import type { Object3D } from "three";
import { Vector3 } from "three";
/**
 * Analytical two-bone IK solver operating in world space.
 *
 * Chain: root → middle → end. The pole controls middle-joint bend direction.
 *
 * Writes local quaternions to `root` and `middle` bones.
 * Does not modify the `end` bone.
 *
 * Call `solve()` after AnimationMixer update each frame.
 */
export declare class TwoBoneIK {
    /** First bone in the chain (e.g. upper leg, upper arm). */
    readonly root: Object3D;
    /** Second bone in the chain (e.g. lower leg, forearm). */
    readonly middle: Object3D;
    /** Terminal bone (e.g. foot, hand). Not rotated by the solver. */
    readonly end: Object3D;
    /** Controls the bend direction of the middle joint. */
    readonly pole: Object3D;
    /** Solve target. When undefined, `solve()` is a no-op. */
    target?: Object3D | undefined;
    /** Numerical stability threshold. */
    epsilon: number;
    /**
     * Twists the root bone around its aim axis so that `rootPoleAxis` aligns toward the pole.
     */
    rootPoleTwist: boolean;
    /**
     * Root bone's local-space axis aligned toward the pole when `rootPoleTwist` is enabled.
     * Default: `(0, 1, 0)`.
     */
    rootPoleAxis: Vector3;
    /**
     * Twists the middle bone around its aim axis so that `middlePoleAxis` aligns toward the pole.
     */
    middlePoleTwist: boolean;
    /**
     * Middle bone's local-space axis aligned toward the pole when `middlePoleTwist` is enabled.
     * Default: `(0, 1, 0)`.
     */
    middlePoleAxis: Vector3;
    private readonly rootPosition;
    private readonly middlePosition;
    private readonly endPosition;
    private readonly targetPosition;
    private readonly polePosition;
    private readonly chainDirection;
    private readonly perpendicularDirection;
    private readonly middleTarget;
    private readonly currentDirection;
    private readonly desiredDirection;
    private readonly bonePosition;
    private readonly childPosition;
    private readonly aimAxis;
    private readonly currentUp;
    private readonly desiredUp;
    private readonly deltaRotation;
    private readonly boneWorldQuaternion;
    private readonly parentWorldQuaternion;
    private readonly twistRotation;
    constructor(
    /** First bone in the chain (e.g. upper leg, upper arm). */
    root: Object3D, 
    /** Second bone in the chain (e.g. lower leg, forearm). */
    middle: Object3D, 
    /** Terminal bone (e.g. foot, hand). Not rotated by the solver. */
    end: Object3D, 
    /** Controls the bend direction of the middle joint. */
    pole: Object3D, 
    /** Solve target. When undefined, `solve()` is a no-op. */
    target?: Object3D | undefined);
    /** No-op when `target` is undefined. */
    solve(): void;
    /**
     * Twist `bone` around its aim axis (bone→child) so that `poleAxis`
     * (bone's local space) points toward the pole.
     *
     * Resolves the roll ambiguity left by `aimBone`,
     * which constrains aim direction but not roll.
     */
    private twistBoneTowardPole;
    /**
     * Rotate `bone` so that `child` points toward `worldTarget`.
     * Writes `bone.quaternion` in local space.
     */
    private aimBone;
}