BulletSim: add parameter to optionally disable vehicle linear deflection.

Add parameter to not apply vehicle linear deflection Z forces if
vehicle is not colliding. This defaults to 'true' so vehicles will fall
even if there is some linear deflection to apply.

OpenSim/Region/Physics/BulletSPlugin/BSDynamics.cs

@@ -905,6 +905,7 @@ namespace OpenSim.Region.Physics.BulletSPlugin
                 return VehicleVelocity * Quaternion.Inverse(Quaternion.Normalize(VehicleOrientation));
             }
         }
+
         private float VehicleForwardSpeed
         {
             get
@@ -1040,6 +1041,8 @@ namespace OpenSim.Region.Physics.BulletSPlugin
             Vector3 linearDeflectionV = Vector3.Zero;
             Vector3 velocityV = VehicleForwardVelocity;
 
+            if (BSParam.VehicleEnableLinearDeflection)
+            {
                 // Velocity in Y and Z dimensions is movement to the side or turning.
                 // Compute deflection factor from the to the side and rotational velocity
                 linearDeflectionV.Y = SortedClampInRange(0, (velocityV.Y * m_linearDeflectionEfficiency) / m_linearDeflectionTimescale, velocityV.Y);
@@ -1055,12 +1058,21 @@ namespace OpenSim.Region.Physics.BulletSPlugin
                 // Subtract the sideways and rotational velocity deflection factors while adding the correction forward
                 linearDeflectionV *= new Vector3(1, -1, -1);
 
-            // Correciont is vehicle relative. Convert to world coordinates and add to the velocity
+                // Correction is vehicle relative. Convert to world coordinates.
-            VehicleVelocity += linearDeflectionV * VehicleOrientation;
+                Vector3 linearDeflectionW = linearDeflectionV * VehicleOrientation;
+
+                // Optionally, if not colliding, don't effect world downward velocity. Let falling things fall.
+                if (BSParam.VehicleLinearDeflectionNotCollidingNoZ && !m_controllingPrim.IsColliding)
+                {
+                    linearDeflectionW.Z = 0f;
+                }
+
+                VehicleVelocity += linearDeflectionW;
 
                 VDetailLog("{0},  MoveLinear,LinearDeflection,linDefEff={1},linDefTS={2},linDeflectionV={3}",
                             ControllingPrim.LocalID, m_linearDeflectionEfficiency, m_linearDeflectionTimescale, linearDeflectionV);
             }
+        }
 
         public void ComputeLinearTerrainHeightCorrection(float pTimestep)
         {

OpenSim/Region/Physics/BulletSPlugin/BSParam.cs

@@ -155,6 +155,8 @@ public static class BSParam
     public static Vector3 VehicleInertiaFactor { get; private set; }
     public static float VehicleGroundGravityFudge { get; private set; }
     public static float VehicleAngularBankingTimescaleFudge { get; private set; }
+    public static bool VehicleEnableLinearDeflection { get; private set; }
+    public static bool VehicleLinearDeflectionNotCollidingNoZ { get; private set; }
     public static bool VehicleEnableAngularVerticalAttraction { get; private set; }
     public static int VehicleAngularVerticalAttractionAlgorithm { get; private set; }
     public static bool VehicleEnableAngularDeflection { get; private set; }
@@ -609,10 +611,14 @@ public static class BSParam
             0.2f ),
         new ParameterDefn<float>("VehicleAngularBankingTimescaleFudge", "Factor to multiple angular banking timescale. Tune to increase realism.",
             60.0f ),
+        new ParameterDefn<bool>("VehicleEnableLinearDeflection", "Turn on/off vehicle linear deflection effect",
+            true ),
+        new ParameterDefn<bool>("VehicleLinearDeflectionNotCollidingNoZ", "Turn on/off linear deflection Z effect on non-colliding vehicles",
+            true ),
         new ParameterDefn<bool>("VehicleEnableAngularVerticalAttraction", "Turn on/off vehicle angular vertical attraction effect",
             true ),
         new ParameterDefn<int>("VehicleAngularVerticalAttractionAlgorithm", "Select vertical attraction algo. You need to look at the source.",
-            1 ),
+            0 ),
         new ParameterDefn<bool>("VehicleEnableAngularDeflection", "Turn on/off vehicle angular deflection effect",
             true ),
         new ParameterDefn<bool>("VehicleEnableAngularBanking", "Turn on/off vehicle angular banking effect",