/**
 * SpineChain - Core physics for procedural fish animation
 *
 * Based on inverse kinematics chain simulation where:
 * - Each joint follows its predecessor
 * - Distance constraints maintain segment lengths
 * - Angle constraints limit bending between segments
 * - Swimming motion emerges from tail oscillation propagating through chain
 *
 * References:
 * - FABRIK algorithm: http://www.andreasaristidou.com/FABRIK.html
 * - argonaut procedural animation: https://github.com/argonautcode/animal-proc-anim
 */
export interface SpineJoint {
    x: number;
    y: number;
    angle: number;
    width: number;
    segmentLength: number;
}
export interface SpineConfig {
    jointCount: number;
    widthProfile: number[];
    angleConstraint: number;
    segmentLength: number;
}
export declare class SpineChain {
    joints: SpineJoint[];
    angleConstraint: number;
    constructor(config: SpineConfig, startX: number, startY: number, direction: 1 | -1);
    /**
     * Update spine positions - head moves to target, body follows
     * Uses forward reaching: each joint pulls toward its predecessor
     */
    update(targetX: number, targetY: number): void;
    /**
     * Apply swimming wave through entire spine
     * Creates natural S-curve motion that propagates from tail to head
     * @param amplitude - Max swing at tail (decreases toward head)
     * @param phase - Current phase of oscillation (0-2PI)
     */
    applyTailOscillation(amplitude: number, phase: number): void;
    /**
     * Get position along spine using parametric interpolation
     * @param t - Position from 0 (head) to 1 (tail)
     */
    getPositionAt(t: number): {
        x: number;
        y: number;
        angle: number;
        width: number;
    };
    /**
     * Get curvature at a specific joint (angle difference from previous)
     * Used for fin deflection
     */
    getCurvatureAt(jointIndex: number): number;
    /**
     * Get the head position
     */
    get head(): {
        x: number;
        y: number;
    };
    /**
     * Get the tail position
     */
    get tail(): {
        x: number;
        y: number;
    };
    /**
     * Get head angle (fish's facing direction)
     */
    get headAngle(): number;
    /**
     * Constrain an angle to be within angleConstraint of reference
     */
    private constrainAngle;
    /**
     * Normalize angle to -PI to PI range
     */
    private normalizeAngle;
    /**
     * Interpolate between two angles, handling wraparound
     */
    private lerpAngle;
    /**
     * Set body widths from a profile array (for species variation)
     */
    setWidthProfile(profile: number[], maxWidth: number): void;
    /**
     * Get total length of spine
     */
    get totalLength(): number;
}
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