如何在层中访问物理世界 [英] How to access Physics World in Layer

问题描述

我需要在两个物体之间创建连接。关节将在物理世界中添加。我如何在层中访问物理世界？

I need to create joint between two bodies in layer. Joints are to be added in physics world. How can i access physics world in layer?

推荐答案

您有四个选择：

1）-覆盖Layer :: onEnter（）或onEnterTransitionDidFinish（）
方法，然后从这样的主题进行访问：

1)- override Layer::onEnter() or onEnterTransitionDidFinish () methods then access from theme like this:

    Layer::onEnter(){
        Layer::onEnter();
        auto world = _director->getRunningScene()->getPhysicsWorld();
    }

2）-创建自定义图层：： createScene（）方法然后从Layer :: init（）进行访问，如下所示：

2)- create a custom Layer::createScene() method then access from Layer::init() like this:

Scene* GameScene::createScene()
{
    auto layer = new (std::nothrow) GameScene;
    if (layer)
    {
        auto scene = Scene::createWithPhysics();
        layer->autorelease();
        scene->addChild(layer);
        if (layer->init()) return scene;
    }
    CC_SAFE_DELETE(layer);
    return nullptr;
}

// then in Layer::init() you do this:

Layer::init(){
    auto world = _director->getRunningScene()->getPhysicsWorld();
}

3）-将PhysicsWorld getter方法添加到导演（涉及一些库代码定制）：

3)- add a PhysicsWorld getter method to the director (involves some library code customization's):

首先转到CCDirector.h，然后在NS_CC_BEGIN下添加场景类的前向声明，如下所示：

first go to CCDirector.h and then add a forward declaration of the scene class under NS_CC_BEGIN like this:

NS_CC_BEGIN
class cocos2d::Scene;

然后转到Director类的private部分，并添加如下两行：

then go to the private section of the Director class and add these two lines like this:

private:
cocos2d::PhysicsWorld* _myPhysicsWorld;
friend class Scene;

然后转到Director类的public部分，并添加如下这样的getter方法：

then go to the public section of the Director class and add this getter method like this:

public:
cocos2d::PhysicsWorld* getWorld() const{
    return _myPhysicsWorld;
};

这是CCDirector.h文件中所做更改的概述：

this is an overview of the changes made in CCDirector.h file:

// CCDirector.h
NS_CC_BEGIN

// 1
class cocos2d::Scene;

class Director : public Ref{

public:
    //2
    cocos2d::PhysicsWorld* getWorld() const{
        return _myPhysicsWorld;
    };
private:
    // 3
    cocos2d::PhysicsWorld* _myPhysicsWorld;
    friend class cocos2d::Scene;
};

NS_CC_END

所以之后，我们进入CCScene.cpp方法带有此签名（bool Scene :: initWithPhysics（））的您会发现对PhysicsWorld :: construct（this）的调用在该方法之后立即添加此行：

so after that we go to CCScene.cpp into a method with this signature (bool Scene::initWithPhysics()) in it you will find a call to PhysicsWorld::construct(this) add just right after that method call this line:

_director->_myPhysicsWorld = _physicsWorld;

这应该是我们在CCScene.cpp中所做的概述：

and this should be the overview of what we did in CCScene.cpp:

// CCScene.cpp
class Scene : public Node{

    bool Scene::initWithPhysics(){

         _physicsWorld = PhysicsWorld::construct(this);
         // 4 since Director is a singleton class, we can access its instance from anywhere
        _director->_myPhysicsWorld = _physicsWorld;

    }
};  

现在，只要Scene :: createWithPhysics（）被调用，导演就会得到副本的副本。 PhysicsWorld指针，可随时使用我们的导演getWorld（）方法进行访问！ （因为您所知道的是导演是一个单身人士），仅此而已，就不会将_myPhysicsWorld暴露给用户，这意味着他只能从外部读取_myPhysicsWorld ！！

now as soon as Scene::createWithPhysics() gets called anywhere the director will get a copy of the PhysicsWorld pointer which can be accessed using our director getWorld() method anywhere anytime!! (because the director is a singleton as you know) and thats all without exposing _myPhysicsWorld to the user meaning he can only read _myPhysicsWorld from the outside!!

4 ）-制作自己的Custom PhysicsWorld类，由于PhysicsWorld :: construct（）受保护，因此可以轻松继承。

4)- make your own Custom PhysicsWorld class and since PhysicsWorld::construct() is protected which means it can be easily inherited.

// PhysicsManager.h

class PhysicsManager : public cocos2d::PhysicsWorld
{
public:

    static PhysicsManager* createWorld(cocos2d::Scene* scene) {
        _myPhysicsWorld = PhysicsWorld::construct(scene);
    }

    PhysicsWorld* getWorld() const { return _myPhysicsWorld; }

private:
    static cocos2d::PhysicsWorld* _myPhysicsWorld;
};

//PhysicsManager.cpp

PhysicsManager::PhysicsWorld* _myPhysicsWorld;

现在您可以像这样使用它：

now you can use it like this:

Layer::init(){

    auto physicsManager = PhysicsManager::createWorld(this->getScene());

    auto world = physicsManager->getWorld();

}

请记住，如果您甚至可以将其设置为单例课程

remember that you can even make it a singleton class if you want to!

编辑：

我忘了还有另一个此处的好解决方案：

I forgot to mention that there is another good solution in here:

http://discuss.cocos2d-x.org/t/physics-joint-distance-problem/17926/2

这篇关于如何在层中访问物理世界的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！