bitecs-proxies.ts

import * as bit from "bitecs";

type ComponentBundle = { [componentName: string]: bit.ComponentType<any> };

type NumProxy<T> = { [key in keyof T]: number };

export function makeCmpProxyForEnt<T>(cmp: T, eid: number) {
  const getterSetterProps = Object.fromEntries(
    Object.entries(cmp).map(([k, v]) => [
      k,
      {
        get() {
          return v[eid];
        },
        set(value: number) {
          v[eid] = value;
        },
      },
    ])
  );

  const prox = <NumProxy<T>>Object.defineProperties({}, getterSetterProps);
  return prox;
}

export function makeCmpProxy<T>(cmp: T) {
  let eid = 0;
  const setProxEid = (newEid: number) => {
    eid = newEid;
  };

  const getterSetterProps = Object.fromEntries(
    Object.entries(cmp).map(([k, v]) => [
      k,
      {
        get() {
          return v[eid];
        },
        set(value: number) {
          v[eid] = value;
        },
      },
    ])
  );

  const prox = <NumProxy<T>>Object.defineProperties({}, getterSetterProps);
  return [prox, setProxEid] as const;
}

type BundleProxy<T> = { [key in keyof T]: NumProxy<T[key]> };

export function makeBundleProxy<T extends ComponentBundle>(cmpBundle: T) {
  const bundleProx: any = {};
  const eidSetters: ((eid: number) => void)[] = [];

  Object.entries(cmpBundle).forEach(([k, cmp]) => {
    const [prox, eidSetter] = makeCmpProxy(cmp);
    bundleProx[k] = prox;
    eidSetters.push(eidSetter);
  });

  const setProxEid = (newEid: number) => {
    eidSetters.forEach((eidSetter) => eidSetter(newEid));
  };

  return [<BundleProxy<T>>bundleProx, setProxEid] as const;
}

type BundleMutatorFn<T> = (bundle: {
  [key in keyof T]: NumProxy<T[key]>;
}) => void;

export function createComponentBundleForEachSystem<T extends ComponentBundle>(
  cmpBundle: T,
  bundleMutator: BundleMutatorFn<T>
): bit.System {
  const query = bit.defineQuery(Object.values(cmpBundle));

  const [prox, eidSetter] = makeBundleProxy(cmpBundle);

  return function (world) {
    const eids = query(world);

    for (let eid of eids) {
      eidSetter(eid);
      bundleMutator(prox);
    }
    return world;
  };
}

const vec2_f32 = { x: bit.Types.f32, y: bit.Types.f32 };
const size2_i16 = { width: bit.Types.i16, height: bit.Types.i16 };
const index2_i16 = { i: bit.Types.i16, j: bit.Types.i16 };

const Position = bit.defineComponent(vec2_f32);
const Velocity = bit.defineComponent(vec2_f32);
const GridIndex = bit.defineComponent(index2_i16);
const Size = bit.defineComponent(size2_i16);

createComponentBundleForEachSystem(
  { pos: Position, vel: Velocity, GridIndex, Size},
  (ent) => {
    ent.pos.x += ent.vel.y
    ent.GridIndex.j
    ent.Size.height
  }
);