In this section, we'll go through very briefly on the usage of GAS and GAS Companion in the context of AI and Behavior Trees.
Character / Controller Setup #
Character #
For AI/NPC Characters that are intended to use Gameplay Abilities, they need to inherit from GSCModularCharacter.
This class has all the necessary Gameplay Ability System setup (such as initialization of the Ability System Component and Attribute Sets). GSCModularCharacter differs from GSCModularPlayerStateCharacter by not relying on a PlayerState for GAS setup, and the ASC / Attribute Sets are attached directly to the Pawn Character.
Create a new Blueprint Class with GSCModularCharacter as a parent class (or re-parent your AI Character blueprint to use GSCModularCharacter):
Once done, don't forget to configure your Character Abilities, Attributes and Effects if you have them in the ASC properties, like we did in the Quick Start section.
AI Controller #
To setup Behavior Tree, we need an AIController for this Pawn, from which we'll be able to run a Behavior Tree.
Create a new Blueprint with AIController as a parent class:
In this BP, simply run your Behavior Tree at some point (in either Begin Play or OnPossess)
Finally, update your Character Blueprint to use this AIController, in Details > Pawn > AI Controller Class:
Tasks #
When you want to trigger abilities from BT, it is most likely done via Behavior Tree Tasks.
Dealing with Finish Execute #
Tasks need to notify the Behavior Tree that they have finished the execution of their task, which requires knowing when an ability ends.
To that end, GAS Companion GSCGameplayAbility exposes a OnAbilityEnded delegate you can bind an event to from within your BT Tasks.
You can decide to activate abilities either by Class, or by Tags. The latter providing a much more flexible way to deal with activation (Like trying to activate any ability with the Tags Ability.Meleee or Ability.Range)
GAS Companion provides both option as simple Blueprint-based Behavior Tree Tasks you can use directly.
BTTask_TriggerAbilityByClass #
If you want to activate a specific Gameplay Ability, you can make use of this task.
which exposes a single AbilityToActivate property
The Blueprint Graph for this task, if you would like to use your own Blueprint-based variation:
BTTask_TriggerAbilityByTags #
This one will try to activate an ability by tags.
A Gameplay Tag Container is exposed for you to specify from the Behavior Tree any number of tags to search for.
The task will search for all abilities matching the tag requirements, and try to activate a single one from one of the matching abilities (See ActivateAbilityByTags).
The Blueprint Graph for this task, if you would like to use your own Blueprint-based variation:
