I have been working with 3 different Render Delegates and plugins: Karma, V-Ray, and Redshift. Of these 3, only Redshift seems to support the Edit Material Network LOP. Even simple shading graphs destined for Karma don't rebuild with it. And by simple I mean like a single Material Builder with a principled shader in it.

I guess I'm confused, because this was the case in 18.5, and I figured it was just early still, but this is happening in 19.0 and 19.5. And yet... Redshift material graphs still load fine inside an Edit Material Network LOP, in 18.5 and 19.0 (have not tested in 19.5 yet), while Karma ones do not.

Doesn't work with Vray either, but the easy reply there is "well it's not supported natively anyway, so..."

So I guess my main question is.... is the Edit Material Network LOP actually supposed to work with Karma VOP graphs? I understand the potential complexity issues, but again... I can't get this node to work with even the most basic materials.

Tim Crowson
And by simple I mean like a single Material Builder with a principled shader in it.

There's no network to rebuild. Material builders are translated to code snippets. You would need to use a materialX network or a principled shader with nothing connected to it.

Tim Crowson
So I guess my main question is.... is the Edit Material Network LOP actually supposed to work with Karma VOP graphs? I understand the potential complexity issues, but again... I can't get this node to work with even the most basic materials.

It does work, but there has to be a network to rebuild. Otherwise, it can only edit parameters.

In the case of a material network authored from Redshift shading nodes (whether in a RS Material Builder or not), it will rebuild the full network. If the target material is itself a Redshift Material Builder, it rebuilds its contents exactly.

In the case of native Houdini material network, I cannot get it to rebuild the network period, regardless of whether that network is inside a Builder or not. Same with V-Ray.

So what is it about Redshift networks that allows them to work when native networks do not?

Tim Crowson
In the case of a material network authored from Redshift shading nodes (whether in a RS Material Builder or not), it will rebuild the full network. If the target material is itself a Redshift Material Builder, it rebuilds its contents exactly.

In the case of native Houdini material network, I cannot get it to rebuild the network period, regardless of whether that network is inside a Builder or not. Same with V-Ray.

So what is it about Redshift networks that allows them to work when native networks do not?

A Houdini vop material network isn't a node network, it's code; so there's nothing to rebuild. The redshift network isn't code, it's a node graph representation of a network of nodes.

If you inspect the USDShade shader prims in the scene graph details, you'll see that the Material builder just contains a lump of code, it has no child prims or node graphs.

Also, for Karma if you use MaterialX VOPs, it will rebuild.

As mentioned, if you use VEX VOPs, they get converted to a single USD Shader primitive that has a block of code rather than a bunch of USD Shader primitives connected together (as is the case for Redshift). Once VEX VOPs get dconverted to as ingle USD Shader, then Edit Mat Net LOP is no longer able to recreate the original VOPs; they are merely code fragments in the whole block of shader code.

So, no, Edit Mat Net LOP won't be able to load VEX VOPs. At some point we were planning to encode the VEX VOP topology in a USD Shader prim (along with the block of VEX code), but since Karma is focusing on MaterialX, that is much less of a priority now.