[vtkusers] Enable depth peeling after initialization

[Ignacio Fernández Galván]

Hi all,

I'm trying to enable depth peeling with VTK. Currently my goal is using 
it with Mayavi and python. My problem, and a sample code, is in 
https://stackoverflow.com/questions/47738246/depth-peeling-in-mayavi.

I think the reason is that depth peeling must be enabled before 
initializing the window, but Mayavi initializes the window as soon as it 
is declared, so changing the settings after does nothing. Consider the 
following simple, pure VTK, code:

#=============================================================
import vtk

init_before = True

ren = vtk.vtkRenderer()
renWin = vtk.vtkRenderWindow()
renWin.AddRenderer(ren)
ren.SetBackground([.2, .2, .2])

if init_before:
   # create a renderwindowinteractor
   iren = vtk.vtkRenderWindowInteractor()
   iren.SetRenderWindow(renWin)
   iren.Initialize()

# enable depth peeling
ren.SetUseDepthPeeling(1)
ren.SetOcclusionRatio(0.1)
ren.SetMaximumNumberOfPeels(100)
renWin.SetMultiSamples(0)
renWin.SetAlphaBitPlanes(1)

if not init_before:
   # create a renderwindowinteractor
   iren = vtk.vtkRenderWindowInteractor()
   iren.SetRenderWindow(renWin)
   iren.Initialize()

# create source
source = vtk.vtkCylinderSource()
source.SetCenter(0, 0, 0)
source.SetRadius(5.0)
source.SetHeight(7.0)
source.SetResolution(100)
source.Update()

# mapper
mapper = vtk.vtkPolyDataMapper()
mapper.SetInputData(source.GetOutput())

# actor
actor = vtk.vtkActor()
actor.SetMapper(mapper)
actor.GetProperty().SetOpacity(0.5)

# assign actor to the renderer
ren.AddActor(actor)
ren.ResetCamera()

# enable user interface interactor
renWin.Render()
print ren.GetLastRenderingUsedDepthPeeling()
iren.Start()
#=============================================================

With init_before=False I get that depth peeling was used, but not with 
init_before=True.

Is there anything I can do to force and update of the render window to 
pick up the new settings? I tried iren.Reinitialize() to no avail. The 
only way I could find was removing renWin and iren and creating new 
ones, but that doesn't help with Mayavi.

Thanks,
Ignacio