Automatic merge of T1.5.1-919-gf19642ebc and 15 pull requests

- Pull request #570 at 3539862: Experimental glTF 2.0 support with PBR lighting
- Pull request #839 at d00beb9: First phase of https://blueprints.launchpad.net/or/+spec/additional-cruise-control-parameters
- Pull request #876 at f92de76: docs: add source for documents previously on website to source Documentation folder
- Pull request #882 at 1a5693d: Blueprint/train car operations UI window
- Pull request #885 at d714b11: feat: Add notifications to Menu
- Pull request #886 at 6c0785b: Scene viewer extension to TrackViewer
- Pull request #892 at 1f5ba4c: Signal Function OPP_SIG_ID_TRAINPATH
- Pull request #896 at 5866028: First implementation of https://blueprints.launchpad.net/or/+spec/specific-sounds-for-ai-trains
- Pull request #903 at 29f3d1a: Downloading route content (Github, zip)
- Pull request #912 at f7b85e4: New Triple Valve Features Vol. 2
- Pull request #919 at 1a376fa: Added mouse wheel support for controls which can be moved by pressing t…
- Pull request #923 at e0f3c55: Add curve squeal to route
- Pull request #924 at 6c2c3cd: Default Asset Improvements
- Pull request #925 at e3b1688: Fix brakeshoe force bug
- Pull request #926 at 729e0b7: Lights Bugfixes

Author: openrails-bot

Source/RunActivity/Viewer3D/Lights.cs

@@ -287,7 +287,7 @@ bool UpdateState()
             // Should prevent some unneeded computation, but is a little messy. May revise in the future
 
             // Headlight
-			int newTrainHeadlight = !Car.Lights.IgnoredConditions[0] ? (Car.Train != null ? Car.Train.TrainType != Train.TRAINTYPE.STATIC ? leadLocomotiveCar.Headlight : 0 : 0) : 0;
+			int newTrainHeadlight = !Car.Lights.IgnoredConditions[0] ? (Car.Train?.TrainType != Train.TRAINTYPE.STATIC ? (leadLocomotiveCar != null ? leadLocomotiveCar.Headlight : 2) : 0) : 0;
             // Unit
             bool locomotiveFlipped = leadLocomotiveCar != null && leadLocomotiveCar.Flipped;
             bool locomotiveReverseCab = leadLocomotive != null && leadLocomotive.UsingRearCab;
@@ -320,11 +320,11 @@ bool UpdateState()
             // Friction brakes, activation force is arbitrary
             bool newBrakeOn = !Car.Lights.IgnoredConditions[9] && Car.BrakeForceN > 250.0f;
             // Reverser: -1: reverse, 0: within 10% of neutral, 1: forwards. Automatically swaps if this car is reversed
-            int newReverserState = !Car.Lights.IgnoredConditions[10] ? ((Car.Train.MUDirection == Direction.N || Math.Abs(Car.Train.MUReverserPercent) < 10.0f) ? 0 : 
+            int newReverserState = (!Car.Lights.IgnoredConditions[10] && Car.Train != null) ? ((Car.Train.MUDirection == Direction.N || Math.Abs(Car.Train.MUReverserPercent) < 10.0f) ? 0 : 
                 Car.Train.MUDirection == Direction.Forward ? 1 : -1) * (Car.Flipped ? -1 : 1) : 0;
             // Passenger doors
-            bool newLeftDoorOpen = !Car.Lights.IgnoredConditions[11] && Car.Train.DoorState(DoorSide.Left) != DoorState.Closed;
-            bool newRightDoorOpen = !Car.Lights.IgnoredConditions[11] && Car.Train.DoorState(DoorSide.Right) != DoorState.Closed;
+            bool newLeftDoorOpen = !Car.Lights.IgnoredConditions[11] && Car.Train?.DoorState(DoorSide.Left) != DoorState.Closed;
+            bool newRightDoorOpen = !Car.Lights.IgnoredConditions[11] && Car.Train?.DoorState(DoorSide.Right) != DoorState.Closed;
             // Horn and bell (for flashing ditch lights)
             bool newHornOn = !Car.Lights.IgnoredConditions[12] && leadLocomotive != null && leadLocomotive.HornRecent;
             bool newBellOn = !Car.Lights.IgnoredConditions[13] && leadLocomotive != null && leadLocomotive.BellRecent;