that collided belongs to. In my game, I have an Entity, and from that I have a PhisicsEntity. A PhysicsEntity holds a pointer to a b2Body. It also has a sendMessage method that comes from Entity. The problem is, from the b2Body, how do I send the PhysicsEntity a collision message. What I thought of doing was to set the userData void* of the b2Body to its corresponding PhysicsEntity. It seems very wrong to have to cast a void* to do this though.
Is there a better way that I could very quickly know the Physics Entity associated with the b2Body without casting or lookup?
Thanks
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这正是 userData 字段之类的字段的用途 - 引用与库对象相关的应用程序数据。这是
void *的完全正确的使用。如果您询问有关 C 的问题，我会说您也不应该使用任何强制转换，因为可以在不进行任何强制转换的情况下完成与
void *的转换，并且需要使用强制转换是一个标志一个可能的问题，但如果我没记错的话，C++ 需要这些转换（我使用 C++ 的程度不足以确定）。This is exactly the purpose that fields like that userData field are for — to refer to your application's data related to the library's object. This is an entirely appropriate use of
void *.If you were asking about C, I would say that you should also not have to use any casts, as converting to and from
void *can be done without any casts and needing to use a cast is a sign of a possible problem, but if I recall correctly C++ requires those casts (I do not use C++ enough to be sure).这实际上正是 userData 指针的用途。这是一个相当标准的范例 - 看看 pthread_create 或 CreateThread 等函数作为另一个例子。
如果您遇到一个不允许您使用 void * 的库（或者不安全 - 例如将其存储为 int 本地），那么您可以使用 std::map 来解析该类型。但这会更慢并且开销更大。
That's actually exactly what the userData pointer is meant for. It's a fairly standard paradigm - look at functions such as pthread_create or CreateThread for another example.
If you encounter a library that doesn't allow you to use a void * (or not safely - such as storing it locally as an int) then you can use an std::map to resolve the type. That's slower and with much more overhead though.