mtk-rs 0.1.0-beta.3

Muse Toolkit
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pub fn sample_curve_x(t: f64, p1x: f64, p2x: f64) -> f64 {
    let cx = 3.0 * p1x;
    let bx = 3.0 * (p2x - p1x) - cx;
    let ax = 1.0 - cx - bx;
    ((ax * t + bx) * t + cx) * t
}

pub fn sample_curve_y(t: f64, p1y: f64, p2y: f64) -> f64 {
    let cy = 3.0 * p1y;
    let by = 3.0 * (p2y - p1y) - cy;
    let ay = 1.0 - cy - by;
    ((ay * t + by) * t + cy) * t
}

pub fn sample_curve_derivative_x(t: f64, p1x: f64, p2x: f64) -> f64 {
    let cx = 3.0 * p1x;
    let bx = 3.0 * (p2x - p1x) - cx;
    let ax = 1.0 - cx - bx;
    (3.0 * ax * t + 2.0 * bx) * t + cx
}

pub fn solve_curve_t(time_x: f64, p1x: f64, p2x: f64) -> f64 {
    let mut t2 = time_x;

    for _ in 0..8 {
        let current_x = sample_curve_x(t2, p1x, p2x) - time_x;
        if current_x.abs() < 1e-5 {
            return t2;
        }
        let derivative = sample_curve_derivative_x(t2, p1x, p2x);
        if derivative.abs() < 1e-6 {
            break;
        }
        t2 -= current_x / derivative;
    }

    // Fallback to binary search if Newton-Raphson fails
    t2.clamp(0.0, 1.0)
}