flowchart TB
    hlsl["HLSL compute shader<br/>ddx(), Sample(), CalculateLevelOfDetail()"] --> dxil["dxil-spirv<br/>2D group → linear quads<br/>(lanes 4k..4k+3)"]
    dxil --> spirv["SPIR-V OpDPdx / implicit-LOD sample"]
    spirv --> before["stock SPIRV-Cross: dfdx() in a kernel"]
    before -->|"Metal: unsupported builtin"| fail["pipeline creation fails"]
    spirv --> patched["patch 0018"]
    patched --> shuffle["ddx = quad_shuffle(v, 1) − quad_shuffle(v, 0)<br/>ddy = quad_shuffle(v, 2) − quad_shuffle(v, 0)"]
    patched --> grad["sample(..., gradient2d(ddx, ddy))"]