From 8510f57ad48db5f97dacc2a9be63c64e62477d14 Mon Sep 17 00:00:00 2001
From: Robert Adams <Robert.Adams@intel.com>
Date: Sun, 17 Mar 2013 18:44:09 -0700
Subject: [PATCH] BulletSim: add terrain contact processing threshold
 parameter. Initialize contact processing threshold for static object as well
 as mesh terrain.

---
 .../Region/Physics/BulletSPlugin/BSParam.cs   | 19 +++++++++++++++++++
 .../Region/Physics/BulletSPlugin/BSPrim.cs    |  2 +-
 .../Physics/BulletSPlugin/BSTerrainManager.cs |  1 +
 .../Physics/BulletSPlugin/BSTerrainMesh.cs    |  2 ++
 4 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/OpenSim/Region/Physics/BulletSPlugin/BSParam.cs b/OpenSim/Region/Physics/BulletSPlugin/BSParam.cs
index 77bdacb458..cb0d92946a 100755
--- a/OpenSim/Region/Physics/BulletSPlugin/BSParam.cs
+++ b/OpenSim/Region/Physics/BulletSPlugin/BSParam.cs
@@ -39,6 +39,20 @@ public static class BSParam
 {
     private static string LogHeader = "[BULLETSIM PARAMETERS]"; 
 
+    // Tuning notes:
+    // From: http://bulletphysics.org/Bullet/phpBB3/viewtopic.php?t=6575
+    //    Contact points can be added even if the distance is positive. The constraint solver can deal with
+    //    contacts with positive distances as well as negative (penetration). Contact points are discarded
+    //    if the distance exceeds a certain threshold.
+    //    Bullet has a contact processing threshold and a contact breaking threshold.
+    //    If the distance is larger than the contact breaking threshold, it will be removed after one frame.
+    //    If the distance is larger than the contact processing threshold, the constraint solver will ignore it.
+
+    //    This is separate/independent from the collision margin. The collision margin increases the object a bit
+    //    to improve collision detection performance and accuracy.
+    // ===================
+    // From: 
+
     // Level of Detail values kept as float because that's what the Meshmerizer wants
     public static float MeshLOD { get; private set; }
     public static float MeshCircularLOD { get; private set; }
@@ -77,6 +91,7 @@ public static class BSParam
     public static float TerrainFriction { get; private set; }
     public static float TerrainHitFraction { get; private set; }
     public static float TerrainRestitution { get; private set; }
+    public static float TerrainContactProcessingThreshold { get; private set; }
     public static float TerrainCollisionMargin { get; private set; }
 
     public static float DefaultFriction { get; private set; }
@@ -458,6 +473,10 @@ public static class BSParam
             0f,
             (s) => { return TerrainRestitution; },
             (s,v) => { TerrainRestitution = v;  /* TODO: set on real terrain */ } ),
+        new ParameterDefn<float>("TerrainContactProcessingThreshold", "Distance from terrain to stop processing collisions" ,
+            0.0f,
+            (s) => { return TerrainContactProcessingThreshold; },
+            (s,v) => { TerrainContactProcessingThreshold = v;  /* TODO: set on real terrain */ } ),
         new ParameterDefn<float>("TerrainCollisionMargin", "Margin where collision checking starts" ,
             0.08f,
             (s) => { return TerrainCollisionMargin; },
diff --git a/OpenSim/Region/Physics/BulletSPlugin/BSPrim.cs b/OpenSim/Region/Physics/BulletSPlugin/BSPrim.cs
index a465613b8a..2cbbe9a3fd 100644
--- a/OpenSim/Region/Physics/BulletSPlugin/BSPrim.cs
+++ b/OpenSim/Region/Physics/BulletSPlugin/BSPrim.cs
@@ -947,9 +947,9 @@ public class BSPrim : BSPhysObject
             ZeroMotion(true);
 
             // Set various physical properties so other object interact properly
-            MaterialAttributes matAttrib = BSMaterials.GetAttributes(Material, false);
             PhysicsScene.PE.SetFriction(PhysBody, Friction);
             PhysicsScene.PE.SetRestitution(PhysBody, Restitution);
+            PhysicsScene.PE.SetContactProcessingThreshold(PhysBody, BSParam.ContactProcessingThreshold);
 
             // Mass is zero which disables a bunch of physics stuff in Bullet
             UpdatePhysicalMassProperties(0f, false);
diff --git a/OpenSim/Region/Physics/BulletSPlugin/BSTerrainManager.cs b/OpenSim/Region/Physics/BulletSPlugin/BSTerrainManager.cs
index e8040d856b..a60946dbbd 100755
--- a/OpenSim/Region/Physics/BulletSPlugin/BSTerrainManager.cs
+++ b/OpenSim/Region/Physics/BulletSPlugin/BSTerrainManager.cs
@@ -263,6 +263,7 @@ public sealed class BSTerrainManager : IDisposable
 
                 if (MegaRegionParentPhysicsScene == null)
                 {
+                    // This terrain is not part of the mega-region scheme. Create vanilla terrain.
                     BSTerrainPhys newTerrainPhys = BuildPhysicalTerrain(terrainRegionBase, id, heightMap, minCoords, maxCoords);
                     m_terrains.Add(terrainRegionBase, newTerrainPhys);
 
diff --git a/OpenSim/Region/Physics/BulletSPlugin/BSTerrainMesh.cs b/OpenSim/Region/Physics/BulletSPlugin/BSTerrainMesh.cs
index 57a5ff2a6f..c9a75ae915 100755
--- a/OpenSim/Region/Physics/BulletSPlugin/BSTerrainMesh.cs
+++ b/OpenSim/Region/Physics/BulletSPlugin/BSTerrainMesh.cs
@@ -112,11 +112,13 @@ public sealed class BSTerrainMesh : BSTerrainPhys
             // Something is very messed up and a crash is in our future.
             return;
         }
+        physicsScene.PE.SetShapeCollisionMargin(m_terrainShape, BSParam.TerrainCollisionMargin);
 
         // Set current terrain attributes
         PhysicsScene.PE.SetFriction(m_terrainBody, BSParam.TerrainFriction);
         PhysicsScene.PE.SetHitFraction(m_terrainBody, BSParam.TerrainHitFraction);
         PhysicsScene.PE.SetRestitution(m_terrainBody, BSParam.TerrainRestitution);
+        PhysicsScene.PE.SetContactProcessingThreshold(m_terrainBody, BSParam.TerrainContactProcessingThreshold);
         PhysicsScene.PE.SetCollisionFlags(m_terrainBody, CollisionFlags.CF_STATIC_OBJECT);
 
         // Static objects are not very massive.