The blackboards of behavior trees

My understanding of behavior trees is that you define a whole bunch of functions in your game code that return a boolean. These can be functions that get information about the situation (Is there an enemy nearby? Do I have ammo? Is my health above 60%?) or functions that actually do something and return whether they succeeded (Move to take cover. Shoot at the weakest enemy within range. Say "Halt!"). A behavior tree is then an expression that joins these functions with the equivalent of the operators || and && from C.

The strength of this paradigm is that it's impossible for the game designer to go crazy with the complexity of the behaviors. If you need to define a whole bunch of variables in a blackboard, perhaps this very simple architecture is not a good fit for your task.

Well I did a bit more research and tried implementing my own to at least understand BT's better. Using the actual object that the behavior tree controls looks like a much better alternative then some examples show. This however makes it mandatory to have to have references of everything the behavior tree might need inside it. But I have always found that a creature should be aware of the map and it's surroundings itself instead of having some kind of handler class for it.

Another way I have been trying is to just pass a Map along the tree, an attack task would be run after a SearchEnemyTask task in sequence. The SearchEnemyTask tries to find an appropriate enemy and sets something along the lines of blackboard.put("target", targetEntity). Now this is a little less "safe" but does seem to be more versatile, if I ever want to create an automatic door using a BT I can just reuse openDoorTask on it instead of the above method where I would need to create a new Task with a Door as a blackboard.

It's still hard to wrap my head around the complete concept but I'm getting there, but I was hoping for some more input here.

This sounds like you are making it a bit more complicated than it should be. Also, there really is little difference between the way a BT process its environment and some other architectures.

10 hours ago, IADaveMark said:

This sounds like you are making it a bit more complicated than it should be.

That happened before ?. But how would you pass data around then? I am currently playing around with the behavior tree library of GdxAI. In the example they are using the object itself as a blackboard, it gets passed to every task in the behavior tree so it can manipulate it or use it's methods. It is also working with a Map where I would test the data needed for a task in the start() method and immediately return failure when data is incomplete, like when there is a AttackTask without a prior task that sets an enemy for it in the Map. Then there is the blackboard I spoke about earlier, a class specially catered to that and grows in size when the amount of task and needs grow. I could pass this as well along the tree but it does not seem a good choice compared to the other two.

Well a lot of the world info isn't going to need to get passed. Passing copies of the data isn't a great idea for a lot of reasons. Just look it up from the behavior objects as needed. Same thing for the character's data... just look it up. You can pass in a reference to the world or character if needed, too.

Methinks you skipped a few parts of the behavior tree tutorial.