Balloon callback structure
typedef struct Pt_balloon_callback {
    PtWidget_t *widget;
    void (*event_f)( PtWidget_t *wgt, 
                     void *data, 
                     PtCallbackInfo_t *cbinfo);
    } PtBalloonCallback_t;
The PtBalloonCallback_t structure lets you
attach a balloon callback to a widget's container. The
container invokes the specified function whenever a balloon
action is warranted.
This structure contains at least the following members:
- widget
- Pointer to the widget the callback is being attached to.
- event_f
    
- Pointer to an inflate/deflate function that's called
    whenever a balloon action is required for
    widget.
    The arguments passed to this function are:
    
- wgt
    
- Pointer to the widget whose balloon is being affected.
    
- data
    
- A value of NULL.
    
- cbinfo
    
- In the cbinfo structure, the reason member is
    Pt_CB_BALLOONS, and the reason_subtype
    member is one of the following:
      
- Pt_INFLATE_BALLOON-the
         balloon should be made visible
         
      
- Pt_POP_BALLOON-the balloon should be
         removed.
         
      
 
 
Photon
PtCallbackInfo_t,
PtContainer