Natura

A simple, efficient spring animation library for smooth, natural motion in Rust

Usage

Natura is framework-agnostic and works well in 2D and 3D contexts. Simply call Spring::new with your settings to initialize and update on each frame to animate.

For details, see the examples

Examples

• cargo run -p simple

// A thing we want to animate.
#[derive(Default)]
struct Sprite {
    x: f64,
    x_velocity: f64,
    y: f64,
    y_velocity: f64,
}

// Where we want to animate it.
const TARGET_X: f64 = 50.0;
const TARGET_Y: f64 = 100.0;

fn main() {
    let mut sprite = Sprite::default();
 
    // initialize a spring with frame-rate, angular frequency, and damping values.
    let mut spring = Spring::new(natura::fps(60), 6.0, 0.5);

    loop {
        let (sprite_x, sprite_x_velocity) = spring.update(sprite.x, sprite.x_velocity, TARGET_X);
        sprite.x = sprite_x;
        sprite.x_velocity = sprite_x_velocity;

        let (sprite_y, sprite_y_velocity) = spring.update(sprite.y, sprite.y_velocity, TARGET_Y);
        sprite.y = sprite_y;
        sprite.y_velocity = sprite_y_velocity;

        sleep(Duration::from_millis(10000));

        // use new position here on every frame
        println!(
            "Sprite x:{}, y:{}, x_vel:{}, y_vel:{}",
            sprite.x, sprite.y, sprite.x_velocity, sprite.y_velocity
        )
    }
}

• cargo run -p coffee-2d
  Example with 2D engine coffee

Settings

Spring::new takes three values:

• Time Delta: the time step to operate on. Game engines typically provide a way to determine the time delta, however if that's not available you can simply set the framerate with the included fps(u64) utility function. Make the framerate you set here matches your actual framerate.
• Angular Velocity: this translates roughly to the speed. Higher values are faster.
• Damping Ratio: the springiness of the animation, generally between 0 and 1, though it can go higher. Lower values are springier. For details, see below.

Damping Ratios

The damping ratio affects the motion in one of three different ways depending on how it's set.

Under-Damping

A spring is under-damped when its damping ratio is less than 1. An under-damped spring reaches equilibrium the fastest, but overshoots and will continue to oscillate as its amplitude decays over time.

Critical Damping

A spring is critically-damped the damping ratio is exactly 1. A critically damped spring will reach equilibrium as fast as possible without oscillating.

Over-Damping

A spring is over-damped the damping ratio is greater than 1. An over-damped spring will never oscillate, but reaches equilibrium at a slower rate than a critically damped spring.

Acknowledgements

This library is a fairly straightforward port of Ryan Juckett’s excellent damped simple harmonic oscillator originally writen in C++ in 2008 and published in 2012. Ryan’s writeup on the subject is fantastic.

License

MIT