Possible for Group Node in Maya as input to Houdini Engine?

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All of the Houdini Engine examples I have seen tend to have a single shape node as input to the Houdini Engine OTL, or individually selecting different shape nodes separately as inputs into the OTL. Is it possible to just select the top group node of the rig hierarchy in Maya as input to the OTL?

I would like to create a Houdini Engine OTL where I could have a character animator select the top node of their character rig and the OTL would use all of the incoming geometry as a fluid source for simulation for them to visualize. Eash character has a different set of meshes and it would not be practical if each mesh would need to be selected and merged into the OTL separately.

Also is it possible to gain access to patch names from Maya inside of the OTL? ie: separate a mesh named “body” from a mesh named “pants”?
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There's no way to input the entire group at the moment. The workaround at the moment is to use Maya's mesh combine to combine multiple meshes into one, and then use that as the input. However, after combining the mesh, you won't be able to distinguish the individual objects. It's a useful feature. I'll add this as a RFE.
Andrew / アンドリュー
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We have implemented the multiple inputs already here in our own custom plugin. We didn't go for using a “group” but a “set” instead.
A group in Maya is really a transform used for hierarchy.
A set in Maya is more a selection similar to groups in Houdini.
So the set has multiple members and is connected as a single input to the Houdini Engine HDA.

You can have multiple sets existing in parallel and any hierarchy using groups can stay intact.
The only downside is that these “sets” are not manageable. As far as I could find out you can only create or delete them rather than adding items or removing items.

Anyway sets are worth looking at..

cheers,
benS
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Yeah, sets is a good idea too. It's been discussed at some point before. It could also be used to select partial components of an object to be used as an input.
Andrew / アンドリュー
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hi,

any update on this subject? will sets be supported?

cheers,
Kustaa
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kustaa
hi,

any update on this subject? will sets be supported?

cheers,
Kustaa

Yes, support for sets has been added shortly after this thread. See post:
https://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=39248 [sidefx.com]
Andrew / アンドリュー
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Hi Andrew,
this is great addition but i guess it doesnt allow to supply a set as an geometry input to an asset?

What im really needing is ability to input multiple meshes into one input. Ideally i would be able to input either a group that contains multiple meshes or a set.
Using mayas combine node can overcome this but it is not very handy when it comes to updating the geometries.

Is there any other way to do it?

cheers,
Kustaa
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A way I have overcome this us to have my asset have a lot of inputs (in houdini, you can have up to 999, although maya chokes at a out 100), and have a script which plugs all the leaf shapes of the selected group to the houdiniAsset node.

The nice thing about this approach is that you can use a for loop sop to import the geo as individual pieces in houdini, add groups to keep them separate, and wrangle them out as separate geos matching the original (bUT still get a huge speed up advantage from consuming all your geo at once)

This would be a great feature though. We could even import each mesh into houdini with a dagpath attribute to mimic the excellent alembic node behaviour
-G
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thanks for that workaround grayOlorin!

Andrew, do you think adding that “group node as input” support possible in near future?

K
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This feature request had come up in the past. I have taken a look at it. However, the tricky part is how to make the connection from the group to the asset node, and still have it “work nicely” for the user.

Maya relies on attribute connections for DG evaluation. So ideally, when the user chooses a group for input, the plugin would connect all the children mesh nodes to the asset.

But after the initial connections, what happens when a new node is parented under the group? A new connection needs to be made. Ideally, this should happens “automatically”. Otherwise, the user would have to disconnect the input group, and connect it again. Though, other built-in Maya tools that can use groups as an input probably have the same limitation. So thinking about it now, maybe this scenario is rare enough that we can just live with it…

But after the group is inputted, there are still (at least) two things that need to be considered.
1. Since the group has multiple mesh nodes, the user is likely to expect that multiple mesh nodes to be outputted. This is currently not easy to do, because in the Houdini side, the polygons are all bundled together as one “geometry” (e.g. one SOP or one connection). So when outputting this geometry back into Maya, there needs to be a good way of separating the geometry back into multiple pieces. The “Houdini way” would be to make use of the “name” attribute to identify the pieces. So this is doable.
2. The original transform hierarchy is lost. All the meshes that are inputted have the world transforms baked in. And the user probably wants this to be maintained somehow. This would affect both inputting and outputting sides.

Anyway, I'll end my rant.
Andrew / アンドリュー
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Hi Andrew and thanks for the rant!

For updating the new geometries under the group, could we have a away to force rereading the inputs? a button to refresh them? If not i wouldnt mind even if i had to reconnect the input. It would still be much handier than other approaches.

Name attribute sounds like a very good way to go.

Obviously being able to return a hierarchy from houdini back to maya would be great and it would open new possibilities but in my case i would be just happy if i could get them in
Ive done an asset that builds geometry around contact areas between two inputs (ground and building) and building usually has multiple maya geometries. So in my case im not returning that group back to maya.
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After the last couple of days working with the Houdini Engine for Maya plugin, my first time doing anything with it beyond loading it to see if it works, I have to throw my vote in for a way to use Maya group nodes as asset inputs. It could be something as blunt as adding a DAG path prim attribute instead of a detail attribute.

Merge ‘em all, let God sort ’em out.

I might have to do this in my asset anyway. From that, I could build a parallel hierarchy in the Houdini session, away from Maya's interest, then save that whole thing out as FBX or ABC for import into Maya as a new root node.

It would sure be nice to build a new DAG root from a Houdini hierarchy, so I'm adding a +1 for that feature too.

Of course, this is a fairly naive perspective. My experience with Maya can still be measured in hours.
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Hi,
Has there been any update on this?
It would be great if using multiple meshes as input would be more convenient. Sets would still be my suggestion

Kustaa
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