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In my tests, Light Path -> Is Camera always seems to be 1.0, and Ray Depth always seems to be 0.0. I'm trying to have an object be invisible to the camera, only appearing through a glass object in the scene.

Background: This is because the scene has a background video, handled with motion tracking, and I need some semi-realistic refractions through a glass within the scene. I placed an object, matching the motion-tracked ground, under the object, with a frame uv-mapped to it, but it's obviously in 3-space and won't match the background properly, so I was trying to use only the refracted "light" through the object, and the rest be transparent to the camera (thus showing only the background video there). You can safely ignore my messy shader experiments in this screenshot -- but it does show the oddly-shaped mesh object on which a frame is uv-mapped

enter image description here

Ray depth 0? enter image description here

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Eevee has no real concept of rays. But in order to ease the workflow between Cycles and Eevee some of the outputs are supported in particular cases. This node makes it possible to tweak indirect lighting in the shader.

Only a subset of the outputs is supported and the ray depth has not exactly the same meaning:

  • Is Camera: Supported.
  • Is Shadow: Supported.
  • Is Diffuse: Supported.
  • Is Glossy: Supported.
  • Is Singular: Not supported. Same as Is Glossy.
  • Is Reflection: Not supported. Same as Is Glossy.
  • Is Transmission: Not supported. Same as Is Glossy.
  • Ray Length: Not supported. Defaults to 1.0.
  • Ray Depth: Indicates the current bounce when baking the light cache.
  • Diffuse Depth: Same as Ray Depth but only when baking diffuse light.
  • Glossy Depth: Same as Ray Depth but only when baking specular light.
  • Transparent Depth: Not supported. Defaults to 0.
  • Transmission Depth: Not supported. Same as Glossy Depth.

See https://docs.blender.org/manual/en/latest/render/eevee/materials/nodes_support.html

In your specific case you could use the compositor with multiple view layers to achieve the same results.

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  • $\begingroup$ In my tests, Is Camera is not equivalent to Cycles' functionality. For the above scene, it appears to be 1.0 everywhere. Ray Depth appears to be 0 everywhere. I might be using in invalid way of examining the outputs directly, but those seem to be the case. I am updating my post with an example screenshot where Ray Depth seems to be 0. $\endgroup$
    – Jaggz
    Jun 24, 2020 at 8:04
  • $\begingroup$ The support of this node is to easy the workflow when using cycles as your scene renderer, but have some indication when in material preview mode. Some outputs are supported in particular cases, but it cannot match exactly as EEVEE is a rasterizer and uses screen space effects. So yes it is not equivalent to Cycles functionality. If you want to achieve the described effect you can use the compositor. $\endgroup$
    – J. Bakker
    Jun 24, 2020 at 8:29
  • $\begingroup$ I wonder if we can get some technical information into the docs there -- about what's actually happening in Eevee with those items. Perhaps a more-detailed "advanced" section lower down. $\endgroup$
    – Jaggz
    Jun 24, 2020 at 9:21

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