Behaviour Tree In Unreal Engine 4

In this blog, I will be talking about the Behaviour Tree In Unreal Engine 4 based on my own experience. Keep in mind, I am using Unreal Engine 4.15 but I guess the version may not affect the topic of this post.

It would be good if I can get a confirm or correction from a more experienced person. Thanks in advance.

1.  Tick

This post explains the tick behaviour of Behaviour Tree in UE4 very clearly. (I will add my own understanding in the future when I have time. Maybe in Chinese as well.)

UE4 的 Behaviour Tree Tick 和其他的 BT 有一些不同就是它的每次 Tick 只 Tick 活跃 Active 的节点，比如 Service 或者有 Event Receive Tick 的 Task， 而不会在每次 Tick 的过程中都从头遍历节点树。

2. Abort

当你点击一个 Condition 的时候，所有被绿色 (self) 和蓝色 (low priority) 包裹的node都会被abort (如果这些task里有Event Receive Abort AI会被调用到)

3. In behaviour tree tasks, there are three types of events.  Event Receive Execute AI, Event Receive Tick AI, Event Receive Abort AI. What do they mean and when do they get fired?

Event Receive Execute AI will be called once the Task has started.

Event Receive Tick AI will be called in a specific tick rate. (You can check the Delta Seconds to see the tick rate)

Event Receive Abort AI only gets called when the task has been aborted ( mentioned above)