Hello!

I apologize if this is an overly basic question, but I was wondering what would be the most straightforward way to import an animation such as this one into UE4:

https://vimeo.com/116709749 [vimeo.com]

Is it possible to create something like this in Houdini, and then directly import it into UE4, fully animated, and apply materials on top of it?

Thank you!

You can create a Houdini asset that does this. We have limited animation support for Houdini assets in Unreal, but it is possible. You can a have time dependent animation. Basically, our Unreal plugin sets time, sends it back to Houdini Engine, Houdini Engine cooks, sends geometry back, and this goes on. So basically we do cook every frame, every time it runs. It would be slow, but it would work. We have tested this with simple assets.

I think a better approach would be to bake individual static meshes (either inside Houdini or through Houdini Engine Unreal plugin) and piece them together into an animation inside Unreal. This way your animation will not rely on Houdini Engine for cooking afterwards.

okay I see what you're saying about Houdini having to cook the animation in the background. So that's not really an option in my case.

The only way I can think of to piece this into an animation inside UE4 would be to bake these meshes individually as you say, then hide and reveal them one by one every frame inside UE4. Kind of like a flipbook, but with meshes.

I'd really like to try this. I think can figure out how to create the mesh and animate it on my own, but how would I go about baking let's say 10 frames worth of meshes one by one so I end up with 10 different meshes?

I don't think it would be easy to do, or the export process might somehow give problems, but basically I would rig and animate the effect in Houdini and export it as an FBX with animation baked into the bones.
- If you try this, I would love to hear what issues you ran into and how you solved them.

https://forums.unrealengine.com/showthread.php?66771-Tutorial-Houdini-Fracturing-to-Unreal-Engine-4 [forums.unrealengine.com]!&p=271779#post271779

If you want to create something like that using individual uniform geometry, the best approach I can think of is to create geo nodes with just a box in them, and then animate them via keyframing their transforms (NOT THE xform SOP!…otherwise that's considering a vertex animation which is no good for UE4).

You'd want to do something like this:

-subnet
–box1
–box2
–box3
–box…
–box#

An option could be to create a box in a geo node, copy it according to the Fibonacci sequence, make sure they're named properly, and animate the pieces over time. Then, put together a bit of python to break out all the pieces into their own geo nodes inside a single subnet, automatically scrub the timeline, and keyframe their transforms. If you export that subnet as an FBX and import it into UE4, UE4 will automatically generate the skeleton for you and skip the entire skinning process in Houdini.

My destruction tool has a similar process using a Rigid Body Packed Object DOP node as its input. You could use that as a basis to create another tool that uses any SOP node.

https://github.com/sideeffects/GameDevelopmentShelf [github.com]

If you want to skip the python part, you might be able to animate it at the SOP level, pack the geometry using an assemble SOP, import it into a DOP network via Rigid Body Packed Object DOP, and then use the above tool.

If I get the chance, I'll see about putting a little example together.

I was actually going to follow your destruction tutorial before I even thought about this project :p So I'll definitely be following your tutorial very closely including the python part. I am new to Houdini so this is probably going to teach me a lot.

I was going to animate it in UE4 using multiple splines in a spiral shape and move the emitter along the spline but it's not nearly as interesting as doing it the way you explained it in houdini, so I would love to see how you'd do this using the actual Fibonacci sequence :p

Do you guys know if Unreal can read a cached sim and play it via HDA?

Essentially not at runtime, unless it's a bone animation. A bone animation could be baked out by the HDA to a standard Unreal Asset (I think). But I think Unreal 4.13 (or a future version) is supposed to support Alembic import and vertex animation playback. So you could export vertex animations to Alembic and get it in that way.
(Not 100% sure about any of this.)