Cast shadows of objects hidden by section plane

For example: if I use a section plane to show the interior of a house (and if I have shadows enabled), the sun will stream into that space as if the exterior wall doesn’t exist. This impacts daylight studies. And I suspect the current behavior isn’t often useful.

I suggest having an option in the section plane, or the object casting the shadow, or perhaps a global toggle. Maybe even just change the default behavior.

I’m aware of a workaround involving transparent PNG textures. I haven’t tried it, but it seems like a hassle.


Hear, hear. or word, or whatever they say.

A transparent plane over 70% will block the light but still allow visibility, I assume the workaround you mention. (second image on right)
Another option is available with Thea Render, which will respect the normal lighting in a scene despite a section plane in place. ( 1st image )

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Yeah, I’ve been working on some sections with Thea render and it’s pretty cool, you get lighting, reflections and all as if the rest of the room is still there.

I remembered that you could also play with the effect you get by painting one side of a face with an opaque and the other with a transparent material, but unfortunately it doesn’t work. Shadow casting is determined by the material that the sun rays encounter first, so what you see depends on the side you are looking at and how the material has been applied. From inside the space you either see paradoxically an opaque face that light passes through, or a transparent face that casts a shadow.

Thanks for the helpful responses. The first method (2nd picture) doesn’t really work with a double-faced wall – at 70% opacity it’s barely see-through. I did have success using a PNG texture extracted from the model linked in my original post – fully invisible wall which casts shadows.

Twilight Render also handles section planes this way.

I didn’t know that for Twilight Is that a special setting? Off hand it doesn’t seem to work (v. 2).

Actually, though I thought I remembered being able to do that in TWL, it seems I got it wrong. :man_shrugging:t2: (I just did a test with a model I’m working on and it renders section shadows just as SU itself does.)

Time to make a feature request over at the Twilight forum, I guess!