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82 lines
2.9 KiB
Markdown
82 lines
2.9 KiB
Markdown
# Pareen
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[](https://docs.rs/pareen)
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[](https://github.com/leod/pareen/blob/master/LICENSE)
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[](https://crates.io/crates/pareen)
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Pareen is a small Rust library for *par*ameterized inbetw*een*ing.
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The intended application is in game programming, where you sometimes have
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two discrete game states between which you want to transition smoothly for
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visualization purposes.
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Pareen gives you tools for composing animations that are parameterized by
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time (i.e. mappings from time to some animated value) without constantly
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having to pass around time variables; it hides the plumbing, so that you
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need to provide time only once: when evaluating the animation.
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Animations are composed similarly to Rust's iterators, so no memory
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allocations are necessary. The downside to this is that it is diffcult to store
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pareen's animations. The recommended approach is to construct and evaluate
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animations on the fly.
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## Current Status
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I consider `pareen` to be an experimental approach, and I'm not sure if I'm
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still happy with it. Anyway, the integration of easing functions could use
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some love. Contributions are very much welcome!
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Unfortunately, it looks like heavily nested animations can cause an exponential
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slowdown in compilation time. For now, boxing intermediate animations serves as
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a workaround, but this comes with a decrease of both readability and efficiency.
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## Examples
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```rust
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// An animation returning a constant value
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let anim1 = pareen::constant(1.0f64);
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// Animations can be evaluated at any time
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let value = anim1.eval(0.5);
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// Animations can be played in sequence
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let anim2 = anim1.seq(0.7, pareen::prop(0.25) + 0.5);
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// Animations can be composed and transformed in various ways
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let anim3 = anim2
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.lerp(pareen::circle().cos())
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.scale_min_max(5.0, 10.0)
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.backwards(1.0)
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.squeeze(3.0, 0.5..=1.0);
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let anim4 = pareen::cubic(&[1.0, 2.0, 3.0, 4.0]) - anim3;
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let value = anim4.eval(1.0);
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```
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### Easer
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Optionally, you can enable support for integrating easing functions from
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[`easer`](https://docs.rs/easer/0.2.1/easer/index.html).
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```rust
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let first_anim = pareen::constant(2.0);
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let second_anim = pareen::prop(1.0f32);
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// Transition from first_anim to second_anim at time 0.5, applying cubic easing
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// for 0.3 time units.
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let anim = first_anim.seq_ease_in_out(
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0.5,
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easer::functions::Cubic,
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0.3,
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second_anim,
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);
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```
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### Plots
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There is an example that shows some animations as plots via
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[RustGnuplot](https://github.com/SiegeLord/RustGnuplot) in
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[examples/plots.rs](examples/plots.rs). Given that `gnuplot` has been
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installed, it can be executed like this:
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```bash
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cargo run --example plots --feature easer
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```
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If everything works, you should see something like this:
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