[vtkusers] vtkColorTransferFunction

[Vishal Shah]

hi .  i have just started some development using vtk. i have to display an slc file, and provide 'user editable' transfer functions. 
  background: 
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i am using the following, and it works fine: 
      colTransFunc->AddRGBPoint (     0.0, 0.0, 0.0, 0.0); 
    colTransFunc->AddRGBPoint (    64.0, 1.0, 0.0, 0.0); 
    colTransFunc->AddRGBPoint (   128.0, 0.0, 0.0, 1.0); 
    colTransFunc->AddRGBPoint (   192.0, 0.0, 1.0, 0.0); 
    colTransFunc->AddRGBPoint (   255.0, 0.0, 0.2, 0.0); 
      opacTransFunc->AddPoint(  20,   0.0); 
    opacTransFunc->AddPoint(  255,  0.2); 
  this obviousy maps (0 to 255) to (0 to 1).  my understanding is that the 0 to 255 represents in xyz plane, distance of a point from the origin. so if i have a point at say 23, and its corresponding RGB is (1,0,0), that means i am telling the vtk renderer to color all 'innermost' points as red. 
  my questions: 
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1) is my understanding correct? 
2)isnt it wrong to hardcode 255? shudn't i be getting a 'range' for the given slc file? 
i tried: 
                  poly->ShallowCopy(reader->GetOutput()); 
        reader->Update(); 
        poly->GetScalarRange(Range); 
  where poly = vtkPolyData and reader = vtkSLCReader, but then i always get the range as (0 to 1). so then i will be mapping (0 to 1) to (0 to 1). that obviously does not give me correct results. 
3) after i figure out the correct mapping, how do i change the transfer functions? say i have sliders for red , green and blue each, when the user changes the slider, what should happen ? can you give an example of how the above mentioned functions should change ? 
4) do the solutions to the above questions also apply to the changing of opacity using vtkPiecewiseFunction? 
  thanks for your patience in reading the long list . hope to get some guidance soon. thanks again. 
  -vishal

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