src/anim.js

// Clip playback. Rate and frame count come from the manifest; this file has no
// opinion about either.

export function createPlayer(clip) {
  return {
    clip,
    time: 0,
    reset() { this.time = 0; },
    advance(dt) { this.time += dt; },
    get index() {
      const raw = Math.floor(this.time * this.clip.fps);
      if (!this.clip.loop) return Math.min(Math.max(raw, 0), this.clip.count - 1);
      return ((raw % this.clip.count) + this.clip.count) % this.clip.count;
    },
    get finished() {
      return !this.clip.loop && this.time * this.clip.fps >= this.clip.count - 1;
    },
    frame() { return this.clip.frames[this.index]; },
  };
}