KFX

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KineFX - Rigs, Retarget, Animation

Related notes: CFX, Unreal Animation, Animation

Files: SOP_KineFX.hiplc

Kine FX

Attributes

  • Joint
    • Point that is part of hierarchy (defined by hierarchy). In world space
      • v@P - position
      • s@name unique per point + As topology change rest of points stays where supposed to
      • 3@transform (9flt - matrix) - global transform: (matrix3) rotation, scale (joints orientation)
  • Controls
    • Control animation with UI handle
      • @name on prims
  • Stash Pose / Bind Pose
    • T or A pose saved into attribute.
      • 4@rest_transform - (16flt - matrix) - add 4x4 [ Rig Stash Pose ] > @rest_transform
  • Geometry
    • Mesh with weights
      • s@name on prim
      • @boneCapture on point

Export

  • Mesh / Bind Pose / Animation

Skeleton

  • Rotation order, Rz Ry Rx depend on skeleton and its joint rotation (unreal Y is -Y in Houdini) 1. one with bone (look at from parent to child) 2. component represent twist toward twist.
  • Splines starts from root to child. Create from Poly line or L-system.
  • When to apply rotation:
    • Pre-multiply - local
    • Post-multiply - parent

Components

  • Hierarchy
    • Determined by vertex index order (always in specific order - always follow curve)
      • PolyPath SOP can fix hierarchy by rebuilding vertex order.
      • Reverse SOP change direction.
  • Transforms
    • Worlds space For rigging. Ground truth.
      • @transform (9flt) - Rotation and scale only. Position from @P.
    • Local space For animation. Calculated per operation.
      • @localtransform (16flt). - Position, rot and scale.
      • Compute transforms - recalculate local transform
    • Scale Inheritance - What happen to other bones when we scale one
      • @scale inheretance
      • @_efectivelocaltransform (16flt)
  • Names
    • Unique string on points.

Create Skeleton from scratch

Manual setup

  • Name
    • Name SOP
    • Enumerate SOP (string on points)
  • Orientation
    • Orient Joints SOP - Orientation mater only for hand drawn Houdini rigs. To fix orientation. Re-orient joints with direction picking.
    • Orient along curve SOP - Mor options to create transform. ([x] 3x3 transform, [x] next edge for tangent, [ ] t urn off N and tangentu)

Automatic setup

  • Skeleton SOP - Click stash input to freeze (like cache). you can disconnect. not for procedural update
  • Rig doctor SOP - Create all missing attribs: name s@name, transforms: point: v@transform, p@localtransform and debug hierarchy.

![[createskeleton.png]]

Skeleton Create Tool

Skeleton SOP

  • Can control bone placement, rename bones, orient selected bones. It create @localtransform. (with correct orientation)
  • Shortcuts
    • RMB menu
    • P - details of joints.
    • placement type - can place in middle of geo or on top
  • Add to Skeleton
    • in separated skeleton and capture

Skeleton Operations Nodes

Skeleton Mirror SOP

Parent Joints SOP

Delete Joints SOP

  • Delete with reparent.

Configure Joints SOP

  • Create dictionary attribute @fbik_jointconfig on points. witch:
    • rest xform Local ! (rest transform attribute is recomputed),
    • rot low limits in radians, (limits - shown as orange rect )
    • and rot order
  • Modes:
    • Full Body IK - most complex - local center of mass, … rotation weights/limits
    • Ragdoll - only rotation constraints limits
    • Rig Pose - rotation and translation limits
  • Shortcuts:
    • Shift + 7/ 8 - to configure limit.
    • Shift + F - to flip handle

Skeleton Blend SOP

  • Blend skeletons / anims (feed with 2 animations)

Repair Nodes

Realistic Shoulder SOP -

Reverse Foot SOP -

Stabilize Joints SOP
- Select joints to stabilize, will identify automaticly - not solve. > Delete SOP to get only joints to stablize > use : full body ik

Capture

Capture rigid

  • [ Capture Packed SOP] - [x] pack input & unpack Output. Manual capture: geo: * joint name of joint

Capture soft

![ 1200](/src/kine/skin.png)

Capture pipeline:

  1. [ Bone Capture Line SOP ] - define capture regions @joints
  2. [ Tet Embed SOP ] - create mesh weightings op2 bonecapture
  3. [ Bone Capture Biharmonic SOP ] - transfers weights to skin op1: , op2: tet

Paint Capture

  • [ Capture Layer Paint SOP ] - Use for overpaint rig weights. (per region name so semi procedural)
    • RMB to switch between functionalitie. Can loose information simetimes so cache bgeo.sc later !!!! bonecapture attribute@points
- boneCapture region
bone Capture w
region with highest influence will be first . by default 6 regions


https://youtu.be/p3zG1wos2nk

LIMIT Regions from 6 to 4 for games


`capture attrib pack / unpack SOP]``
  • [ Capture Layer Paint ] older. ?
  • [ cpature mirror ]

Rig ( Legacy KineFx )

Constraints

Control only selected bones through other bones in a specific way. Control Skeleton control Source Constrain to match.

  • IK / FK
  • Offset Transform -
  • Blend Transform -
  • Parent Constraint -
  • Re-Parten Constraint
  • Look at Constraint or Look at (kinefx) - drag 3 vectors from viewport

constraints YT

IK Constraint

IK - Target and Control bones to steer each other. Target bone + Elbo to control rotation

IK Chain

IK Chain SOP.

  • op1: skeleton. op2 control points with same name (reparent sop with *)
  • select root mid and tip bones points.
  • set! match by name or names for controllers
  • manipulate pose before 2 op of ik chain

VOP
  • Two Bone IK VOP - Copy of IK Chain SOP
    VEX
    solvefbik()
solvephysfbik()
solveik()

Full body IK

Have different solvers types:

  • Physical full body IK - default
  • FABRIK (forward / backward reaching) - We lose feature (no rotation, more robotic)

How To Setup:

  1. Input controls to second op2
    • Delet joints - rest will become controls
    • Parent joints SOP with *
  2. Setup Fullbody IK SOP solver.
    • match by attribute (name) - names must match!
    • can pin root
    • can compute weight
    • Damping - can smooth.
      VOP
      - `Solve IK` VOP - Mix IK chain SOP & Fullbody IK. We can have many bones in between

FK Constraint

FK Transfer

doc

Solve Curve - Spline IK VOP

Solve curve with normalized bone lengths

RIG VOP: take all points from in and out and drive one another.

  • get point transforms VOP - from first input
  • get point transforms VOP - from second input
  • solve curve - set targets and ctrl & ctrl files
    • type curve: must match type curve from ctrl curve input
  • set transform VOP - > points and xforms to out https://youtu.be/ZUBSQ-2BkMo?t=1071

Controls

Control (or any geo) + prim name
AtachControlGeo SOP

  • attach joint geo (as 3op of pose tool) still technical approach. (next release for artists approach)

Rig (APEX )

APEX

Rigs as operations - a separation of concerns. (Shadow rig) hierarchy to control rig > clean for export

https://youtu.be/-0KbPtoP5MU

  1. skeleton to: Pack folder SOP name: Base (defauolt naming conv), Type: skel (can choose from list )
    1. Autorig Component SOP dropdown list: FK
      1. you need to promote transformgroup: * rotationgoup: * scalegroup * (or use point* if ‘point’ in name )
    2. Configure Controls SOP

Animation

Motion

Motion Clips

Geometry place in space. To chop anims. Give sense of timing, (timeing is spaceing) [ Motion Clip ] . Not time dependent (see all frames at once). One packed primitive per frame with @time attrribute. To operate on neighbour frames.
[ Motion Clip Evaluate ] - Time dependent Animation - One pose per frame.

  • [ Configure Clip Info ]
  • [ Motion Clip Extract ] - Extract Frames
  • [ Motion clip retime ] –
  • …

Mix Animations

  • [ Motion Clip Blend ] - kitbash 2 files. 1 as base second for mix. Can delete some bones and apply partial animation.
  • [ Motion Clip Cycle ] - show locomotionb joint (root) / blend start to end
  • [ Motion Clip Sequence ] - blend (Mode: different match transition), blend frames

Animation

Procedural Animation

Rig Attribute Wrangle & VOP

Curl few points.

  • Rig Attrib Vop SOP - inside for each we have offsettransform node where we can do operation. ![[transformanim.png]]
  • Rig attrib wrangler SOP
    • rotate(3@localtransform, @Time, {1,0,0});
    • prerotate(3@localtransform, @Time, {1,0,0}); - it applies the rotation to the matrix before move
rotate(4@localtransform, radians(10), {1,0,0})
// scale()
// translate()

float f = @ptnum / (npoints(0)-1.0);
    //f= fit(@ptnum,0,npoints(0)-1.0,0.0,1.0);

float maxang = chf('maxang');
maxang *= f;
matrix rotmat = ident();
rotate(rotmat,radians(5), set(1,0,0));
4@localtransform *= rotmat;

Look At other bone

  • Rig Attrib Vop- Get root and target bones from input 0 & 1 then look at constraint ![[Pasted image 20250511233735.png]]

Key Animation

[ Rig Pose ] - initial frame or per frame anim

  • rotation limits of your joints in the

Bake - .???

Shortcuts

  • Q, A, Z, Z+Shift - cycle through joints.
  • Motion Path LMB - Add MMB - move timeline
  • Ctrl+ LMB - Add key on path

Mocap

Root motion

[ Extract Locomotion ] - extract root motion

  • use hip joint
  • create temporal joint named locomotion > later transfer this motion to root.
  • apply motion back: [Rig pose] with: point("/obj/geo/extractlocomotion",24, "P", 0)

Optimize

  • motion clip extract key poses - optimize mocap

Secondary motion

  1. [ Rig Statch Pose ]
  2. [ Secondary Motion ] - to convert to clips
    • source joint group as root It need to be animated. (have delta in local transform)
    • secondary motion - jiggle / spring / lag/overshoot
  3. [ Evaluate Motion Clip ]

Simulation Ragdoll

Bullet and scale must be accurate

  1. [ Rig Stash Pose ]
  2. [ Configure Joints ] - Mode: Ragdoll
  3. [ Ragdoll Collision Shape ]
    • Setup spheres [in construction of colliision shape can use custom but name on prims is required, and collision should be packed]
    • Aan add properties like: mass
  4. [ Ragdoll Constraints ]
    • Internal Constraint: op1: ceeate cone (limit) constraints on collision spheres. (soft and hard constr.) (can use additional outside go (3op)) That will hold collisions toghether
    • External Constraint op2: constraint joint to geometry group (glue, hard (pin and stuck), soft)
    • if no group will take closest ??
  5. [ Ragdoll Solver ]
    • type:
    • RDB Impact Data ()

Simulation Vellum

Retarget

![[retarget.png]]

Retarget

  1. [ Rig Match Pose ] - lineup pose in viewport (Align target skeleton 2op is master )
  2. [ Map Points ] - 2 . match points
  3. [ Full Body IK ] - final retargeting > can weight here. fist place to correct retergeted motion // Crack IK transfers & rotates:
  4. [ FK Transfer ] -
  5. [ Skeleton Blend ] - i.e. fullbodyik/fktransfer

[ Rig Match Pose SOP ]

  • March size: Source Skeleton - to leave UE5 source character (not anim)

VEX

[Rig Attrib Wrangle] SOP

Find root

#include <kinefx.h>

int ancestors[] = getancestors(0,@ptnum,-1);
int root = ancestors[-1];
s@root_path = point(0,"path",root);

[ Rig Attribute VOP ]

![[constraintsa.png]]

RIG VOP is in Detail mode

  • Get Point Transform Import point to VOP (like bind) can drag points directly from viewport.
  • Set Point Transform - Export data from VOP

Transform

  • xform - is working param (world transform of joints)
  • localxform - (relative to parent) local transform - (relative to parent) scale not effecting need 2 joints
  • effective localxform - scale inheritance attribute i@scaleinheritance = chi("scale_inheritancei");

YT Rok Andic cgwiki
V Ron Andic channel YT KineFX A Simple IK/FK
KineFX Masterclass | Houdini Illume | Jeff Wagner
Henry HIVE
Houdini KineFX 101: Tutorial One - FBX Import, Rig Pose, Skeleton Blend
Agent from skeleton - crowds

https://www.youtube.com/watch?v=RTNVyGbpwv0&ab_channel=RohanDalvi

https://www.sidefx.com/community-main-menu/character-workflow-rig-animate-secondary-motion/

Kurs Vimeo + PDF YT SideFX - Fur dude, YT SideFX PDF YT Jeff Masterclass
YT Rok Andic channle
YT Rok Andic patreon
YT Rok Andic site
SideFx Elephant
SideFX Tokyomegaplex CHRISTOPHER RUTLEDGE

Rebelway Trailer + talk

YT siggraph hive 2022
Junichiro Horikawa - Robot rig
Junichiro Horikawa - Plant rig mechanic Rus
mechanic Entagma
curve solver VOP
Mixamo to Cascadeur to Houdini

https://vimeo.com/686814178?embedded=true&source=vimeo_logo&owner=1723479

  • [smoth motion] SOP