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Resolution independent tets

  • Tetrahedra are now independent from changes in mesh density/polygon count and scale. For example, if you upscale an object, you had to adjust constraints and other simulation parameters to get the same result. With resolution-independent tets, you can change scale and achieve almost identical results without having to readjust the simulation.

  • See the Vellum Constraints SOP for additional information.

Shape matching


Shape match simulations require the latest driver for NVIDIA Ampere (or later) cards. Older chipset architectures aren’t supported. If you experience problems, go to Houdini’s main menu. Open Edit ▸ Preferences ▸ Miscellaneous and set OpenCL Device to CPU. Then, restart Houdini to apply the changes.

  • Shape matching lets you quickly simulate rigid-body-like objects directly inside Vellum. Shape matching is based on Vellum grains and uses a sphere packing method to fill an input object with differently sized spheres to approximate its volume. Collision detection is very fast, because it is calculated from the spheres.

  • In the Vellum Configure Grain node, turn on Create Points from Volume. Under Method you can find a new Sphere Packing entry. Use the associated parameters to adjust packing and fill the object with spheres. Mass changes might lead to false results, esp. when you use differently sized spheres.

    1. To get spheres of different size, define a Max Radius Scale.

    2. For better packing, turn on Overlapping. With Max Spheres.

    3. You can determine the number of spheres through Max Spheres, e.g. for fast preview iterations.

    4. Turn on Define Pieces.

    5. Turn on Transfer Piece Attribute.

  • The Vellum Constraints provides a Shape Match entry in the Constraint Type dropdown. This mode was introduced in Houdini 19.0 already, and now it can be used to drive the rigid body simulation. To make simulation work, change the following parameters.

    1. Set Group Type to Points.

    2. Change Define Pieces to From Attribute.

    3. For Piece Attrib enter piece. Now you can see the constraints between the spheres.

  • A Vellum Transform Pieces node is required downstream to the Vellum Solver. This node transfers the transformations of the packed spheres to the original object. The node’s first two inputs are connected to the solver’s first two outputs. The third input is wired to the base object’s output.

Vellum I/O 2.0

  • The Vellum I/O 2.0 node is now streamlined with the pyro, FLIP fluid, and RBD I/O nodes in terms of UI structure, parameters, and overall functionality.

Static Topology

  • The Vellum Constraints SOP has a new Static Topology parameter to flag the output constraint primitives as static, meaning they will not slide or be broken, removed, or welded during the simulation. This specification allows the Vellum Solver to skip these constraints if required to re-graph color the constraints. This option is most useful when a large number of dense static constraints, e.g. high-resolution tetrahedra, would otherwise require frequent, expensive re-coloring when connected together with sliding or breaking stitch constraints, as in a muscle or tissue simulation. You can find the Static Topology option in the Attributes sub-pane.

Vellum Attach Constraints SOP

  • The new Vellum Attach Constraints node allows you to edit existing or create entirely new Attach to Geometry and Stitch constraints for Vellum. You can interactively draw connection lines between a point on the cloth mesh and a point or a surface position on the target mesh you want to be attach to or stitch. The workflow is very similar to the RBD Constraints from Lines node.

What’s new in Houdini 19.5