/** Column-major 4x4 multiply (glTF convention): out = a * b. */
export declare function mul4(a: readonly number[], b: readonly number[]): number[];
/** Full 4x4 inverse (column-major), via cofactor expansion (gl-matrix). Throws on a singular matrix. */
export declare function invert4(m: readonly number[]): number[];
/** Transform a point (w=1) by a column-major 4x4; returns [x,y,z] (affine, no perspective divide). */
export declare function transformPoint(m: readonly number[], p: readonly [number, number, number]): [number, number, number];
/** Transform a direction (w=0) by the upper 3x3 of a column-major 4x4 (no translation). */
export declare function transformDir(m: readonly number[], d: readonly [number, number, number]): [number, number, number];
/**
 * Strips scale from a column-major TRS matrix: normalizes the three basis columns (leaving pure
 * rotation) and keeps the translation. Used to build scale-free world frames for retargeting, so a
 * rig authored at a non-unit armature scale (e.g. Meshy's 0.01) doesn't leak its scale into the
 * rest-to-rest delta.
 */
export declare function rigidize(m: readonly number[]): number[];
export type Vec3 = readonly [number, number, number];
export declare const sub3: (a: Vec3, b: Vec3) => [number, number, number];
export declare const dot3: (a: Vec3, b: Vec3) => number;
export declare const cross3: (a: Vec3, b: Vec3) => [number, number, number];
export declare function normalize3(a: Vec3): [number, number, number];
/**
 * Builds an orthonormal world frame (column-major 4x4) from a bone's geometric DIRECTION and position,
 * NOT its stored local axes — the key to convention-free retargeting. The primary column X = `axis`
 * (the bone's world direction); a roll reference (world-up, or world-forward when the axis is
 * near-vertical) is Gram-Schmidt'd against X for Y; Z = X×Y. Building this identically for the source
 * and target rigs makes frameDst·frameSrc⁻¹ cancel the bone-axis convention, leaving only the real
 * direction/pose/position difference.
 */
export declare function frameFromAxis(axis: Vec3, pos: Vec3): number[];
/**
 * Minimal (shortest-arc) rotation taking direction `from` onto direction `to`, as a column-major 4x4
 * with zero translation. Unlike frameFromAxis pairs, it adds NO roll about the target axis — the roll
 * DOF a bone direction can't express stays untouched. Antiparallel inputs get a π turn about an
 * arbitrary perpendicular axis.
 */
export declare function shortestArc4(from: Vec3, to: Vec3): number[];