static/src/engine/trailing_position.ts


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import { ComponentType, TrailingPositionComponent } from "./component";
import { Game } from "./game";
import { System, SystemType } from "./system";

interface Point {
  x: number;
  y: number;
  time: number;
}

export class TrailingPositionSystem extends System {
  constructor(
    private readonly point_filter: (trail_point: Array<Point>) => Array<Point>
  ) {
    super(SystemType.TRAILING_POSITION);
  }

  public update(_dt: number, game: Game) {
    game.for_each_entity_with_component(
      ComponentType.TRAILING_POSITION,
      (entity) => {
        const trailing_position = entity.components[
          ComponentType.TRAILING_POSITION
        ] as TrailingPositionComponent;
        trailing_position.trails = this.point_filter(trailing_position.trails);
      }
    );
  }
}