Each band's delta was scaled by the summed weight of the bands that happened
to be adjusted:
d_hue = d_hue / w_total;
d_sat = d_sat / w_total;
The divisor is the wrong quantity, and it fails in two directions.
A band adjusted on its own divides by its own weight and cancels it — w*v/w is
v — so the falloff does nothing. Green saturation at +100 hit a pixel at 179°
exactly as hard as one at 120° and not at all at 181°: full strength across the
whole window, then a cliff. That seam is the thing the overlap exists to
prevent, and it was there the moment a single band was touched.
Worse, the divisor counts a band's weight even for a channel that band says
nothing about, so the controls compete. `red_hue` at +100 shifts a pure red
pixel +30°. Set `orange_sat` as well and the same pixel shifts +20°, while
orange's saturation bleeds into pure red at a third strength. Hue and
saturation on *neighbouring* colours were trading against each other — the two
sliders behaving as though only one of them could be spent.
The real fault is upstream of the division: the falloff window was ±60° while
the bands sit 30° apart, so the twelve weights sum to 2.0 rather than 1.0 and
*something* had to correct for it. Narrowing the window to the band spacing
makes them a partition of unity, and then nothing has to. The division is gone;
`w_total` stays, demoted to what it should always have been — the test for
whether any adjusted band reaches this pixel at all.
Everything the module header claimed is now true rather than aspirational: a
band reaches zero at its neighbours' centres, a hue halfway between two gets
half of each, twelve bands at +100 equals global +100, and a band pushed alone
reaches the full 30° of travel its own comment documents instead of whatever
fraction the other sliders left it.
`overlapping_weights_are_normalised` asserted the broken arithmetic verbatim,
so it is replaced rather than repaired. In its place: no delta may be divided
by w_total, the guard must survive, two adjacent bands must emit independent
terms, and — the property the rest now rests on — the twelve weights must sum
to one, swept at 0.1° around the wheel. That last test carries a Rust mirror of
`band_weight`, so a third test pins the mirror to the shader's own constants;
a copy nothing checks is how the window and the spacing drifted apart in the
first place.
Also gone: the red branch of `rgb_to_hcl` computed its hue twice and threw the
first away.
This changes how existing edits render. Mixer adjustments are more selective,
and where they were quietly cancelling each other they no longer are, so a
saved sidecar will not come back looking the same.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
dtourolleandClaude Opus 5
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