使用spritekit做游戏开发时候，图片的素材可能是序列帧，也可能是多帧显示在一张图片上。如果一帧显示在一张图片上的时候，怎么获取每张想要的图片那？

let birdTexture = SKTexture(imageNamed: "bird")
        let bird1 = SKTexture(rect:CGRect(origin:birdTexture.textureRect().origin,size:CGSize(width:
            birdTexture.textureRect().maxX / 3,height:birdTexture.size().height)),in: birdTexture)
        主角帧.append(bird1)
        var rect2 = birdTexture.textureRect().origin
        rect2.x = rect2.x + birdTexture.textureRect().maxX / 3
        let bird2 = SKTexture(rect:CGRect(origin:rect2,size:CGSize(width:birdTexture.textureRect().maxX / 3,in: birdTexture)
        主角帧.append(bird2)

        var rect3 = birdTexture.textureRect().origin
        rect3.x = rect3.x + birdTexture.textureRect().maxX / 3 * 2
        let bird3 = SKTexture(rect:CGRect(origin:rect3,in: birdTexture)
        主角帧.append(bird3)

这样就拿到了一个图片texture的数组。