@thi.ng/timestep/state.js

Deterministic fixed timestep simulation updates with state interpolation

import { mix } from "@thi.ng/math/mix";
import { mixN2, mixN3, mixN4 } from "@thi.ng/vectors/mixn";
import { set2, set3, set4 } from "@thi.ng/vectors/set";
class NumericState {
  constructor(value, update) {
    this.value = value;
    this.update = update;
    this.reset(value);
  }
  curr;
  prev;
  deref() {
    return this.value;
  }
  /**
   * Sets {@link NumericState.prev}, {@link NumericState.curr} and
   * {@link NumericState.value} to given new value.
   *
   * @param value
   */
  reset(value) {
    this.prev = this.curr = this.value = value;
  }
  integrate(dt, ctx) {
    this.prev = this.curr;
    this.curr = this.update(this.curr, dt, ctx);
  }
  interpolate(alpha, _) {
    this.value = mix(this.prev, this.curr, alpha);
  }
}
class VectorState {
  constructor(api, value, update) {
    this.value = value;
    this.update = update;
    this.setFn = api.set;
    this.mixFn = api.mixN;
    this.prev = this.setFn([], value);
    this.curr = this.setFn([], value);
  }
  prev;
  curr;
  setFn;
  mixFn;
  deref() {
    return this.value;
  }
  /**
   * Copies given vector to {@link VectorState.prev}, {@link VectorState.curr}
   * and {@link VectorState.value}.
   *
   * @param value
   */
  reset(value) {
    const set = this.setFn;
    set(this.prev, value);
    set(this.curr, value);
    set(this.value, value);
  }
  integrate(dt, ctx) {
    this.setFn(this.prev, this.curr);
    this.update(this.curr, dt, ctx);
  }
  interpolate(alpha) {
    this.mixFn(this.value, this.prev, this.curr, alpha);
  }
}
const defNumeric = (x, update) => new NumericState(x, update);
const defVector = (api, v, update) => new VectorState(api, v, update);
const defVector2 = (v, update) => new VectorState({ set: set2, mixN: mixN2 }, v, update);
const defVector3 = (v, update) => new VectorState({ set: set3, mixN: mixN3 }, v, update);
const defVector4 = (v, update) => new VectorState({ set: set4, mixN: mixN4 }, v, update);
export {
  NumericState,
  VectorState,
  defNumeric,
  defVector,
  defVector2,
  defVector3,
  defVector4
};