I'm still trying to wrap my head around USD workflow in Houdini. I have an animated L-system tree. It's got changing topology, animated attributes, the works. I'm trying to understand the best way to get this into disk, then into a USD stage.

Component builder only seems to export a static USD file, even if I enable "Topology Attributes: Animated" and "Author Time Samples if SOP is time dependent".

USD Render ROP seems to work, but is that the suggested way to do it? It seems less elegant than the component builder.

Thanks!

Brad T.

Currently to output an animated asset with component builder, try appending a Cache LOP after the Component Geometry. This will bake all of the time samples, and then when you reference the asset from the Component Output node, or from the file on-disk, you should have all of the animation built in. Does that make sense?

Thanks Goldleaf,

It does make sense and I'll give it a try. Is this the preferred/suggested way of exporting animated assets for USD?

goldleaf
Currently to output an animated asset with component builder, try appending a Cache LOP after the Component Geometry. This will bake all of the time samples, and then when you reference the asset from the Component Output node, or from the file on-disk, you should have all of the animation built in. Does that make sense?

I tried this, but it doesn't work for me, When I save its still static geo. I enabled time sampled dependencies on both the component geometry and the component output.

I managed to get it working with:
(Component Geometry LOP) Author Time Samples = "If SOP is Time Dependent"
(Cache LOP) Behavior = "Always Cache All Frames"

Hi

Does this still work for you. Following what you were doing does not work for me. H19.5.303

Best. Mark

There was a change to the Cache LOP's default settings that affects this workflow. When a ROP starts rendering, it sets the context options @ropstart and @ropend to match its own Valid Frame Range. This prevents the LOP from caching the entire timeline for the sake of one frame. Normally a great idea. However, the ROP inside Component Output is set to render only the current frame, which therefore modifies the Cache LOP's behavior unexpectedly (and somewhat invisibly to the end user).

Under most circumstances, a static asset is what we want to see from Component Builder—animation is typically layered on afterward. In cases where you actually do want a keep-alive animation or something of the sort to be saved with your base asset, the simple solution is to delete the channels on the Cache LOP's Start/End/Inc parameter and either set the frame range explicitly or use $RFSTART/$RFEND/$RFINC.

The slightly more complex solution is to break open the Component Output HDA and modify the USD ROP inside so it renders the range you want.

Hi Bryan

So the issue with layering the animation latter is you have to manually reconstruct the stage hierarchy just for the animation. The component geometry creatures a structure like ASSET/geo etc. This is a very manual process leaving room for human error.

My other issue is I cannot even get an external abc/usd file that is animated to load into component geometry at all, let alone worry about breaking open the output part of it.

It is such a shame as it means I cannot use any of these tools. What I have done is make my own that suck in static or animated ABC/USD files with the option to either create stitch files and/or create a model and animation sublayered file. This does mean that none of your layout LOP are usable however. Which is another shame.

Im attaching and example ABC file that I generally test with. Best. Mark

Hi Mark, I hope this helps illustrate how you can use references to overlay animation from alembic caches. Obviously this example would look better if there was a static alembic pose for the asset, but I hope it still illustrates the idea. There's also a sticky note in there explaining the approach and alternatives a bit more.

Just put the hip file in the same location as the alembic file attached above.

Hope this helps!

Hi goldleft. This is super helpful. Thank you!

Hi again Goldleft. Thanks again. I have just looked at the file you sent. I noticed you have also fixed the eye issue (thats for that). They eyes were parent constrained in Maya rather than skinned. I just had not figured out why the eyes were behaving oddly before. I got two answers for the price of one question!

Best

Hi Goldleft.

Im just going though your file you sent me. In it you said regarding abc imports with double transforms

"If you block the xformOps on the meshShape, after referencing the abc animation, then the eyes are no longer offset ('block_xformOps_on_shapes')".

On the Reference LOP
Is turning Parent Primitive Type to "None", rather than the default "Xform" what you are refering to?

Best. Mark

Edit: sorry. Im being dumb. I missed the edit properties LOP. Sorry for the noise ;-)

The component output renders current frame by default. You have to break into the node contents( Allow editing of contents), locate the usd rop for assets in the node tree and set "Valid Frame Range" to Render specific Frame range. You can also add this to the component output node parameter interface.

Hi Ude.

I have submitted an RFE to ask to have the frame range exposed which would be super handy. Best. Mark

Is it possible to have a looped animation built in an asset with component builder, e.g. a waving flag or burning tree?
I'm experimenting this with putting value clip in component builder, doesn't seem to work.

NMVHS
Is it possible to have a looped animation built in an asset with component builder, e.g. a waving flag or burning tree?
I'm experimenting this with putting value clip in component builder, doesn't seem to work.

I'm sure you've either solved this by now or given up, but I needed to do this very thing this week, so I've worked it out, and I present this solution for the benefit of those who come behind.

The Geometry Clip Sequence LOP creates "value clips," which are the typical way you'd make an animation loop. Consult the docs for that LOP for full details. I'll just give the procedure and brief explanations here.

To use Geometry Clip Sequence inside a Component Builder requires a couple of tweaks. First, since you're not getting the geometry directly from the Component Geometry node any more, go to the Component Output and change the Source to "Input Primitives." Otherwise, the composition arc created by Geometry Clip Sequence will prevent Component Output from being able to use it.

Place a Geometry Clip Sequence LOP and connect the output of Component Material to input2. Append a Cache LOP after Geometry Clip Sequence, and the output of Cache goes to Component Output.



In Geometry Clip Sequence:
Set Primitive Path to /ASSET
Tick "Get Geometry From Second Input"
Change the Manifest File Save Path and Topology File Save Paths to match the Component Output's Location.
You could, of course, use an expression to drive this. For example:

• $HIP/usd/assets/`chs("../componentoutput1/name")`/manifest.usd
  
• $HIP/usd/assets/`chs("../componentoutput1/name")`/topology.usd
  

This is a little fragile since you have to manage the name of Component Output to ensure these files don't go to the wrong place. It'll typically update as desired if you change the node name, but it's not terribly difficult to break the link.

Change Clip Primitive Path to /ASSET
If you want your asset animation to loop, tick End Frame and enter the end frame of the animation.

In the Cache LOP:
Set Cache Behavior to "Always Cache All Frames."
Delete the channels on Start/End/Inc, and in the End field, enter a value larger than the longest clip you will ever need for this asset. It's a good idea to set the Update Mode to Manual before doing this, as it will cook every frame specified, which could take some time.

The presence of the Geometry Clip Sequence will break whatever internal mechanism sets the path for the materials, so between the Component Material and Geometry Clip Sequence nodes, add a Configure Layer LOP. Tick "Save Path" and enter an appropriate path for the material.usd file. Again, you can use the same kind of expression as above:
$HIP/usd/assets/`chs("../componentoutput1/name")`/materials.usd