BGE Fix: apply velocity clamping on every physics subtick

This patch uses the Bullet "internal tick callback" functionality to
ensure that velocity clamping is performed after every physics update.
This makes a difference when physics subticks > 1, as in that case the
too-high velocity could have impacted the simulation.

This patch follows the examples at [1] and [2]; the latter example
also explains that the way we limit velocity in the BGE (before this
patch) is wrong.

[1] http://bulletphysics.org/mediawiki-1.5.8/index.php/Simulation_Tick_Callbacks
[2] http://www.bulletphysics.org/mediawiki-1.5.8/index.php/Code_Snippets#I_want_to_cap_the_speed_of_my_spaceship;

Reviewed by: panzergame

Differential Revision: https://developer.blender.org/D1364

1 files changed, 17 insertions, 0 deletions

diff --git a/source/gameengine/Physics/Bullet/CcdPhysicsEnvironment.cpp b/source/gameengine/Physics/Bullet/CcdPhysicsEnvironment.cpp
index 89c8c124bc8..14a19fdfb41 100644
--- a/source/gameengine/Physics/Bullet/CcdPhysicsEnvironment.cpp
+++ b/source/gameengine/Physics/Bullet/CcdPhysicsEnvironment.cpp
@@ -452,6 +452,7 @@ m_scalingPropagated(false)
 	SetSolverType(1);//issues with quickstep and memory allocations
 //	m_dynamicsWorld = new btDiscreteDynamicsWorld(dispatcher,m_broadphase,m_solver,m_collisionConfiguration);
 	m_dynamicsWorld = new btSoftRigidDynamicsWorld(dispatcher,m_broadphase,m_solver,m_collisionConfiguration);
+	m_dynamicsWorld->setInternalTickCallback(&CcdPhysicsEnvironment::StaticSimulationSubtickCallback, this);
 	//m_dynamicsWorld->getSolverInfo().m_linearSlop = 0.01f;
 	//m_dynamicsWorld->getSolverInfo().m_solverMode=	SOLVER_USE_WARMSTARTING +	SOLVER_USE_2_FRICTION_DIRECTIONS +	SOLVER_RANDMIZE_ORDER +	SOLVER_USE_FRICTION_WARMSTARTING;
 
@@ -677,6 +678,22 @@ void CcdPhysicsEnvironment::DebugDrawWorld()
 			m_dynamicsWorld->debugDrawWorld();
 }
 
+void CcdPhysicsEnvironment::StaticSimulationSubtickCallback(btDynamicsWorld *world, btScalar timeStep)
+{
+	// Get the pointer to the CcdPhysicsEnvironment associated with this Bullet world.
+	CcdPhysicsEnvironment *this_ = static_cast<CcdPhysicsEnvironment*>(world->getWorldUserInfo());
+	this_->SimulationSubtickCallback(timeStep);
+}
+
+void CcdPhysicsEnvironment::SimulationSubtickCallback(btScalar timeStep)
+{
+	std::set<CcdPhysicsController*>::iterator it;
+
+	for (it = m_controllers.begin(); it != m_controllers.end(); it++) {
+		(*it)->SimulationTick(timeStep);
+	}
+}
+
 bool	CcdPhysicsEnvironment::ProceedDeltaTime(double curTime,float timeStep,float interval)
 {
 	std::set<CcdPhysicsController*>::iterator it;