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I'm currently modeling a bedroom scene that has very thin curtains over each side of the window. I'm able to make them transmit light from the back side with no issue, however they either cast no shadow or full black shadow.

The curtains are wavy/folded like you'd picture curtains being, and the light is hitting them from an angle that should allow for a shadow to be cast that still shows those folds with a variable density of shadow on the walls/floors.

I've tried editing everything I can think of in the material, combining my Principled BSDF and a Translucent BSDF (as well as trying Transparent) but can't get the shadows to act anywhere close to how they should. I'm using Cycles.

Has anybody successfully created an overlapping translucent shadow before, and how did you do it?

Thanks for the help!!

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    $\begingroup$ Hi :). Could you please add some images comparing your result with real curtains? Thanks. $\endgroup$
    – jachym michal
    Commented Nov 23, 2021 at 22:36

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Using a Mix Shader with Transparent BSDF gets us the shadows we want, but also affects the object's shading in a way we don't want.

enter image description here

We can fix this using the Light Paths node. The Is Shadow Ray output can be used as the Factor of the Mix Shader.

enter image description here

You can use the color values of the Transparent BSDF to control how much shadow appears.

enter image description here

Areas with many folds like the dark areas you can see leftover may require more Total and Transparency bounces under Render Properties -> Light Paths -> Max Bounces.

enter image description here

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  • $\begingroup$ Thank you so much for your response! I could have sworn I've tried this exact thing, though. Let me go follow these instructions real quick and see with what I can come up. Yeah, I absolutely have tried exactly this prior to asking my question. However, I never gave it a test render outside of the viewport, and have only viewed it very grainy-ly. I think that, combined with the fact that my light source isn't hitting at hard enough of an angle to get that result is why it looked incorrect. Thanks again for your response and help!! $\endgroup$
    – Bugiboop
    Commented Nov 24, 2021 at 13:27
  • $\begingroup$ @Bugiboop glad I could help $\endgroup$
    – Allen Simpson
    Commented Nov 24, 2021 at 14:41

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