Developing interactors

Defining an interactor involves deciding the interaction style you need, the interaction feedback you want, the command to execute, and using the correct GrafEdit interaction classes for your purpose.

Interaction style

• Drag interactor (TCanvasDragInteractor): Interaction begins with a mousedown event, ends with a mouse-up event, and move events between the mouse-down and mouse-up events.
• Multiclick interactor (TCanvasMulticlickInteractor): Interaction begins with a mouse click, ends with a double click, and includes any number of mousedown events between the first mouse down and the double click.

Interaction feedback

• TCanvasLineDragInteractor draws a rubber band line from the point of mouse down to the current cursor location and erases the rubber band when the interaction ends upon mouse up.
• TCanvasPolylineDragInteractor draws a polyline starting with the point of mouse down and passing through each point of the mouse move during interaction. It erases the polyline when the interaction ends upon mouse up.
• TCanvasRectDragInteractor draws a rubber band rectangle starting with the point of mouse down to the current cursor location, and erases the rectangle when the interaction ends upon mouse up.
• TCanvasPolylineMulticlickInteractor draws a polyline starting with the first click, passing through each point where the mouse clicks during interaction, draws an additional rubber band from the last click point to the current cursor location, and erases the polyline and rubber band when interaction ends upon double click.

Action

Command creation and execution

  virtual void AdoptAndDo( TToolCommandBinding* );
  virtual void DoBegin( TToolCommandBinding& );
  virtual void DoIncrement( TToolCommandBinding& );
  virtual void AdoptAndDoEnd( TToolCommandBinding* );

The TToolCommandBinding parameter binds the command to its target. It is constructed from the command and the target. This binding is always adopted in the last function call, AdoptAndDo for a single command or AdoptAndDoEnd for an incremental command. The interactor class forgets about the binding, command, and target after adopting them because storage responsibilities are transferred to the interactor's base class.

For example, TCanvasLineCreationInteractor, which is provided in GrafEdit, derives from TCanvasLineDragInteractor. TCanvasLineCreationInteractor needs two implementations:

• A constructor that takes a tool target and a tool handler and passes these into the constructor of the Document framework class TLineDragInteractor.
• An EndInteraction function with a command to adopt a line into the canvas.

  void
  TCanvasLineCreationInteractor::EndInteraction()
  {
      if( GetNumberOfPoints() > 1 ) {
          TGPoint firstPoint = GetFirstPoint();
          TGPoint lastPoint = GetLastPoint();
  
          if( fTarget && firstPoint != lastPoint ) {
              TGLine line( firstPoint, lastPoint );
              TCanvasLine* theLine = new TCanvasLine( 1ine );
  
              TAdoptCanvasGraphicCmd* cmd = new TAdoptCanvasGraphicCmd( theLine );
              AdoptAndDo( new TToolCommandBindingTo < MCanvasSelection > ( cmd,
                  fTarget() ) ) ;
          }
      }
  }