comparison-sampler-without-comparison-op
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/comparison-sampler-without-comparison-op.md contains the canonical detection logic + GPU reasoning.
TL;DR
SamplerComparisonState is a distinct descriptor type from SamplerState on every modern API and IHV. It carries a ComparisonFunc field (LESS, LESS_EQUAL, GREATER, etc.) that drives a hardware comparison-and-blend path inside the sampler unit. On AMD RDNA 2/3 the TMU has a dedicated PCF (percentage-closer filtering) hardware path that, given a comparison sampler, performs four texel comparisons against the reference value and returns a blended in-shadow / out-of-shadow ratio in one sampler-unit cycle. NVIDIA Turing/Ada and Intel Xe-HPG document equivalent comparison hardware. The descriptor's ComparisonFunc field is only consumed by the SampleCmp* and GatherCmp* methods; non-Cmp calls ignore the field entirely.
What the rule fires on
A SamplerComparisonState declaration that, across all reflection-visible call sites against textures bound with this sampler, is only used with non-Cmp-suffixed sample methods (Sample, SampleLevel, SampleGrad, SampleBias) and never with the comparison-suffixed variants (SampleCmp, SampleCmpLevelZero, SampleCmpLevel, GatherCmp). The detector enumerates sampler bindings via reflection, finds every Sample* call against textures that reference each comparison sampler, and fires when no call site uses a comparison method. It does not fire when at least one call site uses a Cmp variant against the sampler.
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 comparison-sampler-without-comparison-op.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.