BUlletSim: move safeynet ground plane to lower altitude. Define new BulletSim

parameter 'TerrainGroundPlane' which defaults to -500.

BulletSim had assumed altitudes never went negative but that is not true. The
ground plane is just a safety net so things wouldn't fall to infinity.

2 files changed, 6 insertions, 2 deletions

diff --git a/OpenSim/Region/Physics/BulletSPlugin/BSParam.cs b/OpenSim/Region/Physics/BulletSPlugin/BSParam.cs
index f2ad528..6683446 100755
--- a/OpenSim/Region/Physics/BulletSPlugin/BSParam.cs
+++ b/OpenSim/Region/Physics/BulletSPlugin/BSParam.cs
@@ -97,6 +97,7 @@ public static class BSParam
 
     public static float TerrainImplementation { get; set; }
     public static int TerrainMeshMagnification { get; private set; }
+    public static float TerrainGroundPlane { get; private set; }
     public static float TerrainFriction { get; private set; }
     public static float TerrainHitFraction { get; private set; }
     public static float TerrainRestitution { get; private set; }
@@ -544,6 +545,8 @@ public static class BSParam
             (float)BSTerrainPhys.TerrainImplementation.Heightmap ),
         new ParameterDefn<int>("TerrainMeshMagnification", "Number of times the 256x256 heightmap is multiplied to create the terrain mesh" ,
             2 ),
+        new ParameterDefn<float>("TerrainGroundPlane", "Altitude of ground plane used to keep things from falling to infinity" ,
+            -500.0f ),
         new ParameterDefn<float>("TerrainFriction", "Factor to reduce movement against terrain surface" ,
             0.3f ),
         new ParameterDefn<float>("TerrainHitFraction", "Distance to measure hit collisions" ,
diff --git a/OpenSim/Region/Physics/BulletSPlugin/BSTerrainManager.cs b/OpenSim/Region/Physics/BulletSPlugin/BSTerrainManager.cs
index 3013077..9067a2c 100755
--- a/OpenSim/Region/Physics/BulletSPlugin/BSTerrainManager.cs
+++ b/OpenSim/Region/Physics/BulletSPlugin/BSTerrainManager.cs
@@ -136,9 +136,10 @@ public sealed class BSTerrainManager : IDisposable
     {
         DetailLog("{0},BSTerrainManager.CreateInitialGroundPlaneAndTerrain,region={1}", BSScene.DetailLogZero, m_physicsScene.RegionName);
         // The ground plane is here to catch things that are trying to drop to negative infinity
-        BulletShape groundPlaneShape = m_physicsScene.PE.CreateGroundPlaneShape(BSScene.GROUNDPLANE_ID, 1f, BSParam.TerrainCollisionMargin);
+        BulletShape groundPlaneShape = m_physicsScene.PE.CreateGroundPlaneShape(BSScene.GROUNDPLANE_ID, 1f, BSParam.TerrainCollisionMargin);

+        Vector3 groundPlaneAltitude = new Vector3(0f, 0f, BSParam.TerrainGroundPlane);
         m_groundPlane = m_physicsScene.PE.CreateBodyWithDefaultMotionState(groundPlaneShape,
-                                        BSScene.GROUNDPLANE_ID, Vector3.Zero, Quaternion.Identity);
+                                        BSScene.GROUNDPLANE_ID, groundPlaneAltitude, Quaternion.Identity);
 
         // Everything collides with the ground plane.
         m_groundPlane.collisionType = CollisionType.Groundplane;