Set default constraint solver mode more compatible to Blender 2.48 settings, this fixes rigid body stacking in this blend file:

http://blenderartists.org/forum/showpost.php?p=1382653&postcount=102

(todo: expose this setting in World setting GUI)

Expose contact processing threshold in Advanced GUI, next to rigid body margin, called CPT.
Default to 1, makes rigid body stacking a bit more stable, smaller values makes sliding easier (at the cost of easier jittering).
Disabled for 'dynamic' objects that don't rotate, because characters etc. always need smooth sliding.

2 files changed, 11 insertions, 1 deletions

diff --git a/source/gameengine/Physics/Bullet/CcdPhysicsController.cpp b/source/gameengine/Physics/Bullet/CcdPhysicsController.cpp
index 6b00011b693..710d0656f6d 100644
--- a/source/gameengine/Physics/Bullet/CcdPhysicsController.cpp
+++ b/source/gameengine/Physics/Bullet/CcdPhysicsController.cpp
@@ -519,6 +519,8 @@ void CcdPhysicsController::CreateRigidbody()
 		{
 			body->setAngularFactor(0.f);
 		}
+		body->setContactProcessingThreshold(m_cci.m_contactProcessingThreshold);
+
 	}
 	if (m_object && m_cci.m_do_anisotropic)
 	{
diff --git a/source/gameengine/Physics/Bullet/CcdPhysicsController.h b/source/gameengine/Physics/Bullet/CcdPhysicsController.h
index fc8de0e2ded..d73759bac76 100644
--- a/source/gameengine/Physics/Bullet/CcdPhysicsController.h
+++ b/source/gameengine/Physics/Bullet/CcdPhysicsController.h
@@ -231,7 +231,8 @@ struct CcdConstructionInfo
 		m_physicsEnv(0),
 		m_inertiaFactor(1.f),
 		m_do_anisotropic(false),
-		m_anisotropicFriction(1.f,1.f,1.f)
+		m_anisotropicFriction(1.f,1.f,1.f),
+		m_contactProcessingThreshold(1e10)
 	{
 	}
 
@@ -317,6 +318,13 @@ struct CcdConstructionInfo
 	btScalar	m_fh_distance;           ///< The range above the surface where Fh is active.    
 	bool		m_fh_normal;             ///< Should the object slide off slopes?
 	float		m_radius;//for fh backwards compatibility
+	
+	///m_contactProcessingThreshold allows to process contact points with positive distance
+	///normally only contacts with negative distance (penetration) are solved
+	///however, rigid body stacking is more stable when positive contacts are still passed into the constraint solver
+	///this might sometimes lead to collisions with 'internal edges' such as a sliding character controller
+	///so disable/set m_contactProcessingThreshold to zero for sliding characters etc.
+	float		m_contactProcessingThreshold;///< Process contacts with positive distance in range [0..INF]
 
 };