Houdini 13.0 What’s new What's new in Houdini 13

Particles

  • Houdini 13 introduces a new particle simulation engine in the dynamics network (DOPs). This is intended to obsolete and replace the old particle network type. You can use the tools on the new Particles shelf tab to set up and manipulate these new particles.

  • Dynamics particle nodes are re-implemented in DOPs through a collection of dedicated particle nodes which a POP Solver applies to the particles in a POP Object. This allows you to wire the new particle nodes together similarly to the old particle networks.

  • The new particle nodes include force nodes such as POP Force and POP Wind designed to be wired together in the new particle way. These duplicate the regular DOP forces, and regular DOP forces (such as the default gravity node) affect particles as well. You can turn off non-POP forces on the POP Solver.

  • The behavior of the old Follow POP is now in the POP Attract node.

  • The new particles are much faster, especially for very large particle systems.

  • You can use particle nodes to manipulate the fluid particles in FLIP fluids and objects in the Bullet RBD solver.

See the new particles chapter for more information.

Solid objects (FEM)

  • Houdini 13 includes tools for simulating hard and soft solid objects using finite element method (FEM). This allows you to model, for example, internal shifts of mass in a soft body, and realistic fracturing of objects from impacts.

  • The tools on the new Solid shelf tab let you create and work with solid objects.

See solid object simulations for more information.

RBD

  • Significant improvements to the Bullet RBD solver

    • Bullet solver is significantly faster and uses less memory. The majority of the performance and memory usage improvements come from using the RBD Packed Object, which stores large numbers of objects in a much more efficient manner than the RBD Fractured Object, RBD Point Object, etc.

    • Bullet simulations are interruptible and show progress in the status bar.

    • Bullet solver now works on more geometry types including packed primitives, NURBS and Bezier curves, meshes, polygon soups, VDB primitives, and metaballs.

    • Bullet solver uses faster shrinking algorithm when Shrink Collision Geometry is on, which may change simulation results. Removed the obsolete “optimized” option from the Bullet Data DOP.

    • When Shrink Collision Geometry is off, importing geometry may be slightly slower than in previous versions, but subsequent frames will cook faster.

    • The collision padding now works consistently for all collision representations. The Shrink Collision Geometry option is now used for more representations including box, sphere, cylinder, and capsule.

    • Simulations with convex hull shapes may now take slightly longer for initial setup but run significantly faster in many cases. When using convex hull representation with Compute Mass on, the Bullet solver now computes the volume from the convex hull instead of the original geometry.

    • You can now use Bullet’s parallel constraint solver instead of the default single-threaded constraint solver. This should improve simulation speed, however it does not support Split impulses and objects often lose less energy in collisions versus single threaded.

  • The new Debris shelf tool creates debris particles from animated rigid bodies. This tool works with both RBD Packed Objects and regular RBD Objects.

  • The Point Position DOP detects a pivot attribute on input points and uses it to set the p attribute on the Position data, which for RBD objects usually represents the center of mass.

  • The DOP Import SOP has been updated to handle RBD Packed Objects. You can import them directly as packed geometry or unpack them during import. The new Add DOP Object Path Attribute parameter creates an objectid primitive attribute on the imported geometry containing the path of the DOP network and the DOP object ID from which the geometry was imported.

  • You can now animate the Constrained object and Goal object parameters in constraint nodes.

  • The RBD Packed Object DOP can be used to set up large numbers of instanced rigid body objects more efficiently.

  • The Constraint Network DOP replaces the Glue Network Constraint DOP, and can be used to procedurally generate constraints of any type (such as glue, spring, pin, etc). The Constraint Network DOP is compatible with both the RBD Packed Object and regular RBD Objects.

  • The Glue Adjacent shelf tool now sets up a Constraint Network DOP instead of a Glue Network Constraint DOP, and also uses the new Connect Adjacent Pieces SOP. This is faster and supports RBD Packed Objects (which currently only work with constraint networks).

  • Voronoi fracture is about 2x faster with the Cluster pieces option on. Improved performance of the Voronoi Fracture Solver when handling large numbers of impacts.

  • The Impact Analysis DOP works with RBD Packed Objects. It sets the impactprimnum and parentprimnum attributes to identify the packed primitive involved in the impact.

Fluids

  • Many improvements to FLIP solver performance and fluid behavior

    • Improved velocity extrapolation with better accuracy around the surface of curved containers.

    • More accurate tetrahedral method for computing collision weights.

    • Uses new POP-style forces and other particle DOPs connected to its “Particle velocity” input.

    • Separate controls for Age Particles and Reap Particles.

    • Moved less frequently used controls to the new Behavior tab.

    • “Stick on collision” functionality was reimplemented using the Gas Stick on Collision node. You now have separate control over normal and tangent sticking forces, and a control/mask field.

    • Better particle uniformity when reseeding, with no grid artifacts.

    • A new “Extrapolated velocity” option for under-resolved particles reduces stringiness in splashes. You can still switch to the previous “Treat as ballistic” behavior to match previous results.

  • The new VDB from particle fluid SOP surfacer used for FLIP fluids is 5-10x faster, uses less memory, gives smoother (less lumpy) results, and has much better “sheeting” (narrow tendrils will appear as connected fluid, instead of a line of droplets). It replaces the Particle Fluid Surface node.

  • Source Volume DOP can control life expectancy and variance with a life attribute on the emitted particles. It can also group particles by source using the Output group parameter.

  • The FLIP Object DOP and Source Volume DOP no longer add a mass attribute to FLIP particles, and the Ignore mass on particle forces parameter was removed.

  • The Points from volume SOP, Particle Fluid Tank SOP, and Fluid source SOP now have Scattering density and Oversampling parameters. These let you create extra particles at and below the surface of geometry or volumes. These additional points help create a flat stable fluid surface for the solver’s initial state. In the rigs created by the shelf tools, this parameter is linked to the solver’s reseeding oversampling parameter.

  • Converting native fog volumes to VDB now ignores the signed flood fill option in the Convert VDB SOP and in the HDK.

  • The Gas Feedback DOP can now use fractional collision weights for smoother feedback forces. The FLIP solver can now use these weights. Using this feature will change the output of FLIP simulations that use feedback. You should set the Feedback scale about 50% higher when using this feature.

  • The new Gas Stick on Collision DOP adjusts a fluid velocity field to match collision velocities within a thin layer around collisions.

  • The Gas SDF to Fog DOP has a new, more accurate volume fraction method.

  • The Whitewater solver and Particle solver now have an animatable Timescale parameter. The Whitewater shelf tool sets up the node with the timescale linked to the timescale of the FLIP solver.

  • New Mist tool on the Particle fluids shelf tab.

Ocean FX tools

  • The new Ocean FX shelf tab contains a number of useful ocean rigs.

  • The new Ocean Surface material is automatically assigned to ocean rigs created using the new shelf tools.

  • The Ocean evaluate SOP can now add a UV attribute to the geometry. You can use this attribute to do texture lookups on baked displacement maps.

  • The Whitewater Solver supports a new ballistic particle type when the ballistic attribute is greater than 1. This particle is not affected by whitewater forces. These particles are yellow when Color particles by type is on in the Whitewater Object.

  • You can now customize the colors of Color particles by type on the Whitewater Object.

  • The Whitewater Solver now allows you specify behavior at the tank limits for all particle types.

  • The Whitewater Emitter DOP simplifies whitewater emission. The shelf tools now create rigs using this new node.

Fur

  • The Fur SOP now gives better results on non-planar polygons. This causes the Fur SOP and the Mantra Fur Procedural shader to place hairs differently.

  • You can provide a point cloud to the Fur SOP to use as hair root positions.

  • You can set the Fur object to not use the Mantra fur procedural shader.

  • The Fur object supports guide and clump hairs groomed by external geometry networks.

  • Fur procedural is faster at handling skin geometry containing lots of small primitives.

  • The Fur object now preserves any N (normal) attribute on the skin geometry.

General

  • New simulations are no longer cached to disk by default (Allow caching to disk on the DOP Network node is off by default).

  • The performance monitor now reports the time a simulation network spends saving cache entries to disk.

  • You can now use the op: path syntax to refer to DOP data. For example op:/obj/AutoDopNetwork:0/Geometry references the Geometry data in the first DOP object in the AutoDopNetwork object. The second : (colon) character separates the node path from the DOP data path.

  • The performance monitor now shows more detail for the Bullet solver, and correctly shows the cooking time for dynamics networks.

  • The Geometry VOP node lets you add up to four extra geometry “inputs” to the VOP network. You can grab the geometry from a SOP path, a DOP data path, the DOP network’s context geometry, or Geometry data in the node’s input.

Fixes

  • Simulations now reset correctly at frame 1 even if that frame is not in the cache.

  • Bend force in a cloth object now behaves similarly at different resolutions.

  • The Bullet solver now correctly computes the position and orientation of a “Compound” collision shape when Use object transform is on.

  • Better stability of collisions with cloth or solid matter objects near hard constraints.