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I am working on an automotive project and the client wants me to show a translucent model of a car on top of the engine assembly. The issue is with transparency layering of cycles. I know cycles is making it look the proper way but is there any hack to make it look like the result in the material preview?

Materal Preview Mode Material preview

Cycles preview Cycles

I have tried backface culling, but that does not work in this case. Is there any hack to do this in Cycles? Setting up view layers and doing this in compositing seems to be an overkill. This means I would have to set up Holdout layers and much more. Any simple hack for this??

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  • $\begingroup$ Do you have to do it in Cycles? Why not use Eevee because that's the engine for the material preview as well...? $\endgroup$ May 30, 2023 at 13:57
  • $\begingroup$ Well, the project is completely set up for cycles. And that quality is needed too. Rest of the shots are already rendered in cycles. $\endgroup$
    – Arun Babu
    May 30, 2023 at 13:59
  • $\begingroup$ I don't even see what you want to achieve. In the Material Preview there is only the cube slightly transparent, everything else seems opaque? By the way, translucency is not transparency. $\endgroup$ May 30, 2023 at 14:04
  • $\begingroup$ So the engine will come under the body where the cube is present. At present, cube is opaque. Only body has to be made semi transparent. Just faded on top of engine. $\endgroup$
    – Arun Babu
    May 30, 2023 at 14:40

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For Cycles, an Option would indeed be the compositor with one view layer for the car (shading without transparency/alpha - imho the Velvet BSDF does very well) and another layer for the motor.

The compositing is not that heavy:

enter image description here

With the two annotated sliders, you can fine-tune the 'fading' of Car and Motor separately.

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  • $\begingroup$ Thank you. This could also work. Will check this out! $\endgroup$
    – Arun Babu
    May 30, 2023 at 17:07
  • $\begingroup$ @ArunBabu I thought you said in your question this would be overkill? That's why I asked how exactly you want it, because I excluded this as possible solution. $\endgroup$ May 31, 2023 at 9:05
  • $\begingroup$ Hi. Finally I did it with compositing itself. I said overkill because there were a lot of background and foreground objects. So I had to set up holdout layers and all (which was a lengthy outliner cleanup and organisation) But if some hack was available for this, it wouldn't have been necessary. But it's fine for now. $\endgroup$
    – Arun Babu
    Jun 2, 2023 at 19:18
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If you use the Principled Shader for your materials, the Principled's Alpha value does quite a nice job of it:

Principled Alpha

To reproduce that with any other shader, you can simply mix whatever shader tree you have with a Transparent BSDF Shader:

Transparent BSDF

You can even have fun with it and add a little bit of flavor to your transparency:

fun transparency

To add backface culling in Cycles, you can mix the Geometry node's Backfacing data as a factor to another mix shader with transparent shader:

backfacing setup

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  • $\begingroup$ Hi thanks for the reply. I have tried this. Here in this case i actually don't want transparent objects to layer up. In eevee, apart from backface culling, there is a show backface toggle. That disables layering of transparency. Only first transparent layer is rendered. Is something similar available in cycles? A hack? $\endgroup$
    – Arun Babu
    May 30, 2023 at 15:06
  • $\begingroup$ You can recreate backface culling in Cycles yes, i added it in my answer. But it will not occlude frontfacing geometry that is behind (I.E. here the monkey's ears will remain visible even if "hidden" by the head, only the insides are). Editing my answer. $\endgroup$
    – L0Lock
    May 30, 2023 at 19:16
  • $\begingroup$ @L0Lock If backface culling in Eevee is okay for Arun, your Cycles version should be, too... Eevee's backface culling would show the opposite ear as well. $\endgroup$ May 31, 2023 at 9:02

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