Fix (needs more testing) in btRigidBody::setCenterOfMassTransform, assign m_interpolationWorldTransform = xform; instead of m_worldTransform;

Thanks Jay for reporting
Added braking capability to btRaycastVehicle, see Bullet/Demos/VehicleDemo/VehicleDemo.cpp
Added glutKeyboardUpFunc, for vehicle demo (keep accelerating/breaking, until key released/UP). Hope this is compatible with most GLUT implementations.

Demos/OpenGL/DemoApplication.cpp

@@ -368,6 +368,13 @@ void DemoApplication::keyboardCallback(unsigned char key, int x, int y)
 
 }
 	
+void DemoApplication::specialKeyboardUp(int key, int x, int y)
+{
+
+		glutPostRedisplay();
+
+}
+
 void DemoApplication::specialKeyboard(int key, int x, int y)	
 {
 	(void)x;

Demos/OpenGL/DemoApplication.h

@@ -155,6 +155,8 @@ public:
 
 	virtual void specialKeyboard(int key, int x, int y);
 
+	virtual void specialKeyboardUp(int key, int x, int y);
+
 	virtual void reshape(int w, int h);
 
 	virtual void mouseFunc(int button, int state, int x, int y);

Demos/OpenGL/GlutStuff.cpp

@@ -32,6 +32,12 @@ static void glutSpecialKeyboardCallback(int key, int x, int y)
 	gDemoApplication->specialKeyboard(key,x,y);
 }
 
+static void glutSpecialKeyboardUpCallback(int key, int x, int y)
+{
+	gDemoApplication->specialKeyboardUp(key,x,y);
+}
+
+
 static void glutReshapeCallback(int w, int h)
 {
 	gDemoApplication->reshape(w,h);
@@ -75,6 +81,8 @@ int glutmain(int argc, char **argv,int width,int height,const char* title,DemoAp
 
 	glutKeyboardFunc(glutKeyboardCallback);
 	glutSpecialFunc(glutSpecialKeyboardCallback);
+	glutSpecialUpFunc(glutSpecialKeyboardUpCallback);
+
 	glutReshapeFunc(glutReshapeCallback);
     //createMenu();
 	glutIdleFunc(glutMoveAndDisplayCallback);

Demos/VehicleDemo/VehicleDemo.cpp

@@ -55,13 +55,17 @@ const int maxOverlap = 65535;
 ///notice that for higher-quality slow-moving vehicles, another approach might be better
 ///implementing explicit hinged-wheel constraints with cylinder collision, rather then raycasts
 float	gEngineForce = 0.f;
-float	maxEngineForce = 3000.f;
+float	gBreakingForce = 0.f;
+
+float	maxEngineForce = 1000.f;//this should be engine/velocity dependent
+float	maxBreakingForce = 100.f;
+
 float	gVehicleSteering = 0.f;
 float	steeringIncrement = 0.04f;
 float	steeringClamp = 0.3f;
 float	wheelRadius = 0.5f;
 float	wheelWidth = 0.4f;
-float	wheelFriction = 1e30f;//1000;//1e30f;
+float	wheelFriction = 1000;//1e30f;
 float	suspensionStiffness = 20.f;
 float	suspensionDamping = 2.3f;
 float	suspensionCompression = 4.4f;
@@ -103,6 +107,10 @@ m_maxCameraDistance(10.f)
 
 void VehicleDemo::setupPhysics()
 {
+
+	extern btScalar	gJitterVelocityDampingFactor;
+	gJitterVelocityDampingFactor = 1.f;
+	
 #ifdef FORCE_ZAXIS_UP
 	m_cameraUp = btVector3(0,0,1);
 	m_forwardAxis = 1;
@@ -147,7 +155,8 @@ const float TRIANGLE_SIZE=20.f;
 		for (int j=0;j<NUM_VERTS_Y;j++)
 		{
 			float wl = .2f;
-			float height = 20.f*sinf(float(i)*wl)*cosf(float(j)*wl);
+			//height set to zero, but can also use curved landscape, just uncomment out the code
+			float height = 0.f;//20.f*sinf(float(i)*wl)*cosf(float(j)*wl);
 #ifdef FORCE_ZAXIS_UP
 			gVertices[i+j*NUM_VERTS_X].setValue(
 				(i-NUM_VERTS_X*0.5f)*TRIANGLE_SIZE,
@@ -222,7 +231,7 @@ const float TRIANGLE_SIZE=20.f;
 	tr.setOrigin(btVector3(0,0.f,0));
 
 	m_carChassis = localCreateRigidBody(800,tr,compound);//chassisShape);
-	m_carChassis->setDamping(0.2,0.2);
+	//m_carChassis->setDamping(0.2,0.2);
 	
 	
 	clientResetScene();
@@ -323,6 +332,24 @@ void VehicleDemo::clientMoveAndDisplay()
 
 	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 
 
+	
+	{			
+		int wheelIndex = 2;
+		m_vehicle->applyEngineForce(gEngineForce,wheelIndex);
+		m_vehicle->setBrake(gBreakingForce,wheelIndex);
+		wheelIndex = 3;
+		m_vehicle->applyEngineForce(gEngineForce,wheelIndex);
+		m_vehicle->setBrake(gBreakingForce,wheelIndex);
+
+
+		wheelIndex = 0;
+		m_vehicle->setSteeringValue(gVehicleSteering,wheelIndex);
+		wheelIndex = 1;
+		m_vehicle->setSteeringValue(gVehicleSteering,wheelIndex);
+
+	}
+
+
 	float dt = m_clock.getTimeMicroseconds() * 0.000001f;
 	m_clock.reset();
 	if (m_dynamicsWorld)
@@ -334,7 +361,7 @@ void VehicleDemo::clientMoveAndDisplay()
 
 		int numSimSteps = m_dynamicsWorld->stepSimulation(dt,maxSimSubSteps);
 
-#define VERBOSE_FEEDBACK
+//#define VERBOSE_FEEDBACK
 #ifdef VERBOSE_FEEDBACK
 		if (!numSimSteps)
 			printf("Interpolated transforms\n");
@@ -356,18 +383,6 @@ void VehicleDemo::clientMoveAndDisplay()
 	
 	
 
-	{			
-		int wheelIndex = 2;
-		m_vehicle->applyEngineForce(gEngineForce,wheelIndex);
-		wheelIndex = 3;
-		m_vehicle->applyEngineForce(gEngineForce,wheelIndex);
-		wheelIndex = 0;
-		m_vehicle->setSteeringValue(gVehicleSteering,wheelIndex);
-		wheelIndex = 1;
-		m_vehicle->setSteeringValue(gVehicleSteering,wheelIndex);
-
-	}
-
 
 
 
@@ -417,7 +432,6 @@ void VehicleDemo::displayCallback(void)
 
 void VehicleDemo::clientResetScene()
 {
-	gEngineForce = 0.f;
 	gVehicleSteering = 0.f;
 	m_carChassis->setCenterOfMassTransform(btTransform::getIdentity());
 	m_carChassis->setLinearVelocity(btVector3(0,0,0));
@@ -437,10 +451,32 @@ void VehicleDemo::clientResetScene()
 
 
 
+void VehicleDemo::specialKeyboardUp(int key, int x, int y)
+{
+   switch (key) 
+    {
+    case GLUT_KEY_UP :
+		{
+			gEngineForce = 0.f;
+		break;
+		}
+	case GLUT_KEY_DOWN :
+		{			
+			gBreakingForce = 0.f; 
+		break;
+		}
+	default:
+		DemoApplication::specialKeyboardUp(key,x,y);
+        break;
+    }
+
+}
+
+
 void VehicleDemo::specialKeyboard(int key, int x, int y)
 {
 
-	printf("key = %i x=%i y=%i\n",key,x,y);
+//	printf("key = %i x=%i y=%i\n",key,x,y);
 
     switch (key) 
     {
@@ -467,7 +503,7 @@ void VehicleDemo::specialKeyboard(int key, int x, int y)
 		}
 	case GLUT_KEY_DOWN :
 		{			
-			gEngineForce = -maxEngineForce;
+			gBreakingForce = maxBreakingForce; 
 		break;
 		}
 	default:

Demos/VehicleDemo/VehicleDemo.h

@@ -51,6 +51,8 @@ class VehicleDemo : public DemoApplication
 
 	virtual void specialKeyboard(int key, int x, int y);
 
+	virtual void specialKeyboardUp(int key, int x, int y);
+
 	void renderme();
 
 	void setupPhysics();

Glut/GL/glut.h

@@ -91,7 +91,8 @@ extern "C" {
  glutJoystickFunc, glutForceJoystickFunc (NOT FINALIZED!).
 **/
 #ifndef GLUT_API_VERSION  /* allow this to be overriden */
-#define GLUT_API_VERSION		3
+//#define GLUT_API_VERSION		3
+#define GLUT_API_VERSION		4
 #endif
 
 /**

src/BulletDynamics/Dynamics/btRigidBody.cpp

@@ -297,7 +297,7 @@ btQuaternion btRigidBody::getOrientation() const
 	
 void btRigidBody::setCenterOfMassTransform(const btTransform& xform)
 {
-	m_interpolationWorldTransform = m_worldTransform;
+	m_interpolationWorldTransform = xform;//m_worldTransform;
 	m_interpolationLinearVelocity = getLinearVelocity();
 	m_interpolationAngularVelocity = getAngularVelocity();
 	m_worldTransform = xform;

src/BulletDynamics/Vehicle/btRaycastVehicle.cpp

@@ -18,6 +18,7 @@
 #include "BulletDynamics/Dynamics/btDynamicsWorld.h"
 #include "btVehicleRaycaster.h"
 #include "btWheelInfo.h"
+#include "LinearMath/btMinMax.h"
 
 
 #include "BulletDynamics/ConstraintSolver/btContactConstraint.h"
@@ -458,6 +459,63 @@ void	btRaycastVehicle::updateSuspension(btScalar deltaTime)
 
 }
 
+
+struct btWheelContactPoint
+{
+	btRigidBody* m_body0;
+	btRigidBody* m_body1;
+	btVector3	m_frictionPositionWorld;
+	btVector3	m_frictionDirectionWorld;
+	btScalar	m_jacDiagABInv;
+	btScalar	m_maxImpulse;
+
+
+	btWheelContactPoint(btRigidBody* body0,btRigidBody* body1,const btVector3& frictionPosWorld,const btVector3& frictionDirectionWorld, btScalar maxImpulse)
+		:m_body0(body0),
+		m_body1(body1),
+		m_frictionPositionWorld(frictionPosWorld),
+		m_frictionDirectionWorld(frictionDirectionWorld),
+		m_maxImpulse(maxImpulse)
+	{
+		btScalar denom0 = body0->computeImpulseDenominator(frictionPosWorld,frictionDirectionWorld);
+		btScalar denom1 = body1->computeImpulseDenominator(frictionPosWorld,frictionDirectionWorld);
+		btScalar	relaxation = 1.f;
+		m_jacDiagABInv = relaxation/(denom0+denom1);
+	}
+
+
+
+};
+
+btScalar calcRollingFriction(btWheelContactPoint& contactPoint)
+{
+
+	btScalar j1=0.f;
+
+	const btVector3& contactPosWorld = contactPoint.m_frictionPositionWorld;
+
+	btVector3 rel_pos1 = contactPosWorld - contactPoint.m_body0->getCenterOfMassPosition(); 
+	btVector3 rel_pos2 = contactPosWorld - contactPoint.m_body1->getCenterOfMassPosition();
+	
+	btScalar maxImpulse  = contactPoint.m_maxImpulse;
+	
+	btVector3 vel1 = contactPoint.m_body0->getVelocityInLocalPoint(rel_pos1);
+	btVector3 vel2 = contactPoint.m_body1->getVelocityInLocalPoint(rel_pos2);
+	btVector3 vel = vel1 - vel2;
+
+	btScalar vrel = contactPoint.m_frictionDirectionWorld.dot(vel);
+
+	// calculate j that moves us to zero relative velocity
+	j1 = -vrel * contactPoint.m_jacDiagABInv;
+	GEN_set_min(j1, maxImpulse);
+	GEN_set_max(j1, -maxImpulse);
+
+	return j1;
+}
+
+
+
+
 btScalar sideFrictionStiffness2 = btScalar(1.0);
 void	btRaycastVehicle::updateFriction(btScalar	timeStep)
 {
@@ -539,6 +597,26 @@ void	btRaycastVehicle::updateFriction(btScalar	timeStep)
 			btWheelInfo& wheelInfo = m_wheelInfo[wheel];
 			class btRigidBody* groundObject = (class btRigidBody*) wheelInfo.m_raycastInfo.m_groundObject;
 
+			btScalar	rollingFriction = 0.f;
+
+			if (groundObject)
+			{
+				if (wheelInfo.m_engineForce != 0.f)
+				{
+					rollingFriction = wheelInfo.m_engineForce* timeStep;
+				} else
+				{
+					btScalar defaultRollingFrictionImpulse = 0.f;
+					btScalar maxImpulse = wheelInfo.m_brake ? wheelInfo.m_brake : defaultRollingFrictionImpulse;
+					btWheelContactPoint contactPt(m_chassisBody,groundObject,wheelInfo.m_raycastInfo.m_contactPointWS,forwardWS[wheel],maxImpulse);
+					rollingFriction = calcRollingFriction(contactPt);
+				}
+			}
+
+			//switch between active rolling (throttle), braking and non-active rolling friction (no throttle/break)
+			
+
+
 
 			forwardImpulse[wheel] = btScalar(0.);
 			m_wheelInfo[wheel].m_skidInfo= btScalar(1.);
@@ -552,7 +630,8 @@ void	btRaycastVehicle::updateFriction(btScalar	timeStep)
 
 				btScalar maximpSquared = maximp * maximpSide;
 			
-				forwardImpulse[wheel] = wheelInfo.m_engineForce* timeStep;
+
+				forwardImpulse[wheel] = rollingFriction;//wheelInfo.m_engineForce* timeStep;
 
 				btScalar x = (forwardImpulse[wheel] ) * fwdFactor;
 				btScalar y = (sideImpulse[wheel] ) * sideFactor;