public b2Vec2 GetSearchDirection()
{
switch (m_count)
{
case 1:
return(-m_vertices[0].w);
case 2:
{
b2Vec2 e12 = m_vertices[1].w - m_vertices[0].w;
float sgn = b2Math.b2Cross(e12, -m_vertices[0].w);
if (sgn > 0.0f)
{
// Origin is left of e12.
return(e12.NegUnitCross()); // b2Math.b2Cross(1.0f, e12);
}
else
{
// Origin is right of e12.
return(e12.UnitCross()); // b2Math.b2Cross(e12, 1.0f);
}
}
default:
Debug.Assert(false);
return(b2Vec2.Zero);
}
}
public virtual void WarmStart()
{
// Warm start.
for (int i = 0; i < m_count; ++i)
{
b2ContactVelocityConstraint vc = m_velocityConstraints[i];
int indexA = vc.indexA;
int indexB = vc.indexB;
float mA = vc.invMassA;
float iA = vc.invIA;
float mB = vc.invMassB;
float iB = vc.invIB;
int pointCount = vc.pointCount;
b2Vec2 vA = m_velocities[indexA].v;
float wA = m_velocities[indexA].w;
b2Vec2 vB = m_velocities[indexB].v;
float wB = m_velocities[indexB].w;
b2Vec2 normal = vc.normal;
b2Vec2 tangent = normal.UnitCross(); // b2Math.b2Cross(normal, 1.0f);
for (int j = 0; j < pointCount; ++j)
{
b2VelocityConstraintPoint vcp = vc.points[j];
b2Vec2 P = vcp.normalImpulse * normal + vcp.tangentImpulse * tangent;
wA -= iA * b2Math.b2Cross(ref vcp.rA, ref P);
vA -= mA * P;
wB += iB * b2Math.b2Cross(ref vcp.rB, ref P);
vB += mB * P;
}
m_velocities[indexA].v = vA;
m_velocities[indexA].w = wA;
m_velocities[indexB].v = vB;
m_velocities[indexB].w = wB;
}
}
public virtual void SolveVelocityConstraints()
{
for (int i = 0; i < m_count; ++i)
{
b2ContactVelocityConstraint vc = m_velocityConstraints[i];
int indexA = vc.indexA;
int indexB = vc.indexB;
float mA = vc.invMassA;
float iA = vc.invIA;
float mB = vc.invMassB;
float iB = vc.invIB;
int pointCount = vc.pointCount;
b2Vec2 vA = m_velocities[indexA].v;
float wA = m_velocities[indexA].w;
b2Vec2 vB = m_velocities[indexB].v;
float wB = m_velocities[indexB].w;
b2Vec2 normal = vc.normal;
b2Vec2 tangent = normal.UnitCross(); // b2Math.b2Cross(normal, 1.0f);
float friction = vc.friction;
Debug.Assert(pointCount == 1 || pointCount == 2);
// Solve tangent constraints first because non-penetration is more important
// than friction.
for (int j = 0; j < pointCount; ++j)
{
b2VelocityConstraintPoint vcp = vc.points[j];
// Relative velocity at contact
/*
* b.m_x = -s * a.m_y;
* b.m_y = s * a.m_x;
*/
// b2Vec2 dv = vB + b2Math.b2Cross(wB, ref vcp.rB) - vA - b2Math.b2Cross(wA, ref vcp.rA);
b2Vec2 dv;
dv.x = vB.x + (-wB * vcp.rB.y) - vA.x - (-wA * vcp.rA.y);
dv.y = vB.y + (wB * vcp.rB.x) - vA.y - (wA * vcp.rA.x);
// Compute tangent force
float vt = dv.x * tangent.x + dv.y * tangent.y; // b2Math.b2Dot(dv, tangent);
float lambda = vcp.tangentMass * (-vt);
// b2Math.b2Clamp the accumulated force
float maxFriction = friction * vcp.normalImpulse;
float newImpulse = b2Math.b2Clamp(vcp.tangentImpulse + lambda, -maxFriction, maxFriction);
lambda = newImpulse - vcp.tangentImpulse;
vcp.tangentImpulse = newImpulse;
// Apply contact impulse
// P = lambda * tangent;
b2Vec2 P;
P.x = lambda * tangent.x;
P.y = lambda * tangent.y;
// vA -= mA * P;
vA.x -= mA * P.x;
vA.y -= mA * P.y;
// wA -= iA * b2Math.b2Cross(vcp.rA, P);
wA -= iA * (vcp.rA.x * P.y - vcp.rA.y * P.x);
// vB += mB * P;
vB.x += mB * P.x;
vB.y += mB * P.y;
// wB += iB * b2Math.b2Cross(vcp.rB, P);
wB += iB * (vcp.rB.x * P.y - vcp.rB.y * P.x);
//vc.points[j] = vcp;
}
// Solve normal constraints
if (vc.pointCount == 1)
{
b2VelocityConstraintPoint vcp = vc.points[0];
// Relative velocity at contact
// b2Vec2 dv = vB + b2Math.b2Cross(wB, ref vcp.rB) - vA - b2Math.b2Cross(wA, ref vcp.rA);
b2Vec2 dv;
dv.x = vB.x + (-wB * vcp.rB.y) - vA.x - (-wA * vcp.rA.y);
dv.y = vB.y + (wB * vcp.rB.x) - vA.y - (wA * vcp.rA.x);
// Compute normal impulse
float vn = dv.x * normal.x + dv.y * normal.y; //b2Math.b2Dot(ref dv, ref normal);
float lambda = -vcp.normalMass * (vn - vcp.velocityBias);
// b2Math.b2Clamp the accumulated impulse
float newImpulse = Math.Max(vcp.normalImpulse + lambda, 0.0f);
lambda = newImpulse - vcp.normalImpulse;
vcp.normalImpulse = newImpulse;
// Apply contact impulse
//b2Vec2 P = lambda * normal;
b2Vec2 P;
P.x = lambda * normal.x;
P.y = lambda * normal.y;
// vA -= mA * P;
vA.x -= mA * P.x;
vA.y -= mA * P.y;
// wA -= iA * b2Math.b2Cross(vcp.rA, P);
wA -= iA * (vcp.rA.x * P.y - vcp.rA.y * P.x);
// vB += mB * P;
vB.x += mB * P.x;
vB.y += mB * P.y;
// wB += iB * b2Math.b2Cross(vcp.rB, P);
wB += iB * (vcp.rB.x * P.y - vcp.rB.y * P.x);
//vc.points[0] = vcp;
}
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 = vn0 - 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 = a + d
//
// a := old total impulse
// x := new total impulse
// d := incremental impulse
//
// For the current iteration we extend the formula for the incremental impulse
// to compute the new total impulse:
//
// vn = A * d + b
// = A * (x - a) + b
// = A * x + b - A * a
// = A * x + b'
// b' = b - A * a;
b2VelocityConstraintPoint cp1 = vc.points[0];
b2VelocityConstraintPoint cp2 = vc.points[1];
b2Vec2 a = new b2Vec2(cp1.normalImpulse, cp2.normalImpulse);
Debug.Assert(a.x >= 0.0f && a.y >= 0.0f);
// Relative velocity at contact
// vB + b2Math.b2Cross(wB, ref cp1.rB) - vA - b2Math.b2Cross(wA, ref cp1.rA);
b2Vec2 dv1;
dv1.x = vB.x + (-wB * cp1.rB.y) - vA.x - (-wA * cp1.rA.y);
dv1.y = vB.y + (wB * cp1.rB.x) - vA.y - (wA * cp1.rA.x);
// vB + b2Math.b2Cross(wB, ref cp2.rB) - vA - b2Math.b2Cross(wA, ref cp2.rA);
b2Vec2 dv2;
dv2.x = vB.x + (-wB * cp2.rB.y) - vA.x - (-wA * cp2.rA.y);
dv2.y = vB.y + (wB * cp2.rB.x) - vA.y - (wA * cp2.rA.x);
// Compute normal velocity
float vn1 = dv1.x * normal.x + dv1.y * normal.y; // b2Math.b2Dot(ref dv1, ref normal);
float vn2 = dv2.x * normal.x + dv2.y * normal.y; // b2Math.b2Dot(ref dv2, ref normal);
b2Vec2 b;
b.x = vn1 - cp1.velocityBias;
b.y = vn2 - cp2.velocityBias;
// Compute b'
// (A.ex.x * v.x + A.ey.x * v.y, A.ex.y * v.x + A.ey.y * v.y)
b.x -= (vc.K.ex.x * a.x + vc.K.ey.x * a.y);
b.y -= (vc.K.ex.y * a.x + vc.K.ey.y * a.y);
// b -= b2Math.b2Mul(vc.K, a);
// float k_errorTol = 1e-3f;
#region Iteration
while (true)
{
//
// Case 1: vn = 0
//
// 0 = A * x + b'
//
// Solve for x:
//
// x = - inv(A) * b'
//
b2Vec2 x = -b2Math.b2Mul(ref vc.normalMass, ref b);
if (x.x >= 0.0f && x.y >= 0.0f)
{
// Get the incremental impulse
b2Vec2 d = x - a;
// Apply incremental impulse
b2Vec2 P1 = d.x * normal;
b2Vec2 P2 = d.y * normal;
vA -= mA * (P1 + P2);
wA -= iA * (b2Math.b2Cross(ref cp1.rA, ref P1) + b2Math.b2Cross(ref cp2.rA, ref P2));
vB += mB * (P1 + P2);
wB += iB * (b2Math.b2Cross(ref cp1.rB, ref P1) + b2Math.b2Cross(ref cp2.rB, ref P2));
// Accumulate
cp1.normalImpulse = x.x;
cp2.normalImpulse = x.y;
#if B2_DEBUG_SOLVER
// Postconditions
dv1 = vB + b2Math.b2Cross(wB, cp1.rB) - vA - b2Math.b2Cross(wA, cp1.rA);
dv2 = vB + b2Math.b2Cross(wB, cp2.rB) - vA - b2Math.b2Cross(wA, cp2.rA);
// Compute normal velocity
vn1 = b2Math.b2Dot(dv1, normal);
vn2 = b2Math.b2Dot(dv2, normal);
Debug.Assert(b2Abs(vn1 - cp1.velocityBias) < k_errorTol);
Debug.Assert(b2Abs(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 + b2'
//
x.x = -cp1.normalMass * b.x;
x.y = 0.0f;
vn1 = 0.0f;
vn2 = vc.K.ex.y * x.x + b.y;
if (x.x >= 0.0f && vn2 >= 0.0f)
{
// Get the incremental impulse
b2Vec2 d = x - a;
// Apply incremental impulse
b2Vec2 P1 = d.x * normal;
b2Vec2 P2 = d.y * normal;
vA -= mA * (P1 + P2);
wA -= iA * (b2Math.b2Cross(ref cp1.rA, ref P1) + b2Math.b2Cross(ref cp2.rA, ref P2));
vB += mB * (P1 + P2);
wB += iB * (b2Math.b2Cross(ref cp1.rB, ref P1) + b2Math.b2Cross(ref cp2.rB, ref P2));
// Accumulate
cp1.normalImpulse = x.x;
cp2.normalImpulse = x.y;
#if B2_DEBUG_SOLVER
// Postconditions
dv1 = vB + b2Math.b2Cross(wB, cp1.rB) - vA - b2Math.b2Cross(wA, cp1.rA);
// Compute normal velocity
vn1 = b2Math.b2Dot(dv1, normal);
Debug.Assert(b2Abs(vn1 - cp1.velocityBias) < k_errorTol);
#endif
break;
}
//
// Case 3: vn2 = 0 and x1 = 0
//
// vn1 = a11 * 0 + a12 * x2 + b1'
// 0 = a21 * 0 + a22 * x2 + b2'
//
x.x = 0.0f;
x.y = -cp2.normalMass * b.y;
vn1 = vc.K.ey.x * x.y + b.x;
vn2 = 0.0f;
if (x.y >= 0.0f && vn1 >= 0.0f)
{
// Resubstitute for the incremental impulse
b2Vec2 d = x - a;
// Apply incremental impulse
b2Vec2 P1 = d.x * normal;
b2Vec2 P2 = d.y * normal;
vA -= mA * (P1 + P2);
wA -= iA * (b2Math.b2Cross(ref cp1.rA, ref P1) + b2Math.b2Cross(ref cp2.rA, ref P2));
vB += mB * (P1 + P2);
wB += iB * (b2Math.b2Cross(ref cp1.rB, ref P1) + b2Math.b2Cross(ref cp2.rB, ref P2));
// Accumulate
cp1.normalImpulse = x.x;
cp2.normalImpulse = x.y;
#if B2_DEBUG_SOLVER
// Postconditions
dv2 = vB + b2Math.b2Cross(wB, cp2.rB) - vA - b2Math.b2Cross(wA, cp2.rA);
// Compute normal velocity
vn2 = b2Math.b2Dot(dv2, normal);
Debug.Assert(b2Abs(vn2 - cp2.velocityBias) < k_errorTol);
#endif
break;
}
//
// Case 4: x1 = 0 and x2 = 0
//
// vn1 = b1
// vn2 = b2;
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
b2Vec2 d = x - a;
// Apply incremental impulse
b2Vec2 P1 = d.x * normal;
b2Vec2 P2 = d.y * normal;
vA -= mA * (P1 + P2);
wA -= iA * (b2Math.b2Cross(ref cp1.rA, ref P1) + b2Math.b2Cross(ref cp2.rA, ref P2));
vB += mB * (P1 + P2);
wB += iB * (b2Math.b2Cross(ref cp1.rB, ref P1) + b2Math.b2Cross(ref cp2.rB, ref 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;
}
#endregion
//vc.points[0] = cp1;
//vc.points[1] = cp2;
}
m_velocities[indexA].v = vA;
m_velocities[indexA].w = wA;
m_velocities[indexB].v = vB;
m_velocities[indexB].w = wB;
//m_velocityConstraints[i] = vc;
}
}
// TODO_ERIN might not need to return the separation
public float Initialize(ref b2SimplexCache cache,
b2DistanceProxy proxyA, ref b2Sweep sweepA,
b2DistanceProxy proxyB, ref b2Sweep sweepB,
float t1)
{
m_proxyA = proxyA;
m_proxyB = proxyB;
int count = cache.count;
Debug.Assert(0 < count && count < 3);
m_sweepA = sweepA;
m_sweepB = sweepB;
b2Transform xfA, xfB;
m_sweepA.GetTransform(out xfA, t1);
m_sweepB.GetTransform(out xfB, t1);
if (count == 1)
{
m_type = SeparationType.e_points;
b2Vec2 localPointA = m_proxyA.GetVertex((int)cache.indexA[0]);
b2Vec2 localPointB = m_proxyB.GetVertex((int)cache.indexB[0]);
b2Vec2 pointA = b2Math.b2Mul(xfA, localPointA);
b2Vec2 pointB = b2Math.b2Mul(xfB, localPointB);
m_axis = pointB - pointA;
float s = m_axis.Normalize();
return(s);
}
else if (cache.indexA[0] == cache.indexA[1])
{
// Two points on B and one on A.
m_type = SeparationType.e_faceB;
b2Vec2 localPointB1 = proxyB.GetVertex((int)cache.indexB[0]);
b2Vec2 localPointB2 = proxyB.GetVertex((int)cache.indexB[1]);
float b21x = localPointB2.x - localPointB1.x;
float b21y = localPointB2.y - localPointB1.y;
m_axis.x = -b21y;
m_axis.y = b21x;
// m_axis = b2Math.b2Cross(localPointB2 - localPointB1, 1.0f);
m_axis.Normalize();
b2Vec2 normal = b2Math.b2Mul(xfB.q, m_axis);
m_localPoint = 0.5f * (localPointB1 + localPointB2);
b2Vec2 pointB = b2Math.b2Mul(xfB, m_localPoint);
b2Vec2 localPointA = proxyA.GetVertex((int)cache.indexA[0]);
b2Vec2 pointA = b2Math.b2Mul(xfA, localPointA);
b2Vec2 aminusb = pointA - pointB;
float s = b2Math.b2Dot(ref aminusb, ref normal);
if (s < 0.0f)
{
m_axis = -m_axis;
s = -s;
}
return(s);
}
else
{
// Two points on A and one or two points on B.
m_type = SeparationType.e_faceA;
b2Vec2 localPointA1 = m_proxyA.GetVertex(cache.indexA[0]);
b2Vec2 localPointA2 = m_proxyA.GetVertex(cache.indexA[1]);
b2Vec2 a2minusa1 = localPointA2 - localPointA1;
m_axis = a2minusa1.UnitCross();// b2Math.b2Cross(localPointA2 - localPointA1, 1.0f);
m_axis.Normalize();
b2Vec2 normal = b2Math.b2Mul(xfA.q, m_axis);
m_localPoint = 0.5f * (localPointA1 + localPointA2);
b2Vec2 pointA = b2Math.b2Mul(xfA, m_localPoint);
b2Vec2 localPointB = m_proxyB.GetVertex(cache.indexB[0]);
b2Vec2 pointB = b2Math.b2Mul(xfB, localPointB);
b2Vec2 bminusa = pointB - pointA;
float s = b2Math.b2Dot(ref bminusa, ref normal);
if (s < 0.0f)
{
m_axis = -m_axis;
s = -s;
}
return(s);
}
}
