https://developer.arm.com/-/media/Files/pdf/graphics-and-multimedia/Efficient%20Rendering%20with%20Tile%20Local%20Storage.pdf?revision=055f4bd5-2be0-4540-ac91-b34ae28701ef
metal里面 管framebuffer fetch这个事情叫 programmableblending 定义input 为output就可以 fs里面直接拿来用