grom's play test, in Ironforge: "some edges, and seems to be only in
interiors, are shining really bright, like flashing colors". His config
has `autoExposure = "1"`, so the lane I landed last commit was live, and
"interiors only" is its exact signature — the gain is 1.0 outdoors by
construction and only ever rises indoors.
The apply pass was a plain multiply, and a plain multiply pushes ordinary
bright surfaces past the white point. Everything downstream reads a value
above 1.0 as EMISSIVE: `post/bloom.wgsl`'s extract is literally
`max(c - 1, 0)`, and FFXGlow squares its blur. So a lamp surround, gold
trim or a window frame sitting just under white crossed the line and grew
a bloom halo it had no business having — and because the gain drifts with
what is on screen, the set of pixels across that line kept changing and
the haloes FLASHED. It also scaled the HDR headroom itself, doubling the
bloom of everything that genuinely was emissive.
Measured, pixels at or above 250/255 — which is the bloom's fuel:
off Subtle Full
vista 0.338% 0.338% 0.338% (gain is 1.0: untouched)
inn, noon 0.024% 1.930% 9.779% ( 80x / 407x)
inn kitchen 0.001% 0.312% 1.549% (312x / 1549x)
Interiors only, exactly as reported.
The fix is a tone curve instead of a multiply: extended Reinhard with its
white point AT the gain. Three properties, each load-bearing — it is the
exact identity at gain 1 (`e(1+e)/(1+e) = e`), so a daylight exterior is
untouched; it maps the white point to white at every gain, so it can NEVER
produce a value above 1.0 and cannot manufacture an emissive pixel; and it
is monotonic, so highlights roll off toward white instead of flattening
onto it, which a hard clamp would have done. The HDR headroom now passes
through unscaled: it belongs to whatever was actually emissive, and how
bright the room is has no bearing on it.
After, same measurement at his tier: the inn goes 1.930% -> 0.388% and the
kitchen 0.312% -> 0.061%, while the brightening is kept whole (kitchen
median 35.8 -> 35.4, pixels under 32 40.3% -> 41.0%). What remains is
genuinely bright pixels rather than manufactured ones — a surface that was
never emissive now cannot bloom at all, because the picture path cannot
reach 1.0 from below.
`the_tone_curve_cannot_manufacture_an_emissive_pixel` pins all three
properties over the tier range, and a second test pins the Rust mirror to
the shader text so they cannot drift.
The exterior is a no-op to within 0.12% of pixels at mean |d| 0.16 — a few
dozen shadowed-foliage pixels where the gain lands a hair over 1.0. Below
anything visible, and stated rather than rounded away.
Verified: ALL GATES GREEN (290 s); `benilla-app --lib` against the install
at the exact 269-failure baseline, set-identical by `comm`.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SgstFWtn1RxEJ5kVrpgYwn
gromandClaude Opus 5
113572b8e2