tween

SDK-side frame-based interpolation (manual tween).

For most use cases, prefer renderer-side descriptors (plushie/animation/transition, plushie/animation/spring) which animate with zero wire traffic. Use this module when you need frame-by-frame control over interpolation in the app model.

Drive with subscription.on_animation_frame(), create with new, start with start, then advance each frame.

Types

Animation

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An animation interpolating between two values over time.

pub type Animation {
  Animation(
    from: Float,
    to: Float,
    duration_ms: Int,
    started_at: option.Option(Int),
    easing: easing.Easing,
    value: Float,
    finished: Bool,
    repeat: Repeat,
    auto_reverse: Bool,
    cycles_completed: Int,
    reversed: Bool,
  )
}

Constructors

Animation(
  from: Float,
  to: Float,
  duration_ms: Int,
  started_at: option.Option(Int),
  easing: easing.Easing,
  value: Float,
  finished: Bool,
  repeat: Repeat,
  auto_reverse: Bool,
  cycles_completed: Int,
  reversed: Bool,
)

Arguments

cycles_completed: Track how many complete cycles have been played.
reversed: Track whether the current cycle is playing forward or reversed.

Repeat

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Repeat mode for animations.

pub type Repeat {
  Once
  Times(Int)
  Forever
}

Constructors

```
Once
```
Play once and stop.
```
Times(Int)
```
Repeat a fixed number of times.
```
Forever
```
Repeat indefinitely.

Values

advance

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pub fn advance(anim: Animation, now: Int) -> Animation

Advance the animation to the given timestamp. Returns updated animation. Check finished field to know when it’s done.

is_finished

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pub fn is_finished(anim: Animation) -> Bool

Check if the animation has finished.

lerp

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pub fn lerp(from: Float, to: Float, t: Float) -> Float

Linear interpolation between two values.

looping

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pub fn looping(
  from: Float,
  to: Float,
  duration_ms: Int,
  easing: easing.Easing,
) -> Animation

Create a looping animation that repeats forever with auto-reverse.

Shorthand for new with repeat: Forever and auto_reverse: True. The animation bounces between from and to indefinitely.

new

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pub fn new(
  from: Float,
  to: Float,
  duration_ms: Int,
  easing: easing.Easing,
) -> Animation

Create a new animation (not yet started).

Uses the same Easing type as renderer-side transitions, so the full set of named curves is available (e.g. easing.EaseOutBounce, easing.CubicBezier(0.25, 0.1, 0.25, 1.0)).

set_auto_reverse

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pub fn set_auto_reverse(
  anim: Animation,
  enabled: Bool,
) -> Animation

Enable or disable auto-reverse. When enabled, the animation plays in reverse on alternate cycles.

set_repeat

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pub fn set_repeat(anim: Animation, repeat: Repeat) -> Animation

Set the repeat mode on an animation.

start

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pub fn start(anim: Animation, now: Int) -> Animation

Start the animation at the given timestamp (monotonic ms).

value

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pub fn value(anim: Animation) -> Float

Get the current value.