///
/// 加载一个Sprite
///
private Sprite LoadSprite(string assetName)
{
Texture texture = (Texture)Resources.Load(assetName);
Sprite sprite = Sprite.Create((Texture2D)texture, new Rect(0, 0, texture.width, texture.height), new Vector2(0.5f, 0.5f));
return sprite;
}