anisotropy-without-anisotropic-filter
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/anisotropy-without-anisotropic-filter.md contains the canonical detection logic + GPU reasoning.
TL;DR
The MaxAnisotropy field of a sampler descriptor is consumed by the hardware anisotropic filtering path only when the Filter selector requests anisotropic filtering. AMD RDNA 2/3 routes anisotropic samples through the TMU's anisotropic footprint estimator, which computes the elongation of the sample footprint in texture space and issues up to MaxAnisotropy taps along the major axis. NVIDIA Turing/Ada and Intel Xe-HPG document equivalent anisotropic taps. The field is ignored under linear or point filtering: the hardware does not consult MaxAnisotropy because the chosen filter does not invoke the anisotropic footprint estimator.
What the rule fires on
A SamplerState (or SamplerComparisonState) whose descriptor sets MaxAnisotropy > 1 while the Filter field is not one of the anisotropic filter modes (D3D12_FILTER_ANISOTROPIC, D3D12_FILTER_COMPARISON_ANISOTROPIC, D3D12_FILTER_MINIMUM_ANISOTROPIC, D3D12_FILTER_MAXIMUM_ANISOTROPIC). The detector enumerates sampler descriptors via Slang reflection and matches the MaxAnisotropy field against the Filter field on each. It does not fire when MaxAnisotropy is 1 (the trivial default) or when the filter is anisotropic; it fires on the silent-misconfiguration case where MaxAnisotropy was set with the intent of enabling AF but the filter selector was left on linear/point.
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 anisotropy-without-anisotropic-filter.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.