fx_puff

Surface shader for the car-effects puff population (nring.carfx): camera-facing cards drawn as one hardware-instanced draw. Each card reads its look from its instance lanes: lane0 = linear albedo + opacity, lane1 = shape (0 a billowing noise-rimmed smoke puff, 1 a hard-edged turf/dirt clump), seed, age 0..1. Smoke is lit as a translucent medium — wrapped sun on a rounded, up-leaning normal, a forward-scattering glow when backlit, sky ambient, and the sun's shadow map — so a burnout cloud reads white in sun and grey in shade. Clumps are lit as small rough solids. Soft-faded where a card meets the ground or the car (scene-depth fade). Alpha-blended, no depth write.