 the remaining points while keeping the effector point
        // anchored at its current position
        let ii;
        for( let i=1; i < lIdx; i++ ){
            ii = i+1;
            distanceConstraint( bpos[i], bpos[ii], 
                chain.links[ i ].len, 
                ( i  == this._effectorIdx ),
                ( ii == this._effectorIdx )
            );
        }
    }

    // Handle Forward or Backward application of the distance constraint on a chain
    _applyDistanceConstraint( lnks, idx,