Whenever a user is digitizing a polygon, he expects feedback when moving the cursor before actually adding a point, the system should ‘rubberband’ the position under the cursor and only add it to a collection of points after the user left-mouse clicks in the Window. Key to rubberbending in G/Technology is responding to three events :

1. CustomCommandHelper_Click
2. CustomCommandHelper_MouseMove
3. CustomCommandHelper_DblClick

CustomCommandHelper_Click

private void CustomCommandHelper_Click( object sender, GTMouseEventArgs e )
{
  if( this.PntCnt == 0)
  {
    this.PntCnt++;

    this.Idx = this.GeometryCreationService.AddGeometry( GTClassFactory.Create<IGTPolygonGeometry>(), StyleId);
    this.GeometryCreationService.AppendPoint( this.Idx, e.WorldPoint);
    return;
  }

  this.GeometryCreationService.AppendPoint( this.Idx, e.WorldPoint);
}

CustomCommandHelper_MouseMove

private void CustomCommandHelper_MouseMove( object sender, GTMouseEventArgs e )
{
  if( this.PntCnt == 0)
  {
    this.setGtStatusBar( "Click to start digitizing");
    return;
  }

  if( this.PntCnt == 1)
  {
    this.setGtStatusBar( "Click to add point");
    this.GeometryCreationService.SetDynamicPoint( this.Idx, e.WorldPoint);
    return;
  }
				
  this.setGtStatusBar( "Click to add point, Doubleclick to end");
  this.GeometryCreationService.SetDynamicPoint( this.Idx, e.WorldPoint);
}

CustomCommandHelper_DblClick

private void CustomCommandHelper_DblClick( object sender, GTMouseEventArgs e )
{
  this.PntCnt = 0;
}

Besides these 3 events, the following general code is used:

general code

private IGTApplication _GTApp = null;
private IGTApplication GTApp
{
  get
  {
    if( this._GTApp == null)
    {
      this._GTApp = GTClassFactory.Create<IGTApplication>();
    }

    return( this._GTApp);
   }
}

private IGTGeometryCreationService GeometryCreationService { get; set; } = GTClassFactory.Create<IGTGeometryCreationService>();

private void setGtStatusBar( string message)
{
  this.GTApp.SetStatusBarText( GTStatusPanelConstants.gtaspcMessage, message);
}

private int Idx { get; set; }
private const int StyleId = 5010;

The complete code can be downloaded from here.