好吧，其實這篇也是臨時冒出來的，最近朋友要做個物理遊戲，以前做物理還是用box2d，呃，確實要花些功夫才能搞懂其中的精髓，但是聽講這套引擎重新封裝了一次，要容易很多，所以就簡單嘗試了一下，感覺確實要簡單不少，不過在這其中還是遇到了些問題，首先就來說說onContactBegin這個回撥函式響應問題。

先說說情況，簡單做了一個打磚塊的遊戲，前面一切都很順利，只是做到碰撞檢測的時候，發現回撥函式弄死都不呼叫。開始我以為函式寫錯了，後來查了api，testCpp都沒有錯，在3.0的api中，沒有關於PhysicsBody，PhysicsWorld這些類的說明，所以大家想查移步到3.2的api中吧。

onContactBegin函式的引數就一個，

bool onContactBegin(PhysicsContact& contact)，這和3.0beta版本又有些不同，以前是2個，所以在新增事件監聽的時候，不要寫錯，like this，

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auto contactListener = EventListenerPhysicsContact::create(); contactListener->onContactBegin = CC_CALLBACK_1(HelloWorld::onContactBegin, this); _eventDispatcher->addEventListenerWithSceneGraphPriority(contactListener, this);

回撥函式是在當兩個物體有接觸的時候就會響應一次，裡面的引數從名字中也能看出來，Contact接觸，自然會涉及到兩個物體。

好了，下面該到重點了，為啥這個onContactBegin函式不響應呢？問題出在三個掩碼值上，這裡推薦一下看下這篇博文。

或者開啟引擎的原始碼，可以在CCPhysicsShape這個標頭檔案裡看下這段程式碼，

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/** * A mask that defines which categories this physics body belongs to. * Every physics body in a scene can be assigned to up to 32 different categories, each corresponding to a bit in the bit mask. You define the mask values used in your game. In conjunction with the collisionBitMask and contactTestBitMask properties, you define which physics bodies interact with each other and when your game is notified of these interactions. * The default value is 0xFFFFFFFF (all bits set). */ inline void setCategoryBitmask(int bitmask) { _categoryBitmask = bitmask; } inline int getCategoryBitmask() const { return _categoryBitmask; }

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/** * A mask that defines which categories of bodies cause intersection notifications with this physics body. * When two bodies share the same space, each body’s category mask is tested against the other body’s contact mask by performing a logical AND operation. If either comparison results in a non-zero value, an PhysicsContact object is created and passed to the physics world’s delegate. For best performance, only set bits in the contacts mask for interactions you are interested in. * The default value is 0x00000000 (all bits cleared). */ inline void setContactTestBitmask(int bitmask) { _contactTestBitmask = bitmask; } inline int getContactTestBitmask() const { return _contactTestBitmask; }

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