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       CSolver - enforces connector semantics


       #include <Unidraw/csolver.h>


       A CSolver object defines and implements a model for specifying connectivity semantics that
       connector subclasses can build upon to implement their specialized  semantics.   Normally,
       only  one  CSolver  instance  is  used per application, and only connector subclasses need
       access it.  The Unidraw class constructor initializes the csolver global  to  point  to  a
       CSolver instance it creates.  Thus applications should not instantiate CSolver directly.

       CSolver  models  a  connection  between  two  connectors  (regardless  of their particular
       subclass or semantics) as a pair of generic connectors with a piece of  CGlue  interposed.
       The  CGlue  characterizes  the  relationship between the connectors' centers in terms of a
       natural size (which corresponds to the distance  between  the  centers),  elasticity,  and
       deformation limits.  Connector subclasses specify their connectivity behavior with a CGlue
       instance and subsequently rely on  the  CSolver  to  reorient  them  to  conform  to  that
       behavior.   For example, when a pin is told to connect itself to another pin, it registers
       with the global csolver a connection containing the two connectors (the  pins  themselves)
       and  a  piece of CGlue having zero natural size, elasticity, and deformation limits.  This
       specification  effectively  constrains  the  connectors'   centers   to   coincide.    The
       connectivity   semantics  of  other  connector  combinations,  including  those  involving
       application-specific connectors, must be specified using CGlue.


              Create a new instance.  Application programs do not  normally  instantiate  CSolver

       virtual void Connect(Connector*, Connector*, CGlue* = nil)
              Specify  a  connection  between  two  connectors,  optionally with a piece of CGlue
              interposed.  Omitting the CGlue parameter is equivalent to specifying a  connection
              with CGlue having zero natural size, elasticity, and deformation limits.

       void Disconnect(Connector*, Connector*)
       void Disconnect(Connector*)
              Destroy  the  connection(s)  established  between two connectors (the two-parameter
              form), or destroy all connections to a given connector (the one-parameter form).

       void Solve()
              Solve instructs the CSolver to reorient connected connectors to  conform  to  their
              connectivity  semantics  as  reflected  by its connection specifications.  Normally
              this function is called automatically and only in response to Unidraw::Update.

       CSolverState* GetState(Connector*)
       void SetState(CSolverState*)
              CSolverState is a class that encapsulates all the information about the connections
              in  which  a connector participates.  Only CSolver can create or do anything with a
              CSolverState instance. GetState initializes and returns a CSolverState instance for
              the  given  connector, and SetState establishes the connections that a CSolverState
              instance specifies without disturbing existing connections.  These  operations  are
              useful  when  it  is  necessary to reestablish a connector's connections after they
              have been lost, for example, by removing the connector from the component hierarchy
              (as caused by a command to delete the component).

       void Read(istream&)
       void Write(ostream&)
              Explicitly read/write the csolver's contents from/to disk.  Normally only a catalog
              calls these operations.


       Catalog(3U), GGlue(3U), Connector(3U), globals(3U)