The device context identified by the $hDC parameter must contain a closed path.
The _WinAPI_WidenPath() function is successful only if the current pen has a width, in device units, of more than one.
Any Bezier curves in the path are converted to sequences of straight lines approximating the widened curves.
As such, no Bezier curves remain in the path after _WinAPI_WidenPath() is called.