[vtkusers] How to get detailed information of a point after moving in vtkChartXY

[Zhang Chuanting]

Hi, everyone:
Now I am using VTK 5.10 to implement a GUI color and opacity transfer function editor. I found a test in VTK called "TestControlPointsHandleItem.cxx" which can basically meet my requirment in the website of http://vtk.org/gitweb?p=VTK.git;a=blob;f=Charts/Core/Testing/Cxx/TestControlPointsHandleItem.cxx. 
In the test, I add 3 points:
  vtkNew<vtkPiecewiseFunction> opacityFunction;
  opacityFunction->AddPoint(-3024, 0, 0.5, 0.0 );
  opacityFunction->AddPoint(217, .68, 0.33, 0.45 );
  opacityFunction->AddPoint(3071, .80, 0.5, 0.0);


  vtkNew<vtkColorTransferFunction> colorTransferFunction;
  colorTransferFunction->SetColorSpaceToRGB();
  colorTransferFunction->AddRGBPoint( -3024, 0, 0, 0, 0.5, 0.0 );
  colorTransferFunction->AddRGBPoint( 217, .88, .60, .29, 0.33, 0.45 );
  colorTransferFunction->AddRGBPoint( 3071, .83, .66, 1, 0.5, 0.0 );


the rendering effect is as follows:
I can select any point of these 3 points and move it to other position. My question is: how to get the detailed information (scalar value, opacity value and RGB value) of a point after moving. I want to get these value and then update the rendering effect of my medical images.


Thanks a lot.
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