vehicle: Implement per-wheel brake torque

Based upon the same calculations that regular VPhysics does, calculate the per-wheel brake torque.

Improves vehicle feel and matches it more closely.

vphysics_jolt/vjolt_controller_vehicle.cpp

@@ -403,6 +403,9 @@ void JoltPhysicsVehicleController::CreateWheel( JPH::VehicleConstraintSettings &
 	const float steeringAngle = DEG2RAD( Max( m_VehicleParams.steering.degreesSlow, m_VehicleParams.steering.degreesFast ) );
 	const float additionalLength = SourceToJolt::Distance( axle.wheels.springAdditionalLength );
 
+	Vector gravity;
+	m_pEnvironment->GetGravity( &gravity );
+
 	JPH::WheelSettingsWV *wheelSettings = new JPH::WheelSettingsWV;
 	wheelSettings->mPosition			= SourceToJolt::Distance( wheelPositionLocal );
 	wheelSettings->mDirection			= JPH::Vec3( 0, 0, -1 );
@@ -431,6 +434,14 @@ void JoltPhysicsVehicleController::CreateWheel( JPH::VehicleConstraintSettings &
 		wheelSettings->mLongitudinalFriction.AddPoint( 1.0f, axle.wheels.frictionScale );
 	}
 
+	// TODO: We may want to update this every pre-simulation to account for changing gravity.
+	wheelSettings->mMaxBrakeTorque =
+		0.5f *
+		SourceToJolt::Distance( gravity.Length() ) *
+		( m_pCarBodyObject->GetMass() + m_TotalWheelMass ) *
+		axle.brakeFactor *
+		SourceToJolt::Distance( axle.wheels.radius );
+
 	vehicleSettings.mWheels.push_back( wheelSettings );
 	m_InternalState.LargestWheelRadius = Max( m_InternalState.LargestWheelRadius, SourceToJolt::Distance( wheelWidth ) );
 }
@@ -442,6 +453,10 @@ void JoltPhysicsVehicleController::CreateWheels( JPH::VehicleConstraintSettings
 	m_Wheels.reserve( m_VehicleParams.axleCount * m_VehicleParams.wheelsPerAxle );
 	vehicleSettings.mAntiRollBars.reserve( m_VehicleParams.axleCount );
 
+	m_TotalWheelMass = 0.0f;
+	for ( int axle = 0; axle < m_VehicleParams.axleCount; axle++ )
+		m_TotalWheelMass += m_VehicleParams.axles[ axle ].wheels.mass * m_VehicleParams.wheelsPerAxle;
+
 	for ( int axle = 0; axle < m_VehicleParams.axleCount; axle++ )
 	{
 		for ( int wheel = 0; wheel < m_VehicleParams.wheelsPerAxle; wheel++ )

vphysics_jolt/vjolt_controller_vehicle.h

@@ -83,6 +83,7 @@ private:
 
 	std::vector< JoltPhysicsWheel >			m_Wheels;
 
+	float									m_TotalWheelMass = 0.0f;
 	JoltPhysicsInternalVehicleState			m_InternalState;
 
 	JPH::Ref< JPH::VehicleConstraint >		m_VehicleConstraint;