flowchart TD
  F["one fragment covers<br/>samples 0 and 1"] --> M["Metal runs the shader<br/>once per covered sample"]
  M --> C0["copy, sample_id 0<br/>mask 0b0011"]
  M --> C1["copy, sample_id 1<br/>mask 0b0011"]
  C0 --> G{"sample_id ==<br/>ctz(mask)?"}
  C1 --> G
  G -- yes --> S["UAV stores, atomics,<br/>ordered read-modify-write"]
  G -- no --> H["treated as a helper:<br/>stores skipped"]
  C0 --> O["colour to sample 0"]
  C1 --> O1["colour to sample 1"]