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//! Easing curves. To add one: new variant + match arm in [`Easing::apply`].
/// An easing curve. Applied to normalized time before interpolation.
#[derive(Debug, Clone, Copy, PartialEq, Default)]
pub enum Easing {
Linear,
InQuad,
OutQuad,
InOutQuad,
InCubic,
OutCubic,
#[default]
InOutCubic,
/// Overshoots past the target, then settles.
OutBack,
/// Springy oscillation into place.
OutElastic,
OutBounce,
}
impl Easing {
/// Map normalized time `u ∈ [0,1]` through this curve.
pub fn apply(self, u: f32) -> f32 {
let u = u.clamp(0.0, 1.0);
match self {
Easing::Linear => u,
Easing::InQuad => u * u,
Easing::OutQuad => u * (2.0 - u),
Easing::InOutQuad => {
if u < 0.5 {
2.0 * u * u
} else {
-1.0 + (4.0 - 2.0 * u) * u
}
}
Easing::InCubic => u * u * u,
Easing::OutCubic => {
let v = u - 1.0;
v * v * v + 1.0
}
Easing::InOutCubic => {
if u < 0.5 {
4.0 * u * u * u
} else {
let v = 2.0 * u - 2.0;
0.5 * v * v * v + 1.0
}
}
Easing::OutBack => {
const C1: f32 = 1.70158;
const C3: f32 = C1 + 1.0;
let v = u - 1.0;
1.0 + C3 * v * v * v + C1 * v * v
}
Easing::OutElastic => {
const C4: f32 = std::f32::consts::TAU / 3.0;
if u == 0.0 || u == 1.0 {
u
} else {
(2.0f32).powf(-10.0 * u) * ((u * 10.0 - 0.75) * C4).sin() + 1.0
}
}
Easing::OutBounce => {
const N1: f32 = 7.5625;
const D1: f32 = 2.75;
let mut u = u;
if u < 1.0 / D1 {
N1 * u * u
} else if u < 2.0 / D1 {
u -= 1.5 / D1;
N1 * u * u + 0.75
} else if u < 2.5 / D1 {
u -= 2.25 / D1;
N1 * u * u + 0.9375
} else {
u -= 2.625 / D1;
N1 * u * u + 0.984375
}
}
}
}
}