BulletSim: implement the SL bug where VEHICLE_HOVER_UP_ONLY disables

the vehicle buoyancy if the vehicle is above its hover height.

This is a known misfeature of this vehicle flag which has been accepted
since it would break too many implementations. The problem is noticed
when creating a jetski-like vehicle that jumps over sand bars. A boat
normally is configured with neutral buoyancy and hovering at water
height. When it jumps the sandbar, it needs to have gravity applied
to get back to water level.

1 files changed, 12 insertions, 0 deletions

diff --git a/OpenSim/Region/Physics/BulletSPlugin/BSDynamics.cs b/OpenSim/Region/Physics/BulletSPlugin/BSDynamics.cs
index f0d17d3..7b98f9d 100644
--- a/OpenSim/Region/Physics/BulletSPlugin/BSDynamics.cs
+++ b/OpenSim/Region/Physics/BulletSPlugin/BSDynamics.cs
@@ -1125,7 +1125,19 @@ namespace OpenSim.Region.Physics.BulletSPlugin
                 {
                     // If body is already heigher, use its height as target height
                     if (VehiclePosition.Z > m_VhoverTargetHeight)
+                    {
                         m_VhoverTargetHeight = VehiclePosition.Z;
+
+                        // A 'misfeature' of this flag is that if the vehicle is above it's hover height,
+                        //     the vehicle's buoyancy goes away. This is an SL bug that got used by so many
+                        //    scripts that it could not be changed.
+                        // So, if above the height, reapply gravity if buoyancy had it turned off.
+                        if (m_VehicleBuoyancy != 0)
+                        {
+                            Vector3 appliedGravity = ControllingPrim.ComputeGravity(ControllingPrim.Buoyancy) * m_vehicleMass;
+                            VehicleAddForce(appliedGravity);
+                        }
+                    }
                 }
 
                 if ((m_flags & VehicleFlag.LOCK_HOVER_HEIGHT) != 0)