( function () {

    class CSS2DObject extends THREE.Object3D {

        constructor( element = document.createElement( 'div' ) ) {

            super();
            this.element = element;
            this.element.style.position = 'absolute';
            this.element.style.userSelect = 'none';
            this.element.setAttribute( 'draggable', false );
            this.addEventListener( 'removed', function () {

                this.traverse( function ( object ) {

                    if ( object.element instanceof Element && object.element.parentNode !== null ) {

                        object.element.parentNode.removeChild( object.element );

                    }

                } );

            } );

        }

        copy( source, recursive ) {

            super.copy( source, recursive );
            this.element = source.element.cloneNode( true );
            return this;

        }

    }

    CSS2DObject.prototype.isCSS2DObject = true; //

    const _vector = new THREE.Vector3();

    const _viewMatrix = new THREE.Matrix4();

    const _viewProjectionMatrix = new THREE.Matrix4();

    const _a = new THREE.Vector3();

    const _b = new THREE.Vector3();

    class CSS2DRenderer {

        constructor( parameters = {} ) {

            const _this = this;

            let _width, _height;

            let _widthHalf, _heightHalf;

            const cache = {
                objects: new WeakMap()
            };
            const domElement = parameters.element !== undefined ? parameters.element : document.createElement( 'div' );
            domElement.style.overflow = 'hidden';
            this.domElement = domElement;

            this.getSize = function () {

                return {
                    width: _width,
                    height: _height
                };

            };

            this.render = function ( scene, camera ) {

                if ( scene.autoUpdate === true ) scene.updateMatrixWorld();
                if ( camera.parent === null ) camera.updateMatrixWorld();

                _viewMatrix.copy( camera.matrixWorldInverse );

                _viewProjectionMatrix.multiplyMatrices( camera.projectionMatrix, _viewMatrix );

                renderObject( scene, scene, camera );
                zOrder( scene );

            };

            this.setSize = function ( width, height ) {

                _width = width;
                _height = height;
                _widthHalf = _width / 2;
                _heightHalf = _height / 2;
                domElement.style.width = width + 'px';
                domElement.style.height = height + 'px';

            };

            function renderObject( object, scene, camera ) {

                if ( object.isCSS2DObject ) {

                    const visible = object.visible && _vector.z >= - 1 && _vector.z <= 1 && object.layers.test( camera.layers );
                    object.element.style.display = visible ? '' : 'none';

                    if ( visible ) {

                        object.onBeforeRender( _this, scene, camera );

                        _vector.setFromMatrixPosition( object.matrixWorld );

                        _vector.applyMatrix4( _viewProjectionMatrix );

                        const element = object.element;

                        if ( /apple/i.test( navigator.vendor ) ) {

                            // https://github.com/mrdoob/three.js/issues/21415
                            element.style.transform = 'translate(-50%,-50%) translate(' + Math.round( _vector.x * _widthHalf + _widthHalf ) + 'px,' + Math.round( - _vector.y * _heightHalf + _heightHalf ) + 'px)';

                        } else {

                            element.style.transform = 'translate(-50%,-50%) translate(' + ( _vector.x * _widthHalf + _widthHalf ) + 'px,' + ( - _vector.y * _heightHalf + _heightHalf ) + 'px)';

                        }

                        const objectData = {
                            distanceToCameraSquared: getDistanceToSquared( camera, object )
                        };
                        cache.objects.set( object, objectData );

                        if ( element.parentNode !== domElement ) {

                            domElement.appendChild( element );

                        }

                        object.onAfterRender( _this, scene, camera );

                    }

                }

                for ( let i = 0, l = object.children.length; i < l; i ++ ) {

                    renderObject( object.children[ i ], scene, camera );

                }

            }

            function getDistanceToSquared( object1, object2 ) {

                _a.setFromMatrixPosition( object1.matrixWorld );

                _b.setFromMatrixPosition( object2.matrixWorld );

                return _a.distanceToSquared( _b );

            }

            function filterAndFlatten( scene ) {

                const result = [];
                scene.traverse( function ( object ) {

                    if ( object.isCSS2DObject ) result.push( object );

                } );
                return result;

            }

            function zOrder( scene ) {

                const sorted = filterAndFlatten( scene ).sort( function ( a, b ) {

                    const distanceA = cache.objects.get( a ).distanceToCameraSquared;
                    const distanceB = cache.objects.get( b ).distanceToCameraSquared;
                    return distanceA - distanceB;

                } );
                const zMax = sorted.length;

                for ( let i = 0, l = sorted.length; i < l; i ++ ) {

                    sorted[ i ].element.style.zIndex = zMax - i;

                }

            }

        }

    }

    THREE.CSS2DObject = CSS2DObject;
    THREE.CSS2DRenderer = CSS2DRenderer;

} )();