net.stemkoski.bagel

Class Physics

java.lang.Object

net.stemkoski.bagel.Physics

Direct Known Subclasses:

PlatformPhysics

public class Physics
extends java.lang.Object

Used to simulate change in position of an object based on velocity and acceleration; useful in games with a top-down view perspective. (For side-view perspective games, see PlatformPhysics.)

Field Summary

Fields

Modifier and Type	Field and Description
double	accelerationValue Constant amount of acceleration, used by accelerateAtAngle(double).
(package private) Vector2	accelerationVector Acceleration (rate of chance of velocity) of object.
double	decelerationValue Rate of speed reduction to apply when object is not accelerating.
double	maximumSpeed Maximum speed possible for object.
(package private) Vector2	positionVector Position of object.
(package private) Vector2	velocityVector Velocity (rate of change of position) of object.

Constructor Summary

Constructors

Constructor and Description
Physics(double accValue, double maxSpeed, double decValue) Initialize values used by physics simulation.

Method Summary

Modifier and Type	Method and Description
void	accelerateAtAngle(double angleDegrees) Accelerate this object in the direction angleDegrees by the amount specified by accelerationValue.
void	bounceAgainst(double surfaceAngleDegrees) Change angle of motion assuming a collision with a flat surface inclined at an angle of surfaceAngleDegrees.
double	getMotionAngle() Calculate the angle of motion (in degrees) as measured from the x-axis (the vector (1,0)).
double	getSpeed() Calculate speed of object.
void	setMotionAngle(double angleDegrees) Set the angle of motion of this object.
void	setSpeed(double speed) Set speed of object.
void	update(double dt) Update the position of this object according to velocity and acceleration.

Methods inherited from class java.lang.Object

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

Field Detail

positionVector

Vector2 positionVector

Position of object.

velocityVector

Vector2 velocityVector

Velocity (rate of change of position) of object.

accelerationVector

Vector2 accelerationVector

Acceleration (rate of chance of velocity) of object.

accelerationValue

public double accelerationValue

Constant amount of acceleration, used by accelerateAtAngle(double).

maximumSpeed

public double maximumSpeed

Maximum speed possible for object.

decelerationValue

public double decelerationValue

Rate of speed reduction to apply when object is not accelerating.

Constructor Detail

Physics

public Physics(double accValue,
               double maxSpeed,
               double decValue)

Initialize values used by physics simulation. For objects traveling at constant speed, set acceleration and deceleration values to 0.

Parameters:

accValue - acceleration value

maxSpeed - maximum speed

decValue - deceleration value

Method Detail

getSpeed

public double getSpeed()

Calculate speed of object.

Returns:

speed of object

setSpeed

public void setSpeed(double speed)

Set speed of object. If acceleration and deceleration values are 0, the speed will remain constant.

Parameters:

speed - speed of object

getMotionAngle

public double getMotionAngle()

Calculate the angle of motion (in degrees) as measured from the x-axis (the vector (1,0)). If the speed is 0, this method returns 0. Return values are in the range from -180 to +180.

Returns:

angle of motion of object

setMotionAngle

public void setMotionAngle(double angleDegrees)

Set the angle of motion of this object. If the speed is 0, this method has no effect.

Parameters:

angleDegrees - angle of motion of object

bounceAgainst

public void bounceAgainst(double surfaceAngleDegrees)

Change angle of motion assuming a collision with a flat surface inclined at an angle of surfaceAngleDegrees.

Parameters:

surfaceAngleDegrees - inclination of surface this object has collided with

accelerateAtAngle

public void accelerateAtAngle(double angleDegrees)

Accelerate this object in the direction angleDegrees by the amount specified by accelerationValue.

Parameters:

angleDegrees - direction of acceleration

update

public void update(double dt)

Update the position of this object according to velocity and acceleration. Deceleration is applied if no acceleration is present.

Parameters:

dt - elapsed time (seconds) since previous iteration of game loop (typically approximately 1/60 second)