three.js/src/extras/helpers/BoxHelper.js

/**
 * @author mrdoob / http://mrdoob.com/
 */

THREE.BoxHelper = function ( object ) {

	var indices = new Uint16Array( [ 0, 1, 1, 2, 2, 3, 3, 0, 4, 5, 5, 6, 6, 7, 7, 4, 0, 4, 1, 5, 2, 6, 3, 7 ] );
	var positions = new Float32Array( 8 * 3 );

	var geometry = new THREE.BufferGeometry();
	geometry.addAttribute( 'index', new THREE.IndexBufferAttribute( indices, 1 ) );
	geometry.addAttribute( 'position', new THREE.BufferAttribute( positions, 3 ) );

	THREE.LineSegments.call( this, geometry, new THREE.LineBasicMaterial( { color: 0xffff00 } ) );

	if ( object !== undefined ) {

		this.update( object );

	}

};

THREE.BoxHelper.prototype = Object.create( THREE.LineSegments.prototype );
THREE.BoxHelper.prototype.constructor = THREE.BoxHelper;

THREE.BoxHelper.prototype.update = ( function () {

	var box = new THREE.Box3();

	return function ( object ) {

		box.setFromObject( object );

		if ( box.empty() ) return;

		var min = box.min;
		var max = box.max;

		/*
		  5____4
		1/___0/|
		| 6__|_7
		2/___3/

		0: max.x, max.y, max.z
		1: min.x, max.y, max.z
		2: min.x, min.y, max.z
		3: max.x, min.y, max.z
		4: max.x, max.y, min.z
		5: min.x, max.y, min.z
		6: min.x, min.y, min.z
		7: max.x, min.y, min.z
		*/

		var position = this.geometry.attributes.position;
		var array = position.array;

		array[  0 ] = max.x; array[  1 ] = max.y; array[  2 ] = max.z;
		array[  3 ] = min.x; array[  4 ] = max.y; array[  5 ] = max.z;
		array[  6 ] = min.x; array[  7 ] = min.y; array[  8 ] = max.z;
		array[  9 ] = max.x; array[ 10 ] = min.y; array[ 11 ] = max.z;
		array[ 12 ] = max.x; array[ 13 ] = max.y; array[ 14 ] = min.z;
		array[ 15 ] = min.x; array[ 16 ] = max.y; array[ 17 ] = min.z;
		array[ 18 ] = min.x; array[ 19 ] = min.y; array[ 20 ] = min.z;
		array[ 21 ] = max.x; array[ 22 ] = min.y; array[ 23 ] = min.z;

		position.needsUpdate = true;

		this.geometry.computeBoundingSphere();

	}

} )();