A simple spring simulation in one dimension
/*
* $Id: FloatSpring.java,v 1.4 2007/06/25 23:00:10 shingoki Exp $
*
* Copyright (c) 2005-2006 shingoki
*
* This file is part of AirCarrier, see http://aircarrier.dev.java.net/
*
* AirCarrier is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
* AirCarrier is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
* You should have received a copy of the GNU General Public License
* along with AirCarrier; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
*/
/**
* A simple spring simulation in one dimension Useful for getting a property
* (for example a position) to move from one value to another, in a smooth
* looking way. To use, create a spring with appropriate constants (e.g. new
* FloatSpring(100) is a reasonable value) Then set spring position to the
* initial value, and update each frame with target parameter as your desired
* value. The position parameter will "snap to" the desired value.
*
* @author goki
*/
public class FloatSpring {
float position;
float springK;
float dampingK;
float velocity;
/**
* Make a spring with given spring constant and damping constant
*
* @param springK
* Spring constant, the higher this is the "tighter" the spring, and
* the more force it will exert for a given extension
* @param dampingK
* Damping constant, the higher this is the stronger the damping, and
* the more "soggy" the movement.
*/
public FloatSpring(float springK, float dampingK) {
super();
this.position = 0;
this.springK = springK;
this.dampingK = dampingK;
this.velocity = 0;
}
/**
* Create a critically damped spring (or near to critically damped) This
* spring will quickly move to its target without overshooting
*
* @param springK
* The spring constant - the higher this is, the more quickly the
* spring will reach its target. A value of 100 gives a reasonable
* response in about a second, a higher value gives a faster
* response.
*/
public FloatSpring(float springK) {
this(springK, (float) (2 * Math.sqrt(springK)));
}
/**
* Update the position of the spring. This updates the "position" as if there
* were a damped spring stretched between the current position and the target
* position. That is, the spring will tend to pull the position towards the
* target, and if the spring is damped the position will eventually settle
* onto the target.
*
* @param target
* The target towards which the spring is pulling the position
* @param time
* The elapsed time in seconds
*/
public void update(float target, float time) {
// Set v to target - position, this is the required movement
float v = position - target;
// Multiply displacement by spring constant to get spring force,
// then subtract damping force
v = v * -springK - velocity * dampingK;
// v is now a force, so assuming unit mass is is also acceleration.
// multiply by elapsed time to get velocity change
velocity += v * time;
// If velocity isn't valid, zero it
if (Float.isNaN(velocity) || Float.isInfinite(velocity)) {
velocity = 0;
}
// Change the position at the new velocity, for elapsed time
position += velocity * time;
}
/**
* @return Damping constant, the higher this is the stronger the damping, and
* the more "soggy" the movement.
*/
public float getDampingK() {
return dampingK;
}
/**
* @param dampingK
* Damping constant, the higher this is the stronger the damping, and
* the more "soggy" the movement.
*/
public void setDampingK(float dampingK) {
this.dampingK = dampingK;
}
/**
* @return The current position of the simulated spring end point, changes as
* simulation is updated
*/
public float getPosition() {
return position;
}
/**
* @param position
* A new position for simulated spring end point
*/
public void setPosition(float position) {
this.position = position;
}
/**
* @return The spring constant - the higher this is, the more quickly the
* spring will reach its target
*/
public float getSpringK() {
return springK;
}
/**
* @param springK
* The spring constant - the higher this is, the more quickly the
* spring will reach its target
*/
public void setSpringK(float springK) {
this.springK = springK;
}
/**
* @return The current velocity of the position
*/
public float getVelocity() {
return velocity;
}
/**
* @param velocity
* A new value for the current velocity of the position
*/
public void setVelocity(float velocity) {
this.velocity = velocity;
}
}
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