Creating a schedule

A schedule is a list of tasks for an NPC to perform. A new schedule is chosen only when there is no active one; this might be because the NPC has only just spawned, because it has completed a schedule since it last thought, or because the schedule it was running previously encountered an interrupt condition.

Creating a new schedule

Enumeration

Schedules are defined in the NPC's AI_BEGIN_CUSTOM_NPC macro block. Before you start to do that however, you will need to add a new item to the class' enum:

enum
{
     SCHED_DODGE_ENEMY_FIRE = LAST_SHARED_SCHEDULE, 
};

Todo: Elsewhere BaseClass::NEXT_SCHEDULE is used, not LAST_SHARED_SCHEDULE. What's the difference?

Definition

Once the schedule is enumerated, we can start defining it within AI_BEGIN_CUSTOM_NPC. All schedules use the same structure:

DEFINE_SCHEDULE
(
	SCHED_DODGE_ENEMY_FIRE,

	"	Tasks"
	"		TASK_FIND_DODGE_DIRECTION	3"
	"		TASK_JUMP	 		0"
	""
	"	Interrupts"
	"		COND_LIGHT_DAMAGE"
);

Warning:The first character of each string (except for the 'gap') must be a space or a tab. Your schedule will otherwise be invalid!

As you can see, there are two parts to the definition:

1. Tasks is simply the list of sequential tasks an NPC must perform in order to complete the schedule.
   • Every task requires a numeric value to be passed with it! If the task doesn't actually make use of one, just pass 0.
2. Interrupts is a list of conditions that will cause the schedule to be abandoned, and a new one chosen, if any are ever detected.

In the example schedule given above, the NPC will attempt to find a suitable direction to dodge in (checking in a maximum of three directions, judging by the parameter) before using the output of that task, stored somewhere in the class, to perform the movement itself. But if it encounters COND_LIGHT_DAMAGE (any damage greater than zero) during the process, it will abandon the schedule and select another.

The behavioural code that decides what the NPC actually does is defined in the component tasks.

SelectSchedule()

SelectSchedule() is called whenever an NPC finds itself without a schedule, and contains the logic that decides which should be selected to fill the gap. The NPC's current state and conditions usually play a large part in the decision.

A schedule is selected if the function returns it's name - e.g. return SCHED_DODGE_ENEMY_FIRE;.

Tip:If you expect to write a lot of schedule selection logic, you may find it useful to split it into sub-functions of your own making. CAI_BaseNPC for instance has SelectIdleSchedule(), SelectCombatSchedule(), etc. that are called depending on the NPC's state.

Useful functions

HasCondition(int condition)

True if the specified condition has been set for the current think. Of course, you'd use your enumerated names instead of passing an integer directly!

GetState()

Returns the NPC's state. You can also access m_NPCState directly, but GetState() is read-only and therefore safer.

return BaseClass::SelectSchedule()

There are very few situations where you won't want to call the base class' function. Do so at the end of your function, since a return obviously takes precedence over any code that comes after it.

TranslateSchedule()

TranslateSchedule() is called immediately after SelectSchedule(). It is designed to allow child classes to replace their parent's or parents' schedules with those of their own without having to duplicate selection logic.

int CNPC_Custom::TranslateSchedule( int scheduleType )
{
	switch( scheduleType )
	{
		case SCHED_IDLE_WALK:
		{
			return SCHED_CUSTOM_IDLE_WALK;
			break;
		}
	}

	return BaseClass::TranslateSchedule( scheduleType );
}

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