引擎版本 2.13.3

一直有这个问题，PC上检测不出多指的触摸的，必须是手机模式才可以，这个是属于 BUG 吗？
import Input3D = Laya.Input3D;
import Vector2 = Laya.Vector2;

/**
 * 手指。
 */
export class Finger {
    public id: number = 0;  
    public position: Vector2 = new Vector2();
    public deltaPosition: Vector2 = new Vector2();

    constructor(id?: number) {
        if (id != undefined) {
            this.id = id;
        }
    }
}

/**
 * 触摸监听者接口。
 */
export interface ITouchListener {
    onTouchDown(finger: Finger);
    onTouchSwipe(finger: Finger);
    onTouchUp(finger: Finger);
}

/**
 * 多点触摸。
 */
export class Touch {

    private input: Input3D;

    private touchCount: number = 0;

    private touches: Map<number, Laya.Touch> = new Map<number, Laya.Touch>();
    private oldTouches: Map<number, Laya.Touch> = new Map<number, Laya.Touch>();
    private fingers: Map<number, Finger> = new Map<number, Finger>();

    private listener: ITouchListener;

    constructor(input: Input3D) {
        this.input = input;

        if (Laya.Browser.onPC) {

        }
    }

    dispose() {
        if (Laya.Browser.onPC) {
            
        }
    }

    public setListener(listener: ITouchListener) {
        this.listener = listener;
    }

    /** 帧更新函数中调用。 */
    public update() {
        this.touchCount = this.input.touchCount();   // 这个在 PC 上永远是 0。

        // copy touches.
        if (this.oldTouches.size > 0) {
            this.oldTouches.clear();
        }
        for (let [key, value] of this.touches) {
            this.oldTouches.set(key, value);
        }

        // reset touches.
        if (this.touches.size > 0) {
            this.touches.clear();
        }

        // get touches.
        for (let i = 0; i < this.touchCount; ++i) {
            let touch = this.input.getTouch(i);
            // this.touches.set(touch.identifier, touch); // iOS 上是一个不确定的很小的负数，并不是0开始的，且每点击一次都会-1，所以有问题。
            this.touches.set(i, touch);
        }

        // fingers gesture.
        for (let [key, value] of this.touches) {
            // get finger.
            let finger = this.fingers.get(key)
            if (finger == undefined) {
                finger = new Finger();
                finger.id = key;
                this.fingers.set(key, finger);
            }

            if (this.oldTouches.has(key)) {
                // downing.
                finger.deltaPosition.x = value.position.x - finger.position.x;
                finger.deltaPosition.y = value.position.y - finger.position.y;
                finger.position.x = value.position.x;
                finger.position.y = value.position.y;

                if (finger.deltaPosition.x != 0 || finger.deltaPosition.y != 0) {
                    // console.log("Swipe", key, Date.now());
                    if (this.listener) this.listener.onTouchSwipe(finger);
                }
            }
            else {
                // down start.               
                finger.deltaPosition.x = 0;
                finger.deltaPosition.y = 0;
                finger.position.x = value.position.x;
                finger.position.y = value.position.y;

                // console.log("Down", key);
                if (this.listener) this.listener.onTouchDown(finger);
            }
        }

        for (let key of this.oldTouches.keys()) {
            if (!this.touches.has(key)) {
                // up.
                // console.log("Up", key); 
                if (this.listener) this.listener.onTouchUp(this.fingers.get(key));
            }
        }
    }

}