shadowBlur cost scales with the blurred device-pixel area. The lit-sustain
trail can span half the canvas, the canvas is DPR-scaled (4x pixels on a
2x Mac), and the blur ran on every frame exactly while a sustain is HELD
— i.e. at the moment the player most notices a hitch. Sustain-heavy songs
(e.g. fingerpicked acoustic charts) hit this constantly.
Replace the blur with three inflated low-alpha fills of the same trail
quad: reads as the same soft shimmering glow (the shimmer LUT still
drives per-frame flicker, feedBack#254 intent preserved) at a flat,
area-independent cost. Also drops the now-dead shadowBlur reset in the
crackle pass; no shadowBlur uses remain in highway.js.
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
Co-authored-by: Byron Gamatos <xasiklas@gmail.com>
