text: import {
  	BufferGeometry,
  	Float32BufferAttribute,
  	LineSegments,
  	LineBasicMaterial,
  	Vector3
  } from './../../build/three.module.js';
  
  const _v1 = new Vector3();
  const _v2 = new Vector3();
  
  class VertexTangentsHelper extends LineSegments {
  
  	constructor( object, size = 1, color = 0x00ffff ) {
  
  		const objGeometry = object.geometry;
  
  		if ( ! ( objGeometry && objGeometry.isBufferGeometry ) ) {
  
  			console.error( 'THREE.VertexTangentsHelper: geometry not an instance of THREE.BufferGeometry.', objGeometry );
  			return;
  
  		}
  
  		const nTangents = objGeometry.attributes.tangent.count;
  
  		//
  
  		const geometry = new BufferGeometry();
  
  		const positions = new Float32BufferAttribute( nTangents * 2 * 3, 3 );
  
  		geometry.setAttribute( 'position', positions );
  
  		super( geometry, new LineBasicMaterial( { color, toneMapped: false } ) );
  
  		this.object = object;
  		this.size = size;
  		this.type = 'VertexTangentsHelper';
  
  		//
  
  		this.matrixAutoUpdate = false;
  
  		this.update();
  
  	}
  
  	update() {
  
  		this.object.updateMatrixWorld( true );
  
  		const matrixWorld = this.object.matrixWorld;
  
  		const position = this.geometry.attributes.position;
  
  		//
  
  		const objGeometry = this.object.geometry;
  
  		const objPos = objGeometry.attributes.position;
  
  		const objTan = objGeometry.attributes.tangent;
  
  		let idx = 0;
  
  		// for simplicity, ignore index and drawcalls, and render every tangent
  
  		for ( let j = 0, jl = objPos.count; j < jl; j ++ ) {
  
  			_v1.set( objPos.getX( j ), objPos.getY( j ), objPos.getZ( j ) ).applyMatrix4( matrixWorld );
  
  			_v2.set( objTan.getX( j ), objTan.getY( j ), objTan.getZ( j ) );
  
  			_v2.transformDirection( matrixWorld ).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 { VertexTangentsHelper };
  