void panel (x, y, nsides, pcolor, border) SVC.C Level 3
float *x, *y The arrays of x and y values defining the vertices of dimension nsides + 1 to allow the panel to be closed. The units are those of your plot.
int nsides Number of sides of the figure (same as the number of vertices).
int pcolor The color or pattern of the panel fill lines. A number from -15 to 0 indicates a solid color. The numbers are the negative of the IBM color numbers. Geometric patterns may be selected by choosing a number between 1 and 16. Dithered colored patterns may be selected by choosing a number from 50 to 174, and RGB colors may be selected from the range 200 to 447. See color().
int border = 0  No border will be drawn around the panel.
= 1  A border will be drawn around the panel.
Call panel() to define an area to be filled with color pcolor. Units are those of your plot. After the fill area(s) is (are) defined by one or more calls to panel(), call panproc() to complete the process. If you want the border to be a color different from the panel color, set border to 1. The border color will then be that specified by the most recent call to color().

panel() draws horizontal fill lines between alternate pairs of x intercepts at each y level. This rule holds even for figures that go off the page. Thus the area between two concentric rings will be filled, leaving an unfilled hole. The fill line density on the monitor screen is determined by the vertical resolution of the graphics board. For printers and plotters, it is also determined by the resolution of your device.

A problem can occur with printing overlapping panels. On dot matrix printers the underlying panel will show through. If you do not want this effect, draw the top panel in the background color, then redraw it in the desired color. Calling panel() and panproc() twice in this manner will cause the printer bit map to erase the area of the first panel which is overlapped by the second panel. This procedure will not work on vector mode devices such as pen plotters. PostScript 
devices will always hide the underlying panel.

The algorithm used in panel() easily handles multiply connected regions, regions with multiple holes, and lots of sides. However, in gerneral, the fewer the number of sides, the faster the panel can be filled. GraphiC also has the ability to split up panels. This is required, for a correct plot to PostScript level I printers which have a limit of about 400 sides per panel. GraphiC represents panels with too many sides as a collection of smaller panels.