Function subsurface_scattering_approx 

pub fn subsurface_scattering_approx(
    depth: f64,
    scatter_coeff: f64,
    absorption: f64,
) -> f64

Approximate subsurface scattering transmittance.

Models the fraction of light that penetrates to depth below the surface, using a simple exponential Beer-Lambert model modified by the absorption coefficient.

Parameters

• depth – penetration depth (metres, or consistent units).
• scatter_coeff – scattering coefficient (1/m).
• absorption – absorption coefficient (1/m).

Returns a value in \[0, 1\].