convert abc to mesh issue

[Mikhalenko]

Hi everyone,

I’ve encountered an issue with converting VRayProxy to Mesh and the use of custom attributes. I have an Alembic (.abc) file exported from Houdini, which I load via VRayProxy in 3ds Max. The attributes works in both V-Ray GPU and V-Ray CPU while the geometry remains in proxy form. However, once I convert the proxy to a mesh, the attributes stop working.

It seems the problem might lie in the order of channels between the Proxy and the Mesh, which should ideally stay consistent but apparently don’t.

By the way, I found this behavior while worked with Chaos Vantage, that also has some bugs in this situation, but devs already fixed it for Vantage. You can check my post about it on the Chaos Vantage forum here:

https://forums.chaos.com/forum/chaos...e-from-houdini

I can also share the same scene if needed for testing.

As a side note, I’ve had no success using VRayUserScalar or VRayUserColor to map attributes as colors.

[hermit.crab]

Please, share the alembic here or via the contact form so we can troubleshoot.

[hermit.crab]

. ̶I̶n̶d̶e̶e̶d̶,̶ ̶i̶t̶ ̶s̶e̶e̶m̶s̶ ̶t̶h̶a̶t̶ ̶s̶o̶m̶e̶t̶h̶i̶n̶g̶ ̶g̶e̶t̶s̶ ̶m̶e̶s̶s̶e̶d̶ ̶u̶p̶ ̶w̶i̶t̶h̶ ̶t̶h̶e̶ ̶c̶h̶a̶n̶n̶e̶l̶s̶ ̶w̶h̶e̶n̶ ̶t̶r̶a̶n̶s̶f̶o̶r̶m̶i̶n̶g̶ ̶t̶o̶ ̶m̶e̶s̶h̶.̶You can change the channel numbers and order within the V-Ray Proxy in the Alembic sets rollout.

EDIT: Scratch that, switching channels from the proxy doesn't make a difference. I see that some of the alembics have Point attributes, while the other - Vertex attributes. The ones that do not work well after mesh conversion are the Point ones. I need to do some further testing to find out what's going on.

Regarding the custom attribute (r_along_02; g_dist; b_dist2; ), you need to select either of the three sub-channels (r, g, b) in the Vertex Color parameters For all three to work, I guess you need to do a comp. Regarding the VRayUserColor - it works in Standalone. In 3ds Max, the VertexColor node must be used instead.

[Mikhalenko]

. ̶I̶n̶d̶e̶e̶d̶,̶ ̶i̶t̶ ̶s̶e̶e̶m̶s̶ ̶t̶h̶a̶t̶ ̶s̶o̶m̶e̶t̶h̶i̶n̶g̶ ̶g̶e̶t̶s̶ ̶m̶e̶s̶s̶e̶d̶ ̶u̶p̶ ̶w̶i̶t̶h̶ ̶t̶h̶e̶ ̶c̶h̶a̶n̶n̶e̶l̶s̶ ̶w̶h̶e̶n̶ ̶t̶r̶a̶n̶s̶f̶o̶r̶m̶i̶n̶g̶ ̶t̶o̶ ̶m̶e̶s̶h̶.̶You can change the channel numbers and order within the V-Ray Proxy in the Alembic sets rollout.

EDIT: Scratch that, switching channels from the proxy doesn't make a difference. I see that some of the alembics have Point attributes, while the other - Vertex attributes. The ones that do not work well after mesh conversion are the Point ones. I need to do some further testing to find out what's going on.

Regarding the custom attribute (r_along_02; g_dist; b_dist2; ), you need to select either of the three sub-channels (r, g, b) in the Vertex Color parameters For all three to work, I guess you need to do a comp. Regarding the VRayUserColor - it works in Standalone. In 3ds Max, the VertexColor node must be used instead.

Regarding channel switching:
If, for example, you take an Alembic proxy with point attributes and then copy it and convert the copy to a proxy, you’ll notice an issue when using VertexColor. If you change the selected channel in VertexColor, one model (proxy for example) will display the attribute correctly, but the other one will turn black. This seems related to how channels are handled.

As for VRayUserColor, thanks for the information! It would be great if some notes could be added to the documentation, as I couldn’t find such details there.

On a related note, is it possible to set the order of channels in Alembic directly in Houdini? I want to ensure that the required attribute is always used correctly and doesn’t switch around if additional attributes are added later or if the same material is applied to another Alembic with a different attribute order.
Also would be wery usefull to have button to Reload proxy, as when working in realtime and seting this up, I very offen update allembic in Houdini and to Vray update it I need to remove and back 1 letter in the path or open file browser to reload it

[hermit.crab]

Regarding channel switching:
If, for example, you take an Alembic proxy with point attributes and then copy it and convert the copy to a proxy, you’ll notice an issue when using VertexColor.

You convert the .abc to a Editable Mesh, and then convert the Editable Mesh to .vrmesh?

If you change the selected channel in VertexColor, one model (proxy for example) will display the attribute correctly, but the other one will turn black. This seems related to how channels are handled.

Are you sure you are comparing accurately? If you've reordered the channels (0,1,2 to 1,2,3) and all objects still use the same shader and VertexColor node, the reordered ones will get the wrong channel.
I did a test with a duplicate shader with another VertexColor map which is set to the original value plus one. I'm getting similar results with or without the reordering.

The only issue I'm seeing is that the color channels (other than UVs) are not read after converting the point attributes .abc to mesh. Tested with the same .abc in Maya and it works as expected. It must be something specific to the Houdini .abc (point attributes in particular), since exporting a .abc with color sets from Maya, everything works fine.

EDIT: I found an already logged and very similar issue regarding Point attribute alembics in VRayProxies which have a VRayDisplacementMod. It is not yet fixed, and it is probably related to the one you are experiencing here.

On a related note, is it possible to set the order of channels in Alembic directly in Houdini? I want to ensure that the required attribute is always used correctly and doesn’t switch around if additional attributes are added later or if the same material is applied to another Alembic with a different attribute order.

Not my field of expertise. I'll ask a colleague.

Also would be wery usefull to have button to Reload proxy, as when working in realtime and seting this up, I very offen update allembic in Houdini and to Vray update it I need to remove and back 1 letter in the path or open file browser to reload it

I suggest you log your idea to the Portal.

[Mikhalenko]

You convert the .abc to a Editable Mesh, and then convert the Editable Mesh to .vrmesh?



Are you sure you are comparing accurately? If you've reordered the channels (0,1,2 to 1,2,3) and all objects still use the same shader and VertexColor node, the reordered ones will get the wrong channel.
I did a test with a duplicate shader with another VertexColor map which is set to the original value plus one. I'm getting similar results with or without the reordering.

The only issue I'm seeing is that the color channels (other than UVs) are not read after converting the point attributes .abc to mesh. Tested with the same .abc in Maya and it works as expected. It must be something specific to the Houdini .abc (point attributes in particular), since exporting a .abc with color sets from Maya, everything works fine.

EDIT: I found an already logged and very similar issue regarding Point attribute alembics in VRayProxies which have a VRayDisplacementMod. It is not yet fixed, and it is probably related to the one you are experiencing here.



Not my field of expertise. I'll ask a colleague.



I suggest you log your idea to the Portal.

You convert the .abc to a Editable Mesh, and then convert the Editable Mesh to .vrmesh?
I convert it to Editable Poly, I do it because of issue in Vantage, and I need combine leaves with rest of the palm, so for now it nessesary step


EDIT: I found an already logged and very similar issue regarding Point attribute alembics in VRayProxies which have a VRayDisplacementMod. It is not yet fixed, and it is probably related to the one you are experiencing here.

Yes, problem mostly with point attributes, with Vertex one I have no troubles, just not always possible to use exactly vertex atribute, so I think it's just need to work quite strait forward

I will check more closle about conversion and switching chanels

[hermit.crab]

Confirmed: the issue stems from the same report (internal bug-tracker id: VMAX-14263). I have linked your case to it. For now, use alembic with Vertex attributes instead.