An Overview of the Event Triggers for the Popular Game Maker Suite, RPG Maker XP
There are four support triggers for events in Enterbrain's RPG Maker XP engine: Action Button, Player Touch, Event Touch, Autorun, and Parallel Process. These triggers control when the scripted event code for that event will begin to run. Here is a brief summary of how they each work.
Action Button
If an event is set to trigger in response to the action button, this means it will occur if the player's avatar is standing next to the event, facing it, and press the action button (by default, the enter key). The majority visible events in the game will use this trigger. It is the trigger for nonplayer characters (NPCs) and treasure chests.
Player Touch
Player touch events are similar to action button events, however, rather than need that the player press the enter key, they will occur as soon as the player steps into the event's locations (or attempts to step there, if the event is impassible). A probable use for these types of events would be landmines. You would not want a player to volunteer to be hit by a landmine, so RPG Maker XP allow you trigger a landmine event as soon as the player enter the mined location.
Event Touch
Event touch is the similar as the player touch, apart from in reverses. Player touch events are triggered when the player attempts to move into an event. Event touch events are triggered when an event attempts to move into a player, in addition to those instances where a player runs into the event. A high-quality example of an event touch event may be a pick pocket NPC who, upon walking into the player, says "Excuse me." and reduces the party's gold by 10.
Autorun and Parallel Process
As well player touch and event touch the distinction between autorun and parallel process is something that gives new RPG Maker XP users some problem. Both autorun and parallel process will begin as almost immediately as a player enters the map and carry on waiting they either end or the player leaves the map. Autorun will completely stop the game (like other events) until it's script has finished. It's a great way to begin scripted cut scenes as soon as a player enters a map. It can also be used to carry out cut scenes across multiple maps, as described in the milliamp cut scene tutorial.
A parallel process, on the other hand, will authorize the game to carry on running while it executes its script. It is a high-quality choice for timed background effects, such as flashes of lightning or flocks of birds that fly across the screen. One significant thing to keep in mind about parallel processes is that, compared to other events, they consume a great amount of CPU time, so having more a couple of parallel process events on a given map is typically a bad idea.