silphius/app/ecs-systems/attract.js

import {System} from '@/ecs/index.js';
import {distance, normalizeVector} from '@/util/math.js';

export default class Attract extends System {

  static queries() {
    return {
      default: ['Magnet'],
    };
  }

  tick(elapsed) {
    for (const entity of this.select('default')) {
      const {Magnet, Position} = entity;
      const aabb = {
        x0: Position.x - Magnet.strength / 2,
        x1: Position.x + (Magnet.strength / 2) - 1,
        y0: Position.y - Magnet.strength / 2,
        y1: Position.y + (Magnet.strength / 2) - 1,
      };
      let s = Magnet.strength;
      s = s * s;
      for (const other of this.ecs.system('Colliders').within(aabb)) {
        if (other === entity || !other.Magnetic) {
          continue;
        }
        const difference = {
          x: entity.Position.x - other.Position.x,
          y: entity.Position.y - other.Position.y,
        };
        const toward = normalizeVector(difference);
        let d = distance(entity.Position, other.Position);
        if (d > 0) {
          const inv = s * (1 / (d * d));
          let impulse = {
            x: toward.x * inv,
            y: toward.y * inv,
          };
          if (Math.sign(entity.Position.x - (impulse.x * elapsed + other.Position.x)) !== Math.sign(difference.x)) {
            impulse.x = difference.x / elapsed;
          }
          if (Math.sign(entity.Position.y - (impulse.y * elapsed + other.Position.y)) !== Math.sign(difference.y)) {
            impulse.y = difference.y / elapsed;
          }
          other.Forces.applyImpulse(impulse);
        }
      }
    }
  }

}