Five pillars, four colored point lights; closest-hit emits one shadow ray
per light from the same invocation (raysPerPixel = 4, maxDepth = 2), so up
to four rays per pixel rtAccumulate in a single SHADE pass — the contention
case #30 exists for. Each pillar casts four separable colored shadows; an
accumulator race or capacity drop shows as flickering dark noise or a
missing shadow color. Two frames a second apart diff at 2 px / 1.85 M
(last-ulp CAS ordering), confirming no lost updates.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
wfAccum becomes array<atomic<u32>> (4 slots/pixel, f32 bit patterns — same
16 B/pixel footprint) and rtAccumulate CASes each channel, so N rays for one
pixel may resolve in the same SHADE pass without the read-modify-write
racing. GENERATE clears with atomicStore (bitcast(0.0) == 0u); RESOLVE
atomicLoads + bitcasts the vec4 it hands runResolve.
Capacity half: RTPass::raysPerPixel (default 1) scales the wavefront
ray/hit/payload buffers to raysPerPixel·W·H rays per bounce so the
per-light emits actually fit instead of being dropped by rtEmitRay's
capacity guard. The accumulator stays per-pixel.
No flag-gating: uncontended the CAS succeeds first try — RTStress SHADE
stays at its documented ~1.0 ms and master-vs-branch renders are
byte-identical, so single-ray consumers pay nothing.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
