Tool(3U) InterViews Reference Manual Tool(3U)
Tool - base class for tool objects
Tool is an abstract base class for objects that support direct manipulation of components. Tools employ animation and other visual effects
for immediate feedback to reinforce the user's perception that he is dealing with real objects. The user grasps and wields a tool to
achieve a desired effect. The effect may involve a change to one or more components' internal state, or it may change the way components
are viewed, or there may be no effect at all (if for example the tool is used in an inapropriate context).
Conceptually, tools do their work within viewers, in which graphical component views are displayed and manipulated. Whenever a viewer
receives an input event (such as a mouse click or key press), it in turn asks the current tool (defined by the enclosing editor object) to
produce a manipulator object. A tool implements its CreateManipulator operation to create and initialize an appropriate manipulator, which
encapsulates the tool's manipulation semantics by defining the three phases (grasp, wield, effect) of the manipulation. Moreover, a tool
can delegate manipulator creation to one or more of the GraphicView objects in the viewer to allow component-specific interaction. A
tool's InterpretManipulator operation accesses and analyzes information in the manipulator that characterizes the manipulation and then
creates a command that carries out the desired effect. If a tool delegated manipulator creation to a graphical view, then it must delegate
its interpretation to the same view.
virtual Manipulator* CreateManipulator(
Viewer*, Event&, Transformer*
virtual void InterpretManipulator(Manipulator*)
Operations that define how the tool reacts when it is used and its ultimate effect. The tool can defer manipulator creation and
interpretation to a GraphicView. This allows the same tool to behave differently depending on the component it manipulates.
CreateManipulator creates a manipulator that is appropriate for the tool. It receives the viewer in which the manipulation will
take place, an event with which to initialize the manipulator if necessary, and the coordinate transformation that maps canvas coor-
dinates into the subject's coordinate space. InterpretManipulator is called following manipulation and defines how to construct a
command that carries out the manipulation's desired effect.
virtual void SetControlInfo(ControlInfo*)
virtual ControlInfo* GetControlInfo()
Tools use a ControlInfo object to store information from which to build a user interface for engaging the tool. These operations
set and get the ControlInfo object. SetControlInfo does not delete the ControlInfo being replaced.
virtual Component* Copy()
Return a copy of the tool. Subclasses should redefine this operation to return an instance of their type.
virtual void Read(istream&)
virtual void Write(ostream&)
Read and write the tool's contents to a stream to support catalog operations. Read and write typically call first the corresponding
operations defined by their parent class, and then they read or write their class-specific state. Note that you must ensure that
the objects are read in the same order they are written.
virtual ClassId GetClassId()
virtual boolean IsA(ClassId)
GetClassId returns the unique class identifier for the Tool subclass, while IsA returns whether the instance is of a class or sub-
class corresponding to the given identifier. IsA typically checks the given identifier against the instance's own (as defined by
its GetClassId operation) and, failing that, calls its parent classes' IsA operation. All subclasses must redefine GetClassId and
IsA to ensure that their identifiers are unique and that instances are written and read properly.
Tool(ControlInfo* = nil)
The constructor is protected to prevent instatiation of the abstract base class. The ControlInfo object is optional, but only tools
that have no visible manifestion in the interface should omit it.
CopyControlInfo is a convenience function that subclasses may use in their Copy operation. It returns a copy of the tool's Con-
trolInfo object if it non-nil, simply checking for a nil argument before calling the corresponding Copy on the ControlInfo object.
Catalog(3U), Command(3U), ControlInfo(3U), Editor(3U), Event(3I), GraphicView(3U), Manipulator(3U), Transformer(3I), Viewer(3U),
classes(3U), istream(3C++), ostream(3C++)
Unidraw 24 January 1991 Tool(3U)