Houdini as scene assembler part 02 / by Xuan Prada

In the previous post I showed you how to load alembic caches using the file node and then change the viewport visualization to bounding box. This is good enough if you are let's say look-deving a character. If you want to load a heavy alembic cache, like a very detailed city with a lot of buildings, or a huge spaceship, you might want to use a different approach.

Instead of using a file node, it is better to use the alembic node to load you assets, and then set the option Load As: alembic delayed load primitives, and display as bounding box. This isn't actually loading the geometry in memory and it will be way more efficient down the line.

In this post I'm just talking about shading assignment in Houdini.
The easiest and more simple way to assign shaders is by selecting the asset node in the /obj context and assign a shader in the render tab. Your Mantra shaders should be placed in the /mat context and your Arnold shaders in the /shop context as /mat is not fully supported yet.

In the /mat context you can just go and create a Mantra Principled Shader. For Arnold, it is better to create an arnold shader network and then any arnold shader inside connected to the surface input.

Houdini doesn't have an isolation mode for shading components like Maya (as far as I know) but you can drag and drop shaders and textures onto the viewport or IPR while look-deving. This only works in the /mat context (again, as far as I know).

Another way of assigning shaders is creating material nodes inside of the alembic node. This material nodes can be assigned to different parts of your asset using wildcards. To assign multiple materials you can create different tabs in the material node or you can just concatenate material nodes (which I prefer). This technique works with both Mantra and Arnold.

You will find yourself most of the time creating material networks (Mantra) or shop networks (arnold) containing all the shaders of your asset. In a lighting shot you will end up with different subnetworks for each asset on the shot.
This subnetworks of shaders can be place at the /obj level or inside of the alembics containing your assets.

Another clever way of assignment shaders is using the data tree -> object appearance. This only works at object level. If you want to go deeper in your alembic asset, you need to add first a node called packed edit. Then in the data tree you will have access to all the different parts of your asset.

There is another way of controlling looks in Houdini, and that is using the material style sheets. We will cover this tool in future posts.