P is an $N$-by-2 matrix in millimetres with at least two rows. CLOSED is a logical scalar, false by default; when it is true the polyline closes back onto its first vertex.

A closed polyline must not repeat its first vertex at the end. The closed flag does that work, which is the implicitly closed convention the geom namespace uses throughout.

BULGE gives one value per vertex, turning the segment that leaves that vertex into a circular arc. The value is the tangent of a quarter of the arc’s included angle, which is the convention DXF uses: zero is a straight segment and 1 a semicircle.

A positive bulge is the arc that runs counter-clockwise from the vertex to the next, which places it to the right of the direction of travel; a negative one runs clockwise, to the left. That is worth reading twice, because the sign is easy to guess backwards: an arc from [0, 0] to [20, 0] with a bulge of 1 dips below the chord. A polyline of arcs and lines together is how a slot, a rounded plate or an obround is drawn as one entity rather than as a handful that a later edit can pull apart.

Source Code: draw.Drawing