I'm setting up a rather large scene and am exploring ways to speed up IFD compilation. In the past I have been warned not to use too many materials as they each take time to compile. Is this still true with the principled shader? If so would it be faster to use just a few materials but override their parameters per object? Are there any other tricks to handling large scenes that I should be aware of?

When creating IFD's, materials need to compile and I use UDIM whenever possible. I think that more important here is to convert your textures to .rat, otherwise, this will happen internally and I think for every frame of the IFD. I just use a simple batch script that takes in all my textures and turns them into .rat with iconvert and then changes the extensions in the shaders. I also make sure that the geometry is instanced where possible, packed and saved to disk correctly and that when you are ready to write your IFD's you on the display on your file node to bounding box only. Once all this is in place and I write out IFD's, the speed is much faster as well as the file size reduction is ridiculous.

One major thing to be aware of when writing out IFD's is to make sure that you have your shader setting to output all shaders in the ifd, the default won't and you get scenes with the default shader. As well, I think that if you have any rendering effects, Caustics, SS or dielectrics you need to have “Allow all Paths” on the drop-down menu on.

I would love to hear anyone else IFD thoughts…

from artist point of view, go with many materials, overrides are not very user friendly then you open scene in two months or give it to someone else.

I was given scenes where artist used one material with million of overrides. i would break his keyboard if i could.

And definitely big plus for using RAT files. You can easily kill your IFD machines with loading ton of textures that are not RAT files. Dont understand why after so many years mantra still flush all converted textures and converts them every single frame. super slow and super annoying. They should save them as files, similar to Arnold does with TX files.

Thanks guys. Good to know about the .rat file conversion, considering the number and size of the textures I'm dealing with that is probably a considerable factor. I'm already using disk primitives wherever possible and it was still taking me about 30min to compile my IFDs. Hopefully this will cut that down a good bit though.

let us know if RAT helped.
I discovered this bottle neck the hard way

Wow. Yeah IFD generation time just dropped from 10min to 2min. Thanks for your help guys!

glad it helped