@woosh/meep-engine/src/core/math/physics/irradiance/interpolate_irradiance_smith.js

Pure JavaScript game engine. Fully featured and production ready.

// const k = Math.sqrt( (2*0.1*0.1)/Math.PI);
const k = 0.07978845608028655;

/**
 * Using Smith inverse-square bounded approximation
 * @see "An Inexpensive BRDF Model for Physically-based Rendering" by Christophe Schlick
 * @param {number} distance
 * @param {number} min
 * @param {number} max
 * @return {number}
 */
export function interpolate_irradiance_smith(distance, min, max) {

    if (distance <= min) {
        return 1;
    } else if (distance > max) {
        return 0;
    }

    /*
    Original formula:
    G(v) = v / (v - k*v + k)
    k = sqrt(2*(m^2)) / pi)

    we assume M to be 0.1 for our purposes

    where G is the fall-off
     */


    const range = max - min;

    const v = (distance - min) / range;

    const fall_off = v / (v - k * v + k);

    return 1 - fall_off;
}