Rendering object with alpha

I want to render two objects with the first overlaying the second with alpha, like the attached mock up. I think this might be possible by using compositing but I’ve not been able figure out how to make it work.
I’ve tried adding a glass effect to the outer object but I don’t want to add any distortion to the light passing through it.

overlay-test.blend (586 KB)


You can use Geometry to achieve this

That looks exactly what I need, what’s in side the “Inside” and “Outside” groups?

Whatever you fancy, actually. Geometry -> Backfacing makes so that you can assign different materials depending on where face normals point to.
For your object this would be Diffuse (Diffuse/Glossy mix) if object inside faces are being exposed and Transparent if seen from outside. I mixed in a bit of AO to give some lighter translucent look for the outside.

Thanks! It’s taking a while but some of this stuff is starting to make sense.

How you make that layout?

@Rosypeter In case you’re interested in node setup - Ctrl-H hides unused connections on selected node; Ctrl-G groups selected nodes - on N-tab in node editor you’ll find text fields you can rename the Group (Inside, Outside in the example above). Tab key ‘dives’ into selected group node and Tab or Shift-Tab lets you out again. Look at the N-tab where you can rename, reorder, add, delete inputs/outputs of the Group.