text: import {
  	BufferGeometry,
  	Float32BufferAttribute,
  	LineSegments,
  	LineBasicMaterial,
  	Matrix3,
  	Vector3
  } from 'three';
  
  const _v1 = new Vector3();
  const _v2 = new Vector3();
  const _normalMatrix = new Matrix3();
  
  class VertexNormalsHelper extends LineSegments {
  
  	constructor( object, size = 1, color = 0xff0000 ) {
  
  		const geometry = new BufferGeometry();
  
  		const nNormals = object.geometry.attributes.normal.count;
  		const positions = new Float32BufferAttribute( nNormals * 2 * 3, 3 );
  
  		geometry.setAttribute( 'position', positions );
  
  		super( geometry, new LineBasicMaterial( { color, toneMapped: false } ) );
  
  		this.object = object;
  		this.size = size;
  		this.type = 'VertexNormalsHelper';
  
  		//
  
  		this.matrixAutoUpdate = false;
  
  		this.update();
  
  	}
  
  	update() {
  
  		this.object.updateMatrixWorld( true );
  
  		_normalMatrix.getNormalMatrix( this.object.matrixWorld );
  
  		const matrixWorld = this.object.matrixWorld;
  
  		const position = this.geometry.attributes.position;
  
  		//
  
  		const objGeometry = this.object.geometry;
  
  		if ( objGeometry ) {
  
  			const objPos = objGeometry.attributes.position;
  
  			const objNorm = objGeometry.attributes.normal;
  
  			let idx = 0;
  
  			// for simplicity, ignore index and drawcalls, and render every normal
  
  			for ( let j = 0, jl = objPos.count; j < jl; j ++ ) {
  
  				_v1.fromBufferAttribute( objPos, j ).applyMatrix4( matrixWorld );
  
  				_v2.fromBufferAttribute( objNorm, j );
  
  				_v2.applyMatrix3( _normalMatrix ).normalize().multiplyScalar( this.size ).add( _v1 );
  
  				position.setXYZ( idx, _v1.x, _v1.y, _v1.z );
  
  				idx = idx + 1;
  
  				position.setXYZ( idx, _v2.x, _v2.y, _v2.z );
  
  				idx = idx + 1;
  
  			}
  
  		}
  
  		position.needsUpdate = true;
  
  	}
  
  }
  
  
  export { VertexNormalsHelper };
  