How to use Greyscale Vertex to mix Displacement?

[rubberchicken]

I have a vertex weight map to isolate two mesh parts to apply a different image-driven vertex displacement to each part using only one UV. In Modo native, I simply assigned a part tag to each and dropped the texture maps into a group for each that adds to the same material group applied to each. But in Octane, everything has to be 1,000% more work. So I made a weight map and plugged this into the amount on a mix node and this into a vertex displacement node. I also tried this with the mix vertex displacement node. Both options result in a mix of both displacement maps on both mesh parts. If I solo the weight map, it looks correct, and if I plug the result into diffuse, it works correctly. I wasted ages trying every combination I could think of with this and trawling the inter webs to no avail.

Am I hooking this up incorrectly, or does this simply not work?

Ultimately, I made a quick texture map to replace the weight map, which works correctly.

[funk]

This is a plugin limitation. The modo plugin currently requires "load cage" to be enabled for vertex displacement, but unfortunately this removes vertex maps.

I don't know the exact details, but the plugin normally reads modo meshes in chunks, so the vertices aren't actually welded. This causes problems for vertex displacement (tearing).

When you enable "load cage", the plugin reads the complete cage (un-subdivided mesh) with vertices welded correctly. So we are basically using "load cage" as a workaround.

I'm pretty sure it's possible to remove the "load cage" requirement from the plugin, but Paul would need to talk to Foundry to figure it out.

[rubberchicken]

Ah OK. Bummer. What if you use a bake node between? Nope that seems not to work either. Every job I am trying Octane on I build first in Modo shader tree, fast, flexible and easy. Then rebuild in Octane for the materials that need it. octane might be a great engine but it could use a lot of improvement in Modo. Maybe I am rendering things differently than most people, I used to find annoying limits in Vray all the time as well.

Also, the 2022 release notes say disable load cage. If I have load cage on then I need to use Octane subD or it is facetted. octane SubD gives a different result to Modo so I did not go that way. Displacement seems to work with it off.

"4) The Octane Greyscale Vertex Attribute is not working for a mesh : make sure Kernel->Render Cache is disabled, and Live Geometry is enabled and Load Cage is disabled for the mesh."

[funk]

If I have load cage on then I need to use Octane subD or it is facetted. octane SubD gives a different result to Modo so I did not go that way.

That's right. If you use load cage, you only get an unsubdivided cage without any vertex map info (that includes vertex normals for smoothing, weight maps etc). You can use the Octane smoothing angle (which defaults to 89.0) if you don't want subdivision... or subdivide using "subdivide in Octane" (if your modo polys are subdivision/cc polys), or increase the vertex displacement node > subdivision level

Displacement seems to work with it off.

In some cases it may not be obvious it's not working correctly (eg on a single plane). If you have more polys (eg a sphere) it's obvious that each poly ends up tearing and getting subdivided individually

"4) The Octane Greyscale Vertex Attribute is not working for a mesh : make sure Kernel->Render Cache is disabled, and Live Geometry is enabled and Load Cage is disabled for the mesh."

Right, that's telling you that "greyscale vertex attribute" node only works with "load cage" disabled. You can see why this is a problem if we need "load cage" enabled for correct vertex displacement.

If your scene can get away with doing correct vertex displacement without "load cage" enabled (which I find unlikely), then we'd need to see it to figure out what's going on.

[rubberchicken]

Ah right, I should clarify that displacement is working without use cage enabled when I am using the image map rather than vertex map. If I use the vertex weight map without enabling cage then yes there is some polygon edge tearing.

[funk]

Ah right, I should clarify that displacement is working without use cage enabled when I am using the image map rather than vertex map. If I use the vertex weight map without enabling cage then yes there is some polygon edge tearing.

Tearing should still happen with an image map too, so I'm not quite sure why you're not seeing it.

EDIT: Unless you are using "texture displacement" instead of "vertex displacement"

[rubberchicken]

Definitely using vertex displacement. I can send you the scene privately if you are curious enough. But I have a working option so only for your curiosity

[funk]

Sure. I'd be interested to see it