public void Initialize(b2ContactPositionConstraint pc, b2Transform xfA, b2Transform xfB, int index)
{
Debug.Assert(pc.pointCount > 0);
switch (pc.type)
{
case b2Manifold.Type.e_circles:
{
b2Vec2 pointA = Utils.b2Mul(xfA, pc.localPoint);
b2Vec2 pointB = Utils.b2Mul(xfB, pc.localPoints[0]);
normal = pointB - pointA;
normal.Normalize();
point = 0.5f * (pointA + pointB);
separation = Utils.b2Dot(pointB - pointA, normal) - pc.radiusA - pc.radiusB;
}
break;
case b2Manifold.Type.e_faceA:
{
normal = Utils.b2Mul(xfA.q, pc.localNormal);
b2Vec2 planePoint = Utils.b2Mul(xfA, pc.localPoint);
b2Vec2 clipPoint = Utils.b2Mul(xfB, pc.localPoints[index]);
separation = Utils.b2Dot(clipPoint - planePoint, normal) - pc.radiusA - pc.radiusB;
point = clipPoint;
}
break;
case b2Manifold.Type.e_faceB:
{
normal = Utils.b2Mul(xfB.q, pc.localNormal);
b2Vec2 planePoint = Utils.b2Mul(xfB, pc.localPoint);
b2Vec2 clipPoint = Utils.b2Mul(xfA, pc.localPoints[index]);
separation = Utils.b2Dot(clipPoint - planePoint, normal) - pc.radiusA - pc.radiusB;
point = clipPoint;
// Ensure normal points from A to B
normal = -normal;
}
break;
}
}
public b2ContactSolver(b2ContactSolverDef def)
{
m_step = def.step;
m_count = def.count;
m_positionConstraints = Arrays.InitializeWithDefaultInstances <b2ContactPositionConstraint>(m_count);
m_velocityConstraints = Arrays.InitializeWithDefaultInstances <b2ContactVelocityConstraint>(m_count);
m_positions = def.positions;
m_velocities = def.velocities;
m_contacts = def.contacts;
// Initialize position independent portions of the constraints.
for (int i = 0; i < m_count; ++i)
{
b2Contact contact = m_contacts[i];
b2Fixture fixtureA = contact.m_fixtureA;
b2Fixture fixtureB = contact.m_fixtureB;
b2Shape shapeA = fixtureA.GetShape();
b2Shape shapeB = fixtureB.GetShape();
float radiusA = shapeA.m_radius;
float radiusB = shapeB.m_radius;
b2Body bodyA = fixtureA.GetBody();
b2Body bodyB = fixtureB.GetBody();
b2Manifold manifold = contact.GetManifold();
int pointCount = manifold.pointCount;
Debug.Assert(pointCount > 0);
b2ContactVelocityConstraint vc = m_velocityConstraints[i];
vc.friction = contact.m_friction;
vc.restitution = contact.m_restitution;
vc.tangentSpeed = contact.m_tangentSpeed;
vc.indexA = bodyA.m_islandIndex;
vc.indexB = bodyB.m_islandIndex;
vc.invMassA = bodyA.m_invMass;
vc.invMassB = bodyB.m_invMass;
vc.invIA = bodyA.m_invI;
vc.invIB = bodyB.m_invI;
vc.contactIndex = i;
vc.pointCount = pointCount;
vc.K.SetZero();
vc.normalMass.SetZero();
b2ContactPositionConstraint pc = m_positionConstraints[i];
pc.indexA = bodyA.m_islandIndex;
pc.indexB = bodyB.m_islandIndex;
pc.invMassA = bodyA.m_invMass;
pc.invMassB = bodyB.m_invMass;
pc.localCenterA = bodyA.m_sweep.localCenter;
pc.localCenterB = bodyB.m_sweep.localCenter;
pc.invIA = bodyA.m_invI;
pc.invIB = bodyB.m_invI;
pc.localNormal = manifold.localNormal;
pc.localPoint = manifold.localPoint;
pc.pointCount = pointCount;
pc.radiusA = radiusA;
pc.radiusB = radiusB;
pc.type = manifold.type;
for (int j = 0; j < pointCount; ++j)
{
b2ManifoldPoint cp = manifold.points[j];
b2VelocityConstraintPoint vcp = vc.points[j];
if (m_step.warmStarting)
{
vcp.normalImpulse = m_step.dtRatio * cp.normalImpulse;
vcp.tangentImpulse = m_step.dtRatio * cp.tangentImpulse;
}
else
{
vcp.normalImpulse = 0.0f;
vcp.tangentImpulse = 0.0f;
}
vcp.rA.SetZero();
vcp.rB.SetZero();
vcp.normalMass = 0.0f;
vcp.tangentMass = 0.0f;
vcp.velocityBias = 0.0f;
pc.localPoints[j] = cp.localPoint;
}
}
}
// Sequential position solver for position constraints.
public bool SolveTOIPositionConstraints(int toiIndexA, int toiIndexB)
{
float minSeparation = 0.0f;
for (int i = 0; i < m_count; ++i)
{
b2ContactPositionConstraint pc = m_positionConstraints[i];
int indexA = pc.indexA;
int indexB = pc.indexB;
b2Vec2 localCenterA = new b2Vec2(pc.localCenterA);
b2Vec2 localCenterB = new b2Vec2(pc.localCenterB);
int pointCount = pc.pointCount;
float mA = 0.0f;
float iA = 0.0f;
if (indexA == toiIndexA || indexA == toiIndexB)
{
mA = pc.invMassA;
iA = pc.invIA;
}
float mB = 0.0f;
float iB = 0.0F;
if (indexB == toiIndexA || indexB == toiIndexB)
{
mB = pc.invMassB;
iB = pc.invIB;
}
b2Vec2 cA = m_positions[indexA].c;
float aA = m_positions[indexA].a;
b2Vec2 cB = m_positions[indexB].c;
float aB = m_positions[indexB].a;
// Solve normal constraints
for (int j = 0; j < pointCount; ++j)
{
b2Transform xfA = new b2Transform();
b2Transform xfB = new b2Transform();
xfA.q.Set(aA);
xfB.q.Set(aB);
xfA.p = cA - Utils.b2Mul(xfA.q, localCenterA);
xfB.p = cB - Utils.b2Mul(xfB.q, localCenterB);
b2PositionSolverManifold psm = new b2PositionSolverManifold();
psm.Initialize(pc, xfA, xfB, j);
b2Vec2 normal = new b2Vec2(psm.normal);
b2Vec2 point = new b2Vec2(psm.point);
float separation = psm.separation;
b2Vec2 rA = point - cA;
b2Vec2 rB = point - cB;
// Track max constraint error.
minSeparation = Utils.b2Min(minSeparation, separation);
// Prevent large corrections and allow slop.
float C = Utils.b2Clamp(Settings.b2_toiBaugarte * (separation + Settings.b2_linearSlop), -Settings.b2_maxLinearCorrection, 0.0f);
// Compute the effective mass.
float rnA = Utils.b2Cross(rA, normal);
float rnB = Utils.b2Cross(rB, normal);
float K = mA + mB + iA * rnA * rnA + iB * rnB * rnB;
// Compute normal impulse
float impulse = K > 0.0f ? -C / K : 0.0f;
b2Vec2 P = impulse * normal;
cA -= mA * P;
aA -= iA * Utils.b2Cross(rA, P);
cB += mB * P;
aB += iB * Utils.b2Cross(rB, P);
}
m_positions[indexA].c = cA;
m_positions[indexA].a = aA;
m_positions[indexB].c = cB;
m_positions[indexB].a = aB;
}
// We can't expect minSpeparation >= -b2_linearSlop because we don't
// push the separation above -b2_linearSlop.
return(minSeparation >= -1.5f * Settings.b2_linearSlop);
}
// Initialize position dependent portions of the velocity constraints.
public void InitializeVelocityConstraints()
{
for (int i = 0; i < m_count; ++i)
{
b2ContactVelocityConstraint vc = m_velocityConstraints[i];
b2ContactPositionConstraint pc = m_positionConstraints[i];
float radiusA = pc.radiusA;
float radiusB = pc.radiusB;
b2Manifold manifold = m_contacts[vc.contactIndex].GetManifold();
int indexA = vc.indexA;
int indexB = vc.indexB;
float mA = vc.invMassA;
float mB = vc.invMassB;
float iA = vc.invIA;
float iB = vc.invIB;
b2Vec2 localCenterA = new b2Vec2(pc.localCenterA);
b2Vec2 localCenterB = new b2Vec2(pc.localCenterB);
b2Vec2 cA = m_positions[indexA].c;
float aA = m_positions[indexA].a;
b2Vec2 vA = m_velocities[indexA].v;
float wA = m_velocities[indexA].w;
b2Vec2 cB = m_positions[indexB].c;
float aB = m_positions[indexB].a;
b2Vec2 vB = m_velocities[indexB].v;
float wB = m_velocities[indexB].w;
Debug.Assert(manifold.pointCount > 0);
b2Transform xfA = new b2Transform();
b2Transform xfB = new b2Transform();
xfA.q.Set(aA);
xfB.q.Set(aB);
xfA.p = cA - Utils.b2Mul(xfA.q, localCenterA);
xfB.p = cB - Utils.b2Mul(xfB.q, localCenterB);
b2WorldManifold worldManifold = new b2WorldManifold();
worldManifold.Initialize(manifold, xfA, radiusA, xfB, radiusB);
vc.normal = worldManifold.normal;
int pointCount = vc.pointCount;
for (int j = 0; j < pointCount; ++j)
{
b2VelocityConstraintPoint vcp = vc.points[j];
vcp.rA = worldManifold.points[j] - cA;
vcp.rB = worldManifold.points[j] - cB;
float rnA = Utils.b2Cross(vcp.rA, vc.normal);
float rnB = Utils.b2Cross(vcp.rB, vc.normal);
float kNormal = mA + mB + iA * rnA * rnA + iB * rnB * rnB;
vcp.normalMass = kNormal > 0.0f ? 1.0f / kNormal : 0.0f;
b2Vec2 tangent = Utils.b2Cross(vc.normal, 1.0f);
float rtA = Utils.b2Cross(vcp.rA, tangent);
float rtB = Utils.b2Cross(vcp.rB, tangent);
float kTangent = mA + mB + iA * rtA * rtA + iB * rtB * rtB;
vcp.tangentMass = kTangent > 0.0f ? 1.0f / kTangent : 0.0f;
// Setup a velocity bias for restitution.
vcp.velocityBias = 0.0f;
float vRel = Utils.b2Dot(vc.normal, vB + Utils.b2Cross(wB, vcp.rB) - vA - Utils.b2Cross(wA, vcp.rA));
if (vRel < -Settings.b2_velocityThreshold)
{
vcp.velocityBias = -vc.restitution * vRel;
}
}
// If we have two points, then prepare the block solver.
if (vc.pointCount == 2 && Utils.g_blockSolve)
{
b2VelocityConstraintPoint vcp1 = vc.points[0];
b2VelocityConstraintPoint vcp2 = vc.points[1];
float rn1A = Utils.b2Cross(vcp1.rA, vc.normal);
float rn1B = Utils.b2Cross(vcp1.rB, vc.normal);
float rn2A = Utils.b2Cross(vcp2.rA, vc.normal);
float rn2B = Utils.b2Cross(vcp2.rB, vc.normal);
float k11 = mA + mB + iA * rn1A * rn1A + iB * rn1B * rn1B;
float k22 = mA + mB + iA * rn2A * rn2A + iB * rn2B * rn2B;
float k12 = mA + mB + iA * rn1A * rn2A + iB * rn1B * rn2B;
// Ensure a reasonable condition number.
const float k_maxConditionNumber = 1000.0f;
if (k11 * k11 < k_maxConditionNumber * (k11 * k22 - k12 * k12))
{
// K is safe to invert.
vc.K.ex.Set(k11, k12);
vc.K.ey.Set(k12, k22);
vc.normalMass = vc.K.GetInverse();
}
else
{
// The constraints are redundant, just use one.
// TODO_ERIN use deepest?
vc.pointCount = 1;
}
}
}
}