[vtkusers] How do I render a volume from an UnstructuredGrid?

[Ruff]

I've created an unstructured grid and would like to volume render it's scalar
values, but nothing is rendered.
It seems like it is calculating the space I've specified but I cannot see
anything. Like I'm missing some small obvious thing.

I also tried setting a function to the mapper (Not that I know exactly what
it does) but it doesn't seem to do anything.

/I know that my current dataset could easily be used as structuredPoints,
but I am planning to use a more arbitrary structure for the datafiles./

The code is as follows:
#!/usr/bin/env python

import math
from random import*
from vtk import*

#------------------------------------------------------------------#
# Just generating a pretty pattern                                 #
#------------------------------------------------------------------#
cubeSize = 40
atomIndex = 0
coordinates = vtk.vtkPoints()
scalars = vtk.vtkFloatArray()

for z in range(0,cubeSize):
	for y in range(0,cubeSize):
		for x in range(0,cubeSize):
			distX = abs(cubeSize/2 - x)
			distY = abs(cubeSize/2 - y)
			distZ = abs(cubeSize/2 - z)
			dist = math.sqrt(distX*distX + distY*distY + distZ*distZ)
			
			coordinates.InsertPoint(atomIndex, x, y, z)
			scalars.InsertValue(atomIndex, abs(math.cos(dist*.1)*255))
#------------------------------------------------------------------#
# Done generating pretty pattern                                   #
#------------------------------------------------------------------#

#Setting up scalar grid
ScalarGrid = vtk.vtkUnstructuredGrid()
ScalarGrid.SetPoints(coordinates)
ScalarGrid.GetPointData().SetScalars(scalars)

#------------------------------------------------------------------#
# Fixing a bunch of volume properties                              #
#------------------------------------------------------------------#
# Scalars (0-255) mapped to transparency
opacity = vtk.vtkPiecewiseFunction()
opacity.AddPoint(150, 0)
opacity.AddPoint(255, 1)

# Scalars (0-255) mapped to colors
colors = vtk.vtkColorTransferFunction()
colors.AddRGBPoint(0,1,1,1)
colors.AddRGBPoint(230,0,1,0)
colors.AddRGBPoint(250,1,0,0)

# Colors and opacity goes into a property, along with some fancy stuff
volumeProperty = vtk.vtkVolumeProperty()
volumeProperty.SetColor(colors)
volumeProperty.SetScalarOpacity(opacity)
volumeProperty.ShadeOn()
volumeProperty.SetInterpolationTypeToLinear()

#------------------------------------------------------------------#
# End of volume properties                                         #
#------------------------------------------------------------------#

# Mapping the grid
volumeMapper = vtkUnstructuredGridVolumeRayCastMapper()
volumeMapper.SetInput(ScalarGrid)
#This seems to do nothing at all
Function = vtk.vtkUnstructuredGridBunykRayCastFunction()
volumeMapper.SetRayCastFunction(Function)

# Volume using the mapper
volume = vtk.vtkVolume()
volume.SetMapper(volumeMapper)
volume.SetProperty(volumeProperty)

# Standard renderer, render window and interactor
ren = vtk.vtkRenderer()
ren.AddVolume(volume)
ren.SetBackground(1, 1, 1)

# =======THIS IS WRITTEN ONLY TO SEE THAT SOMETHING IS RENDERED=======
cylinder = vtkCylinderSource()
cylinderMapper = vtkPolyDataMapper()
cylinderMapper.SetInput(cylinder.GetOutput())
cylinderActor = vtkActor()
cylinderActor.SetMapper(cylinderMapper)
ren.AddActor(cylinderActor)
# =====================================================================

renWin = vtk.vtkRenderWindow()
renWin.AddRenderer(ren)
renWin.SetSize(600, 600)

iren = vtk.vtkRenderWindowInteractor()
iren.SetRenderWindow(renWin)
iren.Initialize()
iren.Start()




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