我想实现背景无限滚动的效果，用tileSprite可以做，但是图片是放大过的，宽度明显大于屏幕宽度。下面是我的关键代码：

var width = document.documentElement.clientWidth
var height = document.documentElement.clientHeight
var game = new Phaser.Game(width, height, Phaser.AUTO, "game")
var gamebg
var states = {
    preload: function(){
        this.preload = function(){
            game.stage.backgroundColor = '#f0f';
            // 加载游戏资源
            game.load.crossOrigin = 'anonymous'; // 设置跨域
            game.load.image('gamebg', './images/gamebg.png');
            game.load.onLoadComplete.add(function(){
                game.state.start("created")
            });
        }
    },
    created: function(){
        this.create = function(){
            gamebg = game.add.tileSprite(0, 0, width, height,'gamebg');
            console.log(width,height)
        },
        this.update = function(){
            gamebg.tilePosition.y += 2
        }
    }
}
// 添加场景到游戏示例中
Object.keys(states).map(function (key) {
    game.state.add(key, states[key]);
});
// 启动游戏
game.state.start('preload');