Draws a rectangle, using the current line style and color.
procedure Rectangle(x1, y1, x2, y2: Integer);
(X1, Y1) define the upper left corner of the rectangle, and (X2, Y2) define the lower right corner (0 <= X1 < X2 <= GetMaxX, and 0 <= Y1 < Y2 <= GetMaxY).
Draws the rectangle in the current line style and color, as set by SetLineStyle and SetColor. Use SetWriteMode to determine whether the rectangle is copied or XOR'd to the screen.
Must be in graphics mode.