Tag Archives: f_trigger_receiver

Workflow: Interaction triggers

In the RND test project one of the most important systems I developed was the interaction trigger system.

This system is simply a method of binding an action (ie “Interact”) and a specifier, and then wrapped to make a ‘broadcast signal’.

This broadcast signal is then sent. Because the broadcast signal can optionally contain a ‘target’, only those matching the target description can be made to respond to the signal.

The importance of a system like this is the ability to make level-specific scripts. I’ll give a test case from the RND project.

  • In Tiled, a marker is created with a name. This is the trigger name, which can be anything as long as it can be uniquely identified.
  • In C2, a ‘On GridMove reach target’ action is bound so that it wraps the reaching of the tile with the trigger name of the marker it has reached.
  • On reach target, the trigger is sent to a BroadcastTrigger function, which accepts the trigger name, and the intended target of the trigger, if any. The target is comma-delimited, so multiple targets can be specified.
  • The BroadcastTrigger function looks at the targets, tokenises them, and then applies the ‘receivedtrigger’ variable of each of the instances that are able to accept triggers. It applies them only to the targets specified, or all instances if no target was specified.
  • Note that a family called f_trigger_receiver was made and the receivedtrigger variable is called ‘f_receivedtrigger’ in order that BroadcastTrigger can efficiently send it to those concerned.
  • In the level-specific script, the intended target is waiting for its specific f_receivedtrigger to change. BroadcastTrigger would have changed it.
  • When it does, it fires off the events there.

In addition to the trigger, level-specific behaviours are specified, and can override the default AI of any object. This is why this is important, because the scripting is done in a separate event sheet (ie logic) and not predefined in the main logic.

Now, other actions are bound, as needed, to the BroadcastTrigger. For example, in the RND project, the On reach target trigger condition was the first one I implemented. But quickly afterwards, it was easy enough to bind the TalkToNPC function, or the InteractWithNPC function to the broadcast.

Of course, the trigger name changed. In the TalkToNPC trigger, the trigger name was "talk "&cmover.name in which the ‘talk’ keyword was appended by the actual variable name of the NPC that was talked to. The name of the NPC talked to was embedded in the signal and no target was specified because the logic was that either the player or the game world was the receiver. But, it is also possible, or even more beneficial if indeed the recipient of the ‘talk’ action was put in to the trigger target, as I did with the next implementation.

I implemented an ‘InteractWithNPC’ action in the same way, but included the recipient of the ‘interact’ action as the target. In the level script it was intended to add to the accomps to keep track who had been interacted with.

The BroadcastTrigger concept is just a concept, but seems to be a very flexible one, as I am using it currently to design a generic kind of interaction behaviour between a single ‘Useitem’ action to a host of different possible objects, each with their varying results. It’s this reason why BroadcastTrigger is useful, because behaviours are defined in the event sheet, and can be contextual as well as part of the main logic.


Thoughts on triggers

On the RND test, here are some thoughts on triggers.

Triggers are broadcast by a function. Triggers may have a targeted object/instance. In order to target any potential object, they’re put into a Family, which I’ll refer to as f_trigger_receiver (f_tr, for short).

There are 2 parts to triggers. The ‘main’ logic, and the ‘map’ logic. The main logic handles generic logic of triggers.

Main logic


The Family for all trigger receivers. Requires f_name, and f_receivedtrigger variables. f_name is the name of the entity which a trigger will use to refer to this instance. f_receivedtrigger is the string identifying the trigger that has been sent out.

On player GridMove reach target

Fired every time the player moves into a tile. This queries if a trigger area was stepped on.

Also, the player must have a current_trigger variable which keeps track of the trigger area it is on at any given time. This prevents re-triggering when the trigger area covers adjacent tiles. Also, this allows to find out if the player has stepped out of a trigger.


A function which handles the send off to f_trigger_receiver. It accepts a trigger_name, and a trigger_target. The trigger_name is the identifier of the trigger. The trigger_target is a comma-delimited string that identifies the objects/instances that the trigger will be sent to. The f_trigger_receiver family is used in order to go across different object types.

Other interactions

Any other interactions deemed worthy of a trigger only has to call the BroadcastTrigger function, and feed it an object that can accept a trigger.

The RND test, for example, had broadcast an NPC interaction generically by feeding it trigger_name="npctalk", trigger_target="npc1". Then the trigger was broadcast only on npc1 and processed accordingly.

There are no  ‘global’ triggers (ie triggers must always have a target). If a ‘global’-like trigger is needed, it might be better to use the player’s mover token as that, since it’s as global as you’re going to get.

Map logic

Map logic refers to the map/room-specific stuff.

Typically, the triggers for a particular room are stored in a separate event sheet (which I call scripts).

Time triggers

I put the time triggers in the map because it’s more specific to the map/mission. I still call BroadcastTrigger, but the trigger_name is specific to the map, of course.

Time triggers include ‘per-tick’ or any kind of time-related triggers.


Some instances need to init themselves before going into play. For example, a waypoint traveller needs to init the first waypoint index. This is done using the post_tmx boolean check, which is basically a switch that tells that the TMX has been completely read, and all objects have been created (and thus referenceable).

Other triggers and functions

Any other kind of triggers, whether they’re from FSM or TOWT, can be put in the map logic script. In the RND test, I’ve put in unique FSM states (eg “reachpath”) to put it in a special state so that the rest of AI can contextualise itself.

Map-specific functions are put here as well.