What is the "arnold" product type, and why is it needed?

[paulgolter]

Hey all,

we are currently using arnold in houdini and there is some confusinion about the checkbox "Arnold Product Type".

We didn't find proper documentation what this arnold product type actually does, only a few scrambled bits and pieces here and there.

In this doc page it says it uses the "arnold drivers".

What does that mean? Because you can render an image with arnold via husk fine without this being turned on.

Some further observations that we made:

• Without setting the "arnold" product type some AOVs don't seem to render properly like P or N ?
• I have read somewhere that you need the "arnold" prodcut type to render multipart exrs with arnold? But husk is also able to save multipart exrs of an arnold render without this being turned on, so I am not sure if this info is just outdated.

So overall we are a confused what implications this "arnold" product type has and what limiations are running into it if we don't set this checkbox.

Could someone clear this up?

Cheers

Paul

[sebastienblor]

Hi, if I had to summarize this parameter it would be

• Without "arnold" type : husk is responsible for writing the images, it will create these images in the same way it does for other renderers. But then these images might have differences as compared to other arnold renders done in other packages or DCCs. For example, some metadatas might be different, some specific features, etc... might be missing. In particular, any of the arnold "driver" attributes will be ignored.

• With "arnold" type : arnold is responsible for writing the images, so it will render them exactly as when you render arnold files with kick in standalone, or when you render from Maya, etc... and it will consider all the arnold driver parameters.

So the difference between both is usually small, mostly on specific corner cases. From our point of view, it's better to use the arnold product type so that we can have all the usual arnold features, and have the same behaviour as in standalone. It makes sense to let a renderer own the images it renders out. We might end up enabling this attribute by default. At the moment, the main limitation is that, since husk doesn't "own" the output image, it cannot display it in MPlay. We're looking at whether we can support this.
I hope it answers your question.
Cheers

[paulgolter]

Hey @sebastienblor

Thanks for the answer. That certainly cleared up some confusion.

Especially that:

any of the arnold "driver" attributes will be ignored.

So for instance here:

Autocrop / multipart would simply be ignored if the arnold product type is not set.

Regarding what other features or limitations there are when not enabling the arnold product type is something we have to find out learning by doing i would assume, as there is no official list.

So I agree, it would definitely make sense to change the default value to 1 so arnold also owns the "writing the image" process, at least for any proper production rendering on the farm.