city.cs.engine

Class World

java.lang.Object

city.cs.engine.World

public class World
extends Object

A world in which the motion and interaction of a number of rigid bodies is simulated. Bodies are added to the world automatically when they are created.

Quantities in the world are measured using the SI system (metres, kilograms and seconds):

• Displacements and velocities in the world are represented using the Vec2 class. A Vec2 has an x-component (increases to the right) and a y-component (increases upwards).
• Angles are measured in radians; to convert degrees to radians, divide by MathUtils.RAD2DEG; to convert radians to degrees, multiply by MathUtils.RAD2DEG.

Once started, the simulation approximates physical behaviour by computing positions and velocities of bodies at discrete time steps (by default, 1/60 of a second). StepListeners can be registered to invoke application code immediately before and after each simulation step. Once started, the simulation can be stopped and resumed.

Warning: When the simulation is running, the world should only be modified from the AWT thread, i.e. using the listener interfaces of this library, the AWT and Swing. In particular, all initialization must be complete before the world is started.

See Also:

Body.addCollisionListener(city.cs.engine.CollisionListener), Sensor.addSensorListener(city.cs.engine.SensorListener)

Field Summary

Fields

Modifier and Type	Field and Description
static float	DEFAULT_GRAVITY Default strength of gravity in metres per second per second.
static int	version Version of CityEngine

Constructor Summary

Constructors

Constructor and Description
World() Create a new world with the default target frame rate (24).
World(int framesPerSecond) Create a new world with target frame rate.

Method Summary

Modifier and Type	Method and Description
void	addStepListener(StepListener listener) Register a listener to be notified before and after each simulation step.
List<DynamicBody>	getDynamicBodies() Get all the dynamic bodies in the world.
float	getGravity() The strength of gravity in this world.
SimulationSettings	getSimulationSettings() Get the settings for the physics simulation.
List<StaticBody>	getStaticBodies() Get all the static bodies in the world.
boolean	isRunning() Is the simulation running?
void	oneStep() Advance a paused simulation by one step.
void	removeStepListener(StepListener listener) Unregister a step listener.
void	setGravity(float g) Set the strength of gravity in this world.
void	start() Start (or resume) the simulation.
void	stop() Stop the simulation.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

DEFAULT_GRAVITY

public static final float DEFAULT_GRAVITY

Default strength of gravity in metres per second per second.

See Also:

Constant Field Values

version

public static final int version

Version of CityEngine

See Also:

Constant Field Values

Constructor Detail

World

public World(int framesPerSecond)

Create a new world with target frame rate.

Parameters:

framesPerSecond - the target frame rate for the simulation

World

public World()

Create a new world with the default target frame rate (24).

Method Detail

start

public void start()

Start (or resume) the simulation.

stop

public void stop()

Stop the simulation. When stopped, the simulation may be advanced one step at a time using oneStep(), or resumed with start().

If stop() is called during a call to preStep(), the simulation step will not take place.

isRunning

public boolean isRunning()

Is the simulation running?

Returns:

the running attribute

oneStep

public void oneStep()

Advance a paused simulation by one step.

getSimulationSettings

public SimulationSettings getSimulationSettings()

Get the settings for the physics simulation.

Returns:

the settings

setGravity

public void setGravity(float g)

Set the strength of gravity in this world. The new gravity acceleration vector will act vertically downwards with the specified strength. Setting negative gravity strength causes gravity to act upwards instead of downwards. Note that individual bodies have their own gravity scale attribute (default 1.0f) which is multiplied with the global gravity strength when simulating the effect of gravity on bodies.

Parameters:

g - the new gravity strength in metres per second per second

See Also:

DynamicBody.setGravityScale(float)

getGravity

public float getGravity()

The strength of gravity in this world.

Returns:

the strength of gravity in this world in metres per second per second

See Also:

setGravity(float)

addStepListener

public void addStepListener(StepListener listener)

Register a listener to be notified before and after each simulation step. The listener's preStep() method is called immediately before each simulation step. The listener's postStep() method is called immediately after each simulation step. The postStep() methods are called the simulation step has finished and collision listeners have been called.

Parameters:

listener - the listener to add

See Also:

addChangeListener(javax.swing.event.ChangeListener)

removeStepListener

public void removeStepListener(StepListener listener)

Unregister a step listener. Does nothing if the listener is not registered.

Parameters:

listener - the listener to remove

getStaticBodies

public List<StaticBody> getStaticBodies()

Get all the static bodies in the world.

Returns:

a linked list of static bodies

getDynamicBodies

public List<DynamicBody> getDynamicBodies()

Get all the dynamic bodies in the world.

Returns:

a linked list of dynamic bodies