three.js/examples/jsm/nodes/utils/SpecularMIPLevelNode.js

import { TempNode } from '../core/TempNode.js';
import { FunctionNode } from '../core/FunctionNode.js';
import { MaxMIPLevelNode } from './MaxMIPLevelNode.js';

function SpecularMIPLevelNode( roughness, texture ) {

	TempNode.call( this, 'f' );

	this.roughness = roughness;
	this.texture = texture;

	this.maxMIPLevel = undefined;

}

SpecularMIPLevelNode.Nodes = ( function () {

	var getSpecularMIPLevel = new FunctionNode( [
		// taken from here: http://casual-effects.blogspot.ca/2011/08/plausible-environment-lighting-in-two.html
		'float getSpecularMIPLevel( const in float roughness, const in float maxMIPLevelScalar ) {',

		'	float sigma = PI * roughness * roughness / ( 1.0 + roughness );',
		'	float desiredMIPLevel = maxMIPLevelScalar + log2( sigma );',

		// clamp to allowable LOD ranges.
		'	return clamp( desiredMIPLevel, 0.0, maxMIPLevelScalar );',

		'}'
	].join( '\n' ) );

	return {
		getSpecularMIPLevel: getSpecularMIPLevel
	};

} )();

SpecularMIPLevelNode.prototype = Object.create( TempNode.prototype );
SpecularMIPLevelNode.prototype.constructor = SpecularMIPLevelNode;
SpecularMIPLevelNode.prototype.nodeType = 'SpecularMIPLevel';

SpecularMIPLevelNode.prototype.setTexture = function ( texture ) {

	this.texture = texture;

	return this;

};

SpecularMIPLevelNode.prototype.generate = function ( builder, output ) {

	if ( builder.isShader( 'fragment' ) ) {

		this.maxMIPLevel = this.maxMIPLevel || new MaxMIPLevelNode();
		this.maxMIPLevel.texture = this.texture;

		var getSpecularMIPLevel = builder.include( SpecularMIPLevelNode.Nodes.getSpecularMIPLevel );

		return builder.format( getSpecularMIPLevel + '( ' + this.roughness.build( builder, 'f' ) + ', ' + this.maxMIPLevel.build( builder, 'f' ) + ' )', this.type, output );

	} else {

		console.warn( 'THREE.SpecularMIPLevelNode is not compatible with ' + builder.shader + ' shader.' );

		return builder.format( '0.0', this.type, output );

	}

};

SpecularMIPLevelNode.prototype.copy = function ( source ) {

	TempNode.prototype.copy.call( this, source );

	this.texture = source.texture;
	this.roughness = source.roughness;

	return this;

};

SpecularMIPLevelNode.prototype.toJSON = function ( meta ) {

	var data = this.getJSONNode( meta );

	if ( ! data ) {

		data = this.createJSONNode( meta );

		data.texture = this.texture;
		data.roughness = this.roughness;

	}

	return data;

};

export { SpecularMIPLevelNode };