Sweeping a polyline produces a surface composed of many faces. The unbroken helix in the example Helix with cull set false then true is produced by this code (plus a surrounding put rotation to make an interesting view; this has been omitted).
def K [0,0,1]
sweep[cull=false] {
60,
rotate(10, (0,0,0), [K]) then translate(1/6 * [K])
} line[linewidth=2pt](-1,0)(1,0)
Again, 60 segments of the helix
are produced by connecting 61
instances of the swept line. Options
applied to the sweep, here
cull=false, are treated as options for the generated polygon
or polyline. Options of the swept line itself, here
linewidth=2pt, are ignored, though with a warning. This
def is a vector definition,
which must be referenced
with square brackets, e.g. [foo].