class Fl_Free : public Fl_Widget

Emulation of the Forms "free" widget. This emulation allows the free demo to run, and appears to be useful for porting programs written in Forms which use the free widget or make subclasses of the Forms widgets.

There are five types of free, which determine when the handle function is called: 

#define FL_NORMAL_FREE		1
#define FL_SLEEPING_FREE	2
#define FL_INPUT_FREE		3
#define FL_CONTINUOUS_FREE	4
#define FL_ALL_FREE		5

An FL_INPUT_FREE accepts FL_FOCUS events. A FL_CONTINUOUS_FREE sets a timeout callback 100 times a second and provides a FL_STEP event, this has obvious detrimental effects on machine performance. FL_ALL_FREE does both. FL_SLEEPING_FREE are deactivated.

typedef int (*FL_HANDLEPTR)(Fl_Widget *, int , float, float, char);

This function is called from the the handle() method of the Fl_Free in response to most events, and is called by the draw() method. The arguments are the Fl_Free widget, the event value (or FL_DRAW for redrawing), Fl::event_x(), Fl::event_y(), and the Ascii value of the keyboard keystroke. 
// old event names for compatability:
#define FL_MOUSE		FL_DRAG
#define FL_DRAW			0
#define FL_STEP			9
#define FL_FREEMEM		12
#define FL_FREEZE		FL_UNMAP
#define FL_THAW			FL_MAP

Fl_Free(uchar type, int, int, int, int, const char *l, FL_HANDLEPTR hdl);

The constructor takes both the type() and the handle function.

~Fl_Free();

The destructor will call the handle function with the event FL_FREE_MEM.