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Many of Houdini’s RBD nodes experienced a complete UI overhaul. Parameters are now grouped into logical tabs with sub-panes, rarely-used parameters moved to other places to avoid overloaded tabs. The preferred workflow now is to use various configure and property nodes to adjust the simulation, instead of making changes directly inside the solver.

Import and export nodes are now more streamlined throughout Houdini and match the I/O nodes of other solvers, for example pyro. Many improvements are also not exposed directly, but care for higher performance, faster loading, and a better handling of nodes and their inputs and outputs.

RBD Bullet Solver

  • The RBD Bullet Solver got many UI improvements and it’s now more streamlined with the look and feel of the Pyro Solver SOP. The parameters are organized in cleaned-up tabs like Setup, Bounds or Collision. Additionally, rarely used parameters are now attached under the Advanced tab. All tabs have collapsible sub-panes with grouped parameter sets.

  • The Setup tab contains all simulation-related parameters like Time Scale or Substeps.

  • Under Properties you find common rigid body properties for the node’s first three inputs. Normally, there is not very much to edit here and the parameters are mainly kept for your convenience. If you need more complex setups and changes, we recommend using the RBD Configure. This node lets you literally vary any parameter per group.

  • The Collision tab’s parameters affect the solver’s 4th input (Collision Geometry). As with Properties, it’s better to use an upstream RBD Configure node to adjust your simulation parameters. Collision is mainly kept for your convenience.

  • The Forces tab is now better organized. For adding custom forces, dive into the RBD Bullet Solver.

  • Some parameters from the Constraints tab move to Advanced. Constraint parameters are normally not need in SOP-based workflows and it’s better to work with RBD Constraint Properties nodes in most cases. Anyway, it’s still possible to scale all constraint values inside the RBD Constraint Properties node. For example, if you want to scale Soft constraints' Stiffness to 50%, go to the parameter and change Set to Scale. Then, enter 0.5.

  • The Guide tab was cleaned up and rarely used parameters move to to Advanced. The guided simulation parameters moved to the RBD Guide Setup. By default, the solver expects the RBD Guide Setup upstream. If you don’t want to use a RBD Guide Setup node, go to Advanced and turn off Use Pre-Configured Setup. Then you can make all settings in the solver’s Guide tab.

  • The Visualization tab provides all options for visualizing guide geometry.

  • Under Advanced you can find rarely used parameters and those parameters, which are normally controlled through appropriate property and configure nodes. The parameters are now used as scale factors for incoming properties. Here you can also find the RBD emission sub-solver’s Emission Cache Memory settings.

  • The Output tab now matches the Pyro Solver’s outputs and holds all export settings when going from DOP to SOP-based workflows. You can now pull out any impact data, for example points, where impacts occur, and drive secondary effects. This data used to be a separate Impact tab, but is now merged into the Output tab. You can also turn on age to track the lifetime of pieces and control secondary effects, or export any other available attribute.

RBD I/O 2.0

  • I/O nodes are useful for either caching out simulation results or intermediate states like fractured geometry. Furthermore, you can also write out geometry, constraints and proxy geometry at once into a single file. The RBD I/O node’s update supports improved versioning, file paths are now split into name and folder, and the Load from Disk option is turned on automatically once you press Save to Disk or Save to Disk in Background.

  • There are also improvements on the node’s 4th input (Simulation Points). Under Storage Type you can find the modified Simulation Points entry. In previous versions, this option could be confusing, because the node was managing two different caches at once. Internally, the RBD I/O node did, what Transform Pieces does as a separate node: applying point level transformation to the rest geometry. As a result, users often were unsure, if they really cached out the high-resolution geometry. In RBD I/O, the 4th input is now exclusively reserved for Simulation Points (instead of Geometry and Points in previous versions).

  • The new workflow uses the Quick Setup drop-down menu.

    1. Cache High-Res Geometry adds an upstream File Cache and Time Shift node. This option caches out the time-independent high-res and rest geometry from the first input.

    2. Transform High-Res Geometry adds a downstream Transform Pieces node for the time-dependent points and transformations.


  • DOP I/O is a wrapper that adds a DOP Import Field and a downstream File Cache node. The DOP Import Field grabs all fields from a DOP network through Presets for saving them out to disk immediately.

DOP Import 2.0

  • The DOP Import is used to get data out of DOP networks. The new 2.0 version is faster and has a more streamlined UI, while the parameters didn’t change.

  • The new version performs better with heavy scenes, for example crowd simulations or packed primitives.

  • The first three parameters let you choose the DOP Network and the Objects you want to pull out from the network. With Relationships you can import constraints.

  • The old version used many different Import Styles for different data. In DOP Import 2.0, there are only two styles left.

    1. Fetch Geometry from DOP Network imports all geometry from a DOP network and add attributes like name and path.

    2. Create Points to Represent Objects takes every object in the DOP simulation and generates points to describe the transformation. You can transfer any available attribute and group.

  1. Similar to the RBD I/O node you have a Quick Setups drop-down menu with two entries.

    1. Transform High-Res Geometry adds a downstream Transform Pieces node and wires the transformation points to the new node’s 2nd input. The 1st input goes to the high-res geometry itself, e.g. a RBD Material Fracture node.

    2. Cache Simulation adds a downstream File Cache Node to save the simulation to disk.

DOP Import Fields 2.0

  • This node is basically a wrapper for your convenience if you want to import particular data from a DOP network, e.g. pyro fields.

  • Changes in Houdini 19.5 affect performance improvements.

RBD Material Fracture

  • This node experienced performance and memory improvements.

  • Imagine two objects, 100 units apart, but named together and fractured as the same piece. With Material Type set to Wood, for example, the fracturing process became very slow and memory intense. With the new performance improvements, scenarios as the one described, are much faster now.

RBD Transform

  • The new RBD Transform node was added upon user request to simplify the work with the three outputs of a RBD Material Fracture node.

  • RBD Transform is very similar to the standard Transform node, but operates on all three inputs (high-res geometry, constraints, and proxy geometry) at once. It also provides convenient options for transforming constraints.

  • For example, if you want to perform a uniform scale on a fractured object, the RBD Transform will apply the transformation not only to the geometry, but also to constraints and the proxy geometry.

  • Attributes, e.g. restlength will can be updated, also normals.

RBD Match Transforms

  • The idea behind RBD Match Transforms is to take one output stream, edit/transform it through another node, and feed the result back through RBD Match Transform to the other streams. Imagine you want to transform some pieces from a fragmented object. Those individually transformed pieces and their constraints will later match the transformation of the entire fragmented object again.

Delay Syncing of HDAs

  • This improvement is not RBD-specific, but helpful for heavy nodes like RBD Material Fracture.

  • If you dive inside a node, but haven’t done anything to this point, then delay syncing avoids that all nodes inside the RBD Material Fracture are instantiated. Loading and opening time are much shorter.

UX improvements

  • The creation of constraints with RBD Constraints from Curves or RBD Constraints from Lines now support HUDs. You can display the node’s HUD with ⇧ Shift + F1.

  • Selecting and highlighting of constrained pieces also improved. The creation of new lines with ⇧ Shift + LMB highlights pieces in orange, while connected pieces are displayed in dark grey.

  • If you want to select and connect pieces inside an object, you can use a culling plane to virtually cut away occluding pieces.

    1. Add a RBD Constraints from Curves|Lines|Rules node and turn on Geometry Culling.

    2. Move the mouse to the viewport and press 5 to display a customizable bounding box. Everything outside the box will be culled.

What’s new in Houdini 19.5