 lLen, step=1, iLoop=0, modBy ){
        const dir  = [ 0, 0, 0 ];
        const bpos = this._bonePos;

        let iPrev  = idx;
        let bLen   = 0;
        let ii;
        // console.log( '-----' );
        
        for( let i=iLoop; i < lLen; i++ ){
            ii = Maths.mod( idx + i * step, modBy );
            // console.log( i, ii, 'prev', iPrev, 'lenFrom', ( step === 1 )? iPrev : ii );

            // Stepping forward get previous bone's length
            // Stepping backward get current bone's