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A 2D java physics engine, a port of the C++ Box2d engine. This is the core physics engine.
/*******************************************************************************
* Copyright (c) 2011, Daniel Murphy
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without modification,
* are permitted provided that the following conditions are met:
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
******************************************************************************/
/*
* JBox2D - A Java Port of Erin Catto's Box2D
*
* JBox2D homepage: http://jbox2d.sourceforge.net/
* Box2D homepage: http://www.box2d.org
*
* This software is provided 'as-is', without any express or implied
* warranty. In no event will the authors be held liable for any damages
* arising from the use of this software.
*
* Permission is granted to anyone to use this software for any purpose,
* including commercial applications, and to alter it and redistribute it
* freely, subject to the following restrictions:
*
* 1. The origin of this software must not be misrepresented; you must not
* claim that you wrote the original software. If you use this software
* in a product, an acknowledgment in the product documentation would be
* appreciated but is not required.
* 2. Altered source versions must be plainly marked as such, and must not be
* misrepresented as being the original software.
* 3. This notice may not be removed or altered from any source distribution.
*/
package org.jbox2d.dynamics.joints;
import org.jbox2d.common.Mat22;
import org.jbox2d.common.MathUtils;
import org.jbox2d.common.Settings;
import org.jbox2d.common.Vec2;
import org.jbox2d.dynamics.Body;
import org.jbox2d.dynamics.TimeStep;
import org.jbox2d.pooling.IWorldPool;
//Updated to rev 56->130->142 of b2DistanceJoint.cpp/.h
//C = norm(p2 - p1) - L
//u = (p2 - p1) / norm(p2 - p1)
//Cdot = dot(u, v2 + cross(w2, r2) - v1 - cross(w1, r1))
//J = [-u -cross(r1, u) u cross(r2, u)]
//K = J * invM * JT
//= invMass1 + invI1 * cross(r1, u)^2 + invMass2 + invI2 * cross(r2, u)^2
/**
* A distance joint constrains two points on two bodies
* to remain at a fixed distance from each other. You can view
* this as a massless, rigid rod.
*/
public class DistanceJoint extends Joint {
public final Vec2 m_localAnchor1;
public final Vec2 m_localAnchor2;
public final Vec2 m_u;
public float m_impulse;
public float m_mass; // effective mass for the constraint.
public float m_length;
public float m_frequencyHz;
public float m_dampingRatio;
public float m_gamma;
public float m_bias;
public DistanceJoint(IWorldPool argWorld, final DistanceJointDef def) {
super(argWorld, def);
m_localAnchor1 = def.localAnchorA.clone();
m_localAnchor2 = def.localAnchorB.clone();
m_length = def.length;
m_impulse = 0.0f;
m_u = new Vec2();
m_frequencyHz = def.frequencyHz;
m_dampingRatio = def.dampingRatio;
m_gamma = 0.0f;
m_bias = 0.0f;
}
public void setFrequency(float hz) {
m_frequencyHz = hz;
}
public float getFrequency() {
return m_frequencyHz;
}
public float getLength() {
return m_length;
}
public void setLength(float argLength) {
m_length = argLength;
}
public void setDampingRatio(float damp) {
m_dampingRatio = damp;
}
public float getDampingRatio() {
return m_dampingRatio;
}
@Override
public void getAnchorA(Vec2 argOut) {
m_bodyA.getWorldPointToOut(m_localAnchor1, argOut);
}
@Override
public void getAnchorB(Vec2 argOut) {
m_bodyB.getWorldPointToOut(m_localAnchor2, argOut);
}
// djm pooled
@Override
public void getReactionForce(float inv_dt, Vec2 argOut) {
argOut.x = m_impulse * m_u.x * inv_dt;
argOut.y = m_impulse * m_u.y * inv_dt;
}
@Override
public float getReactionTorque(float inv_dt) {
return 0.0f;
}
@Override
public void initVelocityConstraints(final TimeStep step) {
// TODO: fully inline temp Vec2 ops
final Body b1 = m_bodyA;
final Body b2 = m_bodyB;
Vec2 r1 = pool.popVec2();
Vec2 r2 = pool.popVec2();
// Compute the effective mass matrix.
r1.set(m_localAnchor1).subLocal(b1.getLocalCenter());
r2.set(m_localAnchor2).subLocal(b2.getLocalCenter());
Mat22.mulToOut(b1.getTransform().R, r1, r1);
Mat22.mulToOut(b2.getTransform().R, r2, r2);
m_u.x = b2.m_sweep.c.x + r2.x - b1.m_sweep.c.x - r1.x;
m_u.y = b2.m_sweep.c.y + r2.y - b1.m_sweep.c.y - r1.y;
// Handle singularity.
float length = m_u.length();
if (length > Settings.linearSlop) {
m_u.x *= 1.0f / length;
m_u.y *= 1.0f / length;
}
else {
m_u.set(0.0f, 0.0f);
}
float cr1u = Vec2.cross(r1, m_u);
float cr2u = Vec2.cross(r2, m_u);
float invMass = b1.m_invMass + b1.m_invI * cr1u * cr1u + b2.m_invMass + b2.m_invI * cr2u * cr2u;
assert (invMass > Settings.EPSILON);
m_mass = 1.0f / invMass;
if (m_frequencyHz > 0.0f) {
float C = length - m_length;
// Frequency
float omega = 2.0f * MathUtils.PI * m_frequencyHz;
// Damping coefficient
float d = 2.0f * m_mass * m_dampingRatio * omega;
// Spring stiffness
float k = m_mass * omega * omega;
// magic formulas
m_gamma = step.dt * (d + step.dt * k);
m_gamma = m_gamma != 0.0f ? 1.0f / m_gamma : 0.0f;
m_bias = C * step.dt * k * m_gamma;
m_mass = invMass + m_gamma;
m_mass = m_mass != 0.0f ? 1.0f / m_mass : 0.0f;
}
if (step.warmStarting) {
// Scale the impulse to support a variable time step.
m_impulse *= step.dtRatio;
Vec2 P = pool.popVec2();
P.set(m_u).mulLocal(m_impulse);
b1.m_linearVelocity.x -= b1.m_invMass * P.x;
b1.m_linearVelocity.y -= b1.m_invMass * P.y;
b1.m_angularVelocity -= b1.m_invI * Vec2.cross(r1, P);
b2.m_linearVelocity.x += b2.m_invMass * P.x;
b2.m_linearVelocity.y += b2.m_invMass * P.y;
b2.m_angularVelocity += b2.m_invI * Vec2.cross(r2, P);
pool.pushVec2(1);
}
else {
m_impulse = 0.0f;
}
pool.pushVec2(2);
}
@Override
public void solveVelocityConstraints(final TimeStep step) {
final Body b1 = m_bodyA;
final Body b2 = m_bodyB;
final Vec2 r1 = pool.popVec2();
final Vec2 r2 = pool.popVec2();
r1.set(m_localAnchor1).subLocal(b1.getLocalCenter());
r2.set(m_localAnchor2).subLocal(b2.getLocalCenter());
Mat22.mulToOut(b1.getTransform().R, r1, r1);
Mat22.mulToOut(b2.getTransform().R, r2, r2);
final Vec2 v1 = pool.popVec2();
final Vec2 v2 = pool.popVec2();
// Cdot = dot(u, v + cross(w, r))
Vec2.crossToOut(b1.m_angularVelocity, r1, v1);
Vec2.crossToOut(b2.m_angularVelocity, r2, v2);
v1.addLocal(b1.m_linearVelocity);
v2.addLocal(b2.m_linearVelocity);
float Cdot = Vec2.dot(m_u, v2.subLocal(v1));
float impulse = -m_mass * (Cdot + m_bias + m_gamma * m_impulse);
m_impulse += impulse;
float Px = impulse * m_u.x;
float Py = impulse * m_u.y;
b1.m_linearVelocity.x -= b1.m_invMass * Px;
b1.m_linearVelocity.y -= b1.m_invMass * Py;
b1.m_angularVelocity -= b1.m_invI * (r1.x * Py - r1.y * Px);// b2Cross(r1, P);
b2.m_linearVelocity.x += b2.m_invMass * Px;
b2.m_linearVelocity.y += b2.m_invMass * Py;
b2.m_angularVelocity += b2.m_invI * (r2.x * Py - r2.y * Px);// b2Cross(r2, P);
pool.pushVec2(4);
}
@Override
public boolean solvePositionConstraints(float baumgarte) {
if (m_frequencyHz > 0.0f) {
return true;
}
final Body b1 = m_bodyA;
final Body b2 = m_bodyB;
final Vec2 r1 = pool.popVec2();
final Vec2 r2 = pool.popVec2();
final Vec2 d = pool.popVec2();
r1.set(m_localAnchor1).subLocal(b1.getLocalCenter());
r2.set(m_localAnchor2).subLocal(b2.getLocalCenter());
Mat22.mulToOut(b1.getTransform().R, r1, r1);
Mat22.mulToOut(b2.getTransform().R, r2, r2);
d.x = b2.m_sweep.c.x + r2.x - b1.m_sweep.c.x - r1.x;
d.y = b2.m_sweep.c.y + r2.y - b1.m_sweep.c.y - r1.y;
float length = d.normalize();
float C = length - m_length;
C = MathUtils.clamp(C, -Settings.maxLinearCorrection, Settings.maxLinearCorrection);
float impulse = -m_mass * C;
m_u.set(d);
float Px = impulse * m_u.x;
float Py = impulse * m_u.y;
b1.m_sweep.c.x -= b1.m_invMass * Px;
b1.m_sweep.c.y -= b1.m_invMass * Py;
b1.m_sweep.a -= b1.m_invI * (r1.x * Py - r1.y * Px);// b2Cross(r1, P);
b2.m_sweep.c.x += b2.m_invMass * Px;
b2.m_sweep.c.y += b2.m_invMass * Py;
b2.m_sweep.a += b2.m_invI * (r2.x * Py - r2.y * Px);// b2Cross(r2, P);
b1.synchronizeTransform();
b2.synchronizeTransform();
pool.pushVec2(3);
return MathUtils.abs(C) < Settings.linearSlop;
}
}