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use core::ops::{Add, Mul, RangeInclusive, Sub};
#[cfg(any(feature = "std", feature = "libm"))]
use num_traits::Float;
use num_traits::{float::FloatCore, Num, One, Zero};
use crate::{constant, fun, id};
/// A `Fun` represents anything that maps from some type `T` to another
/// type `V`.
///
/// `T` usually stands for time and `V` for some value that is parameterized by
/// time.
///
/// ## Implementation details
/// The only reason that we define this trait instead of just using `Fn(T) -> V`
/// is so that the library works in stable rust. Having this type allows us to
/// implement e.g. `std::ops::Add` for [`Anim<F>`](struct.Anim.html) where
/// `F: Fun`. Without this trait, it becomes difficult (impossible?) to provide
/// a name for `Add::Output`, unless you have the unstable feature
/// `type_alias_impl_trait` or `fn_traits`.
///
/// In contrast to `std::ops::FnOnce`, both input _and_ output are associated
/// types of `Fun`. The main reason is that this makes types smaller for the
/// user of the library. I have not observed any downsides to this yet.
pub trait Fun {
/// The function's input type. Usually time.
type T;
/// The function's output type.
type V;
/// Evaluate the function at time `t`.
fn eval(&self, t: Self::T) -> Self::V;
}
impl<'a, F> Fun for &'a F
where
F: Fun,
{
type T = F::T;
type V = F::V;
fn eval(&self, t: Self::T) -> Self::V {
(*self).eval(t)
}
}
/// `Anim` is the main type provided by pareen. It is a wrapper around any type
/// implementing [`Fun`](trait.Fun.html).
///
/// `Anim` provides methods that transform or compose animations, allowing
/// complex animations to be created out of simple pieces.
#[derive(Clone, Debug)]
pub struct Anim<F>(pub F);
impl<F> Anim<F>
where
F: Fun,
{
/// Evaluate the animation at time `t`.
pub fn eval(&self, t: F::T) -> F::V {
self.0.eval(t)
}
/// Transform an animation so that it applies a given function to its
/// values.
///
/// # Example
///
/// Turn `(2.0 * t)` into `(2.0 * t).sqrt() + 2.0 * t`:
/// ```
/// # use assert_approx_eq::assert_approx_eq;
/// let anim = pareen::prop(2.0f32).map(|value| value.sqrt() + value);
///
/// assert_approx_eq!(anim.eval(1.0), 2.0f32.sqrt() + 2.0);
/// ```
pub fn map<W>(self, f: impl Fn(F::V) -> W) -> Anim<impl Fun<T = F::T, V = W>> {
self.map_anim(fun(f))
}
/// Transform an animation so that it modifies time according to the given
/// function before evaluating the animation.
///
/// # Example
/// Run an animation two times slower:
/// ```
/// let anim = pareen::cubic(&[1.0, 1.0, 1.0, 1.0]);
/// let slower_anim = anim.map_time(|t: f32| t / 2.0);
/// ```
pub fn map_time<S>(self, f: impl Fn(S) -> F::T) -> Anim<impl Fun<T = S, V = F::V>> {
fun(f).map_anim(self)
}
/// Converts from `Anim<F>` to `Anim<&F>`.
pub fn as_ref(&self) -> Anim<&F> {
Anim(&self.0)
}
pub fn map_anim<W, G, A>(self, anim: A) -> Anim<impl Fun<T = F::T, V = W>>
where
G: Fun<T = F::V, V = W>,
A: Into<Anim<G>>,
{
// Nested closures result in exponential compilation time increase, and we
// expect map_anim to be used often. Thus, we avoid using `pareen::fun` here.
// For reference: https://github.com/rust-lang/rust/issues/72408
Anim(MapClosure(self.0, anim.into().0))
}
pub fn map_time_anim<S, G, A>(self, anim: A) -> Anim<impl Fun<T = S, V = F::V>>
where
G: Fun<T = S, V = F::T>,
A: Into<Anim<G>>,
{
anim.into().map_anim(self)
}
pub fn into_fn(self) -> impl Fn(F::T) -> F::V {
move |t| self.eval(t)
}
}
impl<F> Anim<F>
where
F: Fun,
F::T: Clone + Mul<Output = F::T>,
{
pub fn scale_time(self, t_scale: F::T) -> Anim<impl Fun<T = F::T, V = F::V>> {
self.map_time(move |t| t * t_scale.clone())
}
}
impl<F> Fun for Option<F>
where
F: Fun,
{
type T = F::T;
type V = Option<F::V>;
fn eval(&self, t: F::T) -> Option<F::V> {
self.as_ref().map(|f| f.eval(t))
}
}
#[doc(hidden)]
#[derive(Debug, Clone)]
pub struct MapClosure<F, G>(F, G);
impl<F, G> Fun for MapClosure<F, G>
where
F: Fun,
G: Fun<T = F::V>,
{
type T = F::T;
type V = G::V;
fn eval(&self, t: F::T) -> G::V {
self.1.eval(self.0.eval(t))
}
}
impl<T, X, Y, F> Anim<F>
where
F: Fun<T = T, V = (X, Y)>,
{
pub fn fst(self) -> Anim<impl Fun<T = F::T, V = X>> {
self.map(|(x, _)| x)
}
pub fn snd(self) -> Anim<impl Fun<T = F::T, V = Y>> {
self.map(|(_, y)| y)
}
}
impl<F> Anim<F>
where
F: Fun,
F::T: Clone,
{
/// Combine two animations into one, yielding an animation having pairs as
/// the values.
pub fn zip<G, A>(self, other: A) -> Anim<impl Fun<T = F::T, V = (F::V, G::V)>>
where
G: Fun<T = F::T>,
A: Into<Anim<G>>,
{
// Nested closures result in exponential compilation time increase, and we
// expect zip to be used frequently. Thus, we avoid using `pareen::fun` here.
// For reference: https://github.com/rust-lang/rust/issues/72408
Anim(ZipClosure(self.0, other.into().0))
}
pub fn bind<W, G>(self, f: impl Fn(F::V) -> Anim<G>) -> Anim<impl Fun<T = F::T, V = W>>
where
G: Fun<T = F::T, V = W>,
{
fun(move |t: F::T| f(self.eval(t.clone())).eval(t))
}
}
impl<'a, T, V, F> Anim<F>
where
V: 'a + Copy,
F: Fun<T = T, V = &'a V> + 'a,
{
pub fn copied(self) -> Anim<impl Fun<T = T, V = V> + 'a> {
self.map(|x| *x)
}
}
impl<'a, T, V, F> Anim<F>
where
V: 'a + Clone,
F: Fun<T = T, V = &'a V> + 'a,
{
pub fn cloned(self) -> Anim<impl Fun<T = T, V = V> + 'a> {
self.map(|x| x.clone())
}
}
#[doc(hidden)]
#[derive(Debug, Clone)]
pub struct ZipClosure<F, G>(F, G);
impl<F, G> Fun for ZipClosure<F, G>
where
F: Fun,
F::T: Clone,
G: Fun<T = F::T>,
{
type T = F::T;
type V = (F::V, G::V);
fn eval(&self, t: F::T) -> Self::V {
(self.0.eval(t.clone()), self.1.eval(t))
}
}
impl<F> Anim<F>
where
F: Fun,
F::T: Copy + Sub<Output = F::T>,
{
/// Shift an animation in time, so that it is moved to the right by `t_delay`.
pub fn shift_time(self, t_delay: F::T) -> Anim<impl Fun<T = F::T, V = F::V>> {
(id::<F::T, F::T>() - t_delay).map_anim(self)
}
}
impl<F> Anim<F>
where
F: Fun,
F::T: Clone + PartialOrd,
{
/// Concatenate `self` with another animation in time, using `self` until
/// time `self_end` (non-inclusive), and then switching to `next`.
///
/// # Examples
/// Switch from one constant value to another:
/// ```
/// # use assert_approx_eq::assert_approx_eq;
/// let anim = pareen::constant(1.0f32).switch(0.5f32, 2.0);
///
/// assert_approx_eq!(anim.eval(0.0), 1.0);
/// assert_approx_eq!(anim.eval(0.5), 2.0);
/// assert_approx_eq!(anim.eval(42.0), 2.0);
/// ```
///
/// Piecewise combinations of functions:
/// ```
/// let cubic_1 = pareen::cubic(&[4.4034, 0.0, -4.5455e-2, 0.0]);
/// let cubic_2 = pareen::cubic(&[-1.2642e1, 2.0455e1, -8.1364, 1.0909]);
/// let cubic_3 = pareen::cubic(&[1.6477e1, -4.9432e1, 4.7773e1, -1.3818e1]);
///
/// // Use cubic_1 for [0.0, 0.4), cubic_2 for [0.4, 0.8) and
/// // cubic_3 for [0.8, ..).
/// let anim = cubic_1.switch(0.4, cubic_2).switch(0.8, cubic_3);
/// ```
pub fn switch<G, A>(self, self_end: F::T, next: A) -> Anim<impl Fun<T = F::T, V = F::V>>
where
G: Fun<T = F::T, V = F::V>,
A: Into<Anim<G>>,
{
// Nested closures result in exponential compilation time increase, and we
// expect switch to be used frequently. Thus, we avoid using `pareen::fun` here.
// For reference: https://github.com/rust-lang/rust/issues/72408
cond(switch_cond(self_end), self, next)
}
/// Play `self` in time range `range`, and `surround` outside of the time range.
///
/// # Examples
/// ```
/// # use assert_approx_eq::assert_approx_eq;
/// let anim = pareen::constant(10.0f32).surround(2.0..=5.0, 20.0);
///
/// assert_approx_eq!(anim.eval(0.0), 20.0);
/// assert_approx_eq!(anim.eval(2.0), 10.0);
/// assert_approx_eq!(anim.eval(4.0), 10.0);
/// assert_approx_eq!(anim.eval(5.0), 10.0);
/// assert_approx_eq!(anim.eval(6.0), 20.0);
/// ```
pub fn surround<G, A>(
self,
range: RangeInclusive<F::T>,
surround: A,
) -> Anim<impl Fun<T = F::T, V = F::V>>
where
G: Fun<T = F::T, V = F::V>,
A: Into<Anim<G>>,
{
// Nested closures result in exponential compilation time increase, and we
// expect surround to be used frequently. Thus, we avoid using `pareen::fun` here.
// For reference: https://github.com/rust-lang/rust/issues/72408
cond(surround_cond(range), self, surround)
}
}
fn switch_cond<T: PartialOrd>(self_end: T) -> Anim<impl Fun<T = T, V = bool>> {
fun(move |t| t < self_end)
}
fn surround_cond<T: PartialOrd>(range: RangeInclusive<T>) -> Anim<impl Fun<T = T, V = bool>> {
fun(move |t| range.contains(&t))
}
impl<F> Anim<F>
where
F: Fun,
F::T: Clone + PartialOrd,
F::V: Clone,
{
/// Play `self` until time `self_end`, then always return the value of
/// `self` at time `self_end`.
pub fn hold(self, self_end: F::T) -> Anim<impl Fun<T = F::T, V = F::V>> {
let end_value = self.eval(self_end.clone());
self.switch(self_end, constant(end_value))
}
}
impl<F> Anim<F>
where
F: Fun,
F::T: Copy + PartialOrd + Sub<Output = F::T>,
{
/// Play two animations in sequence, first playing `self` until time
/// `self_end` (non-inclusive), and then switching to `next`. Note that
/// `next` will see time starting at zero once it plays.
///
/// # Example
/// Stay at value `5.0` for ten seconds, then increase value proportionally:
/// ```
/// # use assert_approx_eq::assert_approx_eq;
/// let anim_1 = pareen::constant(5.0f32);
/// let anim_2 = pareen::prop(2.0f32) + 5.0;
/// let anim = anim_1.seq(10.0, anim_2);
///
/// assert_approx_eq!(anim.eval(0.0), 5.0);
/// assert_approx_eq!(anim.eval(10.0), 5.0);
/// assert_approx_eq!(anim.eval(11.0), 7.0);
/// ```
pub fn seq<G, A>(self, self_end: F::T, next: A) -> Anim<impl Fun<T = F::T, V = F::V>>
where
G: Fun<T = F::T, V = F::V>,
A: Into<Anim<G>>,
{
self.switch(self_end.clone(), next.into().shift_time(self_end))
}
pub fn seq_continue<G, A, H>(
self,
self_end: F::T,
next_fn: H,
) -> Anim<impl Fun<T = F::T, V = F::V>>
where
G: Fun<T = F::T, V = F::V>,
A: Into<Anim<G>>,
H: Fn(F::V) -> A,
{
let next = next_fn(self.eval(self_end.clone())).into();
self.seq(self_end, next)
}
}
impl<F> Anim<F>
where
F: Fun,
F::T: Clone + Sub<Output = F::T>,
{
/// Play an animation backwards, starting at time `end`.
///
/// # Example
///
/// ```
/// # use assert_approx_eq::assert_approx_eq;
/// let anim = pareen::prop(2.0f32).backwards(1.0);
///
/// assert_approx_eq!(anim.eval(0.0f32), 2.0);
/// assert_approx_eq!(anim.eval(1.0f32), 0.0);
/// ```
pub fn backwards(self, end: F::T) -> Anim<impl Fun<T = F::T, V = F::V>> {
(constant(end) - id()).map_anim(self)
}
}
impl<F> Anim<F>
where
F: Fun,
F::T: Copy,
F::V: Copy + Num,
{
/// Given animation values in `[0.0 .. 1.0]`, this function transforms the
/// values so that they are in `[min .. max]`.
///
/// # Example
/// ```
/// # use assert_approx_eq::assert_approx_eq;
/// let min = -3.0f32;
/// let max = 10.0;
/// let anim = pareen::id().scale_min_max(min, max);
///
/// assert_approx_eq!(anim.eval(0.0f32), min);
/// assert_approx_eq!(anim.eval(1.0f32), max);
/// ```
pub fn scale_min_max(self, min: F::V, max: F::V) -> Anim<impl Fun<T = F::T, V = F::V>> {
self * (max.clone() - min) + min
}
}
#[cfg(any(feature = "std", feature = "libm"))]
impl<F> Anim<F>
where
F: Fun,
F::V: Float,
{
/// Apply `Float::sin` to the animation values.
pub fn sin(self) -> Anim<impl Fun<T = F::T, V = F::V>> {
self.map(Float::sin)
}
/// Apply `Float::cos` to the animation values.
pub fn cos(self) -> Anim<impl Fun<T = F::T, V = F::V>> {
self.map(Float::cos)
}
/// Apply `Float::powf` to the animation values.
pub fn powf(self, e: F::V) -> Anim<impl Fun<T = F::T, V = F::V>> {
self.map(move |v| v.powf(e))
}
}
impl<F> Anim<F>
where
F: Fun,
F::V: FloatCore,
{
/// Apply `FloatCore::abs` to the animation values.
pub fn abs(self) -> Anim<impl Fun<T = F::T, V = F::V>> {
self.map(FloatCore::abs)
}
/// Apply `FloatCore::powi` to the animation values.
pub fn powi(self, n: i32) -> Anim<impl Fun<T = F::T, V = F::V>> {
self.map(move |v| v.powi(n))
}
}
impl<F> Anim<F>
where
F: Fun,
F::T: Copy + FloatCore,
{
/// Transform an animation in time, so that its time `[0 .. 1]` is shifted
/// and scaled into the given `range`.
///
/// In other words, this function can both delay and speed up or slow down a
/// given animation.
///
/// # Example
///
/// Go from zero to 2π in half a second:
/// ```
/// # use assert_approx_eq::assert_approx_eq;
/// // From zero to 2π in one second
/// let angle = pareen::circle::<f32, f32>();
///
/// // From zero to 2π in time range [0.5 .. 1.0]
/// let anim = angle.squeeze(0.5..=1.0);
///
/// assert_approx_eq!(anim.eval(0.5), 0.0);
/// assert_approx_eq!(anim.eval(1.0), std::f32::consts::PI * 2.0);
/// ```
pub fn squeeze(self, range: RangeInclusive<F::T>) -> Anim<impl Fun<T = F::T, V = F::V>> {
let time_shift = *range.start();
let time_scale = F::T::one() / (*range.end() - *range.start());
self.map_time(move |t| (t - time_shift) * time_scale)
}
/// Transform an animation in time, so that its time `[0 .. 1]` is shifted
/// and scaled into the given `range`.
///
/// In other words, this function can both delay and speed up or slow down a
/// given animation.
///
/// For time outside of the given `range`, the `surround` animation is used
/// instead.
///
/// # Example
///
/// Go from zero to 2π in half a second:
/// ```
/// # use assert_approx_eq::assert_approx_eq;
/// // From zero to 2π in one second
/// let angle = pareen::circle();
///
/// // From zero to 2π in time range [0.5 .. 1.0]
/// let anim = angle.squeeze_and_surround(0.5..=1.0, 42.0);
///
/// assert_approx_eq!(anim.eval(0.0f32), 42.0f32);
/// assert_approx_eq!(anim.eval(0.5), 0.0);
/// assert_approx_eq!(anim.eval(1.0), std::f32::consts::PI * 2.0);
/// assert_approx_eq!(anim.eval(1.1), 42.0);
/// ```
pub fn squeeze_and_surround<G, A>(
self,
range: RangeInclusive<F::T>,
surround: A,
) -> Anim<impl Fun<T = F::T, V = F::V>>
where
G: Fun<T = F::T, V = F::V>,
A: Into<Anim<G>>,
{
self.squeeze(range.clone()).surround(range, surround)
}
/// Play two animations in sequence, first playing `self` until time
/// `self_end` (non-inclusive), and then switching to `next`. The animations
/// are squeezed in time so that they fit into `[0 .. 1]` together.
///
/// `self` is played in time `[0 .. self_end)`, and then `next` is played
/// in time [self_end .. 1]`.
pub fn seq_squeeze<G, A>(self, self_end: F::T, next: A) -> Anim<impl Fun<T = F::T, V = F::V>>
where
G: Fun<T = F::T, V = F::V>,
A: Into<Anim<G>>,
{
let first = self.squeeze(Zero::zero()..=self_end);
let second = next.into().squeeze(self_end..=One::one());
first.switch(self_end, second)
}
/// Repeat an animation forever.
pub fn repeat(self, period: F::T) -> Anim<impl Fun<T = F::T, V = F::V>> {
self.map_time(move |t: F::T| (t * period.recip()).fract() * period)
}
}
impl<W, F> Anim<F>
where
F: Fun,
F::T: Copy + Mul<W, Output = W>,
F::V: Copy + Add<W, Output = F::V> + Sub<Output = W>,
{
/// Linearly interpolate between two animations, starting at time zero and
/// finishing at time one.
///
/// # Examples
///
/// Linearly interpolate between two constant values:
/// ```
/// # use assert_approx_eq::assert_approx_eq;
/// let anim = pareen::constant(5.0f32).lerp(10.0);
///
/// assert_approx_eq!(anim.eval(0.0f32), 5.0);
/// assert_approx_eq!(anim.eval(0.5), 7.5);
/// assert_approx_eq!(anim.eval(1.0), 10.0);
/// assert_approx_eq!(anim.eval(2.0), 15.0);
/// ```
#[cfg_attr(any(feature = "std", feature = "libm"), doc = r##"
It is also possible to linearly interpolate between two non-constant
animations:
```
let anim = pareen::circle().sin().lerp(pareen::circle().cos());
let value: f32 = anim.eval(0.5f32);
```
"##)]
pub fn lerp<G, A>(self, other: A) -> Anim<impl Fun<T = F::T, V = F::V>>
where
G: Fun<T = F::T, V = F::V>,
A: Into<Anim<G>>,
{
let other = other.into();
fun(move |t| {
let a = self.eval(t);
let b = other.eval(t);
let delta = b - a;
a + t * delta
})
}
}
impl<V, F> Anim<F>
where
F: Fun<V = Option<V>>,
F::T: Clone,
{
/// Unwrap an animation of optional values.
///
/// At any time, returns the animation value if it is not `None`, or the
/// given `default` value otherwise.
///
/// # Examples
///
/// ```
/// let anim1 = pareen::constant(Some(42)).unwrap_or(-1);
/// assert_eq!(anim1.eval(2), 42);
/// assert_eq!(anim1.eval(3), 42);
/// ```
///
/// ```
/// let cond = pareen::fun(|t| t % 2 == 0);
/// let anim1 = pareen::cond(cond, Some(42), None).unwrap_or(-1);
/// assert_eq!(anim1.eval(2), 42);
/// assert_eq!(anim1.eval(3), -1);
/// ```
pub fn unwrap_or<G, A>(self, default: A) -> Anim<impl Fun<T = F::T, V = V>>
where
G: Fun<T = F::T, V = V>,
A: Into<Anim<G>>,
{
self.zip(default.into())
.map(|(v, default)| v.unwrap_or(default))
}
/// Applies a function to the contained value (if any), or returns the
/// provided default (if not).
///
/// Note that the function `f` itself returns an animation.
///
/// # Example
///
/// Animate a player's position offset if it is moving:
/// ```
/// # use assert_approx_eq::assert_approx_eq;
/// fn my_offset_anim(
/// move_dir: Option<f32>,
/// ) -> pareen::Anim<impl pareen::Fun<T = f32, V = f32>> {
/// let move_speed = 2.0f32;
///
/// pareen::constant(move_dir).map_or(
/// 0.0,
/// move |move_dir| pareen::prop(move_dir) * move_speed,
/// )
/// }
///
/// let move_anim = my_offset_anim(Some(1.0));
/// let stay_anim = my_offset_anim(None);
///
/// assert_approx_eq!(move_anim.eval(0.5), 1.0);
/// assert_approx_eq!(stay_anim.eval(0.5), 0.0);
/// ```
pub fn map_or<W, G, H, A>(
self,
default: A,
f: impl Fn(V) -> Anim<H>,
) -> Anim<impl Fun<T = F::T, V = W>>
where
G: Fun<T = F::T, V = W>,
H: Fun<T = F::T, V = W>,
A: Into<Anim<G>>,
{
let default = default.into();
//self.bind(move |v| v.map_or(default, f))
fun(move |t: F::T| {
self.eval(t.clone())
.map_or_else(|| default.eval(t.clone()), |v| f(v).eval(t.clone()))
})
}
}
/// Return the value of one of two animations depending on a condition.
///
/// This allows returning animations of different types conditionally.
///
/// Note that the condition `cond` may either be a value `true` and `false`, or
/// it may itself be a dynamic animation of type `bool`.
///
/// For dynamic conditions, in many cases it suffices to use either
/// [`Anim::switch`](struct.Anim.html#method.switch) or
/// [`Anim::seq`](struct.Anim.html#method.seq) instead of this function.
///
/// # Examples
/// ## Constant conditions
///
/// The following example does _not_ compile, because the branches have
/// different types:
/// ```compile_fail
/// let cond = true;
/// let anim = if cond { pareen::constant(1) } else { pareen::id() };
/// ```
///
/// However, this does compile:
/// ```
/// let cond = true;
/// let anim = pareen::cond(cond, 1, pareen::id());
///
/// assert_eq!(anim.eval(2), 1);
/// ```
///
/// ## Dynamic conditions
///
/// ```
/// let cond = pareen::fun(|t| t * t <= 4);
/// let anim_1 = 1;
/// let anim_2 = pareen::id();
/// let anim = pareen::cond(cond, anim_1, anim_2);
///
/// assert_eq!(anim.eval(1), 1); // 1 * 1 <= 4
/// assert_eq!(anim.eval(2), 1); // 2 * 2 <= 4
/// assert_eq!(anim.eval(3), 3); // 3 * 3 > 4
/// ```
pub fn cond<F, G, H, Cond, A, B>(cond: Cond, a: A, b: B) -> Anim<impl Fun<T = F::T, V = G::V>>
where
F::T: Clone,
F: Fun<V = bool>,
G: Fun<T = F::T>,
H: Fun<T = F::T, V = G::V>,
Cond: Into<Anim<F>>,
A: Into<Anim<G>>,
B: Into<Anim<H>>,
{
// Nested closures result in exponential compilation time increase, and we
// expect cond to be used often. Thus, we avoid using `pareen::fun` here.
// For reference: https://github.com/rust-lang/rust/issues/72408
Anim(CondClosure(cond.into().0, a.into().0, b.into().0))
}
#[doc(hidden)]
#[derive(Debug, Clone)]
pub struct CondClosure<F, G, H>(F, G, H);
impl<F, G, H> Fun for CondClosure<F, G, H>
where
F::T: Clone,
F: Fun<V = bool>,
G: Fun<T = F::T>,
H: Fun<T = F::T, V = G::V>,
{
type T = F::T;
type V = G::V;
fn eval(&self, t: F::T) -> G::V {
if self.0.eval(t.clone()) {
self.1.eval(t)
} else {
self.2.eval(t)
}
}
}
/// Linearly interpolate between two animations, starting at time zero and
/// finishing at time one.
///
/// This is a wrapper around [`Anim::lerp`](struct.Anim.html#method.lerp) for
/// convenience, allowing automatic conversion into [`Anim`](struct.Anim.html)
/// for both `a` and `b`.
///
/// # Example
///
/// Linearly interpolate between two constant values:
///
/// ```
/// # use assert_approx_eq::assert_approx_eq;
/// let anim = pareen::lerp(5.0f32, 10.0);
///
/// assert_approx_eq!(anim.eval(0.0f32), 5.0);
/// assert_approx_eq!(anim.eval(0.5), 7.5);
/// assert_approx_eq!(anim.eval(1.0), 10.0);
/// assert_approx_eq!(anim.eval(2.0), 15.0);
/// ```
pub fn lerp<T, V, W, F, G, A, B>(a: A, b: B) -> Anim<impl Fun<T = T, V = V>>
where
T: Copy + Mul<W, Output = W>,
V: Copy + Add<W, Output = V> + Sub<Output = W>,
F: Fun<T = T, V = V>,
G: Fun<T = T, V = V>,
A: Into<Anim<F>>,
B: Into<Anim<G>>,
{
a.into().lerp(b.into())
}
/// Build an animation that depends on matching some expression.
///
/// Importantly, this macro allows returning animations of a different type in
/// each match arm, which is not possible with a normal `match` expression.
///
/// # Example
/// ```
/// # use assert_approx_eq::assert_approx_eq;
/// enum MyPlayerState {
/// Standing,
/// Running,
/// Jumping,
/// }
///
/// fn my_anim(state: MyPlayerState) -> pareen::Anim<impl pareen::Fun<T = f64, V = f64>> {
/// pareen::anim_match!(state;
/// MyPlayerState::Standing => pareen::constant(0.0),
/// MyPlayerState::Running => pareen::prop(1.0),
/// MyPlayerState::Jumping => pareen::id().powi(2),
/// )
/// }
///
/// assert_approx_eq!(my_anim(MyPlayerState::Standing).eval(2.0), 0.0);
/// assert_approx_eq!(my_anim(MyPlayerState::Running).eval(2.0), 2.0);
/// assert_approx_eq!(my_anim(MyPlayerState::Jumping).eval(2.0), 4.0);
/// ```
#[macro_export]
macro_rules! anim_match {
(
$expr:expr;
$($pat:pat => $value:expr $(,)?)*
) => {
$crate::fun(move |t| match $expr {
$(
$pat => ($crate::Anim::from($value)).eval(t),
)*
})
}
}