#animation #combinators #easing #tween


A small library for parameterized inbetweening

7 releases

✓ Uses Rust 2018 edition

0.2.2 Feb 12, 2020
0.2.1 Jan 18, 2020
0.1.3 Dec 3, 2019

#13 in Video

Download history 66/week @ 2019-11-29 16/week @ 2019-12-06 118/week @ 2019-12-13 1/week @ 2019-12-20 4/week @ 2019-12-27 8/week @ 2020-01-03 20/week @ 2020-01-10 42/week @ 2020-01-17 1/week @ 2020-01-24 4/week @ 2020-01-31 24/week @ 2020-02-07 35/week @ 2020-02-14 23/week @ 2020-02-21 22/week @ 2020-02-28 17/week @ 2020-03-06 9/week @ 2020-03-13

95 downloads per month

MIT license

578 lines


Docs Status license Crates.io

Pareen is a small Rust library for parameterized inbetweening. The intended application is in game programming, where you sometimes have two discrete game states between which you want to transition smoothly for visualization purposes.

Pareen gives you tools for composing animations that are parameterized by time (i.e. mappings from time to some animated value) without constantly having to pass around time variables; it hides the plumbing, so that you need to provide time only once: when evaluating the animation.

Animations are composed similarly to Rust's iterators, so no memory allocations are necessary.


Just add this line to your dependencies in Cargo.toml:

pareen = "0.2"

Current Status

The core of pareen is mostly stable, but the integration of easing functions could use some love. Contributions are very much welcome!

pareen is currently being tested in development of the game project Ultimate Scale. Unfortunately, it looks like heavily nested animations can cause an exponential slowdown in compilation time. For now, boxing intermediate animations serves as a workaround, but this comes with a decrease of both readability and efficiency.


// An animation returning a constant value
let anim1 = pareen::constant(1.0f64);

// Animations can be evaluated at any time
let value = anim1.eval(0.5);

// Animations can be played in sequence
let anim2 = anim1.seq(0.7, pareen::prop(0.25) + 0.5);

// Animations can be composed and transformed in various ways
let anim3 = anim2
    .scale_min_max(5.0, 10.0)
    .squeeze(3.0, 0.5..=1.0);

let anim4 = pareen::cubic(&[1.0, 2.0, 3.0, 4.0]) - anim3;

let value = anim4.eval(1.0);


Optionally, you can enable support for integrating easing functions from easer.

let first_anim = pareen::constant(2.0);
let second_anim = pareen::prop(1.0f32);

// Transition from first_anim to second_anim at time 0.5, applying cubic easing
// for 0.3 time units.
let anim = first_anim.seq_ease_in_out(


There is an example that shows some animations as plots via RustGnuplot in examples/plots.rs. Given that gnuplot has been installed, it can be executed like this:

cargo run --example plots --feature easer

If everything works, you should see something like this: plots of the example/plots.rs animations