# llimphi-motion

Simple animation over Llimphi's Elm loop.

Llimphi is pure Elm: `update(msg) -> model`. To animate a value over time (an
alpha rising from 0 to 1, a position sliding) the app keeps a `Tween` in its
model and asks the `Handle` to dispatch a `Msg::Tick` periodically (every ~16 ms)
until the animation ends. Each `update` reads `tween.value()` and the `view`
paints it.

This crate is deliberately tiny:

- `Lerp` — generic linear interpolation (impls for `f32`, `(f32, f32)` and
  `Color`).
- `Tween` — timed interpolation with easing between two values.
- `animate` — a helper that starts a self-sufficient tick loop over a `Handle`.

The canonical durations and easings live in `llimphi_theme::motion`.

## Typical pattern

```ignore
use llimphi_motion::{Tween, animate};
use llimphi_theme::motion;

enum Msg { ToastShow, Tick, ToastHidden }
struct Model { toast_alpha: Tween<f32> }

// update:
Msg::ToastShow => {
    model.toast_alpha = Tween::new(0.0, 1.0, motion::NORMAL, motion::ease_out_cubic);
    animate(handle, motion::NORMAL, || Msg::Tick);
    model
}
Msg::Tick => {
    // The internal loop ends by itself once the tween is done;
    // the `view` already reads the current alpha.
    model
}

// view:
toast_view().alpha(model.toast_alpha.value())
```

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Part of **llimphi** — see [llimphi](../README.md).