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─────Run-Time Library───────────────────────────────────────────────────────
 
     The _pie functions draw a pie-shaped wedge by drawing an
     elliptical arc whose center and two endpoints are joined by
     lines. The following list summarizes the arguments to the _pie
     functions:
 
     Argument       Description
 
     <control>      Either the _GFILLINTERIOR or the _GBORDER manifest
                    constant
 
     <x1>, <y1>     Upper-left corner of bounding rectangle
 
     <x2>, <y2>     Lower-right corner of bounding rectangle
 
     <x3>, <y3>     Second point of start vector (center of bounding
                    rectangle is first point)
 
     <x4>, <y4>     Second point of end vector (center of bounding
                    rectangle is first point)
 
     <pwxy1>        Upper-left corner of bounding rectangle
 
     <pwxy2>        Lower-right corner of bounding rectangle
 
     <pwxy3>        Second point of start vector (center of bounding
                    rectangle is first point)
 
     <pwxy4>        Second point of end vector (center of bounding
                    rectangle is first point)
 
     The <control> option given by _GFILLINTERIOR is equivalent to a
     subsequent call to the _floodfill function using the approximate
     center of the pie as the starting point and the current color
     (set by _setcolor) as the boundary color. Use the _getarcinfo
     function to find the exact starting point.
 
     The center of the pie is the center of the bounding rectangle,
     which is defined by points (<x1>, <y1>) and (<x2>, <y2>) for _pie
     and _pie_w and by points <pwxy1> and <pwxy2> for _pie_wxy. The
     pie starts where it intersects an imaginary line extending from
     the center of the arc through (<x3>, <y3>) for _pie and _pie_w
     and through <pwxy3> for _pie_wxy.
 
     The pie is drawn counterclockwise about the center of the arc,
     ending where it intersects an imaginary line extending from the
     center of the arc through (<x4>, <y4>) for _pie and _pie_w and
     through <pwxy4> for _pie_wxy. The wedge is drawn using the current
     color.
 
     The _pie routine uses the view coordinate system. The _pie_w and
     _pie_wxy functions use the real-valued window coordinate system.
     The arc is drawn using the current color. Since an arc does not
     define a closed area, it is not filled.
 
     The <pwxy1>, <pwxy2>, <pwxy3>, and <pwxy4> points are pointers of
     type struct _wxycoord, which is defined in GRAPH.H.
 
     Return Value
 
     The functions return a nonzero value if the pie is drawn
     successfully; otherwise, they return 0.
                                    -♦-