This module corresponds to section 2.10 (Rectangles) of the OpenGL 2.1 specs.
rectv support efficient specification of rectangles as two
corner points. Each rectangle command takes four arguments, organized either
as two consecutive pairs of (x, y) coordinates, or as two pointers to
arrays, each containing an (x, y) pair. The resulting rectangle is
defined in the z = 0 plane.
Note that if the second vertex is above and to the right of the first vertex, the rectangle is constructed with a counterclockwise winding.