Iced Animations

This package is designed to make it easy to animate between values using the Iced framework.

Overview

There are two main widgets exposed: AnimationBuilder and Animation. Both work off the core Animate trait defining how a value is animated, but differ on where the animated state is kept. The AnimationBuilder stores the animated value within the widget itself while the Animation widget takes the animated value from props and allows you to emit a message to update the value.

Both widgets animate values using spring physics instead of easing functions to allow for more natural and interruptible animations.

AnimationBuilder widget

The AnimationBuilder widget takes some sort of value that implements Animate and a closure to build out a UI based on the current interpolated value. The benefit is that you don't have to emit messages for very simple animations but has a couple limitations mentioned below. Typical usage might look something like this, where self.size is an f32 in your app state:

AnimationBuilder::new(self.size, |size| {
    container(text(size as isize))
        .center(size)
        .into()
})
.animates_layout(true)

NOTE: .animates_layout(true) is what allows re-rendering certain properties like the app layout or text. This is off by default to avoid unnecessarily invalidating the app layout, but will be necessary in certain situations.

The UI will automatically re-render when self.size is changed. The closure provides the current animated value and will be called to generate the next view as appropriate. To see more for this particular example, refer to the animated_size example.

Limitations

It might not be easy/possible to pass in non-clonable content like custom elements to AnimationBuilder's closure to due the closure being having to be invoked multiple times to animate between values. Making reusable functions that use this widget and also take a generic element might be difficult.

Nested animations also don't work if both properties are actively being animated. One animation at a time will function correctly, but trying to adjust both at the same time leads to the inner property skipping to the final value. Use the Animation widget if you need any of these properties.

Animation widget

The Animation widget works by taking a Spring<T> value and some element, then emitting a message when the value needs to change. Your app state and message would look something like this:

use iced_anim::{Animation, Spring, SpringEvent};

#[derive(Default)]
struct State {
    size: Spring<f32>,
}

#[derive(Clone)]
enum Message {
    UpdateSize(SpringEvent<f32>),
}

Then, somewhere in your view, have a way to change the spring's target and update the animated value. You can use .into() as a shorthand to create a SpringEvent::Target for changing where the spring should animate towards.

use iced::widget::{Column, button, text};

Column::new()
    .push(
        button(text("+50"))
            .on_press(Message::UpdateSize((self.size.value() + 50.0).into()))
    )
    .push(
        Animation::new(self.size, text(self.size.value().to_string()))
            .on_update(Message::UpdateSize)
    )

Finally, your update function will forward the event to self.size.update to update the spring's inner state correctly.

impl State {
    fn update(&mut self, message: Message) {
        match message {
            Message::UpdateSize(event) => self.size.update(event),
        }
    }
}

See the stateful_animation example for a complete example.

Which one should I use?

Generally, if you're animating a tiny value that might not be directly within your state and the element won't contain any nested animated values, then use AnimationBuilder. Otherwise, use the state-driven Animation to avoid the limitations of widget-driven animations. Also, use Animation anytime you want your state to contain the animated value.

Types that implement Animate

Several types implement Animate by default, such as f32, iced::Color, and iced::Theme, with support for others being added in the future. You can also derive Animate on your own structs if you enable the derive feature and all inner properties already implement Animate:

use iced_anim::Animate;

#[derive(Animate)]
struct CustomRectangle {
    width: f32,
    height: f32,
    color: iced::Color,
}

You can also animate multiple values at once by providing a tuple up to a length of four:

AnimationBuilder::new((self.size, self.color), |(size, color)| {
    container(text(size as isize).color(color))
        .center(size)
        .into()
})
.animates_layout(true)

Controlling the spring motion

The spring motion of an AnimationBuilder can be customized. There are a few defaults like SpringMotion::Smooth and SpringMotion::Bouncy, but you can provide a custom response and damping fraction with SpringMotion::Custom:

AnimationBuilder::new(self.size, |size| {
    container(text(size as isize))
        .center(size)
        .into()
})
.animates_layout(true)
.motion(SpringMotion::Custom { 
    response: Duration::from_millis(500),
    damping: 0.5 
})

Examples

Refer to the examples directory for a variety of ways to use this crate. You can also run these examples locally with cargo run --example <package>, e.g. cargo run --example animated_color.