jumpstorm/engine/systems/Physics.ts

import { System, SystemNames } from '.';
import {
  BoundingBox,
  ComponentNames,
  Forces,
  Gravity,
  Velocity,
  Mass,
  Jump,
  Moment,
  Control
} from '../components';
import { PhysicsConstants } from '../config';
import type { Force2D, Velocity2D } from '../interfaces';
import { Game } from '../Game';

export class Physics extends System {
  constructor() {
    super(SystemNames.Physics);
  }

  public update(dt: number, game: Game): void {
    game.forEachEntityWithComponent(ComponentNames.Forces, (entity) => {
      const mass = entity.getComponent<Mass>(ComponentNames.Mass).mass;
      const forces = entity.getComponent<Forces>(ComponentNames.Forces).forces;
      const velocity = entity.getComponent<Velocity>(
        ComponentNames.Velocity
      ).velocity;
      const inertia = entity.getComponent<Moment>(
        ComponentNames.Moment
      ).inertia;

      // F_g = mg, applied only until terminal velocity is reached
      if (entity.hasComponent(ComponentNames.Gravity)) {
        const gravity = entity.getComponent<Gravity>(ComponentNames.Gravity);
        if (velocity.dCartesian.dy <= gravity.terminalVelocity) {
          forces.push({
            fCartesian: {
              fy: mass * PhysicsConstants.GRAVITY,
              fx: 0
            },
            torque: 0
          });
        }
      }

      // ma = Σ(F), Iα = Σ(T)
      const sumOfForces = forces.reduce(
        (accum: Force2D, { fCartesian, torque }: Force2D) => ({
          fCartesian: {
            fx: accum.fCartesian.fx + (fCartesian?.fx ?? 0),
            fy: accum.fCartesian.fy + (fCartesian?.fy ?? 0)
          },
          torque: accum.torque + (torque ?? 0)
        }),
        { fCartesian: { fx: 0, fy: 0 }, torque: 0 }
      );

      // integrate accelerations
      const [ddy, ddx] = [
        sumOfForces.fCartesian.fy,
        sumOfForces.fCartesian.fx
      ].map((x) => x / mass);
      velocity.dCartesian.dx += ddx * dt;
      velocity.dCartesian.dy += ddy * dt;
      velocity.dTheta += (sumOfForces.torque * dt) / inertia;

      // clear the forces
      entity.getComponent<Forces>(ComponentNames.Forces).forces = [];

      // maybe we fell off the floor
      if (ddy > 0 && entity.hasComponent(ComponentNames.Jump)) {
        entity.getComponent<Jump>(ComponentNames.Jump).canJump = false;
      }
    });

    game.forEachEntityWithComponent(ComponentNames.Velocity, (entity) => {
      const velocityComponent: Velocity = new Velocity();
      const control = entity.getComponent<Control>(ComponentNames.Control);

      velocityComponent.add(
        entity.getComponent<Velocity>(ComponentNames.Velocity).velocity
      );
      if (control) {
        velocityComponent.add(control.controlVelocityComponent.velocity);
      }

      const boundingBox = entity.getComponent<BoundingBox>(
        ComponentNames.BoundingBox
      );

      // integrate velocity
      boundingBox.center.x += velocityComponent.velocity.dCartesian.dx * dt;
      boundingBox.center.y += velocityComponent.velocity.dCartesian.dy * dt;
      boundingBox.rotation += velocityComponent.velocity.dTheta * dt;
      boundingBox.rotation =
        (boundingBox.rotation < 0
          ? 360 + boundingBox.rotation
          : boundingBox.rotation) % 360;

      // clear the control velocity
      if (control) {
        control.controlVelocityComponent = new Velocity();
      }
    });
  }
}