flowchart TD
    S["D3D12 command signature<br/>[INCREMENTING_CONSTANT -> root param 0, DRAW]"] --> P["d3d12: one op per argument {src, dst, words, index}<br/>INCREMENTING_CONSTANT: words = 1, index = 1"]
    A["argument buffer<br/>command i: draw arguments only"] --> K
    P --> K["expand_indirect kernel<br/>thread (word x, command y)"]
    K --> Q{"op.index set?"}
    Q -->|yes| I["write y, the command's index"]
    Q -->|no| C["copy the word from<br/>command y's arguments"]
    I --> R["Metal record y:<br/>draw arguments + root constants"]
    C --> R
    R --> D["the draw reads index<br/>as an ordinary root constant"]