Marker_Pick - Pick, Edit, Create, and Move Markers on Images

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         A Test Bed for marker picking applications
               with the AVS5 Image Viewer
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 Type:      Mapper,
            Image viewer upstream control module

 Language:  K&R C

 Author:    Ian Curington, AVS/UNIRAS Ltd. UK

 Description:

 Allow marker pick identification and display 
 from an input marker list and the image viewer
 system. Takes as input an AVS field with
 a list of coordinates for markers, displays them
 over an image (map) in the image viewer, and
 reacts to mouse picks on these markers, sending
 the pick selection to the output port.
 Markers are defined by geometric polyline vector lists,
 not ROI pixel masks.

 Markers can be created by picking and dragging, where
 the distance of the drag determines marker size,
 centered on the initial pick.

 Undo, Clear, options allow list editing.
 A series of predefined shapes are available from a choice list.

 The input marker field is fully specified.
 You can externally control position, shape, size, etc.
 Any marker field sent out on the output port can
 be read back in to the input field port. This way
 state save and restore are possible. New marker
 lists can be made using the "marker_pick" module.

 Inputs:
   Input Image: Reference image, same as that sent for
                display in the image viewer, used
                for feedback path.
   Mouse Info:  Part of upstream pick feedback communication
                with the image viewer
   IV Struct:   Part of upstream communications with the image viewer.
   Poly_Marker: Input field,
                  for marker pick list definition.
                This field is 1D uniform integer N-vector.
                The marker field is assumed 
                to be a full marker spec as defined
                in "marker.h", usually 7. This can fully specifiy
                variable marker shape, size, position, and hidden
                stroke vector used in the shape creation.

 Outputs:
   Poly_Marker_Output:
                This contains a full marker list, as a mirror to
                to the input list. It is always full 7-vector.
                This port can be saved to a file with the
                "write field" module, and later restored with
                "read_field" on the input port during a later session.

  IV Draw Struct:
                Part of the image viewer upstream communication
                system.

 Parameters:
  Set Pick Mode: A one-shot button that registers the pick operation
                mode with the image viewer, in the case that multiple
                modules are also requesting pick communication with the
                image viewer.

  Pick Status Text Block:
                This is a square read-only text block used to
                show annotation about the picked marker.

  Clear List    Oneshot to clear out the marker list.

  Undo Last     backup the list one entry.