import type { Vec2 } from "./geometry.js";
/** Sum of two 2D vectors.
 * @internal
 */
export declare function add(a: Vec2, b: Vec2): Vec2;
/** Difference `a - b` of two 2D vectors.
 * @internal
 */
export declare function sub(a: Vec2, b: Vec2): Vec2;
/** Scale a 2D vector by a scalar.
 * @internal
 */
export declare function scale(a: Vec2, s: number): Vec2;
/** Negate a 2D vector.
 * @internal
 */
export declare function negate(a: Vec2): Vec2;
/** Dot product of two 2D vectors.
 * @internal
 */
export declare function dot(a: Vec2, b: Vec2): number;
/** 2D cross product (scalar z of the 3D cross), positive when `b` is counter-clockwise from `a`.
 * @internal
 */
export declare function cross(a: Vec2, b: Vec2): number;
/** Euclidean length of a 2D vector.
 * @internal
 */
export declare function length(a: Vec2): number;
/** Squared length of a 2D vector; cheaper than `length` when only comparing magnitudes.
 * @internal
 */
export declare function lengthSquared(a: Vec2): number;
/** Unit vector in the direction of `a`; returns the zero vector when `a` has no length.
 * @internal
 */
export declare function normalize(a: Vec2): Vec2;
/** Distance between two points.
 * @internal
 */
export declare function distance(a: Vec2, b: Vec2): number;
/** Squared distance between two points; cheaper than `distance` for radius comparisons.
 * @internal
 */
export declare function distanceSquared(a: Vec2, b: Vec2): number;
/** Linearly interpolate between points `a` and `b` by fraction `t`.
 * @internal
 */
export declare function lerp(a: Vec2, b: Vec2, t: number): Vec2;
/** Left-hand perpendicular of `a` (rotated 90° counter-clockwise).
 * @internal
 */
export declare function perp(a: Vec2): Vec2;
/** Rotate a 2D vector by `radians` about the origin.
 * @internal
 */
export declare function rotate(a: Vec2, radians: number): Vec2;
/**
 * Reflect a velocity off a surface with unit `normal`, losing energy by `restitution` (0..1). At
 * `restitution` 1 the normal component mirrors elastically (`v − 2(v·n)n`); at 0 it is removed so the
 * vector slides along the surface. Only the normal component is scaled — tangential motion is kept — so
 * this is the wall/paddle/boundary bounce every arcade ball game hand-rolls.
  * @internal
  */
export declare function reflect(v: Vec2, normal: Vec2, restitution?: number): Vec2;
/** Unit vector for a heading measured clockwise from +Y (the engine's XZ-plane convention).
 * @internal
 */
export declare function fromHeading(headingRad: number): Vec2;
/** Heading in radians of a vector, measured clockwise from +Y to match `fromHeading`.
 * @internal
 */
export declare function heading(a: Vec2): number;
/** Wrap an angle in radians into `[0, 2π)`.
 * @internal
 */
export declare function normalizeAngle(angleRad: number): number;
/** Wrap an angle in degrees into `[0, 360)`.
 * @internal
 */
export declare function normalizeAngleDeg(angleDeg: number): number;