MUIM_HandleInput
================

   Compared with BOOPSI, MUI uses a different input handling scheme. Not
only the "active" object but instead all objects may receive input
events at the same time. Since sending input events to every object in
a window would be an incredible overhead, you have to specify what
messages you really need. MUI offers the library calls
MUI_RequestIDCMP() and MUI_RejectIDCMP() for this purpose. Whenever an
arriving input event matches your request, your object will receive a
MUIM_HandleInput method.

   You can call MUI_RequestIDCMP() and MUI_RejectIDCMP() at every time.
Performance affecting critical events like INTUITICKS and MOUSEMOVEs
should only be requested when you really need them. The "Class3" for
example requests MOUSEBUTTONS and RAWKEY during MUIM_Setup. The critical
MOUSEMOVES are only requested when a button was pressed and immediately
rejected after it was released again.

   Beneath the struct IntuiMessage, MUIM_HandleInput receives a longword
describing a MUIKEY as second parameter. If this is set to some other
value as MUIKEY_NONE, your object is the actve object and the input
event translated to a user configured keyboard action.

   MUI will *not* translate input events to your objects coordinates.
This is up to you. A typical input implementation could look like this:


     static ULONG mHandleInput(
        struct IClass *cl,
        Object *obj,
        struct MUIP_HandleInput *msg)
     {
        #define _between(a,x,b) ((x)>=(a) && (x)<=(b))
        #define _isinobject(x,y) (_between(_mleft(obj),(x),_mright (obj))\
                               && _between(_mtop(obj) ,(y),_mbottom(obj)))
     
        struct Data *data = INST_DATA(cl,obj);
     
        if (msg->muikey)
        {
           switch (msg->muikey)
           {
              case MUIKEY_LEFT :
                 data->sx=-1;
                 MUI_Redraw(obj,MADF_DRAWUPDATE);
                 break;
              case MUIKEY_RIGHT:
                 data->sx= 1;
                 MUI_Redraw(obj,MADF_DRAWUPDATE);
                 break;
              case MUIKEY_UP   :
                 data->sy=-1;
                 MUI_Redraw(obj,MADF_DRAWUPDATE);
                 break;
              case MUIKEY_DOWN :
                 data->sy= 1;
                 MUI_Redraw(obj,MADF_DRAWUPDATE);
                 break;
           }
        }
     
        if (msg->imsg)
        {
           switch (msg->imsg->Class)
           {
              case IDCMP_MOUSEBUTTONS:
              {
                 if (msg->imsg->Code==SELECTDOWN)
                 {
                    if (_isinobject(msg->imsg->MouseX,msg->imsg->MouseY))
                    {
                       data->x = msg->imsg->MouseX;
                       data->y = msg->imsg->MouseY;
                       MUI_Redraw(obj,MADF_DRAWUPDATE);
                       MUI_RequestIDCMP(obj,IDCMP_MOUSEMOVE);
                    }
                 }
                 else
                    MUI_RejectIDCMP(obj,IDCMP_MOUSEMOVE);
              }
              break;
     
              case IDCMP_MOUSEMOVE:
              {
                 if (_isinobject(msg->imsg->MouseX,msg->imsg->MouseY))
                 {
                    data->x = msg->imsg->MouseX;
                    data->y = msg->imsg->MouseY;
                    MUI_Redraw(obj,MADF_DRAWUPDATE);
                 }
              }
              break;
           }
        }
     
        /* passing MUIM_HandleInput to the super class is only necessary
           if you rely on area class input handling (MUIA_InputMode). */
     
        return(0);
     }