Retail's SkyDesc::GetLighting at 0x00500ac9 (decomp lines 261317-261331)
lerps each color channel and the brightness scalar SEPARATELY, then
multiplies post-lerp:
arg4.r = lerp(k1.amb_color.r, k2.amb_color.r, u)
arg4.g = lerp(k1.amb_color.g, k2.amb_color.g, u)
arg4.b = lerp(k1.amb_color.b, k2.amb_color.b, u)
arg3 = lerp(k1.amb_bright, k2.amb_bright, u)
final = (arg4.rgb * arg3, ...)
acdream pre-multiplied (color × bright) at LOAD time
(`SkyDescLoader.cs:558-559`) and then lerped the product. For any
keyframe pair where both color and brightness change, the two are
mathematically distinct. Example, k1=(white, b=0.5) k2=(black, b=1.0)
at u=0.5:
- retail: color=gray(0.5), bright=0.75 → final = (0.375, 0.375, 0.375)
- acdream: lerp((0.5,0.5,0.5), (0,0,0), 0.5) = (0.25, 0.25, 0.25)
For Rainy/Cloudy DayGroups transitioning between dim and bright
keyframes, this contributes to subtle brightness divergence vs retail.
Refactor:
SkyKeyframe stores DirColor / DirBright / AmbColor / AmbBright
SEPARATELY (raw, not pre-multiplied).
Computed properties SunColor and AmbientColor return the
post-multiplied product, keeping the shader uniform interface
(uSunColor / uAmbientColor) unchanged.
SkyStateProvider.Interpolate lerps each raw channel, then constructs
a new SkyKeyframe whose computed properties yield the correct
post-lerp multiply.
SkyDescLoader now stores raw values without pre-multiplying.
GameWindow comment updated; no functional change there.
Default factory + tests updated to use the new constructor parameters
with DirBright=AmbBright=1.0 (preserving exact existing behavior).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
User observed: 'time is flipped — supposed to be day/evening, but shows
night/morning.' That's a ~half-day offset.
Root cause in ACE DerethDateTime.cs line 23:
private const double dayZeroTicks = 0; // Morningthaw 1, 10 P.Y. - Morntide-and-Half
ACE anchors tick 0 to Morntide-and-Half (slot 7 on the 0-indexed 16-slot
scale) — NOT Darktide (slot 0 = midnight) as our DayFraction function
assumed. Confirmed by DerethDateTime.cs:145:
private int hour = (int)Hours.Morntide_and_Half;
Fix: shift DayFraction by +7/16 * DayTicks (3333.75) so tick 0 maps to
its real calendar slot. Exposed as DayFractionOriginOffsetTicks constant
for documentation + downstream referencing.
Effect on sun: previously, server tick ~0 (just-booted ACE) produced
dayFraction 0 → midnight sky → night colors at noon real-time.
Now dayFraction 7/16 = 0.4375 → late morning sky → noon-ish colors
within 1/16 of a day, which matches what a user actually sees when
launching during daytime.
Tests updated for the corrected convention:
- DerethDateTime.DayFraction(0) = 7/16 (not 0).
- CurrentHour(0) = MorntideAndHalf (not Darktide).
- IsDaytime(0) = true.
- Midnight (Darktide, slot 0) is 9/16 of a day past tick 0.
- SkyState + WorldTimeDebug tests retargeted to the new frame.
Build green, 711 tests pass.
Ref: references/ACE/Source/ACE.Common/DerethDateTime.cs:23-25 + :145.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Client-side deterministic sky + weather + day/night system per R12.
Retail's model is 95% client-side: the server just delivers its
current PortalYearTicks (double, seconds since boot-seed) at login and
in TimeSync packets; the client computes everything else locally from
the constants in r12 §1.2 + ACE DerethDateTime.cs.
Core layer (AcDream.Core/World):
- DerethDateTime: retail-exact calendar (16 hours/day, 30 days/month,
12 months/year, 7620 ticks/day, 2,743,200 ticks/year). HourName enum
covers all 16 named half-hour slots (Darktide → GloamingAndHalf);
MonthName covers the 12 Derethian months (Snowreap → Frostfell).
DayFraction, CurrentHour, IsDaytime, ToCalendar.
- SkyKeyframe + SkyStateProvider: 4-keyframe default day/dawn/noon/dusk
with linear color + angular-wrap heading interpolation + slerp-like
shortest-arc lerp so heading wraps 350° → 10° don't tween backwards
through 180°. Default keyframe colors tuned to retail screenshots
(sunrise warm, noon white, sunset red, midnight deep blue).
- WorldTimeService: owns the live clock. SyncFromServer(ticks) sets
baseline; NowTicks advances by real-time elapsed. Exposes DayFraction,
CurrentSky, CurrentSunDirection, IsDaytime for the render thread.
This is the foundation Phase G.2 (dynamic lighting) consumes: lighting
uniforms are fed from CurrentSky's SunColor / AmbientColor / sun
direction, varying smoothly across the day.
Tests (16 new):
- DerethDateTime: midnight, half-day, wrap, Dawnsong, Midsong,
day/night flag at dawn vs Darktide-Half, year rollover, month
advance.
- SkyState: 4-default keyframes, noon-exact matches frame data,
midpoint lerps between neighbours, wrap across midnight doesn't
produce NaN, sun direction returns unit vector, WorldTimeService
sync + DayFraction at noon.
Build green, 587 tests pass (up from 570).
Ref: r12 §1 (Portal Year math), §2 (sky objects), §4 (color lerp).
Ref: ACE DerethDateTime.cs + NetworkSession TimeSync handler.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
