Parameterizing Behavior Trees

[Todd Heckel]

Hi Gavalakis,

We’re making heavy use (and reuse) of nested behavior trees and have found it somewhat clunky to create a tree that is generic enough to be used in multiple instances. Generally it means having a number of blackboard variables that must be set prior to executing the nested tree. One approach that would make this cleaner and easier to implement would be to add parameters to the nested behavior tree that can be set directly per instance of the tree. These would be similar to BB variables (one might even think of them as belonging to a private BB that only the nested tree can access). Here is a paper that describes a similar approach. Have you ever considered implementing a feature such as this?

Thanks,

/Todd

[Gavalakis]

Hello Todd,

I had some thoughts on that yes and more people have requested that feature.
The biggest issue is how to properly and nicely implement it editor UI wise, while the paper and it’s implementation is code wise, which makes more sense.
One idea I had VERY similar to what you suggest, is for each nested graph to have it’s own local blackboard so in the nested behaviour graph inspector where the “Defined Parameters” are showing, you would be able to choose if you want the nested behaviour to use the propagated blackboard variable or the local one for each “defined parameter”.

I haven’t fully realized this concept thought, and there are some puzzle pieces still missing.
Feel free to elaborate 🙂

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[Todd Heckel]

That is exactly the approach I was considering, and even started to look into implementing it, but I am not yet familiar enough with the inspector GUI code to have made very much progress. I was able to locate where the “Defined Parameters” are drawn, but don’t quite understand what’s involved in adding editable elements to that area, or the ramifications of having certain BB variables overridden in such a manner.

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