bgra-rgba-swizzle-mismatch
Status: stub. The full-length analysis is queued for a v1.0.x patch release per ADR 0018, section 5, criterion #6. The companion rule page at docs/rules/bgra-rgba-swizzle-mismatch.md contains the canonical detection logic + GPU reasoning.
TL;DR
DXGI_FORMAT_B8G8R8A8_UNORM is the historical swap-chain format for D3D presentation; many older paths (especially UI / IMGUI overlays composited onto the swap-chain) still use BGRA8 throughout. The hardware texture sampler on AMD RDNA 2/3, NVIDIA Turing/Ada, and Intel Xe-HPG reads BGRA8 storage and presents it to the shader as a float4 whose .x lane carries the blue channel and .z lane carries the red channel — the storage order, not the conceptual RGBA order. There is no hardware swizzle on the load path on D3D12; the format-to-shader-view mapping is exactly the storage layout. (Vulkan exposes a per-view componentMapping swizzle that can compensate at descriptor creation; D3D12 does not.)
What the rule fires on
A shader that reads .rgba (or any subset like .r, .rgb, .gb) from a Texture2D<float4> (or analogous typed view) whose underlying resource format, as reported by Slang reflection, is DXGI_FORMAT_B8G8R8A8_UNORM, DXGI_FORMAT_B8G8R8A8_UNORM_SRGB, or DXGI_FORMAT_B8G8R8X8_UNORM, without a corresponding .bgra swizzle to compensate for the BGRA-to-RGBA channel order. The detector cross-references the sample call site's swizzle (or absence thereof) with the resource format from reflection. It does not fire on RGBA-format resources, nor on BGRA resources where the shader explicitly swizzles .bgra (or applies an equivalent component reorder).
See the What it detects section of the rule page for the full pattern definition.
Why it matters
The full GPU-mechanism analysis lives in the Why it matters on a GPU section of the companion rule page.
Examples
The bad / good code snippets are kept canonical on the rule page; see bgra-rgba-swizzle-mismatch.md -> Examples.
See also
- Rule page -- canonical reference + change log.
- texture overview -- broader context.
- ADR 0018 -- v1.0 readiness plan.
This is a v1.0-ship stub. Full analysis pending; track issue link TBD.