Here’s a tool to add filecache and file nodes to your selected node in SOPs geometry context. At Masonry Studios, we base our Houdini geometry caches and its version on the file name (which contains the version number) and the node name, which is the default in Houdini’s file cache node.

However avoid using the file cache’s “Load from Disk” option to load the geometry back in, because:

1. It’s convenient for the file cache node’s “Geometry Path” to stay as the default un-evaluated relative path, in order to generate new caches based on the current file version
2. If we load in the geometry based on this relative path, and we version up our working file, this relative path will fail.
3. Hence, we find it quite an elegant solution to use a file cache and a file node separately. The file node points to the absolute evaluated “Geometry Path” of the file cache node and we’ve since successfully avoided the issue of broken links to caches.

# Author: Ronald Fong
# Date: 29 Sep 2021
# Usage: Add this as a shelf tool. With a SOP node selected, use this tool to quickly create a filecache and a cache node.
# Feature 1: Names the cache nodes based on your selected node
# Feature 2: File node will automatically be the evaluated absolute path of your filecache node
selected_node = hou.selectedNodes()
geo_node = selected_node[0].parent()
name = str(selected_node[0])
filecache_node = geo_node.createNode("filecache", ("filecache_" + name))
file_node = geo_node.createNode("file", ("file_" + name))
file_node.setInput(0, filecache_node)
filecache_node.setInput(0, selected_node[0])
geo_node.layoutChildren()
filecache_node.setDisplayFlag(1)
filecache_node.setRenderFlag(1)
filecache_node.setSelected(1)
filename = filecache_node.parm("file").eval()
file_node.parm("file").set(filename)

Vellum and RBD both have the newer packaged workflows, and while it’s nifty on their own, I haven’t found a way to set up such that they can mutually affect each other properly in a single simulation.

Usually, we’d set this up in a custom dopnet using the multi-solver, but because of the way the packaged node’s geometry and constraints are group together, there’s no straightforward set up setting this up.

So here’s a quick and dirty (but efficient) way to fake the interaction between RBD packed simulation and a Vellum simulation.

The Result

The idea is to first mimic the movement we’d want of the interaction using just the RBD bullet solver. We feed that output to serve as a collisions geometry for another temporary Vellum solve, feed this temporary Vellum output back to a new RBD bullet solver for the final RBD simulation, and once again feed it back to a new Vellum solve for the final vellum interaction.

This multi-phase simulation approach yields decently convincing results. While it’s not technically accurate, it’s artist-friendly to utilise the packaged simulation nodes.

Node Tree

This screenshot of the node tree shows how Vellum and RBD packaged SOP level nodes feed into each other to arrive at the illusion of interaction.