three.js/examples/jsm/nodes/effects/LuminanceNode.js

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

function LuminanceNode( rgb ) {

	TempNode.call( this, 'f' );

	this.rgb = rgb;

}

LuminanceNode.Nodes = ( function () {

	var LUMA = new ConstNode( 'vec3 LUMA vec3( 0.2125, 0.7154, 0.0721 )' );

	var luminance = new FunctionNode( [
		// Algorithm from Chapter 10 of Graphics Shaders
		'float luminance( vec3 rgb ) {',

		'	return dot( rgb, LUMA );',

		'}'
	].join( '\n' ), [ LUMA ] );

	return {
		LUMA: LUMA,
		luminance: luminance
	};

} )();

LuminanceNode.prototype = Object.create( TempNode.prototype );
LuminanceNode.prototype.constructor = LuminanceNode;
LuminanceNode.prototype.nodeType = 'Luminance';

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

	var luminance = builder.include( LuminanceNode.Nodes.luminance );

	return builder.format( luminance + '( ' + this.rgb.build( builder, 'v3' ) + ' )', this.getType( builder ), output );

};

LuminanceNode.prototype.copy = function ( source ) {

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

	this.rgb = source.rgb;

	return this;

};

LuminanceNode.prototype.toJSON = function ( meta ) {

	var data = this.getJSONNode( meta );

	if ( ! data ) {

		data = this.createJSONNode( meta );

		data.rgb = this.rgb.toJSON( meta ).uuid;

	}

	return data;

};

export { LuminanceNode };