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SUBROUTINE PGNA3 (XARRAY,INCX, YARRAY,INCY, ZARRAY,INCZ, NVERTX)
C$ (Polygon Absolute 3-D)
C$ Draw a 3-D polygon. A move is automatically made to the
C$ first vertex, and then implicit closure is provided by
C$ connecting the last vertex to the first, and the current
C$ point is left at the first vertex. If a polygon "plain"
C$ interior style filling and a visible pattern or color has
C$ been selected by a prior call to SETPIS and SETPFI/SETPCI,
C$ the polygon is filled with that pattern or color. The
C$ polygon vertices are assumed to be arranged so that the
C$ interior lies to the left of each line segment between
C$ vertices i and i+1. Drawing and filling is suppressed if
C$ the polygon lies entirely outside the current viewport.
C$ The arguments are:
C$
C$ XARRAY(*)........Array of X coordinates.
C$ INCX.............Displacement between successive X
C$ coordinates in XARRAY(*) (normally 1).
C$ YARRAY(*)........Array of Y coordinates.
C$ INCY.............Displacement between successive Y
C$ coordinates in YARRAY(*) (normally 1).
C$ ZARRAY(*)........Array of Z coordinates.
C$ INCZ.............Displacement between successive Z
C$ coordinates in ZARRAY(*) (normally 1).
C$ NVERTX...........Number of polygon vertices (.GE. 3).
C$
C$ If an increment INCX, INCY, or INCZ is negative, the
C$ starting vertex is taken as (1-N)*INC + 1 instead of 1, so
C$ that the array is stepped through in reverse order.
C$ Because of the ordering convention on the vertices,
C$ reversing the order of traversal of the vertex list
C$ interchanges the interior and the exterior of the polygon.
C$ No error is raised if there are fewer than 3 vertices, but
C$ filling will be suppressed.
C$ (19-MAR-83)