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//! Animation mapping for UI components.
///
/// Cubic ease-in-out mapping (smooth start and end).
/// Input: linear progress in [0.0, 1.0].
/// Output: eased progress in [0.0, 1.0].
pub(crate) fn easing(progress: f32) -> f32 {
// Cubic ease-in-out
let t = progress.clamp(0.0, 1.0);
if t < 0.5 {
4.0 * t * t * t
} else {
1.0 - (-2.0 * t + 2.0).powi(3) / 2.0
}
}
/// Calculates the spring animation value based on physics parameters.
///
/// # Parameters
///
/// - `progress`: Linear time progress in [0.0, 1.0].
/// - `stiffness`: Controls speed. Try **15.0** for UI.
/// - `damping`: Controls bounciness [0.0, 1.0). Try **0.5**.
/// - Lower (0.2) = Very bouncy (oscillation).
/// - Higher (0.9) = Little to no bounce.
///
/// # Returns
///
/// A value that starts at 0.0, overshoots 1.0, and settles at 1.0.
pub fn spring(progress: f32, stiffness: f32, damping: f32) -> f32 {
let t = progress.clamp(0.0, 1.0);
// Boundary checks to avoid expensive math at start/end
if t <= 0.0 {
return 0.0;
}
if t >= 1.0 {
return 1.0;
}
// Ensure damping is < 1.0 to guarantee the "bounce" math works.
// If it is >= 1.0, it becomes critically damped (no overshoot),
// which requires a different formula. We clamp to 0.999 here.
let zeta = damping.clamp(0.0, 0.999);
// Natural Angular Frequency (Speed)
let omega = stiffness;
// Damped Angular Frequency
// ωd = ωn * sqrt(1 - ζ^2)
let omega_d = omega * (1.0 - zeta * zeta).sqrt();
// Decay constant
// decay = ζ * ωn
let decay = zeta * omega;
// Calculate oscillation
// f(t) = 1 - e^(-decay * t) * (cos(ωd * t) + (sin(ωd * t) * decay / ωd))
let oscillation = (omega_d * t).cos() + (omega_d * t).sin() * (decay / omega_d);
1.0 - (-decay * t).exp() * oscillation
}