# Car harmonic alpha normalization diagnostic, r438

The gameplay car shader's harmonic producer calls `0x489ed0` with two
independent controls. The RGB-enable word at `0x82dae4` is zero-filled, so the
image-default experiment leaves RGB harmonics unchanged. The file-backed
fourth-channel inputs at `0x7f39bc/+0x7f39c0` are enable `1` and target norm
`0.8`. An indirect runtime write to the RGB-enable word has not been ruled out;
this is not a captured live packet.

For the existing conditional Route 450 projection, the unnormalized fourth
coefficient norm is `0.7824361174`. Applying the file-backed fourth-channel
target scales those ten alpha coefficients by about `1.0224`; RGB coefficients
are unchanged. The viewer exposes this under
`?carShader=retail-fallback&carHarmonicsNormalization=image-defaults`; leaving
the parameter unset uses the original unnormalized coefficients.

Host Chrome on the Quadro P2000 rendered both choices at 960x540 with the same
L4RA Route 450 start. Both reached `City scene ready` with no page errors or
failed requests. Their visible difference is small: the body remains flat and
the scene still does not match retail NFSU2. Therefore this file-backed
normalization detail is not the missing lighting solution. The normal driving
shader remains unchanged. Loaded pack membership/order, live dynamic lights,
the draw transform and any indirect normalization initialization remain
unresolved; see [the producer trace](car-harmonic-producer-r267.md).