Pareen

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.

Usage

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.

Examples

```rust // 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 .lerp(pareen::circle().cos()) .scaleminmax(5.0, 10.0) .backwards(1.0) .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); ```

Easer

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

```rust let firstanim = pareen::constant(2.0); let secondanim = pareen::prop(1.0f32);

// Transition from firstanim to secondanim at time 0.5, applying cubic easing // for 0.3 time units. let anim = firstanim.seqeaseinout( 0.5, easer::functions::Cubic, 0.3, second_anim, ); ```

Plots

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: bash cargo run --example plots --feature easer

If everything works, you should see something like this: