Day-Night Exposure and Emissive Scaling · CultivatingImmortality

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Three independent "day-night brightness controls" originally ran on different curves; when the night ambience was darkened, character and skill emissive still carried a hundreds-of-times daytime multiplier, blowing out. All three were unified on one shared curve, GetDaylightFactor, and each consumer takes what it needs.

— Origin of the V61 unified curve

1. Three Independent Problems → One Unified Solution

Problem	Root cause	Fix
Scene too bright at night, no night mood	No night darkening on the scene PPV	Negative AutoExposureBias offset
Character emissive patterns overexposed at night	A fixed hundreds-fold multiplier at the end of material Emissive, constant through day and night	Material × EffectBrightness scalar (Lerp to 0.03 at night / 1.0 by day)
Skill VFX as bright as daytime at night	Some Niagara materials were not wired to MPC EmissiveScale	Batch-add Multiply × CollectionParameter(EmissiveScale) to 52 emissive materials

2. The V61 Authoritative Curve (Shared by All Three Consumers)

The static function ATimeOfDayManager::GetDaylightFactor(float Hours) returns a factor from 0 (fully dark at night) to 1 (fully bright by day). The exposure/skill/character consumers each use either "1 − factor" or factor directly.

Time	DaylightFactor	Exposure DimFactor (=1−factor)	Skill EmissiveScale	Character EffectBrightness
09:00–18:15	1 (full bright)	0 (unchanged)	1.0	1.0
18:15–19:30	1→0.762	0→0.238	1→0.762	1→0.762
19:30–21:30	0.762→0	0.238→1	0.762→0	0.762→0
21:30–06:15	0 (fully dark)	1 (max)	0.000024	0.03
06:15–08:00	0→0.538	1→0.462	0.000024→0.538	0.03→0.538
08:00–09:00	0.538→1	0.462→0	0.538→1	0.538→1

Curve Parameters (Tunable Levers)

constexpr float NightDimMaxEV   = 4.0f;   // 夜晚最多压暗的 EV（±1 EV ≈ 亮度 ×2 或 ÷2）
constexpr float DawnStartH      = 6.25f;  // 06:15 开始恢复
constexpr float DawnAccelEndH   = 8.0f;   // 08:00 加速段起点
constexpr float DawnRestoreEndH = 9.0f;   // 09:00 完全恢复
constexpr float DuskStartH      = 18.25f; // 18:15 开始压暗
constexpr float DuskAccelEndH   = 19.5f;  // 19:30 加速段起点
constexpr float DuskEndH        = 21.5f;  // 21:30 全暗
constexpr float NightEndH       = 6.25f;  // 06:15 结束
constexpr float NightEffBright  = 0.03f;  // 角色发光夜晚值（角色材质 Multiply）
constexpr float NightEmissive   = 0.000024f; // 技能特效 MPC 夜晚值

3. Exposure Darkening Implementation (AutoExposureBias)

Iron rule: the sign of UE's AutoExposureBias — positive = brighter, negative = darker (each ±1 EV ≈ brightness ×2 or ÷2). The V48 initial version had the comment wrong, saying "positive = darker"; following the comment made night brighter as exposure increased.

// TimeOfDayManager.cpp · ApplySunMoonIntensity() V61 块
// 缓存 PPV 的原始 EV 基值（避免每帧把上次写入值当基值导致漂移）
float CachedBaseBias = PPVCache.Get(PPV);  // 首次读取 PPV->Settings.AutoExposureBias

const float DimFactor = 1.0f - GetDaylightFactor(CurrentHours);
const float Offset = NightDimMaxEV * DimFactor;
PPV->Settings.AutoExposureBias = CachedBaseBias - Offset;  // 负方向 = 变暗 ✓

4. Character Material EffectBrightness Wiring

Each of the 6 emissive parent materials (M_角色_Emissive / M_角色_Body / M_角色_Clothes / M_角色_Fur / M_角色_Hair / M_角色_Ribbon) gets a new Multiply node chained into the new scalar parameter EffectBrightness (default=1) before the EmissiveColor output.

// TransformCharacter.cpp · UpdateEffectBrightness()
// 白天=1（保持原大乘数不变），夜晚=0.03（压暗到接近默认）
const float Target = FMath::Lerp(NightEffBright, 1.0f,
    ATimeOfDayManager::GetDaylightFactor(GetCurrentGameHours()));

// 对每个骨骼/静态网格材质槽创建 MID 并设 EffectBrightness
for (auto& Slot : MeshComponent->GetMaterials()) {
    UMaterialInstanceDynamic* MID = MeshComponent->CreateAndSetMaterialInstanceDynamicFromMaterial(i, Slot);
    MID->SetScalarParameterValue(TEXT("EffectBrightness"), Target);
}

5. Skill VFX MPC EmissiveScale Wiring

For the 52 skill emissive materials, a Multiply × CollectionParameter(EmissiveScale) node is added at the end of the parent material chain, referencing the MPC /Game/TimeOfDay/MPC_GlobalEffectBrightness. TimeOfDayManager writes the MPC every frame, and the three day-night curves are driven uniformly.

6. Reuse Points (Future Bright/Dark Tuning)

Night too bright → increase NightDimMaxEV (e.g. 4→5); too dark → decrease (e.g. 4→3).
Darkening start/end times off → only the four floats DuskStartH / DuskEndH / NightEndH / DawnRestoreEndH need changing.
Character emissive overexposed at night → raise NightEffBright from 0.03 to 0.05.
Temporarily disable the whole darkening → set NightDimMaxEV to 0, or assign 0 to the consumer's DimFactor.
Add a new emissive parent material → remember to also insert "Multiply × EffectBrightness", or that material will not be controlled by day-night scaling.
Sign iron rule restated → UE exposure bias negative = dark. Verify before copying any engine exposure comment; the V48 comment had the sign reversed.