Function which allows shifting 3D Slicer volume rendering scalar opacity transfer function similar to "Shift" slider in Volume Rendering module

shiftVolumeRenderingGist.py

def shiftVolumeRendering(volumePropertyNode, xOffset=0):
  """ Shift the scalar opacity control point values by an 
  offset value (similar to moving the "Shift" slider in the volume rendering module)
  """
  volProp = volumePropertyNode.GetVolumeProperty()
  scalarOpacity = volProp.GetScalarOpacity() # this is a vtkPiecewiseFunction
  pointIdx = 0
  opacityPointValues = [] # list to hold values
  # Gather Existing Values
  for pointIdx in range( scalarOpacity.GetSize() ):
    opacityPointValue = [0,0,0,0]
    scalarOpacity.GetNodeValue(pointIdx, opacityPointValue)
    # opacityPointValue now holds [xLocation, opacity, midpoint, sharpness] for this control point
    opacityPointValues.append(opacityPointValue) # store values in a list
  # Add offset
  for opacityPointValue in opacityPointValues:
    opacityPointValue[0] = opacityPointValue[0] + xOffset # change the location value (leave all others unchanged)
  # Set new values (not sure if there is any way to batch these?)
  scalarOpacity.RemoveAllPoints()
  for opacityPointValue in opacityPointValues:
    scalarOpacity.AddPoint( *opacityPointValue )
  # Trigger updates (not totally sure if this is necessary or not)
  scalarOpacity.Modified()
  
# Example usage
volumePropertyName = 'CT-AAA' # change this to whatever volume property name you are using
volPropNode = slicer.util.getNode(volumePropertyName)
amountToShiftBy = 100
shiftVolumeRendering(volPropNode, amountToShiftBy)