city.cs.engine

Class DynamicBody

java.lang.Object

city.cs.engine.Body

city.cs.engine.DynamicBody

Direct Known Subclasses:

Walker

public class DynamicBody
extends Body

A dynamic body moves, rotates and collides with other bodies according to the laws of physics. It has finite mass, with a distribution determined by the densities of its constituent shapes.

The underlying physics engine works best with dynamic objects between 0.1 and 10 metres in size.

Constructor Summary

Constructors

Constructor and Description
DynamicBody(World w) Initialise a new dynamic Body with no shapes attached.
DynamicBody(World w, Shape s) Initialise a new dynamic Body with a single shape attached.

Method Summary

Modifier and Type	Method and Description
void	applyForce(Vec2 force) Apply a force to this body at its centre of mass.
void	applyForce(Vec2 force, Vec2 point) Apply a force to this body at a specified position in the world.
void	applyImpulse(Vec2 impulse) Apply an impulse to this body at its centre of mass.
void	applyImpulse(Vec2 impulse, Vec2 point) Apply an impulse to this body at a specified position in the world.
void	applyTorque(float torque) Apply a torque to this body, affecting its rotation about its centre of mass.
float	getGravityScale() Get the gravity scale for this body.
boolean	isBullet() Get the value of the bullet attribute on this body.
void	setAngularVelocity(float angularVelocity) Set this body's angular velocity.
void	setBullet(boolean b) Set the value of the bullet attribute on this body.
void	setGravityScale(float g) Set the gravity scale for this body.
void	setLinearVelocity(Vec2 velocity) Set this body's linear velocity.

Methods inherited from class city.cs.engine.Body

addCollisionListener, addDestructionListener, addImage, contains, destroy, getAngle, getAngleDegrees, getAngularVelocity, getBodiesInContact, getFillColor, getFixtureList, getImages, getLinearVelocity, getLineColor, getMass, getName, getPosition, getWorld, intersects, intersects, isAlwaysOutline, isClipped, move, putOn, putOn, removeAllCollisionListeners, removeAllDestructionListeners, removeAllImages, removeAttachedImage, removeCollisionListener, removeDestructionListener, rotate, rotate, rotateDegrees, rotateDegrees, setAlwaysOutline, setAngle, setAngleDegrees, setClipped, setFillColor, setLineColor, setName, setPosition, toString

Methods inherited from class java.lang.Object

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

Constructor Detail

DynamicBody

public DynamicBody(World w)

Initialise a new dynamic Body with no shapes attached.

Parameters:

w - the world in which this body will exist

DynamicBody

public DynamicBody(World w,
                   Shape s)

Initialise a new dynamic Body with a single shape attached.

Parameters:

w - the world in which this body will exist

s - the initial shape of this body

Method Detail

setLinearVelocity

public void setLinearVelocity(Vec2 velocity)

Set this body's linear velocity. The parameter is a vector; first component is the new speed along the x-axis, second component is the new speed along the y-axis.

Parameters:

velocity - the new velocity

setAngularVelocity

public void setAngularVelocity(float angularVelocity)

Set this body's angular velocity.

Parameters:

angularVelocity - the new angular velocity in radians pers second

applyImpulse

public void applyImpulse(Vec2 impulse)

Apply an impulse to this body at its centre of mass.

Parameters:

impulse - the impulse in Newton seconds (first component in x-direction, second component in y-direction)

applyImpulse

public void applyImpulse(Vec2 impulse,
                         Vec2 point)

Apply an impulse to this body at a specified position in the world. If the position is not the centre of mass it will create a torque, rotating the body.

Parameters:

impulse - the impulse in Newton seconds (first component in x-direction, second component in y-direction)

point - the point at which to apply the impulse (first component is x, second component is y)

applyForce

public void applyForce(Vec2 force)

Apply a force to this body at its centre of mass. The force will be applied for the duration of the next time step.

Parameters:

force - the force in Newtons (first component in x-direction, second component in y-direction)

applyForce

public void applyForce(Vec2 force,
                       Vec2 point)

Apply a force to this body at a specified position in the world. If the position is not the centre of mass it will create a torque, rotating the body. The force will be applied for the duration of the next time step.

Parameters:

force - the force in Newtons (first component in x-direction, second component in y-direction)

point - the point at which to apply the force (first component is x, second component is y)

applyTorque

public void applyTorque(float torque)

Apply a torque to this body, affecting its rotation about its centre of mass.

Parameters:

torque - the torque in Newton metres

setBullet

public void setBullet(boolean b)

Set the value of the bullet attribute on this body. When this attribute is false (the default), collisions between this object and other dynamic bodies are detected only at the moment of each simulation step. This is usually adequate, but sometimes misses collisions that occur between steps, producing a "tunnelling" effect.

This doesn't happen with collisions between dynamic and static bodies, because the engine uses continuous collision detection in that case: the dynamic body is swept from its old position to its new position, and if a collision occurs in the sweep the body is moved back to the time of impact.

Setting the bullet attribute to true turns on continuous collision detection between this body and other dynamic bodies, which is considerably more expensive. It is usually only necessary for small, fast-moving objects (like bullets).

Parameters:

b - the new value for the bullet attribute

isBullet

public boolean isBullet()

Get the value of the bullet attribute on this body.

Returns:

use continuous collision detection between this body and other dynamic bodies?

setGravityScale

public void setGravityScale(float g)

Set the gravity scale for this body. The gravity scale is used as a multiplier with the global gravity vector when simulating the effect of gravity on bodies. The default gravity scale for a body is 1.0. It is not physically realistic for different bodies to experience different scales of gravity but can be useful in games. Setting gravity scale to 0 results in a body which is unaffected by gravity. Bodies with a negative gravity scale will accelerate upwards.

Parameters:

g - the new gravity scale

getGravityScale

public float getGravityScale()

Get the gravity scale for this body.

Returns:

the gravity scale for this body