Implementing Vehicle Physics
Now let's move on to bringing the main character to life. Create a new C# component named Car to control the physical model of the car.
The component will provide a set of vehicle parameters and functions according to which the wheels will rotate and the motors embedded in the wheel joints will be activated.
using System;
using System.Collections;
using System.Collections.Generic;
using Unigine;
[Component(PropertyGuid = "AUTOGENERATED_GUID")] // <-- this line is generated automatically for a new component
public class Car : Component
{
// define two modes of movement: forward and reverse
protected enum MoveDirection
{
Forward,
Reverse,
}
// vehicle parameters: acceleration, maximum speed, and wheel turning angle, torque
public float acceleration = 50.0f;
public float max_velocity = 90.0f;
private float max_turn_angle = 30.0f;
public float default_torque = 5.0f;
// car body length and width
public float car_base = 3.0f;
public float car_width = 2.0f;
// speed of accelerating, braking, and turning
public float throttle_speed = 2.0f;
public float brake_speed = 1.2f;
public float wheel_speed = 2.0f;
// service and hand brake force
public float brake_damping = 8.0f;
public float hand_brake_damping = 30.0f;
// references to wheel nodes
public Node wheel_fl = null;
public Node wheel_fr = null;
public Node wheel_rl = null;
public Node wheel_rr = null;
// references to light nodes: brake and reverse light
public Node brake_light = null;
public Node reverse_light = null;
// wheel joints
private JointWheel joint_wheel_fl = null;
private JointWheel joint_wheel_fr = null;
private JointWheel joint_wheel_rl = null;
private JointWheel joint_wheel_rr = null;
// define the desired and current values for throttle, brake, steering wheel and hand brake
private float target_throttle = 0.0f;
private float target_brake = 0.0f;
private float target_wheel = 0.0f;
private float target_hand_brake = 0.0f;
private float current_throttle = 0.0f;
private float current_brake = 0.0f;
private float current_wheel = 0.0f;
private float current_hand_brake = 0.0f;
// by default, the car moves in the Forward direction
private MoveDirection current_move_direction = MoveDirection.Forward;
// variables for current rotation speed, torque and turn angle
private float current_velocity = 0.0f;
private float current_torque = 0.0f;
private float current_turn_angle = 0.0f;
// car physical body
private BodyRigid CarBodyRigid = null;
private void Init()
{
// at initialization, get wheel joints and car physical body
if (wheel_rl)
joint_wheel_rl = wheel_rl.ObjectBody.GetJoint(0) as JointWheel;
if (wheel_rr)
joint_wheel_rr = wheel_rr.ObjectBody.GetJoint(0) as JointWheel;
if (wheel_fl)
joint_wheel_fl = wheel_fl.ObjectBody.GetJoint(0) as JointWheel;
if (wheel_fr)
joint_wheel_fr = wheel_fr.ObjectBody.GetJoint(0) as JointWheel;
CarBodyRigid = node.ObjectBodyRigid;
}
protected virtual void Update()
{
// get the time it took to render the previous frame in order to be independent from FPS
float deltaTime = Game.IFps;
// smoothly change the current throttle, brake, and steering position towards the required values
current_throttle = MathLib.MoveTowards(current_throttle, target_throttle, throttle_speed * deltaTime);
current_brake = MathLib.MoveTowards(current_brake, target_brake, brake_speed * deltaTime);
current_wheel = MathLib.MoveTowards(current_wheel, target_wheel, wheel_speed * deltaTime);
current_hand_brake = MathLib.MoveTowards(current_hand_brake, target_hand_brake, brake_speed * deltaTime);
// enable the brake light node if the brake is activated (value greater than ~zero)
if (brake_light != null)
brake_light.Enabled = target_brake > MathLib.EPSILON;
// the current torque value is calculated as the product of the throttle position and the standard multiplier
current_torque = default_torque * current_throttle;
// when the throttle is pressed
if (current_throttle > MathLib.EPSILON)
{
// current angular velocity of wheels changes according to acceleration and motion direction
current_velocity += deltaTime * MathLib.Lerp(0.0f, acceleration, current_throttle) * (current_move_direction == MoveDirection.Forward ? 1.0f : -1.0f);
}
else
{
// otherwise decrease the speed exponentially
current_velocity *= MathLib.Exp(-deltaTime);
}
// calculate the brake force depending on the current brake intensity
float damping = MathLib.Lerp(0.0f, brake_damping, current_brake);
float rdamping = MathLib.Lerp(0.0f, hand_brake_damping, current_hand_brake);
// apply braking for all wheels, hand brake is also applied for the rear wheels
joint_wheel_fl.AngularDamping = damping;
joint_wheel_fr.AngularDamping = damping;
joint_wheel_rl.AngularDamping = MathLib.Max(damping, rdamping);
joint_wheel_rr.AngularDamping = MathLib.Max(damping, rdamping);
// calculate the current angular velocity and angle of rotation, limited by the extreme values
current_velocity = MathLib.Clamp(current_velocity, -max_velocity, max_velocity);
current_turn_angle = MathLib.Lerp(-max_turn_angle, max_turn_angle, MathLib.Clamp(0.5f + current_wheel * 0.5f, 0.0f,1.0f));
// simulate differential for the front axle: the wheels should turn by different angles
float angle_0 = current_turn_angle;
float angle_1 = current_turn_angle;
if (MathLib.Abs(current_turn_angle) > MathLib.EPSILON)
{
float radius = car_base / MathLib.Tan(current_turn_angle * MathLib.DEG2RAD);
float radius_0 = radius - car_width * 0.5f;
float radius_1 = radius + car_width * 0.5f;
angle_0 = MathLib.Atan(car_base / radius_0) * MathLib.RAD2DEG;
angle_1 = MathLib.Atan(car_base / radius_1) * MathLib.RAD2DEG;
}
// apply rotation for both front wheels using the rotation matrix along the Z axis
joint_wheel_fr.Axis10 = MathLib.RotateZ(angle_1).GetColumn3(0);
joint_wheel_fl.Axis10 = MathLib.RotateZ(angle_0).GetColumn3(0);
}
// it is important to change the parameters of physical objects in the UpdatePhysics method
private void UpdatePhysics()
{
// apply the calculated values of wheels angular velocity and torque
// all 4 wheels have a 'motor', i.e. the car is all-wheel drive
joint_wheel_fl.AngularVelocity = current_velocity;
joint_wheel_fr.AngularVelocity = current_velocity;
joint_wheel_fl.AngularTorque = current_torque;
joint_wheel_fr.AngularTorque = current_torque;
joint_wheel_rl.AngularVelocity = current_velocity;
joint_wheel_rr.AngularVelocity = current_velocity;
joint_wheel_rl.AngularTorque = current_torque;
joint_wheel_rr.AngularTorque = current_torque;
}
// add methods to control the car: throttle, brake, steering wheel turning and hand brake
protected void SetThrottle(float value)
{
target_throttle = MathLib.Clamp(value, 0.0f, 1.0f);
}
protected void SetBrake(float value)
{
target_brake = MathLib.Clamp(value, 0.0f, 1.0f);
}
protected void SetWheelPosition(float value)
{
target_wheel = MathLib.Clamp(value, -1.0f, 1.0f);
}
protected void SetHandBrake(float value)
{
target_hand_brake = MathLib.Clamp(value, -1.0f, 1.0f);
}
// method for changing the driving mode, it also controls the reverse light
protected void SetMoveDirection(MoveDirection value)
{
if (current_move_direction == value)
return;
current_velocity = 0.0f;
current_move_direction = value;
if (reverse_light != null)
reverse_light.Enabled = current_move_direction == MoveDirection.Reverse;
}
protected MoveDirection CurrentMoveDirection { get { return current_move_direction; } }
// method for the instant car relocation, returns the car to the initial position
public void Reset(mat4 transform)
{
node.WorldTransform = transform;
node.ObjectBodyRigid.LinearVelocity = vec3.ZERO;
node.ObjectBodyRigid.AngularVelocity = vec3.ZERO;
current_velocity = 0.0f;
}
// get speed immediately in km/h
public float Speed { get { return CarBodyRigid.LinearVelocity.Length * 3.6f; } }
}
Last update:
2024-08-16
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