The Fraunhofer diffraction patterns of the triangle, trapezoid, and hexagon are calculated and displayed in moiré plots. The diffraction pattern of the general polygonal aperture with a finite number of vertices can be calculated in terms of elementary functions.
Richard C. Smith and James S. Marsh, "Diffraction patterns of simple apertures," J. Opt. Soc. Am. 64, 798-803 (1974)