(Won't Do) [HOU-2282] Scattering on an "object merge"d heightfield doesn't render. Bug or expected behaviour?

[Monkeybrother]

Hi. I'm learning Houdini and I'm making a scatter HDA that takes a heightfield input, that I then scatter stuff on. When I scatter objects using the "heightfield scatter" node, the scattered objects aren't rendered by v-ray. However, when i put a heightfield inside the HDA network (i.e. not merging), everything works as expected. When I use a for loop and scatter using copy to points on the merged heightfield, everything works as expected. Is this a known thing or is it a bug? Thanks.

edit: Houdini 18.0.566 and vray 4.3

[Gosho.Genchev]

Hey Monkeybrother ,

we only care about the final output - can you please check with the Middle Mouse button over the rendered SOP what is the representation of your geometry ? Could you also please double check that the render flag for your HDA is pointed to the correct node ?
I just tested on my end and there's no issue with geometry scattered over a heightfield using the HeightField Scatter SOP.

Best regards!

[Monkeybrother]

Hey Monkeybrother ,

we only care about the final output - can you please check with the Middle Mouse button over the rendered SOP what is the representation of your geometry ? Could you also please double check that the render flag for your HDA is pointed to the correct node ?
I just tested on my end and there's no issue with geometry scattered over a heightfield using the HeightField Scatter SOP.

Best regards!

Thanks for getting back to me. Heightfield Scatter works when I use a "direct connection" to a heightfield. The problems start when I merge a heightfield into an HDA and try to scatter on it, then it won't render. I did some more digging and noticed that the problems only occur when I try to scatter meshes that is imported via Vray Scene. I think the problem is that the materials get lost on the way.

So, to summarize: Everything works unless I try to scatter meshes imported via a VRay Scene onto a heightfield that is merged into a SOP/HDA, using Heightfield Scatter. When that occurs, I can see the scattered meshes in the viewport, but they don't render. The meshes that render correctly have a "shop_materialpath" attribute, but the VRay Scene meshes do not, that is the only difference I can see. The VRay Scene meshes render correctly when I scatter using a standard for/each/copytopoint loop.

I can't really send you the scene, since the assets I'm using come from commercial packs.

[Monkeybrother]

No tips or workaround for this? Like I said, I'm new to Houdini, so maybe I just need to do something with the VRay Scene node?

[Gosho.Genchev]

Hey Monkeybrother ,

I've had no luck reproducing the issue so far. I'll give it another shot now and message back.

Best regards!

[Gosho.Genchev]

Hey Monkeybrother ,

indeed you are absolutely correct - the VRScenes are being packed by the HeightField Scatter SOP - dropping an unpack after the scatter so that Middle-Mouse-Button clicking on the rendered node shows "VRaySceneRefs" instead of "Packed Geos".
I'll check with the developers if we can do something to circumvent this - the VRScenes are already packed so packing them again serves no purpose yet it can cause confusion, as is the case here.

Best regards!

[Monkeybrother]

Hey Monkeybrother ,

indeed you are absolutely correct - the VRScenes are being packed by the HeightField Scatter SOP - dropping an unpack after the scatter so that Middle-Mouse-Button clicking on the rendered node shows "VRaySceneRefs" instead of "Packed Geos".
I'll check with the developers if we can do something to circumvent this - the VRScenes are already packed so packing them again serves no purpose yet it can cause confusion, as is the case here.

Best regards!

Thank you for looking into this. I'm stuck using stable versions, but since you were not aware of this I assume this is not fixed in VRay 5? My problem is that I have hundreds of assets in Max/VRay format and I need a quick way to transfer/use those in Houdini; VRay Scenes are the only way I've found that does this. Using Alembic/FBX and re-assigning and fixing materials by hand is not really an option. Do you know of any other way I can do this for now?

[Gosho.Genchev]

Hey Monkeybrother

The same behavior is present in V-Ray 5 builds as well. Technically it's not a bug in itself - as I mentioned, VRScenes are already treated as packed primitives. We'll definitely add a note in the docs, hopefully also figure out a way to address this in the future, too.

My problem is that I have hundreds of assets in Max/VRay format and I need a quick way to transfer/use those in Houdini;

Indeed, it sounds as if VRScenes would be the simplest approach.
Please drop an Unpack SOP after the HeightField Scatter SOP to make sure the primitives are treated as VRSceneRefs instead of Packed Geo - that should solve the problem.

Hope that helps!

[Monkeybrother]

Hey Monkeybrother

The same behavior is present in V-Ray 5 builds as well. Technically it's not a bug in itself - as I mentioned, VRScenes are already treated as packed primitives. We'll definitely add a note in the docs, hopefully also figure out a way to address this in the future, too.


Indeed, it sounds as if VRScenes would be the simplest approach.
Please drop an Unpack SOP after the HeightField Scatter SOP to make sure the primitives are treated as VRSceneRefs instead of Packed Geo - that should solve the problem.

Hope that helps!

Oh, I didn't realize that that was a solution, I just thought you meant you could see what the problem was. It seems to work now, so thanks for the help!

[Gosho.Genchev]

Hey Monkeybrother ,

after discussing with the development team, we decided to stick with a note at the top of the documentation page for the V-Ray Scene SOP and not changing the code as it may cause other issues.
I've tagged the forum thread and closed the issue.
If at some point in the future you hit a case where not being able to pass the VRScenes through a Pack SOP poses a limitation, please ping us.

Best regards!