three.js/examples/jsm/nodes/functions/BSDF/D_GGX.js

import { tslFn } from '../../shadernode/ShaderNode.js';

// Microfacet Models for Refraction through Rough Surfaces - equation (33)
// http://graphicrants.blogspot.com/2013/08/specular-brdf-reference.html
// alpha is "roughness squared" in Disney’s reparameterization
const D_GGX = tslFn( ( { alpha, dotNH } ) => {

	const a2 = alpha.pow2();

	const denom = dotNH.pow2().mul( a2.oneMinus() ).oneMinus(); // avoid alpha = 0 with dotNH = 1

	return a2.div( denom.pow2() ).mul( 1 / Math.PI );

} ).setLayout( {
	name: 'D_GGX',
	type: 'float',
	inputs: [
		{ name: 'alpha', type: 'float' },
		{ name: 'dotNH', type: 'float' }
	]
} ); // validated

export default D_GGX;