org.jbox2d.dynamics.contacts.ContactSolver Maven / Gradle / Ivy
Go to download
Show more of this group Show more artifacts with this name
Show all versions of jbox2d-library Show documentation
Show all versions of jbox2d-library Show documentation
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.
******************************************************************************/
package org.jbox2d.dynamics.contacts;
import org.jbox2d.collision.Manifold;
import org.jbox2d.collision.ManifoldPoint;
import org.jbox2d.collision.WorldManifold;
import org.jbox2d.collision.shapes.Shape;
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.Fixture;
// updated to rev 100
// pooled locally, non-threaded
/**
* @author Daniel
*/
public class ContactSolver {
/**
* For each solver, this is the initial number of constraints in the array, which expands
* as needed.
*/
public static final int INITIAL_NUM_CONSTRAINTS = 256;
/**
* Ensure a reasonable condition number. for the block solver
*/
public static final float k_maxConditionNumber = 100.0f;
public ContactConstraint[] m_constraints;
public int m_constraintCount;
public ContactSolver(){
m_constraints = new ContactConstraint[INITIAL_NUM_CONSTRAINTS];
for(int i=0; i< m_constraints.length; i++){
m_constraints[i] = new ContactConstraint();
}
}
// djm pooling
private final WorldManifold worldManifold = new WorldManifold();
private final Vec2 tangent = new Vec2();
private final Vec2 temp1 = new Vec2();
private final Vec2 temp2 = new Vec2();
public final void init(Contact[] contacts, int contactCount, float impulseRatio){
m_constraintCount = contactCount;
// dynamic array
if(m_constraints.length < contactCount){
final ContactConstraint[] old = m_constraints;
final int newLen = MathUtils.max(old.length * 2, m_constraintCount);
m_constraints = new ContactConstraint[newLen];
System.arraycopy(old, 0, m_constraints, 0, old.length);
for(int i=old.length; i< m_constraints.length; i++){
m_constraints[i] = new ContactConstraint();
}
}
for (int i = 0; i < m_constraintCount; ++i){
final Contact contact = contacts[i];
final Fixture fixtureA = contact.m_fixtureA;
final Fixture fixtureB = contact.m_fixtureB;
final Shape shapeA = fixtureA.getShape();
final Shape shapeB = fixtureB.getShape();
final float radiusA = shapeA.m_radius;
final float radiusB = shapeB.m_radius;
final Body bodyA = fixtureA.getBody();
final Body bodyB = fixtureB.getBody();
final Manifold manifold = contact.getManifold();
final float friction = Settings.mixFriction(fixtureA.getFriction(), fixtureB.getFriction());
final float restitution = Settings.mixRestitution(fixtureA.getRestitution(), fixtureB.getRestitution());
final Vec2 vA = bodyA.m_linearVelocity;
final Vec2 vB = bodyB.m_linearVelocity;
final float wA = bodyA.m_angularVelocity;
final float wB = bodyB.m_angularVelocity;
assert(manifold.pointCount > 0);
worldManifold.initialize(manifold, bodyA.m_xf, radiusA, bodyB.m_xf, radiusB);
final ContactConstraint cc = m_constraints[i];
cc.bodyA = bodyA;
cc.bodyB = bodyB;
cc.manifold = manifold;
cc.normal.x = worldManifold.normal.x;
cc.normal.y = worldManifold.normal.y; // have to set actual manifold
cc.pointCount = manifold.pointCount;
cc.friction = friction;
cc.restitution = restitution;
cc.localNormal.x = manifold.localNormal.x;
cc.localNormal.y = manifold.localNormal.y;
cc.localPoint.x = manifold.localPoint.x;
cc.localPoint.y = manifold.localPoint.y;
cc.radius = radiusA + radiusB;
cc.type = manifold.type;
for (int j = 0; j < cc.pointCount; ++j){
final ManifoldPoint cp = manifold.points[j];
final ContactConstraintPoint ccp = cc.points[j];
ccp.normalImpulse = impulseRatio * cp.normalImpulse;
ccp.tangentImpulse = impulseRatio * cp.tangentImpulse;
ccp.localPoint.x = cp.localPoint.x;
ccp.localPoint.y = cp.localPoint.y;
ccp.rA.x = worldManifold.points[j].x - bodyA.m_sweep.c.x;
ccp.rA.y = worldManifold.points[j].y - bodyA.m_sweep.c.y;
ccp.rB.x = worldManifold.points[j].x - bodyB.m_sweep.c.x;
ccp.rB.y = worldManifold.points[j].y - bodyB.m_sweep.c.y;
float rnA = ccp.rA.x * cc.normal.y - ccp.rA.y * cc.normal.x;
float rnB = ccp.rB.x * cc.normal.y - ccp.rB.y * cc.normal.x;
rnA *= rnA;
rnB *= rnB;
final float kNormal = bodyA.m_invMass + bodyB.m_invMass + bodyA.m_invI * rnA + bodyB.m_invI * rnB;
assert(kNormal > Settings.EPSILON);
ccp.normalMass = 1.0f / kNormal;
tangent.x = 1.0f * cc.normal.y;
tangent.y = -1.0f * cc.normal.x;
float rtA = ccp.rA.x * tangent.y - ccp.rA.y * tangent.x;
float rtB = ccp.rB.x * tangent.y - ccp.rB.y * tangent.x;
rtA *= rtA;
rtB *= rtB;
final float kTangent = bodyA.m_invMass + bodyB.m_invMass + bodyA.m_invI * rtA + bodyB.m_invI * rtB;
assert(kTangent > Settings.EPSILON);
ccp.tangentMass = 1.0f / kTangent;
// Setup a velocity bias for restitution.
ccp.velocityBias = 0.0f;
temp2.x = -wA * ccp.rA.y;
temp2.y = wA * ccp.rA.x;
//temp1.addLocal(vB).subLocal(vA).subLocal(temp2);
temp1.x = -wB * ccp.rB.y + vB.x - vA.x - temp2.x;
temp1.y = wB * ccp.rB.x + vB.y - vA.y - temp2.y;
final Vec2 a = cc.normal;
//float vRel = Dot(cc.normal, vB + Cross(wB, ccp.rB) - vA - Cross(wA, ccp.rA));
final float vRel = a.x * temp1.x + a.y * temp1.y;
if (vRel < -Settings.velocityThreshold){
ccp.velocityBias = -restitution * vRel;
}
}
// If we have two points, then prepare the block solver.
if (cc.pointCount == 2){
final ContactConstraintPoint ccp1 = cc.points[0];
final ContactConstraintPoint ccp2 = cc.points[1];
final float invMassA = bodyA.m_invMass;
final float invIA = bodyA.m_invI;
final float invMassB = bodyB.m_invMass;
final float invIB = bodyB.m_invI;
final float rn1A = Vec2.cross(ccp1.rA, cc.normal);
final float rn1B = Vec2.cross(ccp1.rB, cc.normal);
final float rn2A = Vec2.cross(ccp2.rA, cc.normal);
final float rn2B = Vec2.cross(ccp2.rB, cc.normal);
final float k11 = invMassA + invMassB + invIA * rn1A * rn1A + invIB * rn1B * rn1B;
final float k22 = invMassA + invMassB + invIA * rn2A * rn2A + invIB * rn2B * rn2B;
final float k12 = invMassA + invMassB + invIA * rn1A * rn2A + invIB * rn1B * rn2B;
// Ensure a reasonable condition number.
//final float k_maxConditionNumber = 100.0f;
if (k11 * k11 < k_maxConditionNumber * (k11 * k22 - k12 * k12)){
// K is safe to invert.
cc.K.col1.x = k11;
cc.K.col1.y = k12;
cc.K.col2.x = k12;
cc.K.col2.y = k22;
cc.normalMass.col1.x = cc.K.col1.x;
cc.normalMass.col1.y = cc.K.col1.y;
cc.normalMass.col2.x = cc.K.col2.x;
cc.normalMass.col2.y = cc.K.col2.y;
cc.normalMass.invertLocal();
}
else{
// The constraints are redundant, just use one.
// TODO_ERIN use deepest?
cc.pointCount = 1;
}
}
}
}
// djm pooling, and from above
private final Vec2 P = new Vec2();
public void warmStart(){
// Warm start.
for (int i = 0; i < m_constraintCount; ++i){
final ContactConstraint c = m_constraints[i];
final Body bodyA = c.bodyA;
final Body bodyB = c.bodyB;
final float invMassA = bodyA.m_invMass;
final float invIA = bodyA.m_invI;
final float invMassB = bodyB.m_invMass;
final float invIB = bodyB.m_invI;
final Vec2 normal = c.normal;
Vec2.crossToOut(normal, 1f, tangent);
for (int j = 0; j < c.pointCount; ++j){
final ContactConstraintPoint ccp = c.points[j];
//Vec2 P = ccp.normalImpulse * normal + ccp.tangentImpulse * tangent;
// temp.set(normal).mulLocal(ccp.normalImpulse);
// P.set(tangent).mulLocal(ccp.tangentImpulse).addLocal(temp);
// bodyA.m_angularVelocity -= invIA * Vec2.cross(ccp.rA, P);
// temp.set(P).mulLocal(invMassA);
// bodyA.m_linearVelocity.subLocal(temp);
// bodyB.m_angularVelocity += invIB * Vec2.cross(ccp.rB, P);
// temp.set(P).mulLocal(invMassB);
// bodyB.m_linearVelocity.addLocal(temp);
final float Px = ccp.normalImpulse * normal.x + ccp.tangentImpulse * tangent.x;
final float Py = ccp.normalImpulse * normal.y + ccp.tangentImpulse * tangent.y;
bodyA.m_angularVelocity -= invIA * (ccp.rA.x * Py - ccp.rA.y * Px);
bodyA.m_linearVelocity.x -= Px * invMassA;
bodyA.m_linearVelocity.y -= Py * invMassA;
bodyB.m_angularVelocity += invIB * (ccp.rB.x * Py - ccp.rB.y * Px);
bodyB.m_linearVelocity.x += Px * invMassB;
bodyB.m_linearVelocity.y += Py * invMassB;
}
}
}
// djm pooling, and from above
// public final void initVelocityConstraints(TimeStep step){
// // Warm start.
// for (int i = 0; i < m_constraintCount; ++i){
// ContactConstraint c = m_constraints[i];
//
// Body bodyA = c.bodyA;
// Body bodyB = c.bodyB;
// float invMassA = bodyA.m_invMass;
// float invIA = bodyA.m_invI;
// float invMassB = bodyB.m_invMass;
// float invIB = bodyB.m_invI;
// Vec2 normal = c.normal;
// Vec2.crossToOut(normal, 1.0f, tangent);
//
// if (step.warmStarting){
// for (int j = 0; j < c.pointCount; ++j){
// ContactConstraintPoint ccp = c.points[j];
// ccp.normalImpulse *= step.dtRatio;
// ccp.tangentImpulse *= step.dtRatio;
// //Vec2 P = ccp.normalImpulse * normal + ccp.tangentImpulse * tangent;
// temp1.set(normal).mulLocal(ccp.normalImpulse);
// P.set(tangent).mulLocal(ccp.tangentImpulse).addLocal(temp1);
//
// bodyA.m_angularVelocity -= invIA * Vec2.cross(ccp.rA, P);
// //bodyA.m_linearVelocity -= invMassA * P;
// temp1.set(P).mulLocal(invMassA);
// bodyA.m_linearVelocity.subLocal(temp1);
//
// bodyB.m_angularVelocity += invIB * Vec2.cross(ccp.rB, P);
// //bodyB.m_linearVelocity += invMassB * P;
// temp1.set(P).mulLocal(invMassB);
// bodyB.m_linearVelocity.addLocal(temp1);
// }
// }
// else{
// for (int j = 0; j < c.pointCount; ++j){
// ContactConstraintPoint ccp = c.points[j];
// ccp.normalImpulse = 0.0f;
// ccp.tangentImpulse = 0.0f;
// }
// }
// }
// }
//djm pooling from above
private final Vec2 dv = new Vec2();
private final Vec2 a = new Vec2();
private final Vec2 b = new Vec2();
private final Vec2 dv1 = new Vec2();
private final Vec2 dv2 = new Vec2();
private final Vec2 x = new Vec2();
private final Vec2 d = new Vec2();
private final Vec2 P1 = new Vec2();
private final Vec2 P2 = new Vec2();
public final void solveVelocityConstraints(){
for (int i = 0; i < m_constraintCount; ++i){
final ContactConstraint c = m_constraints[i];
final Body bodyA = c.bodyA;
final Body bodyB = c.bodyB;
float wA = bodyA.m_angularVelocity;
float wB = bodyB.m_angularVelocity;
final Vec2 vA = bodyA.m_linearVelocity;
final Vec2 vB = bodyB.m_linearVelocity;
final float invMassA = bodyA.m_invMass;
final float invIA = bodyA.m_invI;
final float invMassB = bodyB.m_invMass;
final float invIB = bodyB.m_invI;
tangent.x = 1.0f * c.normal.y;
tangent.y = -1.0f * c.normal.x;
final float friction = c.friction;
assert(c.pointCount == 1 || c.pointCount == 2);
// Solve tangent constraints
for (int j = 0; j < c.pointCount; ++j){
final ContactConstraintPoint ccp = c.points[j];
final Vec2 a = ccp.rA;
dv.x = -wB * ccp.rB.y + vB.x - vA.x + wA * a.y;
dv.y = wB * ccp.rB.x + vB.y - vA.y - wA * a.x;
// Compute tangent force
final float vt = dv.x * tangent.x + dv.y * tangent.y;
float lambda = ccp.tangentMass * (-vt);
// Clamp the accumulated force
final float maxFriction = friction * ccp.normalImpulse;
final float newImpulse = MathUtils.clamp(ccp.tangentImpulse + lambda, -maxFriction, maxFriction);
lambda = newImpulse - ccp.tangentImpulse;
// Apply contact impulse
//Vec2 P = lambda * tangent;
final float Px = tangent.x * lambda;
final float Py = tangent.y * lambda;
//vA -= invMassA * P;
vA.x -= Px * invMassA;
vA.y -= Py * invMassA;
wA -= invIA * (ccp.rA.x * Py - ccp.rA.y * Px);
//vB += invMassB * P;
vB.x += Px * invMassB;
vB.y += Py * invMassB;
wB += invIB * (ccp.rB.x * Py - ccp.rB.y * Px);
ccp.tangentImpulse = newImpulse;
}
// Solve normal constraints
if (c.pointCount == 1){
final ContactConstraintPoint ccp = c.points[0];
Vec2 a1 = ccp.rA;
// Relative velocity at contact
//Vec2 dv = vB + Cross(wB, ccp.rB) - vA - Cross(wA, ccp.rA);
// Vec2.crossToOut(wA, ccp.rA, temp1);
// Vec2.crossToOut(wB, ccp.rB, dv);
// dv.addLocal(vB).subLocal(vA).subLocal(temp1);
dv.x = -wB * ccp.rB.y + vB.x - vA.x + wA * a1.y;
dv.y = wB * ccp.rB.x + vB.y - vA.y - wA * a1.x;
Vec2 b = c.normal;
// Compute normal impulse
final float vn = dv.x * b.x + dv.y * b.y;
float lambda = -ccp.normalMass * (vn - ccp.velocityBias);
// Clamp the accumulated impulse
float a = ccp.normalImpulse + lambda;
final float newImpulse = (a > 0.0f ? a : 0.0f);
lambda = newImpulse - ccp.normalImpulse;
// Apply contact impulse
float Px = c.normal.x * lambda;
float Py = c.normal.y * lambda;
//vA -= invMassA * P;
vA.x -= Px * invMassA;
vA.y -= Py * invMassA;
wA -= invIA * (ccp.rA.x * Py - ccp.rA.y * Px);
//vB += invMassB * P;
vB.x += Px * invMassB;
vB.y += Py * invMassB;
wB += invIB * (ccp.rB.x * Py - ccp.rB.y * Px);
ccp.normalImpulse = newImpulse;
}
else
{
// Block solver developed in collaboration with Dirk Gregorius (back in 01/07 on Box2D_Lite).
// Build the mini LCP for this contact patch
//
// vn = A * x + b, vn >= 0, , vn >= 0, x >= 0 and vn_i * x_i = 0 with i = 1..2
//
// A = J * W * JT and J = ( -n, -r1 x n, n, r2 x n )
// b = vn_0 - velocityBias
//
// The system is solved using the "Total enumeration method" (s. Murty). The complementary constraint vn_i * x_i
// implies that we must have in any solution either vn_i = 0 or x_i = 0. So for the 2D contact problem the cases
// vn1 = 0 and vn2 = 0, x1 = 0 and x2 = 0, x1 = 0 and vn2 = 0, x2 = 0 and vn1 = 0 need to be tested. The first valid
// solution that satisfies the problem is chosen.
//
// In order to account of the accumulated impulse 'a' (because of the iterative nature of the solver which only requires
// that the accumulated impulse is clamped and not the incremental impulse) we change the impulse variable (x_i).
//
// Substitute:
//
// x = x' - a
//
// Plug into above equation:
//
// vn = A * x + b
// = A * (x' - a) + b
// = A * x' + b - A * a
// = A * x' + b'
// b' = b - A * a;
final ContactConstraintPoint cp1 = c.points[0];
final ContactConstraintPoint cp2 = c.points[1];
a.x = cp1.normalImpulse;
a.y = cp2.normalImpulse;
assert(a.x >= 0.0f && a.y >= 0.0f);
// Relative velocity at contact
//Vec2 dv1 = vB + Cross(wB, cp1.rB) - vA - Cross(wA, cp1.rA);
dv1.x = -wB * cp1.rB.y + vB.x - vA.x + wA * cp1.rA.y;
dv1.y = wB * cp1.rB.x + vB.y - vA.y - wA * cp1.rA.x;
//Vec2 dv2 = vB + Cross(wB, cp2.rB) - vA - Cross(wA, cp2.rA);
dv2.x = -wB * cp2.rB.y + vB.x - vA.x + wA * cp2.rA.y;
dv2.y = wB * cp2.rB.x + vB.y - vA.y - wA * cp2.rA.x;
// Compute normal velocity
float vn1 = dv1.x * c.normal.x + dv1.y * c.normal.y;
float vn2 = dv2.x * c.normal.x + dv2.y * c.normal.y;
b.x = vn1 - cp1.velocityBias;
b.y = vn2 - cp2.velocityBias;
temp2.x = c.K.col1.x * a.x + c.K.col2.x * a.y;
temp2.y = c.K.col1.y * a.x + c.K.col2.y * a.y;
b.x -= temp2.x;
b.y -= temp2.y;
//final float k_errorTol = 1e-3f;
//B2_NOT_USED(k_errorTol);
for (;;)
{
//
// Case 1: vn = 0
//
// 0 = A * x' + b'
//
// Solve for x':
//
// x' = - inv(A) * b'
//
//Vec2 x = - Mul(c.normalMass, b);
final Mat22 R = c.normalMass;
// R.mulToOut(v,out);
x.x = - R.col1.x * b.x - R.col2.x * b.y;
x.y = - R.col1.y * b.x - R.col2.y * b.y;
if (x.x >= 0.0f && x.y >= 0.0f){
// Resubstitute for the incremental impulse
//Vec2 d = x - a;
d.set(x).subLocal(a);
// Apply incremental impulse
//Vec2 P1 = d.x * normal;
//Vec2 P2 = d.y * normal;
P1.set(c.normal).mulLocal(d.x);
P2.set(c.normal).mulLocal(d.y);
/*vA -= invMassA * (P1 + P2);
wA -= invIA * (b2Cross(cp1->rA, P1) + b2Cross(cp2->rA, P2));
vB += invMassB * (P1 + P2);
wB += invIB * (b2Cross(cp1->rB, P1) + b2Cross(cp2->rB, P2));*/
vA.x -= invMassA * (P1.x + P2.x);
vA.y -= invMassA * (P1.y + P2.y);
vB.x += invMassB * (P1.x + P2.x);
vB.y += invMassB * (P1.y + P2.y);
wA -= invIA * (Vec2.cross(cp1.rA, P1) + Vec2.cross(cp2.rA, P2));
wB += invIB * (Vec2.cross(cp1.rB, P1) + Vec2.cross(cp2.rB, P2));
// Accumulate
cp1.normalImpulse = x.x;
cp2.normalImpulse = x.y;
/*#if B2_DEBUG_SOLVER == 1
// Postconditions
dv1 = vB + Cross(wB, cp1.rB) - vA - Cross(wA, cp1.rA);
dv2 = vB + Cross(wB, cp2.rB) - vA - Cross(wA, cp2.rA);
// Compute normal velocity
vn1 = Dot(dv1, normal);
vn2 = Dot(dv2, normal);
assert(Abs(vn1 - cp1.velocityBias) < k_errorTol);
assert(Abs(vn2 - cp2.velocityBias) < k_errorTol);
#endif*/
break;
}
//
// Case 2: vn1 = 0 and x2 = 0
//
// 0 = a11 * x1' + a12 * 0 + b1'
// vn2 = a21 * x1' + a22 * 0 + '
//
x.x = - cp1.normalMass * b.x;
x.y = 0.0f;
vn1 = 0.0f;
vn2 = c.K.col1.y * x.x + b.y;
if (x.x >= 0.0f && vn2 >= 0.0f)
{
// Resubstitute for the incremental impulse
final float dx = x.x - a.x;
final float dy = x.y - a.y;
// Apply incremental impulse
//Vec2 P1 = d.x * normal;
//Vec2 P2 = d.y * normal;
P1.set(c.normal).mulLocal(dx);
P2.set(c.normal).mulLocal(dy);
/*Vec2 P1 = d.x * normal;
Vec2 P2 = d.y * normal;
vA -= invMassA * (P1 + P2);
wA -= invIA * (Cross(cp1.rA, P1) + Cross(cp2.rA, P2));
vB += invMassB * (P1 + P2);
wB += invIB * (Cross(cp1.rB, P1) + Cross(cp2.rB, P2));*/
vA.x -= invMassA * (P1.x + P2.x);
vA.y -= invMassA * (P1.y + P2.y);
vB.x += invMassB * (P1.x + P2.x);
vB.y += invMassB * (P1.y + P2.y);
wA -= invIA * (Vec2.cross(cp1.rA, P1) + Vec2.cross(cp2.rA, P2));
wB += invIB * (Vec2.cross(cp1.rB, P1) + Vec2.cross(cp2.rB, P2));
// Accumulate
cp1.normalImpulse = x.x;
cp2.normalImpulse = x.y;
/*#if B2_DEBUG_SOLVER == 1
// Postconditions
dv1 = vB + Cross(wB, cp1.rB) - vA - Cross(wA, cp1.rA);
// Compute normal velocity
vn1 = Dot(dv1, normal);
assert(Abs(vn1 - cp1.velocityBias) < k_errorTol);
#endif*/
break;
}
//
// Case 3: wB = 0 and x1 = 0
//
// vn1 = a11 * 0 + a12 * x2' + b1'
// 0 = a21 * 0 + a22 * x2' + '
//
x.x = 0.0f;
x.y = - cp2.normalMass * b.y;
vn1 = c.K.col2.x * x.y + b.x;
vn2 = 0.0f;
if (x.y >= 0.0f && vn1 >= 0.0f)
{
// Resubstitute for the incremental impulse
final float dx = x.x - a.x;
final float dy = x.y - a.y;
// Apply incremental impulse
/*Vec2 P1 = d.x * normal;
Vec2 P2 = d.y * normal;
vA -= invMassA * (P1 + P2);
wA -= invIA * (Cross(cp1.rA, P1) + Cross(cp2.rA, P2));
vB += invMassB * (P1 + P2);
wB += invIB * (Cross(cp1.rB, P1) + Cross(cp2.rB, P2));*/
P1.set(c.normal).mulLocal(dx);
P2.set(c.normal).mulLocal(dy);
vA.x -= invMassA * (P1.x + P2.x);
vA.y -= invMassA * (P1.y + P2.y);
vB.x += invMassB * (P1.x + P2.x);
vB.y += invMassB * (P1.y + P2.y);
wA -= invIA * (Vec2.cross(cp1.rA, P1) + Vec2.cross(cp2.rA, P2));
wB += invIB * (Vec2.cross(cp1.rB, P1) + Vec2.cross(cp2.rB, P2));
// Accumulate
cp1.normalImpulse = x.x;
cp2.normalImpulse = x.y;
/*#if B2_DEBUG_SOLVER == 1
// Postconditions
dv2 = vB + Cross(wB, cp2.rB) - vA - Cross(wA, cp2.rA);
// Compute normal velocity
vn2 = Dot(dv2, normal);
assert(Abs(vn2 - cp2.velocityBias) < k_errorTol);
#endif*/
break;
}
//
// Case 4: x1 = 0 and x2 = 0
//
// vn1 = b1
// vn2 = ;
x.x = 0.0f;
x.y = 0.0f;
vn1 = b.x;
vn2 = b.y;
if (vn1 >= 0.0f && vn2 >= 0.0f )
{
// Resubstitute for the incremental impulse
final float dx = x.x - a.x;
final float dy = x.y - a.y;
// Apply incremental impulse
/*Vec2 P1 = d.x * normal;
Vec2 P2 = d.y * normal;
vA -= invMassA * (P1 + P2);
wA -= invIA * (Cross(cp1.rA, P1) + Cross(cp2.rA, P2));
vB += invMassB * (P1 + P2);
wB += invIB * (Cross(cp1.rB, P1) + Cross(cp2.rB, P2));*/
P1.set(c.normal).mulLocal(dx);
P2.set(c.normal).mulLocal(dy);
vA.x -= invMassA * (P1.x + P2.x);
vA.y -= invMassA * (P1.y + P2.y);
vB.x += invMassB * (P1.x + P2.x);
vB.y += invMassB * (P1.y + P2.y);
wA -= invIA * (Vec2.cross(cp1.rA, P1) + Vec2.cross(cp2.rA, P2));
wB += invIB * (Vec2.cross(cp1.rB, P1) + Vec2.cross(cp2.rB, P2));
// Accumulate
cp1.normalImpulse = x.x;
cp2.normalImpulse = x.y;
break;
}
// No solution, give up. This is hit sometimes, but it doesn't seem to matter.
break;
}
}
bodyA.m_angularVelocity = wA;
bodyB.m_angularVelocity = wB;
}
}
public void storeImpulses(){
for( int i=0; i= -_linearSlop because we don't
// push the separation above -_linearSlop.
return minSeparation >= -1.5f * _linearSlop;
}*/
// djm pooling, and from above
private final PositionSolverManifold psolver = new PositionSolverManifold();
private final Vec2 rA = new Vec2();
private final Vec2 rB = new Vec2();
/**
* Sequential solver.
*/
public final boolean solvePositionConstraints(float baumgarte){
float minSeparation = 0.0f;
for (int i = 0; i < m_constraintCount; ++i){
final ContactConstraint c = m_constraints[i];
final Body bodyA = c.bodyA;
final Body bodyB = c.bodyB;
final float invMassA = bodyA.m_mass * bodyA.m_invMass;
final float invIA = bodyA.m_mass * bodyA.m_invI;
final float invMassB = bodyB.m_mass * bodyB.m_invMass;
final float invIB = bodyB.m_mass * bodyB.m_invI;
// Solve normal constraints
for (int j = 0; j < c.pointCount; ++j){
final PositionSolverManifold psm = psolver;
psm.initialize(c, j);
final Vec2 normal = psm.normal;
final Vec2 point = psm.point;
final float separation = psm.separation;
rA.set(point).subLocal(bodyA.m_sweep.c);
rB.set(point).subLocal(bodyB.m_sweep.c);
// Track max constraint error.
minSeparation = MathUtils.min(minSeparation, separation);
// Prevent large corrections and allow slop.
final float C = MathUtils.clamp(baumgarte * (separation + Settings.linearSlop), -Settings.maxLinearCorrection, 0.0f);
// Compute the effective mass.
final float rnA = Vec2.cross(rA, normal);
final float rnB = Vec2.cross(rB, normal);
final float K = invMassA + invMassB + invIA * rnA * rnA + invIB * rnB * rnB;
// Compute normal impulse
final float impulse = K > 0.0f ? - C / K : 0.0f;
final float Px = normal.x * impulse;
final float Py = normal.y * impulse;
bodyA.m_sweep.c.x -= Px * invMassA;
bodyA.m_sweep.c.y -= Py * invMassA;
bodyA.m_sweep.a -= invIA * Vec2.cross(rA, P);
bodyA.synchronizeTransform();
bodyB.m_sweep.c.x += Px * invMassB;
bodyB.m_sweep.c.y += Py * invMassB;
bodyB.m_sweep.a += invIB * Vec2.cross(rB, P);
bodyB.synchronizeTransform();
}
}
// We can't expect minSpeparation >= -linearSlop because we don't
// push the separation above -linearSlop.
return minSeparation >= -1.5f * Settings.linearSlop;
}
}
class PositionSolverManifold{
public final Vec2 normal = new Vec2();
public final Vec2 point = new Vec2();
public float separation;
// djm pooling
private final Vec2 pointA = new Vec2();
private final Vec2 pointB = new Vec2();
private final Vec2 temp = new Vec2();
private final Vec2 planePoint = new Vec2();
private final Vec2 clipPoint = new Vec2();
public void initialize(ContactConstraint cc, int index){
assert(cc.pointCount > 0);
switch (cc.type){
case CIRCLES:{
cc.bodyA.getWorldPointToOut(cc.localPoint, pointA);
cc.bodyB.getWorldPointToOut(cc.points[0].localPoint, pointB);
if (MathUtils.distanceSquared(pointA, pointB) > Settings.EPSILON * Settings.EPSILON){
normal.set(pointB).subLocal(pointA);
normal.normalize();
}
else{
normal.set(1.0f, 0.0f);
}
point.set(pointA).addLocal(pointB).mulLocal(.5f);
temp.set(pointB).subLocal(pointA);
separation = Vec2.dot(temp, normal) - cc.radius;
break;
}
case FACE_A:{
cc.bodyA.getWorldVectorToOut(cc.localNormal, normal);
cc.bodyA.getWorldPointToOut(cc.localPoint, planePoint);
cc.bodyB.getWorldPointToOut(cc.points[index].localPoint, clipPoint);
temp.set(clipPoint).subLocal(planePoint);
separation = Vec2.dot(temp, normal) - cc.radius;
point.set(clipPoint);
break;
}
case FACE_B:
{
cc.bodyB.getWorldVectorToOut(cc.localNormal, normal);
cc.bodyB.getWorldPointToOut(cc.localPoint, planePoint);
cc.bodyA.getWorldPointToOut(cc.points[index].localPoint, clipPoint);
temp.set(clipPoint).subLocal(planePoint);
separation = Vec2.dot(temp, normal) - cc.radius;
point.set(clipPoint);
// Ensure normal points from A to B
normal.negateLocal();
}
break;
}
}
}