This post is a summary of what inputs and outputs are supported for the houdiniAsset node.
inter-asset is supported. This means you can connect one houdiniAsset to another houdiniAsset. Since this connection is made directly within the Engine (i.e. Houdini), everything that an object outputs inside Houdini is sent to the other asset's input.
nurbsCurve is supported.
mesh is supported. UVs, normals, and color sets are transfered to the Engine.
particle is supported. It's possible to connect both a regular particle node or a nParticle node to the asset. Per-particle attributes are all converted. The following Maya attributes are mapped internally to the Houdini equivalent: position->P, velocity->v, acceleration->force, rgbPP->Cd, opacityPP->Alpha, radiusPP->pscale.
inter-asset is supported. See above.
mesh is supported. Basic mesh data is outputted. Normals and UVs are also outputted. There's also basic material support so that textures are extracted and saved to disk. The material parameters that are outputted are: ogl_amb, ogl_diff, ogl_alpha, ogl_spec, ogl_tex1
instancer is supported. Instance geometry in Houdini can be outputted as Maya particle instancer or transform instances. The transform for the instances are outputted. It's possible to switch between the two by toggling “Use Instancer Node”, which is just under “Asset Option”.
fluid is supported. Due to some limitations of Maya API, it's currently only available on Maya 2014 and up. We should be able to have the same support on Maya 2013.5 (extension) too. However, Maya 2013 and older would require a completely different implementation, so there's no support in the older versions yet.
One important thing to note is that Houdini volumes are individual grids, whereas Maya fluidShape contains a fixed number of grids. And currently, multiple Houdini volumes can be mapped to each Maya fluidShape by specific volume names, which are connected to the their respective grids on the Maya fluidShape. The mapped volumes are: density, temperature, fuel, vel., Cd.
particle is supported. Any Houdini group primitives that contain only points (no face, and no vertices) are outputted as Maya nParticles. All point attributes that are either float3, float, or int will be outputted to Maya. The following Houdini attributes have Maya equivalent, so they're mapped to the equivalent Maya names: P->position, v->velocity, force->acceleration, life->lifespanPP, Cd->rgbPP, Alpha->opacityPP, pscale->radiusPP.
Note that when outputting custom attributes, the corresponding attribute needs to be added to nParticle node in order for the values to be accessible/visible on the nParticle node.
curve is supported. Note that each Houdini curve is outputted as one curve node in Maya. This works fine for small number of curves, such as outputting guide curves from an asset. However, it's not very practical to output fur and hair this way, because of the large number of curve nodes that would have to be created inside Maya.