feat: Make precipitation response to camera movement

Author: twpol

Source/RunActivity/Viewer3D/Precipitation.cs

@@ -1,4 +1,4 @@
-// COPYRIGHT 2009 - 2023 by the Open Rails project.
+// COPYRIGHT 2009 - 2023 by the Open Rails project.
 //
 // This file is part of Open Rails.
 //
@@ -261,7 +261,7 @@ public void Update(float currentTime, ElapsedTime elapsedTime, float particlesPe
             var tiles = viewer.Tiles;
             var scenery = viewer.World.Scenery;
             var worldLocation = viewer.Camera.CameraWorldLocation;
-            var particleDirection2D = viewer.Simulator.Weather.WindInstantaneousDirection * viewer.Simulator.Weather.WindInstantaneousSpeedMpS;
+            var particleDirection2D = viewer.World.WeatherControl.PrecipitationSlewMpS;
             var particleDirection3D = new Vector3(particleDirection2D.X, 0, particleDirection2D.Y);
 
             if (TimeParticlesLastEmitted == 0)

Source/RunActivity/Viewer3D/Weather.cs

@@ -48,6 +48,7 @@ public class WeatherControl
         public readonly List<SoundSourceBase> WeatherSounds = new List<SoundSourceBase>();
 
         public Vector4 CloudScalePosition { get => new Vector4(CloudScale.X, CloudScale.Y, CloudPositionM.X / SkyPrimitive.RadiusM, CloudPositionM.Y / SkyPrimitive.RadiusM); }
+        public Vector2 PrecipitationSlewMpS { get; set; }
 
         Vector2 CloudScale;
         Vector2 CloudPositionM;
@@ -240,6 +241,7 @@ private void UpdateWind(ElapsedTime elapsedTime)
 
             WorldLocation.GetDistance(CameraWorldLocation, Viewer.Camera.CameraWorldLocation).Deconstruct(out var x, out var _, out var y);
             CloudPositionM += elapsedTime.ClockSeconds * Weather.WindAverageDirection * Weather.WindAverageSpeedMpS - new Vector2(x, -y);
+            PrecipitationSlewMpS = Weather.WindInstantaneousDirection * Weather.WindInstantaneousSpeedMpS - new Vector2(x, -y) / elapsedTime.ClockSeconds;
             CameraWorldLocation = Viewer.Camera.CameraWorldLocation;
         }