Houdini 18.0

Vellum

Vellum uses a Position Based Dynamics approach to cloth, hair, grains, and softbody objects.

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Vellum is a simulation framework that uses an extended Position Based Dynamics approach. It can be used to create many different things including cloth, hair, softbodies, balloons, and grains. The main advantage of a Position Based Approach is its controllability, stability, and ability to produce believable results quickly.

There are several shelf tools that will create the basic node setup for you. The best example of a SOP setup using Vellum is the Simple Cloth tool, which is available on the Characters tab for Houdini Core users, and on the Vellum tab for Houdini FX users.

It asks you to select a geometry object to solve as cloth, and a geometry object to use as a collider. In this example, a grid is used as the cloth object and a torus is used as a collider. These get wired into the Vellum Constraints node, which creates constraints to act like different materials. The Simple Cloth tool uses a Vellum Configure Cloth node, which is a Vellum Constraints node with common cloth parameters already applied. There are also presets for Vellum Configure Balloon, Vellum Configure Grain, Vellum Configure Hair, and Vellum Configure Softbody that use this same node.

The Vellum Solver allows you to modify things like Substeps and Constraint Iterations to balance the speed and quality of your simulation. The node also has a Forces tab that allows you to set Gravity, Wind, Wind Drag, and Friction.

Note

There is a default Wind Drag force that is set in SOPs. However, the default DOP network does not create a drag force.

The Vellum I/O node saves the output geometry as well as the constraint geometry to disk. There are some default deletes on the Save Filter tab to clean out the most common attributes that aren’t needed in order to cut down on the file size.

The Vellum Post-Process allows you to visualize components like False Color Mode for stretch or bend stress. You can also visualize constraints and thickness, which is useful for troubleshooting your simulation.

Vellum nodes

There are several Vellum SOPs available in the tab menu. Many put down a Vellum Constraints node with a different Constraint Type set and specific parameters exposed for the constraint type.

Vellum Constraints nodes:

Vellum Attach to Geometry

Vellum Configure Balloon

Vellum Configure Cloth

Vellum Configure Hair

Vellum Configure Strut Softbody

Vellum Configure Tetrahedral Softbody

Vellum Glue

Vellum Stitch Points

Vellum Struts

Vellum Weld Points

Using vellum in DOPs

The Vellum Constraints node is still used to configure constraints when using Vellum in DOPs. However, it exists inside a Vellum Source node, which allows it do additional things such as emit.

There are shelf tools for each type of Vellum effect, which are all able to interact with each other. When you use multiple Vellum effects on multiple objects, all objects will be merged into one geometry object and one constraint geometry object in the DOP network.

For more information on each effect, see the following shelf help pages.

You can apply POP forces in Vellum, since it is particle based. It also respects Particle Streams, so a force applied to one object doesn’t have to be applied to all objects.

For example, if the grid is a cloth object and the torus is a softbody object, you can apply a POP Wind force to the cloth by placing the node in between the grid_object1_vellum and merge2 nodes.

However, if you want to apply the wind to the softbody instead, you can move the POP Wind force in between the torus_object1_vellum and merge2 nodes. Similarly, if you want to apply the wind to both objects, you can place it between the merge2 and vellumsolver1 nodes.

Vellum solver SOP and DOP differences

The Vellum Solver SOP is a wrapped up version of the Vellum Solver DOP. However, it has a features that you need to add yourself in DOPs for producing same result.

  • Gravity is on by default. This is the case in some DOP networks, but not all.

  • Wind is on by default with still air. You can add a POP Drag or POP Wind and set its air resistance to 0.1 for equivalence.

  • The ground plane is not on by default, but can be turned on with the Ground Position parameter. You have to explicitly add a ground plane in DOPs.

Masterclass

Subtopics

Houdini 18.0

Getting started

Using Houdini

  • Geometry

    How Houdini represents geometry and how to create and edit it.

  • Copying and instancing

    How to use copies (real geometry) and instances (loaded or created at render time).

  • Animation

    How to create and keyframe animation in Houdini.

  • Character

    How to rig and animate characters in Houdini.

  • Digital assets

    Digital assets let you create reusable nodes and tools from existing networks.

  • Import and export

    How to get scene, object, and other data in and out of Houdini.

  • Executing Tasks

    How to define dependencies and schedule tasks using TOP networks.

  • MPlay viewer

    Using Houdini’s stand-alone image viewer.

Dynamics

  • Particles

    How to create particle simulations.

  • Dynamics

    How to use Houdini’s dynamics networks to create simulations.

  • Vellum

    Vellum uses a Position Based Dynamics approach to cloth, hair, grains, and softbody objects.

  • Pyro

    How to simulate smoke, fire, and explosions.

  • Fluids

    How to set up fluid and ocean simulations.

  • Destruction

    How to break different types of materials.

  • Grains

    How to simulate grainy materials (such as sand).

  • Crowd simulations

    How to create and simulate crowds of characters in Houdini.

  • Hair and Fur

    How to create, style, and add dynamics to hair and fur.

  • Finite Elements

    How to create and simulate deformable objects

Nodes

  • OBJ - Object nodes

    Object nodes represent objects in the scene, such as character parts, geometry objects, lights, cameras, and so on.

  • SOP - Geometry nodes

    Geometry nodes live inside Geo objects and generate geometry.

  • DOP - Dynamics nodes

    Dynamics nodes set up the conditions and rules for dynamics simulations.

  • VOP - Shader nodes

    VOP nodes let you define a program (such as a shader) by connecting nodes together. Houdini then compiles the node network into executable VEX code.

  • LOP - USD nodes

    LOP nodes generate USD describing characters, props, lighting, and rendering.

  • ROP - Render nodes

    Render nodes either render the scene or set up render dependency networks.

  • CHOP - Channel nodes

    Channel nodes create, filter, and manipulate channel data.

  • COP2 - Compositing nodes

    Composite nodes create, filter, and manipulate image data.

  • TOP - Task nodes

    TOP nodes define a workflow where data is fed into the network, turned into "work items" and manipulated by different nodes. Many nodes represent external processes that can be run on the local machine or a server farm.

Lighting, rendering, and compositing

  • Solaris

    Solaris is the umbrella name for Houdini’s scene building, layout, lighting, and rendering tools based on the Universal Scene Description (USD) framework.

  • Rendering

    How to render images and animation from the 3D scene.

  • Materials

    How to assign materials and create custom materials for shading.

  • Compositing

    Houdini’s compositing networks let you create and manipulate images such as renders.

Reference

  • Menus

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  • Viewers

    Viewer pane types.

  • Panes

    Documents the options in various panes.

  • Windows

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    Houdini includes a large number of useful command-line utility programs.

  • Python Scripting

    How to script Houdini using Python and the Houdini Object Model.

  • Expression functions

    Expression functions let you compute the value of parameters.

  • HScript commands

    HScript is Houdini’s legacy scripting language.

  • VEX

    VEX is a high-performance expression language used in many places in Houdini, such as writing shaders.

  • Properties

    Properties let you set up flexible and powerful hierarchies of rendering, shading, lighting, and camera parameters.

  • Python Panels

    You can script custom pane types using Python to create your own UIs.

  • Galleries

    Pre-made materials included with Houdini.

  • Houdini Packages

    How to write and combine multiple environment variable definition files for different plug-ins, tools, and add-ons.