flowchart TB
    subgraph up["buffer → texture"]
        direction LR
        a1["application buffer<br/>12-byte texels"] -->|"rgb32_expand kernel"| a2["scratch<br/>16-byte texels"] -->|"blit"| a3["RGBA32 Metal texture"]
    end
    subgraph down["texture → buffer"]
        direction LR
        b1["RGBA32 Metal texture"] -->|"blit"| b2["scratch<br/>16-byte texels"] -->|"rgb32_pack kernel"| b3["application buffer<br/>12-byte texels"]
    end
    up ~~~ down