Draw polycylinders, polycones, extrusions, etc.
by joining together the different segments and slicing off
the joint at half the angle between the segments. A cap is drawn.
Note that the slicing plane runs through the origin of the contour
coordinate system. Thus, the amount of slice can be varied by offsetting
the contour with respect to the origin.
Note that when two segments meet at a shallow angle, the cut join
style will potentially shave off a whole lot of the contour,
leading to "surprising" results...