feat(desktop): 确定性昼夜光照过渡与夜灯暖光

新增 lightingBlend 纯函数（黎明明 4:00-6:00、暮色 20:00-22:00 线性过渡，边界与 isNightTick 对齐），天空底色/世界 tint 按混合插值渲染，夜晚灯笼暖光晕强度=LanternGlow（纯叠加矩形、无每帧分配风险）；回归测试含锚点/单调斜坡/确定性/光晕开关。

1 files changed, 35 insertions, 10 deletions

diff --git a/src/LivingVillage.Desktop/M6Presentation.fs b/src/LivingVillage.Desktop/M6Presentation.fs
index 8e13183..ea8fd2f 100644
--- a/src/LivingVillage.Desktop/M6Presentation.fs
+++ b/src/LivingVillage.Desktop/M6Presentation.fs
@@ -11,7 +11,9 @@ type M6DayNight =
 type M6RenderProfile =
     { Mode: M6DayNight
       Background: Color
-      WorldTint: Color }
+      WorldTint: Color
+      Blend: float32
+      LanternGlow: float32 }
 
 module M6Presentation =
 
@@ -20,15 +22,38 @@ module M6Presentation =
         | Day -> "白天"
         | Night -> "夜晚"
 
-    let profileAtTick (tick: int64) : M6RenderProfile =
-        if Sim.isNightTick tick then
-            { Mode = Night
-              Background = Color(18, 25, 55)
-              WorldTint = Color(118, 136, 184) }
-        else
-            { Mode = Day
-              Background = Color(100, 160, 210)
-              WorldTint = Color(255, 248, 224) }
+    /// Continuous light blend: 0 = full day, 1 = full night. Ramps are deterministic
+    /// pure functions of the simulation tick (dawn 4:00-6:00, dusk 20:00-22:00), so the
+    /// boundaries agree with Sim.isNightTick (night >= 22:00 or < 6:00).
+    let lightingBlend (tick: int64) : float32 =
+        let hourTicks = Sim.ticksPerDay / 24L
+        let hour = float32 (tick / hourTicks)
+        let clamp01 v = if v < 0.0f then 0.0f elif v > 1.0f then 1.0f else v
+        if hour >= 6.0f && hour < 20.0f then 0.0f
+        elif hour >= 22.0f then 1.0f
+        elif hour < 4.0f then 1.0f
+        elif hour < 6.0f then clamp01 (1.0f - (hour - 4.0f) / 2.0f)
+        else clamp01 ((hour - 20.0f) / 2.0f)
+
+    let private lerp (a: int) (b: int) (blend: float32) : int =
+        a + int (float32 (b - a) * blend)
+
+    let backgroundAtBlend (blend: float32) : Color =
+        Color(lerp 100 18 blend, lerp 160 25 blend, lerp 210 55 blend)
+
+    let worldTintAtBlend (blend: float32) : Color =
+        Color(lerp 255 118 blend, lerp 248 136 blend, lerp 224 184 blend)
+
+    /// Pure day-phase lighting: deterministic tint/background plus lantern warm-glow boost.
+    let lightingAtTick (tick: int64) : M6RenderProfile =
+        let blend = lightingBlend tick
+        { Mode = if blend < 0.5f then Day else Night
+          Background = backgroundAtBlend blend
+          Blend = blend
+          WorldTint = worldTintAtBlend blend
+          LanternGlow = blend }
+
+    let profileAtTick (tick: int64) : M6RenderProfile = lightingAtTick tick
 
     let clockLabel (control: SimulationControl) : string =
         if control.Paused then