试背景图片变化

背景会随着关卡变化
Revert "试背景图片变化"

This reverts commit 6e7c4ab30c03d4fc57bcb80bac90e70ce37204b1.
Revert "Revert "试背景图片变化""

This reverts commit 54e8a6ae3251a51dce046cd7f22ecc18899dc351.