static/src/engine/trailing_position.ts


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

export class TrailingPositionSystem extends System {
  constructor(
    private readonly point_filter: (
      trail_point: {
        x: number;
        y: number;
        time: number;
      }[],
    ) => {
      x: number;
      y: number;
      time: number;
    }[],
  ) {
    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);
      },
    );
  }
}