angular modulo for wind dir

src/net/torvald/terrarum/weather/WeatherMixer.kt

@@ -248,7 +248,7 @@ internal object WeatherMixer : RNGConsumer {
         val currentWindSpeed = weatherbox.windSpeed.getAndUpdate( world.worldTime.timeDelta / WIND_SPEED_TIME_UNIT) {
             currentWeather.getRandomWindSpeed(takeUniformRand(-1f..1f))
         }
-        val currentWindDir = weatherbox.windDir.getAndUpdate( world.worldTime.timeDelta / WIND_DIR_TIME_UNIT) { RNG.nextFloat() } * 2.0 * Math.PI
+        val currentWindDir = weatherbox.windDir.getAndUpdate( world.worldTime.timeDelta / WIND_DIR_TIME_UNIT) { RNG.nextFloat() * 4f } * Math.PI * 0.5
 
 
         if (currentWeather.forceWindVec != null) {

src/net/torvald/terrarum/weather/Weatherbox.kt

@@ -1,18 +1,22 @@
 package net.torvald.terrarum.weather
 
+import net.torvald.terrarum.floorToInt
+import net.torvald.terrarum.gameworld.fmod
+import kotlin.math.absoluteValue
+
 
 class Weatherbox {
 
-    val windDir = WeatherStateBox() // 0 .. 1.0
+    val windDir = WeatherDirBox() // 0 .. 1.0
     val windSpeed = WeatherStateBox() // 0 .. arbitrarily large number
 
 }
 
 
-data class WeatherStateBox(
-    var x: Float = 0f,
-    var pM2: Float = 0f,
-    var pM1: Float = 0f,
+open class WeatherStateBox(
+    var x:  Float = 0f,
+    var pM2:Float = 0f,
+    var pM1:Float = 0f,
     var p0: Float = 0f,
     var p1: Float = 0f,
     var p2: Float = 0f,
@@ -23,11 +27,20 @@ data class WeatherStateBox(
     // - removing p4 and beyond: for faster response to the changing weather schedule and make the forecasting less accurate like irl
 ) {
 
-    fun get() = interpolate(x, p0, p1, p2, p3)
+    open fun value() = interpolate(x, p0, p1, p2, p3)
+    open fun valueAt(x: Float) = when (x.floorToInt()) {
+        -2 -> interpolate(x + 2, pM2,pM1, p0, p1)
+        -1 -> interpolate(x + 1, pM1, p0, p1, p2)
+         0 -> interpolate(x - 0,  p0, p1, p2, p3)
+         1 -> interpolate(x - 1,  p1, p2, p3, p3)
+         2 -> interpolate(x - 2,  p2, p3, p3, p3)
+         3 -> interpolate(x - 3,  p3, p3, p3, p3)
+        else -> throw IllegalArgumentException()
+    }
 
-    fun getAndUpdate(xdelta: Float, next: () -> Float): Float {
+    open fun getAndUpdate(xdelta: Float, next: () -> Float): Float {
         synchronized(WeatherMixer.RNG) {
-            val y = get()
+            val y = value()
             x += xdelta
             while (x >= 1.0) {
                 x -= 1.0f
@@ -46,16 +59,128 @@ data class WeatherStateBox(
             return y
         }
     }
+    protected fun interpolate(u: Float, p0: Float, p1: Float, p2: Float, p3: Float): Float {
+        val c1: Float = p1
+        val c2: Float = -0.5f * p0 + 0.5f * p2
+        val c3: Float = p0 - 2.5f * p1 + 2.0f * p2 - 0.5f * p3
+        val c4: Float = -0.5f * p0 + 1.5f * p1 - 1.5f * p2 + 0.5f * p3
+        return (((c4 * u + c3) * u + c2) * u + c1)
+    }
 
     companion object {
         // fixed with T=0.5
-        fun interpolate(u: Float, p0: Float, p1: Float, p2: Float, p3: Float): Float {
-            val c1: Float = p1
-            val c2: Float = -0.5f * p0 + 0.5f * p2
-            val c3: Float = p0 - 2.5f * p1 + 2.0f * p2 - 0.5f * p3
-            val c4: Float = -0.5f * p0 + 1.5f * p1 - 1.5f * p2 + 0.5f * p3
-            return (((c4 * u + c3) * u + c2) * u + c1)
-        }
 
     }
+}
+
+/**
+ * WeatherStateBox with rotational range of -2..2
+ */
+class WeatherDirBox(
+    x:  Float = 0f,
+    pM2:Float = 0f,
+    pM1:Float = 0f,
+    p0: Float = 0f,
+    p1: Float = 0f,
+    p2: Float = 0f,
+    p3: Float = 0f,
+) : WeatherStateBox(x, pM2, pM1, p0, p1, p2, p3) {
+    override fun value() = valueAt(x)
+
+    override fun valueAt(x: Float): Float {
+        var pM2 = pM2
+        var pM1 = pM1
+        var p0 = p0
+        var p1 = p1
+        var p2 = p2
+        var p3 = p3
+
+        if (x < -2f) {
+            if (pM1 - pM2 > 2f) {
+                pM2 -= 4f
+                pM1 -= 4f
+                p0 -= 4f
+                p1 -= 4f
+                p2 -= 4f
+                p3 -= 4f
+            }
+            else if (pM1 - pM2 < -2f) {
+                pM2 += 4f
+                pM1 += 4f
+                p0 += 4f
+                p1 += 4f
+                p2 += 4f
+                p3 += 4f
+            }
+        }
+
+        if (x < -1f) {
+            if (pM1 - pM2 > 2f) {
+                pM1 -= 4f
+                p0 -= 4f
+                p1 -= 4f
+                p2 -= 4f
+                p3 -= 4f
+            }
+            else if (pM1 - pM2 < -2f) {
+                pM1 += 4f
+                p0 += 4f
+                p1 += 4f
+                p2 += 4f
+                p3 += 4f
+            }
+        }
+
+        if (x < 0f) {
+            if (p0 - pM1 > 2f) {
+                p0 -= 4f
+                p1 -= 4f
+                p2 -= 4f
+                p3 -= 4f
+            }
+            else if (p0 - pM1 < -2f) {
+                p0 += 4f
+                p1 += 4f
+                p2 += 4f
+                p3 += 4f
+            }
+        }
+
+        if (p1 - p0 > 2f) {
+            p1 -= 4f
+            p2 -= 4f
+            p3 -= 4f
+        }
+        else if (p1 - p0 < -2f) {
+            p1 += 4f
+            p2 += 4f
+            p3 += 4f
+        }
+
+        if (p2 - p1 > 2f) {
+            p2 -= 4f
+            p3 -= 4f
+        }
+        else if (p2 - p1 < -2f) {
+            p2 += 4f
+            p3 += 4f
+        }
+
+        if (p3 - p2 > 2f) {
+            p3 -= 4f
+        }
+        else if (p3 - p2 < -2f) {
+            p3 += 4f
+        }
+
+        return when (x.floorToInt()) {
+            -2 -> interpolate(x + 2, pM2,pM1, p0, p1)
+            -1 -> interpolate(x + 1, pM1, p0, p1, p2)
+             0 -> interpolate(x - 0,  p0, p1, p2, p3)
+             1 -> interpolate(x - 1,  p1, p2, p3, p3)
+             2 -> interpolate(x - 2,  p2, p3, p3, p3)
+             3 -> interpolate(x - 3,  p3, p3, p3, p3)
+            else -> throw IllegalArgumentException()
+        }.plus(2f).fmod(4f).minus(2f)
+    }
 }