Sometimes called a scene hierarchy, the scene graph is a hierarchy of every Cocos2d node that's currently active.

We call them nodes because they inherit from the class CCNode (http://www.cocos2d-swift.org/docs/api/Classes/CCNode.html), the base class to display objects in Cocos2d.

The usual picture of a scene graph is a root CCScene node with several node children such as CCButton, CCSprite, and CCLabelTTF. For example, the graph of an initial Cocos2d project looks like the following:

One important feature of CCNode in the current Cocos2d version is that it inherits from CCResponder, which allows all the objects derived from CCNode to handle user touches and mouse events.

I said that CCNode is the base class to display objects, but what are the classes that inherit from it? You can see the CCNode class hierarchy in the following graph:

As I mentioned in the previous section, scenes will no longer derive from CCLayer (as has been the case in previous Cocos2d versions) and if you look closely at the CCNode class hierarchy in the preceding graph, you will realize that this class doesn't appear in it. It means that CCLayer has been deprecated and doesn't exist anymore, due to the fact that CCNode now supports user interaction, which was basically the purpose of CCLayer besides grouping nodes, a task perfectly accomplished by CCScene.

One important CCNode property is positionType. This property makes reference to how a node's position will be interpreted and can take three different values:

Another important property is contentSizeType, which means that the size of the node's content will be interpreted in different ways depending on its value:

This class is one of the most important because our games will have plenty of classes that derive from it, such as CCButton (inherits from CCControl), CCParallaxNode, CCParticleSystemBase, CCSprite, CCLabelTTF (inherits from CCSprite), CCLabelBMFont (inherits from CCSpriteBatchNode), or CCScene.