Rising stone ramp

genshin:parity calibrate solves each hour's stone light as the game's deferred pass casts it: a toon ramp read at the face's facing to the sun, plus the sky's spherical harmonics (login screen). Solved freely, with only its dark end held at no light, the day's and the dusk's ramps fall toward the lit end, so a face turned to the sun reads darker than one turned away. The proposal was to hold the ramp to rise, solving it as non-negative rises from its dark end, and then to solve the sun's direction under that ramp.

Why deferred: the frames score it worse. Held to rise, every hour's light leaves the dawn, the day, the night and the phone's door frame level, and scores the door recording's dusk about a hundredth of FLIP worse. The sun's direction is not what the falling ramp hides. Refined under the rising ramp from the hand-set directions, by the binned residual the light leaves, the day's sun moves a few degrees for nothing measurable and the dusk's barely moves. The sky's linear harmonics take up whatever a ramp's facing term would, so faces' shading cannot settle a direction. Turning the haze's sunward glow toward the dusk's sun instead of its light, and re-solving, scored the dusk the same. Whatever the falling ramp stands in for, it is something the solve's model does not yet hold.

Revisit when: the deferred pass's GGX highlight and reflection cube, and the exports' normal maps, are in the light's solve. Those are the terms that brighten or darken faces by how they turn, which a free ramp can mimic. If the ramp still falls with them in the model, holding it to rise is the next measure.