appli offset point point offset point re slope line find normal slope normal neg reciproc slope recip recipnumer recipdenomin recipdenomin recipnumer point offset line give correct offset len math sqrt recipnumer recipnumer recipdenomin recipdenomin dx recipdenomin offset len dy recipnumer offset len re math ab dx re math ab dy width item fig width recipnumer slope recipdenomin recipnumer factor tanh slope re math ab factor width re width 