I'm trying to create an effect where a creature has a part of its body that's really thin and translucent, and the blurry silhouettes of the bones can be seen inside it when light is behind it.
In technical terms, this means I need to have an object where light rays can pass through it, but only if it's thin enough and there are no obstructions inside the object. Translucency, really. (NOT transparency or SSS.)
This is actually exactly what the Translucent shader does (I tested it, and it does exactly what I need), but that shader literally only has parameters for color and a normal map, making it practically useless unless I can find a way to intelligently mix it with the Principled BSDF node. I don't know why the Principled BSDF shader has no parameter for translucency. I mean, sure, SSS is basically the same effect as translucency in theory, so maybe the developers thought it would be redundant, but with SSS (or maybe it's just Blender's SSS), external obstructions between the SSS object and the light source just aren't as clearly visible as with the Translucency shader, and obstructions inside the the SSS object are completely invisible for some reason.
I could try to fake it with rough transmission, but I need a way to use the thickness of the mesh (or, in more technical terms, how far a light ray must travel to get from its entry point to its exit point in the mesh) to control the transmission, and I haven't figured out where to get that data. Using a hand-painted texture map to manually control the transmission looks like crap, because it just lacks the detail.
Does anyone have any ideas of how I could go about this?