feat: polish nightdrive road sun and signage

src/scene/world/travel-distance.ts

@@ -0,0 +1,31 @@
+export interface TravelDistance {
+  advance(deltaSeconds: number, speed: number, roadEnergy: number): number;
+  snapshot(): number;
+}
+
+const MAX_FRAME_SECONDS = 0.1;
+const CRUISE_UNITS_PER_SECOND = 18;
+const SPEED_UNITS_PER_SECOND = 54;
+const ENERGY_UNITS_PER_SECOND = 48;
+
+export function createTravelDistance(): TravelDistance {
+  let distance = 0;
+
+  return {
+    advance(deltaSeconds, speed, roadEnergy) {
+      if (!Number.isFinite(deltaSeconds) || deltaSeconds <= 0) return distance;
+      const dt = Math.min(MAX_FRAME_SECONDS, deltaSeconds);
+      distance += dt * (
+        CRUISE_UNITS_PER_SECOND
+        + clamp01(speed) * SPEED_UNITS_PER_SECOND
+        + clamp01(roadEnergy) * ENERGY_UNITS_PER_SECOND
+      );
+      return distance;
+    },
+    snapshot: () => distance,
+  };
+}
+
+function clamp01(value: number): number {
+  return Number.isFinite(value) ? Math.min(1, Math.max(0, value)) : 0;
+}