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IKSolver.md

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IKSolver - ThreeJs

Inverse Kinematics Solvers implemented with CCD and FABRIK algorithms for ThreeJs

See IKHelper to visualise information associated with an instance of an IKSolver

import { FABRIKSolver, CCDIKSolver } from "IKSolver.js"
let scene = new THREE.Scene();
// ... scene setup ...

//load some skinned model, or generate a skeleton manually sopmehow
let model = loadModel()
let skeleton = model.getSkeleton() // returns Threejs Skeleton

let target = new THREE.Object3D();
target.position.set(0,0,1);
scene.add( target );

let ikSolver = new FABRIKSolver( skeleton );
//let ikSolver = new CCDIKSolver( skeleton );

ikSolver.setIterations( 1 );
ikSolver.setSquaredDistanceThreshold( 0.0001 );



ikSolver.createChain(
    [5,4,3,2,1,0],
    [ 
        null, // ignored always

        {type: FABRIKSolver.JOINTTYPES.OMNI, twist:[ 0, 0.0001 ] },   

        {type: FABRIKSolver.JOINTTYPES.HINGE, twist:[ 0, 0.0001 ], axis:[1,0,0], min: 0, max: Math.PI * 0.5 },   
        
        {type: FABRIKSolver.JOINTTYPES.HINGE, twist:[ 0, 0.0001 ], axis:[1,0,0] }, // unconstrained angle of hinge   
        
        {type: FABRIKSolver.JOINTTYPES.BALLSOCKET, twist:[ -Math.PI*0.25, Math.PI*0.25 ], axis:[0,1,0] polar:[0, Math.PI*0.5], azimuth:[-Math.PI * 0.6, Math.PI*0.4]},

        {type: FABRIKSolver.JOINTTYPES.BALLSOCKET, twist:[ -Math.PI*0.25, Math.PI*0.25 ], polar:[0, Math.PI*0.5]} // unconstrained azimuth and default axis to 0,0,1
    ],
    target,
    "MyChain"
);


ikSolver.update();

// ... render ...

target.position.set(1,0,0);
ikSolver.update();

// ... render ...

Classes

There are two algorithms implemented, with their own class. Nonetheless, both use the exact same api and methods

  • class FABRIKSolver implements the FABRIK solution
  • class CCDIKSolver implements the CCD solution

Static Members

JOINTTYPES

Enumeration of types

  • OMNI: 0
  • HINGE: 1
  • BALLSOCKET: 2

Can be accessed from both classes as

  • FABRIKSolver.JOINTTYPES
  • CCDIKSolver.JOINTTYPES

Methods

constructor( skeleton )

  • skeleton : (ThreeJs skeleton).

addEventListener( name, callback )

Adds an event callback. The allowed events are onSetConstraint, onCreateChain, onDestroyChain. onCreateChain is first. onSetConstraint is called every time a "set constraint" method is called. Does not trigger when destroying a chain onDestroyChain only event triggered when distroying a chain. No constraint specific events are triggered.

  • name : (string).
  • callback : (function)

setIterations( iterations )

Sets the amount of iterations to compute during update.

  • iterations : (int).

setSquaredDistanceThreshold( sqDist )

Sets the maximum squared distance to consider a certain effector as well positioned.

  • sqDist : (number >= 0).

createChain( newChain, newConstraints, targetObj, name )

Adds a new chain to the internal list. Chains inserted last will have higher priority.

  • newChain : (array) ordered list of bone indices that constitute the chain. [ effector, parent, parent-parent, ... , root chain ].
  • newConstraints : (array or null) list of the same lenght as newChain containing an object for each bone in the chain with its constraints. All nulls will be considered as unconstrained. Effector does not have constraints, meaning the first entry will be ignored
  • targetObj : (object) Target object to follow. Must either be an Object3D in the scene or an object with a 'position' property containing a Vector3
  • name : (string).

removeChain( name )

Removes the specified chain from the internal list if found.

  • name : (string).

Returns true if successful, false otherwise.

removeAllChains( )

Removes all chains from this solver.

getChain( name )

Searches for a chain named as name and returns its description.

  • name : (string).

Returns an object if an existing chain is found, null otherwise.

setChainEnabler( name, isEnabled )

Enables/Disables a chain.

  • name : (string).
  • isEnabled : (boolean)

Returns true if successful, false otherwise.

setChainEnablerAll( isEnabled )

Enables/Disables a all chains at once.

  • isEnabled : (boolean)

setConstraintToBone( chainName, idxBoneInChain, newConstraint )

Modifies a constraint of a bone in an existing chain.

  • chainName : (string) Name of chain to fetch.
  • idxBoneInChain : (int) Index in the chain array (not the actual bone number).
  • newConstraint : (object) Object with all desired attributes for that constraint. See JOINTTYPES Member and Constraint Types.

Returns true if successful, false otherwise.

update( )

Computes the FABRIK or CCD algorithm over all enabled chains.