Function sdf_soft_shadow 

pub fn sdf_soft_shadow<S: Sdf>(
    sdf: &S,
    p: [f64; 3],
    light_pos: [f64; 3],
    k: f64,
    eps: f64,
) -> f64

Estimate a soft-shadow factor for a point p toward a light at light_pos.

Returns a value in [0, 1]: 0 = fully shadowed, 1 = fully lit. Uses Quilez’s soft-shadow ray-march formula with k controlling penumbra sharpness.