Manipulator(3U) 					    InterViews Reference Manual 					   Manipulator(3U)

NAME

       Manipulator - base class for defining direct-manipulation semantics

SYNOPSIS

       #include <Unidraw/manip.h>

DESCRIPTION

       Tools  use  manipulator objects to encapsulate the mechanics of direct manipulation.  Manipulators turn user input events into an animation
       sequence that characterize the manipulation.  Manipulators abstract the manipulation into three phases: the grasping phase, which occurs at
       the  start of the manipulation and lets the manipulator initialize state it will need in later phases; the manipulating phase, during which
       the manipulator accepts input events and generates graphical output that characterizes successive frames of the animation; and finally  the
       effect  phase,  which  occurs  at the end of the manipulation and lets the manipulator finalize its state.  Manipulator is an abstract base
       class.  Subclasses support different manipulation semantics.

MANIPULATOR PUBLIC OPERATIONS

       virtual void Grasp(Event&)
	      Grasp is called once at the beginning of direct manipulation to allow the manipulator to initialize its internal state based on  the
	      initiating event.

       virtual boolean Manipulating(Event&)
	      Manipulating is called repeatedly during the manipulation whenever a new event arrives, until it returns false.  Each call to Manip-
	      ulating should produce a new frame of the animation that characterizes the manipulation.

       virtual void Effect(Event&)
	      Effect is called once at the end of direct manipulation to allow the manipulator to finalize its internal state based  on  the  last
	      event supplied to the Manipulating operation.

       virtual void SetViewer(Viewer*)
       virtual Viewer* GetViewer()
       virtual void SetTool(Tool*)
       virtual Tool* GetTool()
	      Get and set the viewer, in which the manipulator generates graphical output, and the tool that created the manipulator.  These oper-
	      ations do nothing by default; subclasses that require this information must redefine these operations to	assign	and  retrieve  the
	      state they require.

MANIPULATOR PROTECTED OPERATIONS

       Manipulator()
	      The constructor is protected to disallow instantiation of abstract base class objects.

SEE ALSO

       Event(3I), Tool(3U), Viewer(3U)

Unidraw 							   1 August 1990						   Manipulator(3U)