tween

tween is an std-optional tweening library, designed for use in games and animations.

To install, add the following to your Cargo.toml:

tween = "1.0.0"

This trait exports a trait Tween, a variety of structs which implement common tweens (such as Elastic, Quart, etc), and two Tweeners, which wrap around tweens, allowing users to drive them trivially.

First, tweens are simple to create:

use tween::SineIn;

let range = 0.0..=200.0;
let duration = 60;

let mut sine_in = SineIn::new(range, duration);
let _value0 = sine_in.run(0);
let _value1 = sine_in.run(1);
let _value2 = sine_in.run(2);
let _value3 = sine_in.run(3);

Notice how we work over a RangeInclusive to provide values.

However, as the above example shows, it's more typical that you'll want to simply drive a tween over time, rather than giving arbitrary times within a duration.

For that, we use tweeners, which come in two kinds: Tweener and FixedTweener. For both, users provide deltas, rather than arbitrary times. A FixedTweener uses just one delta (appropriate in a game engine with a Fixed Update pipeline), whereas a Tweener can take a fixed delta.

use tween::{SineIn, FixedTweener};

let range = 0.0..=200.0;
let duration = 60;

let sine_in = SineIn::new(range, duration);
let delta = 1;
let mut sine_in_tweener = FixedTweener::new(sine_in, delta);

let _value0: Option<f32> = sine_in_tweener.next();
let _value1: Option<f32> = sine_in_tweener.next();
let _value2: Option<f32> = sine_in_tweener.next();
let _value3: Option<f32> = sine_in_tweener.next();

// we can finish off the tweener by using the iterator interface.
// we only use `&mut` here to demonstrate the `None` after this loop, you can just
// take it by value like normal.
for value in &mut sine_in_tweener {
    // FixedTweener provides an iterator interface
}

assert!(sine_in_tweener.next().is_none());

Std Optional

This library uses std with the default feature std. Disable default features, and enable libm, for a no-std experience. (We need to use libm for the floating point math).

Generics

This library uses generics heavily. There are two core generics used: TweenValue and TweenTime. All built-in numeric types implement both traits. For your own code, you can implement either trait. For example, you could easily implement TweenValue for your favorite math library.