Method centerOn

packages/fairygui/src/widgets/Window.ts:257–267

* Center window on GRoot * 在 GRoot 上居中窗口

(r: GRoot, bRestraint?: boolean)

     * 在 GRoot 上居中窗口
     */
    public centerOn(r: GRoot, bRestraint?: boolean): void {
        this.setXY(
            Math.round((r.width - this.width) / 2),
            Math.round((r.height - this.height) / 2)
        );

        if (bRestraint) {
            this.relations.add(r, ERelationType.CenterCenter);
            this.relations.add(r, ERelationType.MiddleMiddle);
        }
    }

    /**
     * Toggle window visibility