#!/usr/bin/env python

# Create the RenderWindow and Renderer
ren1 = vtk.vtkRenderer()
renWin = vtk.vtkRenderWindow()
renWin.AddRenderer(ren1)
renWin.SetAlphaBitPlanes(1)
iren = vtk.vtkRenderWindowInteractor()
iren.SetRenderWindow(renWin)
# create a default polygonal sphere
sphere = vtk.vtkSphereSource()
sphmapper = vtk.vtkPolyDataMapper()
sphmapper.SetInputConnection(sphere.GetOutputPort())
sphactor = vtk.vtkActor()
sphactor.SetMapper(sphmapper)
# Add the actors to the renderer, set the background to initial
# color (which is also transparent), set size.
ren1.AddActor(sphactor)
ren1.SetBackground(0.1,0.2,0.4)
renWin.SetSize(256,256)
# render first image
renWin.Render()
if (0 == renWin.GetAlphaBitPlanes()):
    print "Failed to find a visual with alpha bit planes."
    exit(0)

    print "GetAlphaBitPlanes: " + renWin.GetAlphaBitPlanes()
    pass
# create window to image filter, grabbing RGB and alpha
w2i = vtk.vtkWindowToImageFilter()
w2i.SetInput(renWin)
w2i.SetInputBufferTypeToRGBA()
# grab window
w2i.Update()
# copy the output
outputData = w2i.GetOutput().NewInstance()
outputData.DeepCopy(w2i.GetOutput())
# set up mappers and actors to display the image
im = vtk.vtkImageMapper()
im.SetColorWindow(255)
im.SetColorLevel(127.5)
im.SetInputData(outputData)
ia2 = vtk.vtkActor2D()
ia2.SetMapper(im)
# now, change the image (background is now green)
sphactor.SetScale(2,2,2)
ren1.SetBackground(0,1,0)
# add the image of the sphere (keeping the original sphere too)
ren1.AddActor(ia2)
ren1.SetViewport(0,0,1,1)
# render result (the polygonal sphere appears behind a smaller image
# of itself).  Background of original image is transparent, so you
# can see through it back to the larger sphere and new background.
renWin.Render()
# prevent the tk window from showing up then start the event loop
outputData.UnRegister(None) # not needed in python
# --- end of script --
