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Drag Gadgets
    Unfortunately, it is not possible to "drag" standard Intuition gadgets.

    An example of a gadget that you can drag would be the disk and file icons in
    Workbench.  You  can click on these and drag them to a new position, even in
    another window.

    Proportional gadgets give you something, but movement is limited to within a
    window and the bounding boxes the gadgets move within can not overlap.

    The routine DragGadget, coupled with the DragInfo data  structure  give  you
    the  ability to drag Intuition gadgets that are defined with an Image. These
    gadgets can move across window boundaries (which is  very  useful  for  some
    user  interfaces)  and  the  bounding  boxes  can overlap, the only possible
    conflict being when the icons themselves overlap.

    The DragInfo Structure

    Because additional information is needed for dragging gadgets, such as the ,
    bounding box, this data structure is used:

    struct DragInfo
    struct Gadget *Gadget;               /* Gadget to drag */

    SHORT LeftEdge,TopEdge,              /* Bounding box. */
          RightEdge, BottomEdge;
    USHORT Flags;                        /* Command flags. */
    SHORT XPos, YPos;                    /* Current position. */
    void (*UpdateRoutine)();             /* User supplied routine. */
    LONG DD;                             /* Leave this alone. */

    A description of each field and how you use it:

         Gadget This is the gadget to drag.

       LeftEdge There is a bounding box you define  that  the  gadget  can  move
                within. This defines the left edge of that, relative to the left
                hand edge of the window. If  you  wish  the  left  edge  of  the
                bounding  box  to be unlimited, specify a large negative number,
                like -1000.

        TopEdge This defines the top edge of that bounding box, relative to  the
                top  of the window. If you wish the top edge of the bounding box
                to be unlimited, specify a large negative number, like1000.

      RightEdge This defines the right edge of the bounding box, relative to the
                left  edge  of  the  window.  If  you wish the right edge of the
                bounding box to be unlimited, specify a large number, like 1000.

     BottomEdge This defines the bottom edge of the bounding box, relative to  w
                the  top  of  the window. If you wish the bottom of the bounding
                box to be unlimited, specify  a  large  number,  like  ....  you

          Flags There are several flags you can set that govern the behavior  of
                the drag gadget.

                DRAG_INWINDOW This indicates that the gadget can only  be  drawn
                              within  the  RastPort  of the window. If clear, it
                              will be drawn directly into the  screen's  bitmap,
                              so  it  will  travel over other windows, including
                              overlapping ones. A WorkBench  file  gadget  would
                              have  this  flag cleared so it could drag anywhere
                              in the screen.

              DRAG_MOVEGADGET If  you  want  the  gadget  to  stay  in  its  new
                              position, set this flag. The gadget's LeftEdge and
                              TopEdge value will be adjusted at the end  of  the
                              drag.  Otherwise,  it springs back to the original
                              position and you are left with  the  knowledge  of
                              where the icon was dragged to.

                 DRAG_OUTLINE If this flag is set, all parts of the gadget image
                              that  are  color pen 0 are transparent. So, rather
                              than a , rectangular box moving over the  picture,
                              you have an outlined shape.

                    XPos,YPos This is  the  current  window  coordinate  of  the
                              gadget. You can read this after a move to find out
                              where the  user  dragged  the  gadget.  And,  your
                              UpdateRoutine (see below) can use this.

                UpdateRoutine You can provide a routine  that  is  called  every
                              time  the  gadget  moves a pixel. For example, you
                              might wish to dynamically display the  coordinates
                              of  the  gadget as it travels in your window title
                              bar. This routine is passed two parameters:

                       Window A pointer to your window.

                     Draglnfo A pointer to the DragInfo  structure.  From  this,
                              you  can  get the current coordinates, the gadget,
                              and any other important information.

    Using Drag Gadgets

    Set up your Intuition gadget as a BOOLGADGET  type  and  give  it  a  gadget
    render  Image. You can also give it a select render Image, which will be the
    one dragged in that case.

    Set up your DragInfo structure.

    When   you   receive   a   GADGETDOWN   event   for   this   gadget,    call
    DragGadget(Window,DragInfo).  When the gadget has finished being dragged, it
    will return. You can  then  read  the  new  coordinates  from  the  DragInfo

    If you are using Drag Gadgets to move icons from one window to another,  you
    need  to  know  which  wsndow  the  gadget  was  dragged to. Use the routine
    WhichWindow. WhichWindow is passed a pointer to the window the  Drag  Gadget
    belongs to and the final X and Y positions of the gadget (in the originating
    window's coordinate system.) It returns a pointer to the topmost window that
    is under the coordinates, if such a window exists.