NAME

       LinkComp,   LinkView,   PSLink   -   component  subject,  view,  and  PostScript  external
       representation for lines with connectable endpoints

SYNOPSIS

       #include <Unidraw/Components/link.h>

DESCRIPTION

       LinkComp is a GraphicComp defining a line with two pins on each end.  The line's endpoints
       will  always  coincide  with  the  pins,  even  if  they  are moved, thereby maintaining a
       graphical link between the objects to which  it  is  connected.   LinkComp  uses  an  Line
       graphic  to  define  its  initial  geometry  and  graphical  attributes.   LinkView  is  a
       GraphicView for displaying the link.  PSLink is a  PostScriptView  that  externalizes  the
       subject's information in PostScript form.

LINKCOMP PUBLIC OPERATIONS

       LinkComp(Line* = nil)
              The constructor takes an optional line graphic to define its initial appearance.

       virtual void Interpret(Command*)
       virtual void Uninterpret(Command*)
              In  addition  to (un)interpreting the commands GraphicComp (un)interprets, LinkComp
              also (un)interprets DeleteCmd and CutCmd by passing these commands to its pins  for
              (un)interpretation.

       virtual void Update()
              When  the LinkComp's pins move to maintain connectivity, LinkComp will reorient the
              line so that its endpoints and the pins coincide.

       virtual void First(Iterator&)
       virtual void Last(Iterator&)
       virtual void Next(Iterator&)
       virtual void Prev(Iterator&)
       virtual boolean Done(Iterator)
       GraphicComp* GetComp(Iterator)
       void SetComp(GraphicComp*, Iterator&)
              LinkComp redefines GraphicComp's traversal operations to make its  pins  accessible
              to  the  Unidraw library.  Thus Unidraw can determine the connectors that belong to
              the component and  call  its  Update  operation  only  once  for  efficiency.   The
              traversal does not include the line.

       Line* GetLine()
              Return  the  Line  graphic that defines the link's attributes.  GetLine is simply a
              more specific form of the GetGraphic operation.

       void GetConnectors(Connector*&, Connector*&)
              Return the LinkView's pins, which are stored in the  _conn1  and  _conn2  protected
              members.

LINKVIEW PUBLIC OPERATIONS

       LinkView(LinkComp* = nil)
              Create an LinkView, optionally supplying the subject.

       virtual Manipulator* CreateManipulator(
          Viewer*, Event&, Transformer*, Tool*
       )

       virtual void InterpretManipulator(Manipulator*)
              LinkView  redefines  its response to manipulation with a GraphicCompTool.  The user
              clicks to specify the first endpoint of the link and then  drags  to  position  the
              remaining  endpoint.   (Up)clicking  on  an  existing  connector  will  establish a
              connection between it and the LinkComp's  first  (second)  pin.   LinkView  uses  a
              ConnectManip  to produce a gravitational attraction between existing connectors and
              the second pin as the user drags  to  position  it.   The  endpoints  will  not  be
              constrained  by  gravity.   LinkView  will use ConnectCmds to connect the pin(s) to
              their target(s). Pin(s) connected in  this  way  will  receive  floating  mobility;
              unconnected pin(s) will be fixed.

       virtual void First(Iterator&)
       virtual void Last(Iterator&)
       virtual void Next(Iterator&)
       virtual void Prev(Iterator&)
       virtual boolean Done(Iterator)
       GraphicView* GetView(Iterator)
       void SetView(GraphicView*, Iterator&)
              LinkView  redefines  GraphicView's traversal operations to make its pins accessible
              to the Unidraw library.  Thus Unidraw can determine the connectors that  belong  to
              the  component,  for  example,  to  support ConnectManip's gravitational attraction
              effect.

       virtual void GetEndpoints(Coord&, Coord&, Coord&, Coord&)
              Return the link's endpoints, in canvas coordinates.

       LinkComp* GetLinkComp()
              Return the subject.

LINKVIEW PROTECTED OPERATIONS

       virtual void CreateHandles()
              LinkView redefines CreateHandles to use a RubberHandles object  with  two  handles,
              one at each endpoint of the link.

       Line* GetLine()
              Return the line that LinkView draws between its pins.

       virtual LinkComp* NewSubject(Line*)
              A helper function that creates a LinkComp subject with the given line graphic. This
              function produces the proper subject  when  the  GraphicCompTool's  manipulator  is
              interpreted.  Subclasses can redefine this operation to return a LinkComp subclass,
              thus eliminating the need to reimplement InterpretManipulator.

       Manipulator* CreateLinkCompManip(
           Viewer*, Event&, Transformer*, Tool*
       )

       Command* InterpretLinkCompManip(Manipulator*)
              Helper functions that CreateManipulator and InterpretManipulator use to create  and
              interpret the manipulator for GraphicCompTool.

PSLINK PUBLIC OPERATIONS

       PSLink(LinkComp* = nil)
              Construct a PostScript external representation of the given subject, if any.

SEE ALSO

       Event(3I),  Graphic(3U),  GraphicComp(3U), GraphicCompTool(3U), GraphicView(3U), Grid(3U),
       PinComp(3U), PostScriptView(3U), Transformer(3I), align(3U), edit(3U), manips(3U)