@woosh/meep-engine/src/core/math/physics/brdf/diffuse_GGX.js

Pure JavaScript game engine. Fully featured and production ready.

import { PI_RECIPROCAL } from "../../PI_RECIPROCAL.js";

/**
 * GGX diffuse distribution function
 * @see https://google.github.io/filament/Filament.md.html#listing_diffusebrdf
 * @param {number} NoH dot(n,h) where n is surface normal and h is half unit vector between incident light and outgoing light (view vector)
 * @param {number} roughness
 * @returns {number}
 */
export function diffuse_GGX(NoH, roughness) {
    const a = NoH * roughness;

    const k = roughness / (1 - NoH * NoH + a * a);

    return k * k * PI_RECIPROCAL;
}