Re-enables the Phase 2 lighting formula that was reverted in Phase 3b
due to a "blue-green-yellow sweep" across clouds. Root cause of that
earlier regression was NOT the formula — it was that we rolled the
wrong DayGroup (Sunny when retail was Cloudy), producing a sharp warm
sun against a sky that should have been rendered with diffuse
overcast light. After Phase 3g pinned the LCG multiplier to 360
(DaysPerYear) so retail + acdream agree on DayGroup, the same
per-vertex formula now faithfully reproduces retail's visuals.
The formula is verified in decompile agent Q2+Q4+Q6 results,
`docs/research/2026-04-23-sky-material-state.md`:
D3DRS_LIGHTING = ON (FUN_0059da60:10648)
D3DRS_AMBIENT = 0 (never written after init)
Material.Emissive = (Luminosity, Luminosity, Luminosity, 1)
Material.Ambient/Diffuse = defaults (≈1,1,1,1) for non-luminous
light.Ambient = keyframe AmbColor × AmbBright (via SetDirectionalLight)
light.Diffuse = keyframe DirColor × DirBright
Fixed-function lighting per vertex:
lit = Emissive + Ambient × lightAmbient + Diffuse × lightDiffuse × max(N·L, 0)
= Surface.Luminosity + AmbColor×AmbBright + DirColor×DirBright × max(N·L, 0)
Fragment: texture × lit × SkyObjectReplace.Luminosity.
Expected visual:
- Dome (Surface.Luminosity=1): `lit = 1 + amb + diff·N·L` saturates to 1
→ texture passthrough, baked gradient preserved.
- Clouds (Surface.Luminosity=0): `lit = 0 + amb + diff·N·L`
→ purple haze at night (ambient dominates, sun below horizon);
→ warm tan at dusk (ambient + warm sun on west-facing vertices);
→ pale cool gray at noon (ambient + white sun from above).
- Sun/moon (SurfaceType.Additive, Luminosity=1): same as dome +
additive blend — stays bright regardless.
The shader uniforms (uAmbientColor, uSunColor, uSunDir, uEmissive)
were already wired in the C# renderer from Phase 2; Phase 3b just
stopped using them in the shader. This commit re-activates them.
No clamp at the vertex — retail's D3D lighting allows Emissive+sum
to exceed 1, relies on the framebuffer per-channel saturation. We
keep the 1.2 ceiling in the frag (for lightning flash overbright
headroom) consistent with that convention.
No fog yet (Q1 confirmed retail leaves fog enabled for sky; will add
in a follow-up if horizon looks too bright).
Build + 733 tests green.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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