ik

The inverse kinematics library behind the IKChain, IKLimb, IKLookAt, IKAim, and IKRig components. Require this module when you are driving a chain from a script, or writing a solver of your own; the components are the normal way in.

Exports

• chain — resolve a root-to-tip bone run from a rig, run forward kinematics over it, and move it between pose buffers. Everything else operates on a chain.
• solvers — twoBone, ccd, fabrik, aim, lookAt, plus byName and names for looking one up from a component field. The five are also lifted onto this module directly.
• limits — cone and hinge rotation limits, measured from a bone's rest pose.
• grounding — foot probes, slope-clamped surface alignment, pelvis drop, and the framerate-independent smoothing that keeps a foot from popping at a step edge.
• bind — the component-side plumbing: find a body, get an IK node onto the graph driving it, and convert between world and model space.
• ikNode, basePose — the animation nodes IK runs through.

Usage

local ik = require("systems.ik.ik")

local rig = ik.bind.rigOf(bodyId)
local c = ik.chain.fromRole(rig.bones, rig.roles, "rightarm")
ik.chain.forward(c)
ik.twoBone.solve(c, { target = modelSpaceTarget, pole = elbowHint, weight = 1 })

A chain solves in the rig's own model space. bind.worldToModel and bind.modelToWorld convert a world-space point into and out of it, scale included — a target handed to a solver in world space will be wrong by whatever the body is scaled by.

Notes

• chain.forward runs forward kinematics over the chain's own bones; chain.forwardBase runs it over the bones above the chain's root, which is what puts an arm at its shoulder rather than at the character's origin. A solver needs both to have run.
• Solvers rewrite chain.lRot in place and leave translations alone. Call chain.forward after a solve to see the result in gPos / gRot.
• weight 0 is an exact pass-through on every solver and short-circuits before any work happens.
• Every solver tolerates a target it cannot reach: the chain extends toward it rather than producing a degenerate pose or NaN.