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Regular Polygons

The following example creates a pentagon in the x-z plane, centered about the origin, whose enclosing circle has a radius equal to 3cm.

     default_focus.set(2, 3, -10, 2, 3, 10, 10);
     Reg_Polygon p(origin, 5, 3);

[Figure 20. Not displayed.]

Fig. 20.

Three additional arguments cause the pentagon to be rotated about the x, y, and z axes by the amount indicated. In this example, it's rotated 90 degrees

about the x-axis, so that it comes to lie in the x-y plane:

     Reg_Polygon p(origin, 5, 3, 90);

[Figure 21. Not displayed.]

Fig. 21.

In this example, it's rotated 36 degrees

about the y-axis, so that it appears to point in the opposite direction from the first example:

     Reg_Polygon p(origin, 5, 3, 0, 36);

[Figure 22. Not displayed.]

Fig. 22.

In this example, it's rotated 90 degrees

about the z-axis, so that it lies in the z-y plane:

     Reg_Polygon p(origin, 5, 3, 0, 0, 90);

[Figure 23. Not displayed.]

Fig. 23.

In this example, it's rotated 45 degrees

about the x, y, and z-axes in that order:

     Reg_Polygon p(origin, 5, 3, 45, 45, 45);

[Figure 24. Not displayed.]

Fig. 24.

Reg_Polygons need not be centered about the origin. If another Point pt is used as the first argument, the Reg_Polygon is first created with its center at the origin, then the specified rotations, if any, are performed. Finally, the Reg_Polygon is shifted such that its center comes to lie on pt:

     Point P(-2, 1, 1);
     Reg_Polygon hex(P, 6, 4, 60, 30, 30);

[Figure 25. Not displayed.]

Fig. 25.

In the following example, the Reg_Polygon polygon is first declared using the default constructor, which creates an empty Reg_Polygon. Then, the polygon is repeatedly changed using the setting function corresponding to the constructor used in the previous examples. [next figure] demonstrates that a given Reg_Polygon need not always have the same number of sides.

     Point p(0, -3);
     Reg_Polygon polygon;
     for (int i = 3; i < 9; ++i)
         polygon.set(p, i, 3);
         p.shift(0, 1);

[Figure 26. Not displayed.]

Fig. 26.