Some materials are shown dark in their thumbnail and render as the default white material, but not due to missing link

[Anonymous]

Hi,

since one of the last two builds I sometimes run into the problem that my materials are being weirdly displayed in their thumbnail (very dark, also the shading ball background oddly). The textures are linked fine, but the thumbnail does not update when doing any changes, also when rendering every material is just plain white:

This happens to me exclusively with plugin textures, for example with the Greyscalegorilla Arnold Shader pack and the standard forester materials after converting them to Arnold materials.

Do you have any idea what might cause this?

[peter.horvath6V6K3]

Haven't seen this before. I suppose it happens randomly and not really reproducible. Does it render fine after you reopen the scene? Can you send me a log with debug verbosity level when this happens? And a log when everything's fine, so I can compare the two.

[Anonymous]

So it turned out the solution to this was rather simple - reloading the textures in the bitmap shader made everything look normal again. I was confused at first since the material didn't display a missing texture and also didn't have the red error frame around it, I guess the texture was only half loaded - maybe the original link goes to a different location and after reloading it finds the location that I have assigned in my asset paths, or something like this

[Anonymous]

What is a bit weird though, is that I have the same problem with a standard glass shader that does not have any bitmap inputs and is purely procedural, I don't know what to do about this one - but at least it renders fine in the end, only the thumbnail is darkened and doesn't update

[peter.horvath6V6K3]

Not sure. If it was a texture error there should be some entries about it in the log. Anyway, if it happens again, just let me know and I'll investigate a bit.

[peter.horvath6V6K3]

Is it reproducible? I mean does the thumbnail render dark even after you restart Cinema 4D? If so you can send me the scene to take a look? What if you copy & paste the material to a new scene?

[Anonymous]

Sorry, I just saw I had forgotten to answer -

so the bug persists after reopening or copying to a new scene. And the log would not really be of any value as it is always rendering dark for me, there is no occasion when it doesn't.

I am pretty sure it has to do with the materials being set up in an older Arnold version, as it only happens with material packs that I had purchased, that have been from 2018 or so

[Anonymous]

Would it be helpful if I sent you a scene with one of the materials? I mean I am of course not supposed to share them as they are commercial, but sending it to you as a developer would probably be an exception to this

[peter.horvath6V6K3]

Don't think it's a version issue. If you use the default preview scene (e.g. Arnold Sphere), it should be fine since they are shipped with the latest version.

Would be great if you could send me a scene with a material to look at. I'm sure it should be fine. Just send it to support(at)arnoldrenderer(dot)com please.

[Anonymous]

I have just sent you a scene file via mail. I actually found a material that wasn't from a library, but also rendered dark, so I attached a few materials now, it'd be interesting to see if they are also showing up dark for you

I hope the file wasn't too large for the mail it was 14MB in size, let me know if it came through

[peter.horvath6V6K3]

When I open the scene, the previews are dark, so this is the state when you saved the scene. As soon as I change something in the material, it rerenders and the preview looks fine. Except one material, which I guess uses a custom preview scene, so I have to select one of the builtin scenes there (right click on the thumbnail, select Arnold Sphere), but then it renders fine.

Dark preview usually means that the default C4D preview scene is used and not an Arnold specific one. Either the Arnold specific scene can not be found or is corrupted somehow.

[Anonymous]

Hi Peter, thank you so much for looking into it.

Do you have any idea how this could happen? I mean I understand the problem with shaders that uitilize bitmaps, but I also have the problem with atmospheres, gobos and standard surfaces without bitmaps, which really strikes me as very odd (I think I sent you the one called "blinn1" which also renders black for me). And for me, changing the sliders doesn't help for any of these materials unfortunately

I use several instances of Cinema on the PC, could this be the cause of the problem? Or some admin access rights thing?

[peter.horvath6V6K3]

The scenes are installed to the C4D\library\materialpreview. Make sure they are there and readable. Otherwise I'm not sure how this could happen.

Yes, you sent me the "blinn1" material, it renders fine when I change any parameters.

Does this started to happen after you installed a third-party material library?

[Anonymous]

Ok, I will see if I find anything, though I don't remember changing anything and it always worked perfectly fine before

Yes, I think it started after installing the Greyscalegorilla Arnold Pack