Fl_Button | +----Fl_Round_Button
Buttons generate callbacks when they are clicked by the user. You control exactly when and how by changing the values for type() and when().
The Fl_Round_Button subclass display the "on" state by turning on a light, rather than drawing pushed in. The shape of the "light" is initially set to FL_ROUND_DOWN_BOX. The color of the light when on is controlled with selection_color(), which defaults to FL_RED.
Creates a new Fl_Round_Button widget using the given position, size, and label string.
The destructor deletes the check button.