ludic/docs/language/tween/tween-to.md
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feat(anim): animation ergonomics — named clips, Anim.play/Motion.to, frame events, fluent Tween handles (#48)
The ergonomic layer over the engine-owned SpriteAnim/Motion systems (#43):

- Named clips: Anim.clip("run", frames, fps, mode) registers a clip by name and
  Anim.play(entity, "run") plays it; Anim.play(entity, fps, frames, mode) sets
  the clip directly. A name-keyed registry in systems.ludic.
- Frame events: Anim.on_frame(entity, frame) arms optional SpriteAnim
  event_frame/event_fired fields; the engine flags the tick the clip first lands
  on that frame, and Anim.fired(entity) reads it — the game reacts, so it stays
  inside the no-runtime-dispatch event model.
- Motion.to(entity, from, to, dur, ease) starts a value tween over the Motion
  component in one call (reflection-ABI writes, resetting the timer).
- Fluent Tween handles (runtime/native/tween.ludic): Tween.to / Tween.chain /
  Tween.delay build a sequenced, disposable handle advanced by a new engine-owned
  system (esys_tween, run each Update tick); Tween.value / Tween.done /
  Tween.parallel / Tween.stop read and control it. The 1-arg Tween.done(handle)
  is disambiguated from the 2-arg pure Tween.done(timer, dur).

Splicing: g_uses_anim_rt pulls in systems.ludic; g_uses_tween_rt pulls in
tween.ludic and inserts esys_tween into the Update phase. All integer and
deterministic, so animation and motion reproduce exactly under replay/lockstep.

Worked example + regression: examples/library/anim_sugar.ludic
(4 8 2 1 0 100 100 0 0 1 20 20 30 0 1). Twelve new docs pages (Anim, the new
Motion namespace, Tween handles). Full suite 77 passed, self-host C-free fixpoint
intact, no golden drift.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-08-31 16:53:16 +03:00

1.6 KiB

id name category kind tokens sig tip order ns member
tween-to Tween.to tween namespace-method Tween.to Tween.to(from, to, dur, ease) -> handle Start a fluent, engine-advanced tween and return a handle. 30 Tween to

Starts a stateful tween handle — from from to to over dur ticks with easing ease — and returns an integer handle. Unlike the pure Tween.progress interpolators (which the game drives from its own timer), a handle is advanced by the engine one tick per frame: fire it once, then read Tween.value each frame and Tween.done to know when it finishes. Tween.chain and Tween.delay append segments for a sequence. Integer and deterministic, so a sequence plays identically under replay. The handle pool is fixed-size and reuses finished slots.

Parameters:

  • from, to — the start and end values (integer game units)
  • dur — the segment length in engine ticks
  • ease — 0 linear, 1 in, 2 out, 3 in-out
program Demo {
  property SpriteAnim { ticks: int = 0, fps: int = 0, frames: int = 0, mode: int = 0, frame: int = 0 }
  property Pop { h: int = 0 }
  model Coin { SpriteAnim, Pop }
  entry {
    spawn Coin { Pop { h: 0 } }
    let e = World.query_next(World.prop_id("Pop"), 0)
    let f = World.field_id(World.prop_id("Pop"), "h")
    World.set(e, World.prop_id("Pop"), f, Tween.to(0, 40, 20, 2))   # pop upward
    quit()
  }
}