Houdini 20.0 Character KineFX

Animation workflow

On this page
This feature is still under development. The current functionality is unfinished and subject to change, and may have thin or no documentation. Please bear this in mind when using it.

Overview

In the animation workflow, users can add characters and animation to a scene, transfer animation to characters through motion retargeting, and play back scene animation. The animation scene, along with the characters and other scene elements, are organized in a packed character format.

An example file that demonstrates the animation workflow is available here.

Basic animation scene setup

The following is the basic workflow for adding a character to a scene, performing animation, and playing back the animation.

Basic animation workflow setup

For a basic setup using the Electra Test Geometry, see the How-to.

SOP

Description

APEX Scene Add Character SOP

Adds characters to a scene. Characters are stored in the packed character format.

Specify a name for the character:

  • On the APEX Scene Add Character SOP, update the Character Name parameter.

    or

  • Rename the APEX Scene Add Character SOP, which will update the Character Name parameter by default.

The input to the APEX Scene Add Character SOP is a set of character elements (skeleton, shape, rig) that have yet to be packed into a character (.char). We can view the contents of the node in the rig tree view:

  1. Select the character node in the network editor.

  2. Open the rig tree view. At the top of a pane, click the New Tab icon, and select New Pane Tab Type ▸ Animation ▸ Rig Tree.

  3. Select Packed Folders from the Type drop-down menu. In our example, we have the following packed folder structure in the node:

    /
-- Base.rig
-- Base.shp
-- Base.skel
-- controlshapelibrary

The APEX Scene Add Character SOP packs the character elements into a character:

  1. Select the APEX Scene Add Character SOP, add_character, in the network editor.

  2. In the rig tree view, we have:

    /
-- character.char/
    -- Base.rig
    -- Base.shp
    -- Base.skel
    -- controlshapelibrary

APEX Scene Animate SOP

The animate state on the APEX Scene Animate SOP allows you to display, pose, and animate the characters in a scene. To enter the animate state, select the APEX Scene Animate SOP, turn on its display flag, and click Animate on the left toolbar.

Note

The animation in the scene can be played back on this SOP only while in the animate state. Once you exit the animate state, the animation cannot be played back. To play the animation outside of the animate state, use the APEX Scene Invoke SOP.

APEX Scene Invoke SOP

The APEX Scene Invoke SOP allows you to play back the animation in the scene.

  1. Select the APEX Scene Invoke SOP and turn on its display flag.

  2. Click Output All Character Shapes, which finds all the characters in the scene and merges their shapes together.

  3. Press Play on the playbar to see the animation on the character.
To...Do this

Add multiple characters to a scene

  1. Bring each character into the scene using an APEX Scene Add Character SOP.

    Add multiple characters to a scene

  2. On each of the APEX Scene Add Character SOPs, specify a name for the character in the Character Name parameter.

  3. On the APEX Scene Invoke SOP, click Output All Character Shapes to display all the characters in the scene.

    Note

    If you add a character into a network that already has an APEX Scene Invoke SOP, you need to click Output All Character Shapes for the new character to be displayed in the viewport.

Import existing animation onto a character

If you already have existing animation, you can use the APEX Scene Add Animation SOP to import the animation onto a character.

Import existing animation onto a character

SOP

Description

APEX Scene Add Animation SOP

In the Rig Path parameter, specify the rig to put the animation on.

To find the rig to use:

  1. Select the APEX Scene Add Animation SOP.

  2. Open the rig tree view to view the characters in the scene.

  3. Select Packed Folder from the Type drop-down menu. Characters have a .char extension, and within each character is a .rig element. In our example, we set Rig Path to /character.char/Base.rig.

The animation is added to the scene in the form of channel primitives. Channel primitives are animation curves that are stored along with the geometry and are optimized for use in the animate state.

APEX Scene Animate SOP

In the animate state, you can see the animation that is added to the character. The animation data is available in the animation editor graph view as curves that you can edit.

To perform additional animation on top of the imported animation, you can pose the character in the animate state, or manipulate the channel data directly in the animation editor.

To work in the animation editor:

  1. Enter the animate state.

  2. In the viewport, select the controls on the character. Channel data for the controls will be added to the channel list, and you can interact with them in the animation editor graph view.

Add animation to a character

You can add animation to a character by extracting the character’s skeleton control hierarchy, and using the Rig Pose SOP to pose the character and add keyframes.

In this example, the animation is not added back into the scene.

Update skeleton controls

SOP

Description

APEX Control Extract SOP

Extracts the control hierarchy of the skeleton.

  1. Turn on Extract From Folder.

  2. Specify the rig in Graph Geometry Path. In our example, we set Graph Geometry Path to /character.char/Base.rig.

  3. Specify the controls to extract in the Group parameter. If you leave the Group parameter as the default, the entire control hierarchy on the rig is extracted.

Rig Pose SOP

Pose the character and set keyframes.

To see the character while posing with the Rig Pose SOP, set up the APEX Scene Invoke SOP as below, and turn on its display flag.

APEX Control Update Parms SOP

Updates the skeleton controls with the animation performed on the Rig Pose SOP. The APEX Control Update Parms SOP is used together with the APEX Control Extract SOP to update the controls on the skeleton.

APEX Scene Invoke SOP

Play back the animation on the character.

  1. Click Output All Character Shapes to display all the characters in the scene.

  2. Specify the rig to put the animation back onto in the Animation Target parameter. In our example, we set Animation Target to /character.char/Base.rig.

  3. Turn on the display flag, and press Play on the playbar to see the animation on the character.

Add additional animation on top of the Rig Pose animation

To add additional animation on top of the Rig Pose animation, we first save the Rig Pose animation as channel primitives, and add these channel primitives into the scene. We can then perform additional animation using the APEX Scene Animate SOP.

Add additional animation on top of Rig Pose animation

SOP

Description

MotionClip SOP

Creates a MotionClip from the skeleton animation.

APEX Channel Primitives from MotionClip SOP

Creates channel primitives from the MotionClip, and adds a keyframe on every MotionClip pose.

APEX Scene Add Animation SOP

Adds the animation from the channel primitives onto the character.

APEX Scene Animate SOP

In the animate state, you can see the Rig Pose animation on the character. The animation data (from the channel primitives) is available in the animation editor graph view as curves that you can edit.

If too many keyframes are added by the APEX Channel Primitives from MotionClip SOP, use the Reduce Resample tool on the animation toolbar to reduce the number of keyframes:

  1. Select the control(s) in the animate state.

  2. In the animation editor graph view, select the keys.

  3. Adjust the Reduce Resample tool slider.

Retarget animation onto a character

The APEX Control Extract SOP extracts the skeleton control hierarchy of a character and outputs a KineFX skeleton. We can then use any of the KineFX SOPs to modify the transforms of the skeleton, and put the updated transforms back onto the skeleton using the APEX Control Update Parms SOP.

We can use this workflow to retarget animation onto a character in a scene.

Motion retargeting using KineFX operations
Electra added to the scene without animation
Motion to retarget onto Electra
Electra with retargeted animation

How-to

To...Do this

Animate on an Electra Test Geometry

The Electra test geometry can be configured to be output as part of an animation scene. This allows you to animate on Electra with minimal setup steps:

  1. Put down an Electra Test Geometry SOP in the network editor.

  2. On the Electra Test Geometry SOP, set Output to APEX Scene.

  3. Select the Electra Test Geometry SOP, and click Animate on the left toolbar to enter the animate state. An APEX Scene Animate SOP will be automatically placed after the Electra Test Geometry SOP.

To play back your animation:

  1. Add an APEX Scene Invoke SOP.

  2. Select the APEX Scene Invoke SOP and turn on its display flag.

  3. On the APEX Scene Invoke SOP, click Output All Character Shapes.

  4. Press Play on the playbar to see the animation.

To add multiple Electra characters to the scene, use an APEX Scene Add Character SOP for each Electra:

  1. On the Electra Test Geometry SOPs, set Output to APEX Character.

  2. On each of the APEX Scene Add Character SOPs, specify a name for the character in the Character Name parameter.

  3. On the APEX Scene Invoke SOP, click Output All Character Shapes.

Test the state of the scene

Use the APEX Scene Invoke SOP to test out the state of the scene.

  1. Select the APEX Scene Invoke SOP and turn on its display flag.

  2. On the APEX Scene Invoke SOP, click Output All Character Shapes.

  3. In the Animation Target parameter, specify the rig to put the animation back onto.

  4. Press Play on the playbar to see the animation.

Add keyframes only on the key poses when creating channels from a MotionClip

Add a MotionClip Extract Key Poses SOP after the MotionClip SOP in this setup.

Save a scene to a file

  1. Connect a node that contains the scene (APEX Scene Add Character SOP, APEX Scene Add Animation SOP, APEX Scene Animate SOP) to the ROP Geometry Output SOP.

  2. On the ROP Geometry Output SOP, specify the name of the file to save the scene to in the Output File parameter.

  3. Click Save to Disk.

Use a scene file

  1. Put a File SOP in the network editor.

  2. On the File SOP, specify the scene file in Geometry File.

  3. Select the File SOP, and click Animate on the left toolbar to enter the animate state. An APEX Scene Animate SOP will be automatically placed after the File SOP.

KineFX

Preparing rig inputs

Procedural Rigging

Deformation

Animation

Appendix

Animation Retargeting

KineFX 19.5 functionality

Compatibility

Panes