Houdini 20.5 Nodes Object nodes

Bone object node

The Bone Object is used to create hierarchies of limb-like objects that form part of a hierarchy …

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The Bone Object is used to create hierarchies of limb-like objects that form part of a hierarchy or chain of bone objects that are parented to one another. The movement of the chain of Bone objects is “solved” or computed based on several methods including Inverse Kinematics. The parenting attribute of bones is unique in that each bone attaches to the end, not the origin, of the parent bone.

It is recommended that you use the Bones Operation, accessed through the icons above the Viewport, to construct such a chain because placing individual bone objects and establishing their parenting relationships from operator to operator is extremely time consuming and not at all intuitive. In addition, a chain created using the Bones Operation will produce a better behaved bone chain.

By default, bones do not render. They contain two types of display geometry: “link geometry” and “capture region geometry”. The former consists of a narrow diamond shape which has been stretched to the length specified in Bone Length, and placed along the Bone Object’s negative Z-axis. The latter consists of two or more user-controllable pill-shaped regions that are used to define capture regions used in skeleton sops. You can specify whether either of the two types of geometry are displayed.

The actual movement of the Bone objects is controlled through an IK CHOP (when using the standard Capture/Deform model). The IK CHOP overrides the bone rotation parameters. If you want to override this behavior, then you need to delete the bone’s channels such that they are no longer over-ridden by chop control.

When bones are parented as children of bone objects, they are automatically positioned at the tip of their parent bone object. If a bone object is parented as the child of a non-bone object, it will attach to the origin of the parent object.

Using Bones

  1. Click the Bones tool on the Characters tab.

  2. Click to place the chain of bones anywhere in the scene view, and continue clicking to add bones to the chain.

    • You can control interior snapping using the Placement menu in the operation toolbar. This is useful for snapping bones to the midline of character skin geometry.

      By default, if a bone intersects a geometry node it will be placed within the geometry based on the view (“View based”). Otherwise the bone will be grounded on the construction plane.

      “Normal based” snaps within geometry based on the geometry normals rather than the view.

      “Freehand” does no interior snapping.

    • You can add, remove, and change kinematics in the drop-down menu on the operations toolbar, or click the bones in the scene view.

      If you create a chain of bones with inverse kinematics a null object will appear at the end of the chain which allows you to easily move the bones while it is grounded by the chain root.

  3. Press Enter to finish the chain.

  4. Name the chain of bones in the Chain Name field on the operations toolbar.

Using Bones

  1. In the viewport, press ⇥ Tab and type Path.

  2. Draw the curve in the viewport.

  3. Make sure the curve is selected, and click the Bones from Curve tool on the Characters tab.

    You can change the Kinematics to Follow Curve in the drop-down menu on the operations toolbar if you want the bones to be bound to the curve. This allows you to modify the curve and the bone chain is automatically adjusted.

  4. Name the chain of bones in the Chain Name field on the operations toolbar.

    You can also increase or decrease the Number of Bones in the chain by changing the value in the value in the operations toolbar.

Parameters

Transform

Translate

Translation along XYZ axes.

Rotate

Degrees rotation about XYZ axes.

Uniform Scale

Scale the object uniformly along all three axes.

Modify Pre-Transform

This menu contains options for manipulating the pre-transform values. The pre-transform is an internal transform that is applied prior to the regular transform parameters. This allows you to change the frame of reference for the translate, rotate, scale parameter values below without changing the overall transform.

Clean Transform

This reverts the translate, rotate, scale parameters to their default values while maintaining the same overall transform.

Clean Translates

This sets the translate parameter to (0, 0, 0) while maintaining the same overall transform.

Clean Rotates

This sets the rotate parameter to (0, 0, 0) while maintaining the same overall transform.

Clean Scales

This sets the scale parameter to (1, 1, 1) while maintaining the same overall transform.

Extract Pre-transform

This removes the pre-transform by setting the translate, rotate, and scale parameters in order to maintain the same overall transform. Note that if there were shears in the pre-transform, it can not be completely removed.

Reset Pre-transform

This completely removes the pre-transform without changing any parameters. This will change the overall transform of the object if there are any non-default values in the translate, rotate, and scale parameters.

Keep Position When Parenting

When the object is re-parented, maintain its current world position by changing the object’s transform parameters.

Child Compensation

When the object is being transformed, maintain the current world transforms of its children by changing their transform parameters.

Enable Constraints

Enable Constraints Network on the object.

Constraints

Path to a CHOP Constraints Network.

Tip

You can you use the Constraints drop down button to activate one of the Constraints Shelf Tool. If you do so, the first pick session is filled automatically by nodes selected in the parameter panel.

Note

Lookat and Follow Path parameters on object nodes are deprecated in favor of Look At and Follow Path constraints. The parameters are only hidden for now and you can set their visibility if you do edit the node’s parameter interface.

Bone

Display Link

Toggles the displaying of the link geometry

Rest Angles

Defines the relative weighting of rotations about the bone’s x,y,z axis for the Inverse Kinematics solver. These values are relative to the bone’s pre-transform. These are zero by default when created from the object viewer’s Bones tool with the pre-transform rotation values defining the rest angles.

Bone Length

Changes the length of the bone

Kinematic Solver

Specifies the CHOP node from which this bone should obtain its cooking rotations from. This requires that the specified CHOP have 3 tracks that are named as: path:rx, path:ry, and path:rz where path is the full path of this bone without the /obj prefix. This path can be obtained using the opsubpath() expression function.

If this parameter is non-empty on a bone without custom geometry, then the display geometry of the bone will be different to indicate this.

The remaining parameters on this page only affect the solutions generated by InverseKin CHOPs using one of the solvers with constraints.

Dampening

Affects how quickly this bone’s angles can be changed.

Angle Range

Specifies the minimum and maximum rotation angles that this bone can have in each axis. (Only used by IK w/Constraints solver)

Damping Angle

Applies damping to the rotation of the bone when the rotation in each axis falls within the specified angle of its minimum or maximum value. The damping occurs when the solved angle is within this angle value from the angle range. (Only used by IK w/Constraints solver)

Damping Rolloff

Specifies the rate at which damping increases as the rotation varies within the damping angle of the minimum or maximum angles. This can also be thought of as the linear slope value at the damping angle region. (Only used by IK w/Constraints solver)

Capture

Display Capture Region

Toggles the display of the /displaycapture capture region.

Capture Region

Capture Region Center

Position of the center of the bone’s /ccrcenter[xyz] capture region. Note that this co-ordinate in object-space. Also the z component uses a bone length as a multiplier, thus 0.5 equals half way along the bone.

Capture Region Rotates

Rotation of the capture region /ccrrotate[xyz].

Capture Region Scales

Scaling factors. Scaling is performed about the bone local origin in the directions of the local reference frame axes. /ccrscale[xyz].

Capture Top Height

Height of the capture region from the /crtopheight center to the top cap.

Capture Top Cap

X,Y,Z radii of the top hemisphere /ccrtopcap[xyz].

Capture Bot Height

Height of the region from the center /ccrbotheight to the bottom cap.

Capture Bot Cap

X,Y,Z radii of the bottom hemisphere /ccrbotcap[xyz].

Deform Region

This tab contains similar parameters as capture regions, but they are used for animation and deformation of captured geometry. Notably, the scaling factors can be used to squash and stretch the capture regions during animation.

Capture Bone Length

The length of a bone in the capture mode. This is the bone length when a bone is used for capturing geometry. Note that the capture mode can be turned on by selecting Edit ▸ Objects ▸ Bone Kinematic Override: Capture Pose from the main menu.

Capture Bone Translate

The translation of the bone in the capture mode.

Capture Bone Rotate

The rotation angles of the bone in the capture mode. Note that the bone rotation axis order is ZYX. Rotation together with Translate and Scale parameters form a transformation

that positions a bone in the capture position and orientation with respect to the world space. The transform order for this transformation is Scale, Rotate, Translate.

Capture Bone Scale

The scaling of the bone in the capture mode.

Render

Display

Whether or not this object is displayed in the viewport and rendered. Turn on the checkbox to have Houdini use this parameter, then set the value to 0 to hide the object in the viewport and not render it, or 1 to show and render the object. If the checkbox is off, Houdini ignores the value.

Misc

Set Wireframe Color

Use the specified wireframe color

Wireframe Color

The display color of the object

Viewport Selecting Enabled

Object is capable of being picked in the viewport.

Select Script

Script to run when the object is picked in the viewport. See select scripts .

Cache Object Transform

Caches object transforms once Houdini calculates them. This is especially useful for objects whose world space position is expensive to calculate (such as Sticky objects), and objects at the end of long parenting chains (such as Bones). This option is turned on by default for Sticky and Bone objects.

See the OBJ Caching section of the Houdini Preferences window for how to control the size of the object transform cache.

See also

Object nodes

  • Agent Cam

    Create and attach camera to a crowd agent.

  • Alembic Archive

    Loads the objects from an Alembic scene archive (.abc) file into the object level.

  • Alembic Xform

    Loads only the transform from an object or objects in an Alembic scene archive (.abc).

  • Ambient Light

    Adds a constant level of light to every surface in the scene (or in the light’s mask), coming from no specific direction.

  • Auto Bone Chain Interface

    The Auto Bone Chain Interface is created by the IK from Objects and IK from Bones tools on the Rigging shelf.

  • Blend

    Switches or blends between the transformations of several input objects.

  • Blend Sticky

    Computes its transform by blending between the transforms of two or more sticky objects, allowing you to blend a position across a polygonal surface.

  • Bone

    The Bone Object is used to create hierarchies of limb-like objects that form part of a hierarchy …

  • Camera

    You can view your scene through a camera, and render from its point of view.

  • Common object parameters

  • Dop Network

    The DOP Network Object contains a dynamic simulation.

  • Environment Light

    Environment Lights provide background illumination from outside the scene.

  • Extract Transform

    The Extract Transform Object gets its transform by comparing the points of two pieces of geometry.

  • Fetch

    The Fetch Object gets its transform by copying the transform of another object.

  • Formation Crowd Example

    Crowd example showing a changing formation setup

  • Fuzzy Logic Obstacle Avoidance Example

  • Fuzzy Logic State Transition Example

  • Geometry

    Container for the geometry operators (SOPs) that define a modeled object.

  • Groom Merge

    Merges groom data from multiple objects into one.

  • Guide Deform

    Moves the curves of a groom with animated skin.

  • Guide Groom

    Generates guide curves from a skin geometry and does further processing on these using an editable SOP network contained within the node.

  • Guide Simulate

    Runs a physics simulation on the input guides.

  • Hair Card Generate

    Converts dense hair curves to a polygon card, keeping the style and shape of the groom.

  • Hair Card Texture Example

    An example of how to create a texture for hair cards.

  • Hair Generate

    Generates hair from a skin geometry and guide curves.

  • Handle

    The Handle Object is an IK tool for manipulating bones.

  • Indirect Light

    Indirect lights produce illumination that has reflected from other objects in the scene.

  • Instance

    Instance Objects can instance other geometry, light, or even subnetworks of objects.

  • LOP Import

    Imports transform data from a USD primitive in a LOP node.

  • LOP Import Camera

    Imports a USD camera primitive from a LOP node.

  • Labs Fire Presets

    Quickly generate and render fire simulations using presets for size varying from torch to small to 1m high and low

  • Light

    Light Objects cast light on other objects in a scene.

  • Light template

    A very limited light object without any built-in render properties. Use this only if you want to build completely custom light with your choice of properties.

  • Microphone

    The Microphone object specifies a listening point for the SpatialAudio CHOP.

  • Mocap Acclaim

    Import Acclaim motion capture.

  • Mocap Biped 1

    A male character with motion captured animations.

  • Mocap Biped 2

    A male character with motion captured animations.

  • Mocap Biped 3

    A male character with motion captured animations.

  • Null

    Serves as a place-holder in the scene, usually for parenting. this object does not render.

  • Path

    The Path object creates an oriented curve (path)

  • PathCV

    The PathCV object creates control vertices used by the Path object.

  • Python Script

    The Python Script object is a container for the geometry operators (SOPs) that define a modeled object.

  • Ragdoll Run Example

    Crowd example showing a simple ragdoll setup.

  • Reference Image

    Container for the Compositing operators (COP2) that define a picture.

  • Rivet

    Creates a rivet on an objects surface, usually for parenting.

  • Simple Biped

    A simple and efficient animation rig with full controls.

  • Simple Female

    A simple and efficient female character animation rig with full controls.

  • Simple Male

    A simple and efficient male character animation rig with full controls.

  • Sound

    The Sound object defines a sound emission point for the Spatial Audio chop.

  • Stadium Crowds Example

    Crowd example showing a stadium setup

  • Stereo Camera Rig

    Provides parameters to manipulate the interaxial lens distance as well as the zero parallax setting plane in the scene.

  • Stereo Camera Template

    Serves as a basis for constructing a more functional stereo camera rig as a digital asset.

  • Sticky

    Creates a sticky object based on the UV’s of a surface, usually for parenting.

  • Street Crowd Example

    Crowd example showing a street setup with two agent groups

  • Subnet

    Container for objects.

  • Switcher

    Acts as a camera but switches between the views from other cameras.

  • TOP Network

    The TOP Network operator contains object-level nodes for running tasks.

  • VR Camera

    Camera supporting VR image rendering.

  • Viewport Isolator

    A Python Script HDA providing per viewport isolation controls from selection.

  • glTF