Table of contents
Map Entities
What is a map entity?
A map entity, represented by the MapEntity class in the Level package, is any game object that is a part of a map. This includes map tiles (MapTile class), NPCs (NPC class), enhanced map tiles (EnhancedMapTiles class), and Triggers (Trigger class).
What is the purpose of this class?
The main purpose of the MapEntity class, which extends from GameObject, is that the MapEntity class adds a couple of instance variables to give them additional functionality.
Map Entity Fields
Map Entity Features
All map entities have an instance variable mapEntityStatus which the map’s Camera uses to determine if the entity is “active” or not. An active entity means it should be included in the level’s update/draw cycle for a current frame. Entities that are too far offscreen will be removed from the Camera's update/draw cycle until they are back on screen, as the game does not want to waste resources on entities that at that current frame have no effect on the level or the player.
The MapEntityStatus enum in the Level package defines three different possible statuses: ACTIVE, INACTIVE, and REMOVED. An entity generally doesn’t have to mess with this value as the Camera handles the logic for checking active vs inactive entities, however an entity may set its own status to REMOVED to have it permanently removed from the level with no ability to respawn.
Hidden
Setting a map entity’s isHidden attribute to true will prevent its update and draw logic from being run, essentially “hiding” it from the map. At any time, the entity can be “brought back” by setting its isHidden attribute back to false. It’s an alternative to setting an entity’s status to REMOVED that keeps the entity as a part of the map, so that it can be brought back whenever needed.
Uncollidable
Setting a map entity’s isUncollidable attribute to true will prevent other entities from being able to collide with it. Other entities will just ignore it when doing collision logic. However, the map entity that is set to isUncollidable can still perform collision logic against other entities if desired.
Existence Flag
A map entity can optionally define an existenceFlag. A flag is a boolean value, and the game keeps track of multiple flags in order to track where the player’s progress is at, determine which events should play out, etc. More on flags can be read about here.
If an entity’s existenceFlag becomes set during the game, the entity will no longer “exist”, and the game will not run its update and draw logic anymore. If the entity’s existenceFlag becomes unset, it will “exist” again, and the game will run its logic like normal. This feature is useful for telling certain entities like NPCs and Triggers to disappear after a certain event occurs. An entity with no existenceFlag set is always considered to “exist”.
In the game currently, the TestMap sets the dinosaur NPC’s existenceFlag to "hasTalkedToDinosaur". Once that flag is set (which happens after talking to the dinosaur during a specific part of the game), the dinosaur no longer “exists” and is no longer shown on the map.
Dinosaur dinosaur = new Dinosaur(2, getMapTile(13, 4).getLocation());
// existence flag is set here
dinosaur.setExistenceFlag("hasTalkedToDinosaur");
dinosaur.setInteractScript(new DinoScript());
npcs.add(dinosaur);
Triggers often use this feature to ensure they only are able to be triggered one time.
Interact Script
Any entity in the game can define its own interact script, which is a Script that executes when the player interacts with the entity. The player interacts with an entity by walking up to it in a close enough proximity and pressing the space key.
Read more about scripts here. This game is built around interact and trigger scripts, and is one of the most important pieces of the game to understand.
In the game currently, TestMap adds interact scripts to the walrus NPC, dinosaur NPC, all three sign tiles, and the bottom tree trunk tile (where the player finds their ball at the end of the game). The below code in TestMap shows an example of setting an interact script on specific map tiles (like the sign tiles):
@Override
public void loadScripts() {
// set interact script on sign to say "Cat's house" when talked to
getMapTile(21, 19).setInteractScript(new SimpleTextInteractScript("Cat's house"));
// ...
}