this._bg = new Graphics();
this._bg.beginFill(0x000000, 0.5);
this._bg.drawRect(0, 0, GAME_WIDTH, GAME_HEIGHT);
this._bg.endFill();
const g = new PIXI.Graphics()
g.beginFill(0xFFF);
g.lineStyle(20, 0xFFF);
g.moveTo(50, 50);
g.lineTo(100, 100);
g.lineTo(150, 50);
g.endFill();
this._bg.mask = g;
this.addChild(this._bg);