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How do I make a box mesh whose interior is visible but exterior is invisible?

So, basically I have a hollow/open box mesh (basically, the box has an opening, 5 faces instead of 6) that I created in Blender. This mesh consists of two separate meshes put together in a single Blueprint. One mesh is the exterior of the box (created by letting all 5 faces be a flat plane mesh) and the other mesh is the interior of the box (same exact mesh as the first one but with it’s normals inverted/flipped).

Now, I want to make it so that the player (or any camera really) can only see the interiors of the box (interior mesh) if they are looking “into” the box (through the opening) or are standing inside the box itself. The interior should not be visible if you look at it from other angle (at any of the 5 faces). The exterior of the box should NEVER be visible. Basically, the exterior of the box should “isolate” the interior preventing it from being viewable from the “outside”.

The solution also needs to be multiplayer-friendly. Basically, if Player 2 is standing outside the box and Player 1 is overlapping the opening/standing inside the box. Player 2 should not be able to see the box or it’s interiors.

I hope you understand what I mean. Do you have any ideas of how this can be achieved?

Thanks!

Unless I’m miunderstanding what you are trying to do, it seems that a single-sided material applied to the internal faces should work.

@JeKyran You’re misunderstanding. If I apply a single-sided material to the interior mesh, then the interior will still be visible if the exterior mesh is invisible. As an example, if the exterior is invisible and the interior is using a single-sided material (and is visible) and I look at the left face of the box (while standing outside the box) I will still be able to see all of the faces of the interior mesh except for the left face.

What I want is for the exterior mesh to act as an “isolating mask” for the interior mesh where the box is invisible (exterior + interior) if looking at an exterior face but visible if looking at an interior face (that isn’t occluded by an exterior face).

I basically want the box to work like the “invisibility cloak” from Harry Potter:

but in this case the object inside the cloak/box does not need to be invisible (should just be able to view the insides when looking at an interior face).

Ah, I see. You could use a bump offset to fake the interior, but being able to enter the box makes that a non-starter.

This looks like what you’re trying to do:

That video shows exactly what I am looking for but unfortunately one of the comments on the video says “Cool effect but if you try to put something IN the cup - the effect fall apart.”, so it’s unfortunately not gonna work in this case.