function getWireframeIndex( geometry ) {

	const indices = [];

	const geometryIndex = geometry.index;
	const geometryPosition = geometry.attributes.position;

	if ( geometryIndex !== null ) {

		const array = geometryIndex.array;

		for ( let i = 0, l = array.length; i < l; i += 3 ) {

			const a = array[ i + 0 ];
			const b = array[ i + 1 ];
			const c = array[ i + 2 ];

			indices.push( a, b, b, c, c, a );

		}

	} else {

		const array = geometryPosition.array;

		for ( let i = 0, l = ( array.length / 3 ) - 1; i < l; i += 3 ) {

			const a = i + 0;
			const b = i + 1;
			const c = i + 2;

			indices.push( a, b, b, c, c, a );

		}

	}

	const attribute = new ( arrayNeedsUint32( indices ) ? Uint32BufferAttribute : Uint16BufferAttribute )( indices, 1 );
	attribute.version = getWireframeVersion( geometry );

	return attribute;

}
Returns a wireframe index attribute for the given geometry.

@private
@function
@param {BufferGeometry} geometry - The geometry.
@return {BufferAttribute} The wireframe index attribute.