glissade 0.1.2

Rust library that provides various utilities for animations and transitions
Documentation 
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# Glissade

Glissade is a Rust library that provides various utilities for animations and transitions.

The lib contains two main types: `Animation` and `InertialValue`.
* `Animation` can be used in cases when we know start, end, and in between keyframes.
* `InertialValue` can be used to make an object smoothly follow a target value.
  For example, a particle following a cursor. Background color changing smoothly on theme change.

It also contains a set of easing functions to make animations more natural. See the `Easing` enum for more details.

Animation can be applied to any type that implements `Mix` trait. This trait is used to interpolate between two values.
Mix trait is implemented for common types like `f32`, `f64`, `bool`, `i8` - `i64`, `u8` - `u64`, `Option<T: Mix>`, and tuples like `(Mix, Mix)`, `(Mix, Mix, Mix)`, etc.

Most of the methods receive `SystemTime` as a parameter to allow testing without mocks,
and have a consistent behavior during a single animation frame. It's expected that time is received
from `SystemTime::now()` once in the beginning of the frame, and used lately during the frame rendering.

## Usage

Add this to your `Cargo.toml`:

```toml
[dependencies]
glissade = "0.1.1"
```

And this to your crate root:

```rust
extern crate glissade;
```

## Examples

### Simple two-step animation

```rust
use glissade::{Easing, transition, Transition};
use std::time::{Duration, SystemTime};

// Create an animation template - a transition.
//
// This transition consists of two steps:
// 1. from 0.0 to 10.0 in 1 second linearly,
// 2. and then go to 5.0 with easing function.
let transition = transition(0.0)
    .linear_to(10.0, Duration::from_secs(1))
    .ease_to(5.0, Duration::from_secs(2), Easing::QuadraticInOut);

let now = SystemTime::now();
// Create an animation from the transition and start time.
let animation = transition.run(now);

assert_eq!(animation.get(now), 0.0);
assert_eq!(animation.get(now + Duration::from_millis(500)), 5.0);
assert_eq!(animation.get(now + Duration::from_secs(1)), 10.0);
assert_eq!(animation.get(now + Duration::from_secs(2)), 7.5);
assert_eq!(animation.get(now + Duration::from_secs(3)), 5.0);
```

### Smoothly change color

```rust
use glissade::{InertialValue, Easing};
use std::time::{Duration, SystemTime};

type Color = (f32, f32, f32);

let start_time = SystemTime::now();

// Create initial black value
let value: InertialValue<Color> = InertialValue::new((0.0, 0.0, 0.0), start_time);

assert_eq!(value.get(start_time), (0.0, 0.0, 0.0));
assert_eq!(value.get(start_time + Duration::from_secs(1)), (0.0, 0.0, 0.0));

// Change color to white in one second
let value = value.go_to((1.0, 1.0, 1.0), start_time, Duration::from_secs(1));

assert_eq!(value.get(start_time), (0.0, 0.0, 0.0));
assert_eq!(value.get(start_time + Duration::from_millis(500)), (0.5, 0.5, 0.5));
assert_eq!(value.get(start_time + Duration::from_secs(1)), (1.0, 1.0, 1.0));
assert_eq!(value.get(start_time + Duration::from_secs(2)), (1.0, 1.0, 1.0));

// Change color to red in between the transition
let value = value.ease_to((1.0, 0.0, 0.0), start_time + Duration::from_millis(500), Duration::from_secs(2), Easing::Linear);

assert_eq!(value.get(start_time + Duration::from_millis(500)), (0.5, 0.5, 0.5));
assert_eq!(value.get(start_time + Duration::from_secs(1)), (1.0, 0.75, 0.75));
assert_eq!(value.get(start_time + Duration::from_secs(2)), (1.0, 0.25, 0.25));
assert_eq!(value.get(start_time + Duration::from_millis(2500)), (1.0, 0.0, 0.0));
assert_eq!(value.get(start_time + Duration::from_secs(4)), (1.0, 0.0, 0.0));
```

## License

This project is licensed under the MIT License - see the LICENSE.md file for details.