private static void UpdateWheelVelocity(float deltaTime, ConstraintVehicle vehicle, ConstraintWheel wheel)
{
if (wheel.Tag == 1)
{
wheel.Tag = 0;
if (Numeric.IsZero(wheel.BrakeForce))
{
// We set the angular velocity, so that the wheel matches the moving underground.
Vector3F relativeContactVelocity = vehicle.Chassis.GetVelocityOfWorldPoint(wheel.GroundPosition)
- wheel.TouchedBody.GetVelocityOfWorldPoint(wheel.GroundPosition);
float forwardVelocity = Vector3F.Dot(relativeContactVelocity, wheel.GroundForward);
wheel.AngularVelocity = forwardVelocity / wheel.Radius;
wheel.RotationAngle += wheel.AngularVelocity * deltaTime;
}
else
{
// Braking wheels do not rotate.
wheel.AngularVelocity = 0;
}
}
else
{
// To keep it simple: The wheel continues spinning in the same direction.
// Damp angular velocity and update rotation angle.
wheel.AngularVelocity *= 0.99f;
wheel.RotationAngle += wheel.AngularVelocity * deltaTime;
}
}
// Creates or gets the ConstraintVehicleHandler instance and adds a vehicle.
internal static void Add(ConstraintVehicle vehicle)
{
var simulation = vehicle.Simulation;
var handler = GetHandler(simulation);
if (handler == null)
{
// The first vehicle: Add a new instance of this class to the simulation.
handler = new ConstraintVehicleHandler();
simulation.ForceEffects.Add(handler);
simulation.SubTimeStepFinished += handler.OnSubTimeStepFinished;
}
handler._vehicles.Add(vehicle);
}
// Creates or gets the ConstraintVehicleHandler instance and adds a vehicle.
internal static void Add(ConstraintVehicle vehicle)
{
var simulation = vehicle.Simulation;
var handler = GetHandler(simulation);
if (handler == null)
{
// The first vehicle: Add a new instance of this class to the simulation.
handler = new ConstraintVehicleHandler();
simulation.ForceEffects.Add(handler);
simulation.SubTimeStepFinished += handler.OnSubTimeStepFinished;
}
handler._vehicles.Add(vehicle);
}
// Removes a vehicle. When the last vehicle is removed, the ConstraintVehicleHandler
// instance is removed too.
internal static void Remove(ConstraintVehicle vehicle)
{
Simulation simulation = vehicle.Simulation;
ConstraintVehicleHandler handler = GetHandler(simulation);
if (handler != null)
{
handler._vehicles.Remove(vehicle);
// The last vehicle was removed.
if (handler._vehicles.Count == 0)
{
simulation.ForceEffects.Remove(handler);
simulation.SubTimeStepFinished -= handler.OnSubTimeStepFinished;
}
}
}
// Removes a vehicle. When the last vehicle is removed, the ConstraintVehicleHandler
// instance is removed too.
internal static void Remove(ConstraintVehicle vehicle)
{
Simulation simulation = vehicle.Simulation;
ConstraintVehicleHandler handler = GetHandler(simulation);
if (handler != null)
{
handler._vehicles.Remove(vehicle);
// The last vehicle was removed.
if (handler._vehicles.Count == 0)
{
simulation.ForceEffects.Remove(handler);
simulation.SubTimeStepFinished -= handler.OnSubTimeStepFinished;
}
}
}
//--------------------------------------------------------------
#region Creation & Cleanup
//--------------------------------------------------------------
public ConstraintVehicleObject(IServiceLocator services)
{
Name = "Vehicle";
_services = services;
_inputService = services.GetInstance<IInputService>();
_simulation = services.GetInstance<Simulation>();
// Load models for rendering.
var contentManager = services.GetInstance<ContentManager>();
_vehicleModelNode = contentManager.Load<ModelNode>("Car/Car").Clone();
_wheelModelNodes = new ModelNode[4];
_wheelModelNodes[0] = contentManager.Load<ModelNode>("Car/Wheel").Clone();
_wheelModelNodes[1] = _wheelModelNodes[0].Clone();
_wheelModelNodes[2] = _wheelModelNodes[0].Clone();
_wheelModelNodes[3] = _wheelModelNodes[0].Clone();
// Add wheels under the car model node.
_vehicleModelNode.Children.Add(_wheelModelNodes[0]);
_vehicleModelNode.Children.Add(_wheelModelNodes[1]);
_vehicleModelNode.Children.Add(_wheelModelNodes[2]);
_vehicleModelNode.Children.Add(_wheelModelNodes[3]);
// ----- Create the chassis of the car.
// The Vehicle needs a rigid body that represents the chassis. This can be any shape (e.g.
// a simple BoxShape). In this example we will build a convex polyhedron from the car model.
// 1. Extract the vertices from the car model.
// The car model has ~10,000 vertices. It consists of a MeshNode for the glass
// parts and a MeshNode "Car" for the chassis.
var meshNode = _vehicleModelNode.GetDescendants()
.OfType<MeshNode>()
.First(mn => mn.Name == "Car");
var mesh = MeshHelper.ToTriangleMesh(meshNode.Mesh);
// Apply the transformation of the mesh node.
mesh.Transform(meshNode.PoseWorld * Matrix44F.CreateScale(meshNode.ScaleWorld));
// 2. (Optional) Create simplified convex hull from mesh.
// We could also skip this step and directly create a convex polyhedron from the mesh using
// var chassisShape = new ConvexPolyhedron(mesh.Vertices);
// However, the convex polyhedron would still have 500-600 vertices.
// We can reduce the number of vertices by using the GeometryHelper.
// Create a convex hull for mesh with max. 64 vertices. Additional, shrink the hull by 4 cm.
var convexHull = GeometryHelper.CreateConvexHull(mesh.Vertices, 64, -0.04f);
// 3. Create convex polyhedron shape using the vertices of the convex hull.
var chassisShape = new ConvexPolyhedron(convexHull.Vertices.Select(v => v.Position));
// (Note: Building convex hulls and convex polyhedra are time-consuming. To save loading time
// we should build the shape in the XNA content pipeline. See other DigitalRune Physics
// Samples.)
// The mass properties of the car. We use a mass of 800 kg.
var mass = MassFrame.FromShapeAndMass(chassisShape, Vector3F.One, 800, 0.1f, 1);
// Trick: We artificially modify the center of mass of the rigid body. Lowering the center
// of mass makes the car more stable against rolling in tight curves.
// We could also modify mass.Inertia for other effects.
var pose = mass.Pose;
pose.Position.Y -= 0.5f; // Lower the center of mass.
pose.Position.Z = -0.5f; // The center should be below the driver.
// (Note: The car model is not exactly centered.)
mass.Pose = pose;
// Material for the chassis.
var material = new UniformMaterial
{
Restitution = 0.1f,
StaticFriction = 0.2f,
DynamicFriction = 0.2f
};
var chassis = new RigidBody(chassisShape, mass, material)
{
Pose = new Pose(new Vector3F(0, 2, 0)), // Start position
UserData = "NoDraw", // (Remove this line to render the collision model.)
};
// ----- Create the vehicle.
Vehicle = new ConstraintVehicle(_simulation, chassis);
// Add 4 wheels.
Vehicle.Wheels.Add(new ConstraintWheel { Offset = new Vector3F(-0.9f, 0.6f, -2.0f), Radius = 0.36f, SuspensionRestLength = 0.55f, MinSuspensionLength = 0.25f, Friction = 2 }); // Front left
Vehicle.Wheels.Add(new ConstraintWheel { Offset = new Vector3F(0.9f, 0.6f, -2.0f), Radius = 0.36f, SuspensionRestLength = 0.55f, MinSuspensionLength = 0.25f, Friction = 2 }); // Front right
Vehicle.Wheels.Add(new ConstraintWheel { Offset = new Vector3F(-0.9f, 0.6f, 0.98f), Radius = 0.36f, SuspensionRestLength = 0.55f, MinSuspensionLength = 0.25f, Friction = 1.8f });// Back left
Vehicle.Wheels.Add(new ConstraintWheel { Offset = new Vector3F(0.9f, 0.6f, 0.98f), Radius = 0.36f, SuspensionRestLength = 0.55f, MinSuspensionLength = 0.25f, Friction = 1.8f }); // Back right
// Vehicles are disabled per default. This way we can create the vehicle and the simulation
// objects are only added when needed.
Vehicle.Enabled = false;
}
private static void UpdateWheelVelocity(float deltaTime, ConstraintVehicle vehicle, ConstraintWheel wheel)
{
if (wheel.Tag == 1)
{
wheel.Tag = 0;
if (Numeric.IsZero(wheel.BrakeForce))
{
// We set the angular velocity, so that the wheel matches the moving underground.
Vector3F relativeContactVelocity = vehicle.Chassis.GetVelocityOfWorldPoint(wheel.GroundPosition)
- wheel.TouchedBody.GetVelocityOfWorldPoint(wheel.GroundPosition);
float forwardVelocity = Vector3F.Dot(relativeContactVelocity, wheel.GroundForward);
wheel.AngularVelocity = forwardVelocity / wheel.Radius;
wheel.RotationAngle += wheel.AngularVelocity * deltaTime;
}
else
{
// Braking wheels do not rotate.
wheel.AngularVelocity = 0;
}
}
else
{
// To keep it simple: The wheel continues spinning in the same direction.
// Damp angular velocity and update rotation angle.
wheel.AngularVelocity *= 0.99f;
wheel.RotationAngle += wheel.AngularVelocity * deltaTime;
}
}