fx_spark

Additive, self-lit surface shader for the car-effects spark population (nring.carfx): one hardware-instanced draw of cards. lane0 carries the HDR colour (intensity and fade already applied, well above the bloom threshold); lane1.x picks the shape — 0 a thin hot streak stretched along the spark's travel (guardrail scrape / bottoming-out sparks), 1 a turbulent white-yellow-to-red flame blob (exhaust backfire pop).