Ticking decorators in UE4 Behavior Trees

I had some questions/concerns about how decorators interact with selectors, specifically with the notion of bp-based decorators that can be ticked.

This largely builds off the discussion here:
How to achieve “Active” selector node functionality in UE4 Behavior Trees?

Here’s an example: say I have a decorator that wants to detect (every tick) whether some value has exceeded a threshold (say my “weapon heat”). The only way I can get the effect of testing this every tick is to place weapon-heat in the blackboard. Correct?
This is frustrating for several reasons:

  1. this might be the only decorator in the entire tree that cares about weapon-heat, so it seems wasteful to pollute the global blackboard with this value
  2. I need to create some OTHER mechanism to make sure that weapon-heat is properly fed into the blackboard with the frequency I need, which means that the weapon-heat-threshold decorator is no longer a self-contained piece of logic – I need to know that it won’t work without this OTHER service in place
  3. In other words, you haven’t avoided the need for ticking, you’ve merely obfuscated where that ticking takes place.

I think my high-level observation is: this aversion to ticking is strange, and I’d much prefer to allow some option to tick my bp-authored decorators and take responsibility for the perf implications. In the example above (and I suspect many examples) the freedom to tick significantly simplifies the tree.

tldr: a feature request, for the option to allow ticking of bp-authored decorators.

I am assuming, by the way, that all of this ONLY goes for bp-authored decorators. If I were to implement a “weapon-heat decorator” in c++ I could override the tick() function and request execution every tick. Correct?


  • Damian