Cycles: How to avoid shadows/reflection of an invisible object?

Hi @nathanletwory,

I hope you have an idea and can help me please - I need to show the housing (A+B) and to blend out the upper half part B so that the inner parts can be seen later. I tried an animated alpha value and the upper part B disappears. But at the visible part A the part B is still visible, maybe reflections or shadows or both. So, I did a test and make B as glass with IOR 1 and it’s still visible. Why blocks the glass material the environment? Do you have an idea to avoid it?

I am not sure I understand what I am looking for and what the problem is here. The image shows me the lid part is invisible.

The inner area should be bright like here:

I found the reason - it’s a shadow of an area light:

So the question is - how to avoid the shadow of invisible objects?

Hmm, I see colored shadows and light through alpha is broken.

There was an earlier report about metal, but it appears to be a bit more involved than just that. Added to RH-63279 Glass and transparent objects render incorrectly.

You can confirm it, great! Thank you for your help.

Who is fixing this issue? I would be glad if a quick fix would be possible since I’m in the middle of a project and it would help me to get the desired quality.

Hi Micha -

The bug report is public:


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Unfortunately I have already several items in progress that will take a bit more time before I get to this. Until then you are best of creating the effect in a postpro compositor. I’d do this in Blender by rendering in Rhino two frames:one with the lid on, one without the lid. Then do a cross fade in Blender video editor between the two.

Any other program would do too, but I have no idea about those.

@nathanletwory You are coding the plugin, right? Good to know. :+1: Do you think it will need days or weeks for a fix?

The problem is that blending two frames isn’t enough since the camera is moving during this time. I would need to render a sequence twice. Since the animation is quite complex I hoped this little task could be simple.

I indeed am the one to blame for Raytraced and Rhino Render in v7 and later.

I am currently working on these. At the moment I think these will be next. Note that these are the issues that are publicly visible. There are more on my list than what you can see, though.

If you want you can also see my current public todo list.

I understand.

(Maybe the shadow fix is easier done than other issues. :wink: )

Maybe easier, but I’m right now deep into debugging the CUDA kernel and switching branches for this tricky fix I’m working on is not going to make my work easier. And I need to get these done since they have been already on my list for a long time.

I wouldn’t mind if I had several hands and heads extra on my body, a few that didn’t have to sleep or eat. But unfortunately I’m just a normal(ish) human being.

Anyway, I’m trying to get to your issue ASAP.

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Good luck for all the tasks.

A workaround if on deadline can be to render two animations. One with lid and one without, and then do the blend in post.