Cycles emissive materials interact strangely with Rhino glass

Have a look at this file in raytraced mode.

_MrGlass.3dm (133.6 KB)

There is a cylinder with a cycles emissive material applied to it inside a conical “vase” with a Rhino glass material.

There are a few strange things going on.

  1. The cylinder is only visible through the glass, I can’t see any part of the material that sticks out beyond the glass. I assume that the material is acting like an invisible light source and is seen in its effects on other objects. OTOH I have seen blender videos where objects with emissive materials can be seen directly - they are glowing objects and aren’t “invisible”
  2. The rod’s brightness is related to its distance from the glass. The rod becomes darker the narrower the vase becomes.

I have a model that takes advantage of the second behavior and the effect is really good for what I’m trying to achieve.

but…

there are some cases where I want to have glass closer to a light source AND I want the light source to shine through this glass without becoming too dim. I actually have an outer shell that’s far from the glowing object and a “glass” supporting structure that closely wraps part of the glowing structure.

For most of the time the distance effect works for me but sometimes it works against me.

So I think I need to understand what is going on so I can do whatever it takes to get the effects that I want.

I think that Nathan replaces Rhino glass with a hand crafted cycles xml material when we switch to raytraced. @nathanletwory is this what happens? Are the nodes you use available anywhere? (like GitHub??)

If so then I could explicitly assign cycles xml materials to my objects and play about with the materials to see what I can achieve.

That is because your Cycles Emissive material has the Hide checkbox selected.

Not sure what is causing that. I’m guessing somehow shadow from the object with the glass material. I think the Cycles Emissive material should be set to ignore shadow rays.

No, I use a C# version of the material. The code for it is here: https://github.com/mcneel/RhinoCycles/blob/rhino-6.x/Shaders/RhinoFullNxt.cs

You can create your own Cycles XML materials using the GhShaderNodes Grasshopper plug-in. The GH definition I use for this is https://github.com/mcneel/RhinoCycles/blob/rhino-6.x/conversion/rhino_full_shader.gh , but you’re probably better off creating yours from scratch.

Thanks Nathan, I will look into those things.

If the darkening is due to the shadow rays and you change the material settings…

could you have it as a checkbox so I can use that feature when it helps me?

I might try using a texture to apply “heat gradients” to my material and then I wouldn’t need a hack (or a side-effect) to get the behavior that I want.

The emissive object that I’m modelling is glowing because it’s hot and some parts are colder than others. At least, that’s my head canon. The truth of the matter is that I lucked out with the darkening effect :wink:

Using Cycles + HDRI texture for illumination got me 90% of what I wanted with 0.001% effort. I suspect that the final 10% will take a bit more work.