Iray material conversions - is there a basic flaw, or am I doing it wrong?

SpottedKitty

Anyone else had problems like this in converting D|S materials from 3Delight to Iray?

I've been experimenting with a number of different old prop and scenery sets since 4.8 came out of beta, and tonight it was the turn of Blondie9999's very nice Entry Guardian statues. The Granite and Iron materials look good in 3Delight, so I re-saved everything as proper D|S4 files and started converting the materials.

It so very much didn't work. All the statue parts have a pretty sharp displacement map applied, and the Bench and Pedestal props all have large flat low-res blocks. All the detail on those displacement maps was completely lost, even when I turned the SubD settings up until D|S crashed hard and took about five minutes to give me back control of my frozen solid computer.

Take two, I re-loaded everything and shifted all the displacement maps to the bump channels, then applied the Iray Uber Base shader. This time, everything came out smooth as a billiard ball. All the fairly high-contour settings I'd transferred to the 3Delight bump channels had been squashed down into a value of 0.15. (What is that, exactly? 0.15mm? 0.15cm?) I had to crank the values all the way up to the limit of 50 before I could see the details the same as I'd done in my 3Delight test renders.

Anyone else been bitten by the Iray Bump channel's lack of proper min/max settings? I have good material saves now, just needing a bit more specular tweaking, but I think I could have done it in a fraction of the time if the conversion process had fewer speedbumps (pun, in this case, intended). There were so many things I had to dig out and fix manually after the auto-conversion was done.

mjc1016

Maybe converting/generating normal maps may give better results than the bump?

Also, make sure the maps are true black/white, as Iray is much more picky about them...

SpottedKitty

There's nothing actually wrong with the displacement maps (I think) — those two renders I posted are after I'd figured out what was going wrong and transferred all the settings from the original displacement parameters. It's the conversion-to-Iray process I'm not sure about; as I said, a plain application of the Iray base left me with billiard balls instead of properly bumpmapped meshes, I had to go up to the limit to get a good bump showing in the render. How far can I go if I need to boost the bump value up past the default limit? What do I do if the original 3Delight material has both bump and displacement?

I just noticed what you said about generating normal maps. I've come across mentions of this a few times in the forums over the years, what's the best way to do it?

mjc1016

Best...baking them from a very high res version of the model.

Next best...GIMP or Photoshop plugin.

If the maps aren't true black (0,0,0) black then the range of the map limited, as if you are cutting back the min/max values by a certain amount.

As to starting out...3DL handles displacement better than just about anything else around, because of the way it subdivides the mesh...and how much/when it does so. This means you get a lot finer displacement at a lower memory cost. In Iray, you need to set the level...and on fairly low poly models, you can run out of memory before you get things divided fine enough (that's what your major slow down was...everything was trying to swap out to your hard drive, because you ran out of RAM).

Now, I wonder if you would get a little more 'wiggle room', if you added SubD before you converted it to DS native...

jpb06t

mjc1016 said:

3DL handles displacement better than just about anything else around, because of the way it subdivides the mesh...and how much/when it does so.

3delight does microdisplacement (you can get a wonderfully chiseled surface out of a single quad) but Iray displaces only existing vertices so it is a question of either giving it hi-ish poly models or subdivide them inside Studio.

I think that, if you are satisfied without your mesh profile resolution, normal maps are a much better way to handle things in Iray.

mjc1016

latego said:

mjc1016 said:

3DL handles displacement better than just about anything else around, because of the way it subdivides the mesh...and how much/when it does so.

3delight does microdisplacement (you can get a wonderfully chiseled surface out of a single quad) but Iray displaces only existing vertices so it is a question of either giving it hi-ish poly models or subdivide them inside Studio.

I think that, if you are satisfied without your mesh profile resolution, normal maps are a much better way to handle things in Iray.

That's not all 3DL does...it's also the way it does it and when.

mrposer

Try setting the SubD Displacement Level to 2 in the edit shader listing after applying the Iray Uber Base Shader.... that helped me with FW Dan's dogtags to get the engravings to show up in Iray.

SickleYield

I often apply SubD to the model itself as well, if it doesn't have it already (a lot of props don't). If it wasn't made for that use you might also have to set the subD to Legacy and/or turn off Smooth in the Iray material.

SpottedKitty

Thanks for the tips, everyone, I'll have a go at them when I have the time to mess around with parameter settings.

After a bit of thinking, I've decided I will bug-report this after all as a "basic flaw" — the displacement maps work perfectly when I transfer them to the bump dials, the problem is that the bump values are 15% of +/- 5cm. The auto-conversion to Iray picks this up as a Base Bump value of 0.15 — ignoring the actual min/max values, hence the Iray billiard balls, and the need to push the value up to 50. I'd like to hope it's not supposed to work this way.

Does anyone know why there isn't a Bump min/max value for Iray? Is it something NVidia didn't consider necessary?