/**
 * class vector 2
 */
export declare class Vector2 {
    x: number;
    y: number;
    /**
     * create a vector 2 class
     * @param x
     * @param y
     */
    constructor(x?: number, y?: number);
    clone(): Vector2;
    /**
     * get the length of the vector
     * @returns {number}
     */
    get length(): number;
    /**
     * @return {number}
     */
    get lengthSq(): number;
    /**
     * normalize the vector
     * @returns {Vector2}
     */
    normalize(): Vector2;
    /**
     * set value of the vector
     * @param a
     */
    set(a: Vector2): void;
    /**
     * invert the vector direction
     * @returns {Vector2}
     */
    invert(): Vector2;
    /**
     * rotate 90
     * @returns {Vector2}
     */
    rotate90(): Vector2;
    /**
     * add to another vector
     * @param a
     * @returns {Vector2}
     */
    add(a: Vector2): Vector2;
    /**
     * subtract with another vector
     * @param a
     * @returns {Vector2}
     */
    subtract(a: Vector2): Vector2;
    /**
     * multiply by a number
     * @param a
     * @returns {Vector2}
     */
    multiply(a: number): Vector2;
    /**
     * rotate by an angle
     * @param a
     * @returns {Vector2}
     */
    rotateBy(a: number): Vector2;
    rotateByRadian(a: number): Vector2;
    /**
     * multiply by a vector
     * @param a
     * @returns {Vector2}
     */
    cross(a: Vector2): number;
    /**
     * dot a vector
     * @param a
     * @returns {number}
     */
    dot(a: Vector2): number;
    static perp(v1: number[], v2: number[]): Vector2;
    static neg(v: Vector2): Vector2;
}