Door + key (messages + triggers)

This example shows a common pattern:

• a “key” pickup is a non-solid trigger
• the key sends a message when collected
• the “door” listens and changes its behavior at runtime by swapping its tickFn (setTickFunction)

Key pickup (trigger)

import { GameObject, SquareHitbox, Vector } from "sliver-engine";

class KeyPickup extends GameObject {
  constructor() {
    super("item:key", new Vector(240, 160));
    this.addHitbox(
      new SquareHitbox(Vector.zero(), new Vector(16, 16), this, {
        solid: false,
      })
    );
  }

  override onColision(other: GameObject): void {
    if (other.name !== "player") return;
    this.sendMessage("player:key_obtained", { id: "gold" });
    this.destroy();
  }
}

Door (locks until key obtained)

import { GameObject, SquareHitbox, Vector, renderTile } from "sliver-engine";
import type { CanvasController, GameContext, Scene } from "sliver-engine";

// indexes of the sprites in the spritesheet
const DoorSprites = {
  open: 0,
  closed: 1,
};

class Door extends GameObject {
  public open: boolean = false;

  constructor() {
    super("door", new Vector(400, 160));
    this.addHitbox(new SquareHitbox(Vector.zero(), new Vector(24, 48), this)); // solid
    this.setPhisics({ immovable: true });
  }

  override onAddedToScene(_scene: Scene, _context: GameContext): void {
    this.onceOnMessage<{ id: string }>("player:key_obtained", ({ id }) => {
      if (id !== "gold") return;

      // Make the door non-solid for the player to pass through it
      this.getHitboxes().forEach((h) => (h.solid = false));
    });
  }

  // change the rendering of the door depending on if it's open or closed.
  @renderTile<Door>(
    "interactive_objects", // spritesheet name
    DoorSprites.open, // sprite index
    { when: (door) => door.open }
  )
  @renderTile<Door>(
    "interactive_objects", // spritesheet name
    DoorSprites.closed, // sprite index
    { when: (door) => !door.open }
  )
  override render(canvas: CanvasController, scene: Scene): void {}
}

This keeps coupling low: the key doesn’t need to know where the door is.