Animate for callbacks

on_complete fires once. Callbacks can be used in a cycling animation.

CHANGELOG.md

@@ -180,6 +180,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `PendingApp::with_tracing` and `PendingApp::initialize_tracing` install
   Cushy's tracing Subscriber. The default `PendingApp` has tracing initialized,
   but `PendingApp::new` does not.
+- `Animate` and `IntoAnimate` are now implemented for:
+
+  - `impl FnMut(Duration) -> ControlFlow<Duration> + Send + Sync + 'static`
+  - `SharedCallback<Duration, ControlFlow<Duration>>`
+  - `SharedCallback`
 
 
 [139]: https://github.com/khonsulabs/cushy/issues/139

src/animation.rs

@@ -821,6 +821,31 @@ impl Animate for SharedCallback<Duration, ControlFlow<Duration>> {
     }
 }
 
+impl<F> IntoAnimate for F
+where
+    F: FnMut(Duration) -> ControlFlow<Duration> + Send + Sync + 'static,
+{
+    type Animate = Self;
+
+    fn into_animate(self) -> Self::Animate {
+        self
+    }
+}
+
+impl<F> Animate for F
+where
+    F: FnMut(Duration) -> ControlFlow<Duration> + Send + Sync + 'static,
+{
+    /// Invokes this callback to implement a custom animation.
+    ///
+    /// Returning `ControlFlow::Continue` consumes the entire elapsed duration.
+    /// Returning `ControlFlow::Break` completes the animation and yields the
+    /// provided duration to the next animation.
+    fn animate(&mut self, elapsed: Duration) -> ControlFlow<Duration> {
+        self(elapsed)
+    }
+}
+
 /// Performs a linear interpolation between two values.
 ///
 /// This trait can be derived for structs and fieldless enums.