import type { TrackSamples } from './types';
/**
 * An interpolator produces a sample between two keyframes.
 *
 * - `a`, `b`: bracket keyframe values, each of length = `stride`
 * - `alpha`: interpolation factor in [0, 1]
 * - `out`: caller-owned output buffer, length = `stride`; the function writes into it in place
 */
export type Interpolator = (a: Float32Array, b: Float32Array, alpha: number, out: Float32Array) => void;
/** Per-component linear interpolation. Works for scalar (stride=1) and any vec length. */
export declare const lerp: Interpolator;
/** Step — hold the previous sample. */
export declare const step: Interpolator;
/** Nearest — pick whichever bracket endpoint is closer. */
export declare const nearest: Interpolator;
/**
 * Spherical linear interpolation for unit quaternions `[x, y, z, w]`.
 *
 * - Inputs are assumed to have length 4. Out buffer must also be length 4.
 * - Picks the shortest-arc path by flipping sign of `b` when `dot(a, b) < 0`.
 * - Falls back to `lerp` (and re-normalizes) when the two quats are very close
 *   to avoid division-by-zero.
 */
export declare const slerpQuat: Interpolator;
export interface BracketHint {
    value: number;
}
/**
 * Sample a track at a given time, writing the interpolated value into `out`.
 *
 * Pure function — no React, safe to call inside `clock.on('tick')` or any
 * imperative render loop. Keeps the `findBracket` hint in a caller-owned
 * container so multiple calls amortize to O(1) during sequential playback.
 *
 * Callers must provide `out` sized to `track.stride`.
 */
export declare function sampleTrack(track: TrackSamples, time: number, interp: Interpolator, hint: BracketHint, out: Float32Array): void;
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