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Unigine Basics
1. Introduction
2. Managing Virtual Worlds
3. Preparing 3D Models
4. Materials
5. Cameras and Lighting
6. Implementing Application Logic
7. Making Cutscenes and Recording Videos
8. Preparing Your Project for Release
9. Physics
10. Optimization Basics
11. PROJECT2: First-Person Shooter
13. PROJECT4: VR Application With Simple Interaction

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.

Source code (C#)
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
	// 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);
			// 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)
		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: 2024-04-19
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