VTK: setting transparent renderer background

Question

I am allowed to define the backgroundColor of a renderer by calling

renderer = vtk.vtkRenderer()
renderer.SetBackground(0,255,0)

[![enter image description here][1]][1]

My question:

Is it possible to set the opacity of the background ?

You can see my problem (with multiple viewports) in my example image. I could get rid of this "cutting" by simply using transparent backgrounds...

thanks in advance!

You should post that as solution and accept it. – JohnnyQ Jan 19 '16 at 11:59 — JohnnyQ, Jan 19 '16 at 11:59

score 5 · Accepted Answer · answered Jan 20 '16 at 08:07

I finally found a solution :

you can set a layer for each renderer. Default is Layer 0 (not transparent). Everything greater than layer 0 will be transparent. But keep in mind to set at least a empty renderer (no volume or object) with a background-color on layer 0 to avoid ugly reflections.

renderer.SetBackground(255,255,255)
renderer.SetLayer(0)

# transparency layer
renderer.SetLayer(1)
renderer.addVolume(....)

Result:

score 4 · Answer 2 · edited Aug 12 '21 at 18:53

For those who want to use transparency in a screenshot.

render_window = vtk.vtkRenderWindow()
render_window.AddRenderer(renderer)
render_window.SetAlphaBitPlanes(1)  # Enable usage of alpha channel
...
w2if = vtk.vtkWindowToImageFilter()
w2if.SetInput(render_win)
w2if.SetInputBufferTypeToRGBA()  # Also record the alpha (transparency) channel
...

More details in this official vtk example.

Edit: In addition, if the above is not working (e.g. the background is transparent but the actors are white/not rendered properly), you can try to enable depth peeling.

Before the above code snippet you should add

# the renderer, as in the question
renderer = vtk.vtkRenderer()
renderer.AddActor(actor)
renderer.SetBackground(0,255,0)
renderer.SetBackgroundAlpha(0.2)  # add background opacity value
renderer.SetUseDepthPeeling(1)  # only works with current GPUs
renderer.SetOcclusionRatio(0.2)  # 0. is better, but much slower

You might also need to increase the maximum number of peels (default is 4). Check this VTK Wiki page for more details.

For some reason this makes my `vtkPNGWriter` object write everything almost transparently. Quite odd. Changing back to `w2if.SetInputBufferTypeToRGB()` corrects the transparency of the polygonal data, but makes the background opaque again. — Breno, Aug 05 '21 at 23:18

score 0 · Answer 3 · answered Sep 03 '21 at 07:19

0

for set background on vtkFullScreenRenderWindow function, you can use the File to find your ideal color.

answered Sep 03 '21 at 07:19

Mohammadreza Abdoli

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VTK: setting transparent renderer background

3 Answers3