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. Separate logic with execution (transform) in rigs, which is often bottleneck like when using Rig pose SOP & Rigdeform SOP.

Packed Folders

structure - with proper names and types. clearly define elemets to operate on them explicitly

Pack folder SOP name: Base (defauolt naming conv), Type: skel (can choose from list ) 1. Base.rig (rig) 2. Base.skel (skeleton) 3. Base.shp (shape) 4. Guides.skel

(you can see whats inside with rig tree)

Auto rig Component

Adding and manipulating graph At begining nothing will show up, because we need to define what we want

Component Source: - choose which functionality

Rig - source add/update - depend on what is in packed folder

Skeleton -

	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

APEX resources: https://youtu.be/-0KbPtoP5MU —

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