I have a scene where I'm using a geometry node's backfaces input to mix two shaders. I like the fact that the camera can only see the inside walls of my object (as it is rendering backwards normals), but there are a few issues.

I would like the front-facing normals that the camera can't see to be rendered, and the backwards facing normals of faces the camera can see to not be rendered (as they influence other objects). I have rerouted all rays except the camera rays from before the front faces are cut-out and frankensteined them back on to only the camera rays of the image after the operation so that I can preserve the caustics coming from the correct area.

This shows my nodes and image

The main problem I need to solve now is the fact that the backfaces of the faces closest to the camera are rendering and casting a shadow on the object in the center of the cube.

The second image with some doodles

The red arrows in the second pic show the light coming from the part the camera can't see reflect on the center object. The blue arrows show what actually creates the reflection of the cube sense the backfaces of what the camera CAN see are transparent. Although in the image, the bottom of the cube is being reflected due to my node work-around. I still would like to make it so the backfaces of the faces being deemed transparent to not render. Any help is appreciated!

  • $\begingroup$ Okay, so perhaps another way of doing it is to use the Ray length output on the light path node rather than the backfacing output. The only problem is I don't know the correct combination of math nodes and camera-data nodes to make that work. I'd use ray length as a mix factor and also mix in camera data somehow. If anyone knows how to do this, I'd be very appreciative. $\endgroup$
    – Kext Next
    Feb 1 at 20:58

Okay... I plugged in the camera data node's view distance socket and the light path node's ray length socket into a math node set to compare. The epsilon value is set to .2. I achieved an effect that is good enough, but still not perfect. The transmission, reflections, and light on the floor is correct, although the inside backfaces still cast a shadow+reflect teal light on the question mark. If anyone can help with that, it'd be perfect, but otherwise I'll probably close this question soon.


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