Behaviors

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Revision as of 17:13, 28 May 2008 by TomEdwards (talk | contribs) (Authoring a behavior)

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Behaviors let you abstract AI code to a C++ class of its own which is not tied to any one NPC. You might want to create MensBathroomBehavior for male NPCs and WomensBathroomBehavior for female NPCs, for instance.

Authoring a behavior

Behavior code, for the most part, behaves in the same way and uses the same framework as AI code you would write directly into an NPC. There is a certain amount of 'glue' required between one and the NPCs that will use it however:

The behavior

  • Create bool CanSelectSchedule(), which defines whether or not an NPC will 'defer' to the behavior for a given think.
  • Create virtual const char *GetName() { return "MyBehavior friendly name"; }.
  • Use AI_BEGIN_CUSTOM_SCHEDULE_PROVIDER instead of AI_BEGIN_CUSTOM_NPC (in the body).
  • Use DEFINE_CUSTOM_SCHEDULE_PROVIDER instead of DEFINE_CUSTOM_AI (in the header).
  • Use GetOuter()-> to access the NPC object.

The NPC

  • Include the header for your new behavior, and ai_behavior.h.
  • Create an member instance of your behavior.
  • Register the instance in CreateBehaviors() with AddBehavior( &m_MyBehavior ).
    • None of Valve's NPC base classes have any behaviors registered - it may not be possible to do it at that level.
  • Call BehaviorSelectSchedule() at some point in SelectSchedule(). This probably already happens if you're working with a stock NPC.

Activating a behaviour manually

Behaviours are evaluated on every think with the logic in CanSelectSchedule(). If you want to manually enable a behavior until you disable it:

MyNPC::SelectSchedule()
{
	if ( m_MyBehavior.m_bActive )
	{
		DeferSchedulingToBehavior( &m_MyBehavior );	// Normally happens in BehaviorSelectSchedule()
		return BaseClass::SelectSchedule();		// This will now poll your behavior
	}

	...
}

Warning: Until you release it, this will lock the NPC into your behavior code and only your behavior code.