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SUBROUTINE DEM81 (NIN,NOUT)
C$ (DEM81 - Sierpinski Curves)
C$ This routine demonstrates the translation of the recursive
C$ Sierpinski curve into a non-recursive stack-based algorithm
C$ in SFTRAN3.
C$
C$ Apart from its geometrically interesting shape, tending
C$ toward space filling, the principle interest of the
C$ Sierpinski curve here is that it can be made arbitrarily
C$ long by simply increasing the order, and it therefore may
C$ serve as a useful test of plotter speed.
C$
C$ The Sierpinski curves are closed, and a curve of order N
C$ has 4**(N+1)+1 vertices. When used as a test of a polygon
C$ flood fill algorithm which fills up to, but not including,
C$ the boundary color, both the interior and exterior can be
C$ separately flooded. Such algorithms usually have internal
C$ stacks which keep track of areas to return to, and
C$ Sierpinski curve flooding explores the limits of these
C$ stacks. The curves are also excellent tests of polygon
C$ edge fill algorithms, which may not be limited by internal
C$ stacks, but nevertheless can fail to handle complex
C$ polygons, or polygons with colinear edges.
C$
C$ For amusement, the curves are plotted in five different
C$ coordinate systems.
C$ (19-SEP-85)