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Diffstat (limited to 'Client/ThirdParty/Box2D/src/dynamics/b2_contact_solver.cpp')
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diff --git a/Client/ThirdParty/Box2D/src/dynamics/b2_contact_solver.cpp b/Client/ThirdParty/Box2D/src/dynamics/b2_contact_solver.cpp new file mode 100644 index 0000000..e6f432a --- /dev/null +++ b/Client/ThirdParty/Box2D/src/dynamics/b2_contact_solver.cpp @@ -0,0 +1,843 @@ +// MIT License + +// Copyright (c) 2019 Erin Catto + +// Permission is hereby granted, free of charge, to any person obtaining a copy +// of this software and associated documentation files (the "Software"), to deal +// in the Software without restriction, including without limitation the rights +// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell +// copies of the Software, and to permit persons to whom the Software is +// furnished to do so, subject to the following conditions: + +// The above copyright notice and this permission notice shall be included in all +// copies or substantial portions of the Software. + +// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR +// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, +// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE +// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER +// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, +// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE +// SOFTWARE. + +#include "b2_contact_solver.h" + +#include "box2d/b2_body.h" +#include "box2d/b2_contact.h" +#include "box2d/b2_fixture.h" +#include "box2d/b2_stack_allocator.h" +#include "box2d/b2_world.h" + +// Solver debugging is normally disabled because the block solver sometimes has to deal with a poorly conditioned effective mass matrix. +#define B2_DEBUG_SOLVER 0 + +B2_API bool g_blockSolve = true; + +struct b2ContactPositionConstraint +{ + b2Vec2 localPoints[b2_maxManifoldPoints]; + b2Vec2 localNormal; + b2Vec2 localPoint; + int32 indexA; + int32 indexB; + float invMassA, invMassB; + b2Vec2 localCenterA, localCenterB; + float invIA, invIB; + b2Manifold::Type type; + float radiusA, radiusB; + int32 pointCount; +}; + +b2ContactSolver::b2ContactSolver(b2ContactSolverDef* def) +{ + m_step = def->step; + m_allocator = def->allocator; + m_count = def->count; + m_positionConstraints = (b2ContactPositionConstraint*)m_allocator->Allocate(m_count * sizeof(b2ContactPositionConstraint)); + m_velocityConstraints = (b2ContactVelocityConstraint*)m_allocator->Allocate(m_count * sizeof(b2ContactVelocityConstraint)); + m_positions = def->positions; + m_velocities = def->velocities; + m_contacts = def->contacts; + + // Initialize position independent portions of the constraints. + for (int32 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(); + + int32 pointCount = manifold->pointCount; + b2Assert(pointCount > 0); + + b2ContactVelocityConstraint* vc = m_velocityConstraints + i; + vc->friction = contact->m_friction; + vc->restitution = contact->m_restitution; + vc->threshold = contact->m_restitutionThreshold; + 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 (int32 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; + } + } +} + +b2ContactSolver::~b2ContactSolver() +{ + m_allocator->Free(m_velocityConstraints); + m_allocator->Free(m_positionConstraints); +} + +// Initialize position dependent portions of the velocity constraints. +void b2ContactSolver::InitializeVelocityConstraints() +{ + for (int32 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(); + + int32 indexA = vc->indexA; + int32 indexB = vc->indexB; + + float mA = vc->invMassA; + float mB = vc->invMassB; + float iA = vc->invIA; + float iB = vc->invIB; + b2Vec2 localCenterA = pc->localCenterA; + b2Vec2 localCenterB = 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; + + b2Assert(manifold->pointCount > 0); + + b2Transform xfA, xfB; + xfA.q.Set(aA); + xfB.q.Set(aB); + xfA.p = cA - b2Mul(xfA.q, localCenterA); + xfB.p = cB - b2Mul(xfB.q, localCenterB); + + b2WorldManifold worldManifold; + worldManifold.Initialize(manifold, xfA, radiusA, xfB, radiusB); + + vc->normal = worldManifold.normal; + + int32 pointCount = vc->pointCount; + for (int32 j = 0; j < pointCount; ++j) + { + b2VelocityConstraintPoint* vcp = vc->points + j; + + vcp->rA = worldManifold.points[j] - cA; + vcp->rB = worldManifold.points[j] - cB; + + float rnA = b2Cross(vcp->rA, vc->normal); + float rnB = 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 = b2Cross(vc->normal, 1.0f); + + float rtA = b2Cross(vcp->rA, tangent); + float rtB = 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 = b2Dot(vc->normal, vB + b2Cross(wB, vcp->rB) - vA - b2Cross(wA, vcp->rA)); + if (vRel < -vc->threshold) + { + vcp->velocityBias = -vc->restitution * vRel; + } + } + + // If we have two points, then prepare the block solver. + if (vc->pointCount == 2 && g_blockSolve) + { + b2VelocityConstraintPoint* vcp1 = vc->points + 0; + b2VelocityConstraintPoint* vcp2 = vc->points + 1; + + float rn1A = b2Cross(vcp1->rA, vc->normal); + float rn1B = b2Cross(vcp1->rB, vc->normal); + float rn2A = b2Cross(vcp2->rA, vc->normal); + float rn2B = 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; + } + } + } +} + +void b2ContactSolver::WarmStart() +{ + // Warm start. + for (int32 i = 0; i < m_count; ++i) + { + b2ContactVelocityConstraint* vc = m_velocityConstraints + i; + + int32 indexA = vc->indexA; + int32 indexB = vc->indexB; + float mA = vc->invMassA; + float iA = vc->invIA; + float mB = vc->invMassB; + float iB = vc->invIB; + int32 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 = b2Cross(normal, 1.0f); + + for (int32 j = 0; j < pointCount; ++j) + { + b2VelocityConstraintPoint* vcp = vc->points + j; + b2Vec2 P = vcp->normalImpulse * normal + vcp->tangentImpulse * tangent; + wA -= iA * b2Cross(vcp->rA, P); + vA -= mA * P; + wB += iB * b2Cross(vcp->rB, P); + vB += mB * P; + } + + m_velocities[indexA].v = vA; + m_velocities[indexA].w = wA; + m_velocities[indexB].v = vB; + m_velocities[indexB].w = wB; + } +} + +void b2ContactSolver::SolveVelocityConstraints() +{ + for (int32 i = 0; i < m_count; ++i) + { + b2ContactVelocityConstraint* vc = m_velocityConstraints + i; + + int32 indexA = vc->indexA; + int32 indexB = vc->indexB; + float mA = vc->invMassA; + float iA = vc->invIA; + float mB = vc->invMassB; + float iB = vc->invIB; + int32 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 = b2Cross(normal, 1.0f); + float friction = vc->friction; + + b2Assert(pointCount == 1 || pointCount == 2); + + // Solve tangent constraints first because non-penetration is more important + // than friction. + for (int32 j = 0; j < pointCount; ++j) + { + b2VelocityConstraintPoint* vcp = vc->points + j; + + // Relative velocity at contact + b2Vec2 dv = vB + b2Cross(wB, vcp->rB) - vA - b2Cross(wA, vcp->rA); + + // Compute tangent force + float vt = b2Dot(dv, tangent) - vc->tangentSpeed; + float lambda = vcp->tangentMass * (-vt); + + // b2Clamp the accumulated force + float maxFriction = friction * vcp->normalImpulse; + float newImpulse = b2Clamp(vcp->tangentImpulse + lambda, -maxFriction, maxFriction); + lambda = newImpulse - vcp->tangentImpulse; + vcp->tangentImpulse = newImpulse; + + // Apply contact impulse + b2Vec2 P = lambda * tangent; + + vA -= mA * P; + wA -= iA * b2Cross(vcp->rA, P); + + vB += mB * P; + wB += iB * b2Cross(vcp->rB, P); + } + + // Solve normal constraints + if (pointCount == 1 || g_blockSolve == false) + { + for (int32 j = 0; j < pointCount; ++j) + { + b2VelocityConstraintPoint* vcp = vc->points + j; + + // Relative velocity at contact + b2Vec2 dv = vB + b2Cross(wB, vcp->rB) - vA - b2Cross(wA, vcp->rA); + + // Compute normal impulse + float vn = b2Dot(dv, normal); + float lambda = -vcp->normalMass * (vn - vcp->velocityBias); + + // b2Clamp the accumulated impulse + float newImpulse = b2Max(vcp->normalImpulse + lambda, 0.0f); + lambda = newImpulse - vcp->normalImpulse; + vcp->normalImpulse = newImpulse; + + // Apply contact impulse + b2Vec2 P = lambda * normal; + vA -= mA * P; + wA -= iA * b2Cross(vcp->rA, P); + + vB += mB * P; + wB += iB * b2Cross(vcp->rB, P); + } + } + 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, 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(cp1->normalImpulse, cp2->normalImpulse); + b2Assert(a.x >= 0.0f && a.y >= 0.0f); + + // Relative velocity at contact + b2Vec2 dv1 = vB + b2Cross(wB, cp1->rB) - vA - b2Cross(wA, cp1->rA); + b2Vec2 dv2 = vB + b2Cross(wB, cp2->rB) - vA - b2Cross(wA, cp2->rA); + + // Compute normal velocity + float vn1 = b2Dot(dv1, normal); + float vn2 = b2Dot(dv2, normal); + + b2Vec2 b; + b.x = vn1 - cp1->velocityBias; + b.y = vn2 - cp2->velocityBias; + + // Compute b' + b -= b2Mul(vc->K, a); + + const 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' + // + b2Vec2 x = - b2Mul(vc->normalMass, 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 * (b2Cross(cp1->rA, P1) + b2Cross(cp2->rA, P2)); + + vB += mB * (P1 + P2); + wB += iB * (b2Cross(cp1->rB, P1) + b2Cross(cp2->rB, P2)); + + // Accumulate + cp1->normalImpulse = x.x; + cp2->normalImpulse = x.y; + +#if B2_DEBUG_SOLVER == 1 + // Postconditions + dv1 = vB + b2Cross(wB, cp1->rB) - vA - b2Cross(wA, cp1->rA); + dv2 = vB + b2Cross(wB, cp2->rB) - vA - b2Cross(wA, cp2->rA); + + // Compute normal velocity + vn1 = b2Dot(dv1, normal); + vn2 = b2Dot(dv2, normal); + + b2Assert(b2Abs(vn1 - cp1->velocityBias) < k_errorTol); + b2Assert(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 * (b2Cross(cp1->rA, P1) + b2Cross(cp2->rA, P2)); + + vB += mB * (P1 + P2); + wB += iB * (b2Cross(cp1->rB, P1) + b2Cross(cp2->rB, P2)); + + // Accumulate + cp1->normalImpulse = x.x; + cp2->normalImpulse = x.y; + +#if B2_DEBUG_SOLVER == 1 + // Postconditions + dv1 = vB + b2Cross(wB, cp1->rB) - vA - b2Cross(wA, cp1->rA); + + // Compute normal velocity + vn1 = b2Dot(dv1, normal); + + b2Assert(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 * (b2Cross(cp1->rA, P1) + b2Cross(cp2->rA, P2)); + + vB += mB * (P1 + P2); + wB += iB * (b2Cross(cp1->rB, P1) + b2Cross(cp2->rB, P2)); + + // Accumulate + cp1->normalImpulse = x.x; + cp2->normalImpulse = x.y; + +#if B2_DEBUG_SOLVER == 1 + // Postconditions + dv2 = vB + b2Cross(wB, cp2->rB) - vA - b2Cross(wA, cp2->rA); + + // Compute normal velocity + vn2 = b2Dot(dv2, normal); + + b2Assert(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 * (b2Cross(cp1->rA, P1) + b2Cross(cp2->rA, P2)); + + vB += mB * (P1 + P2); + wB += iB * (b2Cross(cp1->rB, P1) + b2Cross(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; + } + } + + m_velocities[indexA].v = vA; + m_velocities[indexA].w = wA; + m_velocities[indexB].v = vB; + m_velocities[indexB].w = wB; + } +} + +void b2ContactSolver::StoreImpulses() +{ + for (int32 i = 0; i < m_count; ++i) + { + b2ContactVelocityConstraint* vc = m_velocityConstraints + i; + b2Manifold* manifold = m_contacts[vc->contactIndex]->GetManifold(); + + for (int32 j = 0; j < vc->pointCount; ++j) + { + manifold->points[j].normalImpulse = vc->points[j].normalImpulse; + manifold->points[j].tangentImpulse = vc->points[j].tangentImpulse; + } + } +} + +struct b2PositionSolverManifold +{ + void Initialize(b2ContactPositionConstraint* pc, const b2Transform& xfA, const b2Transform& xfB, int32 index) + { + b2Assert(pc->pointCount > 0); + + switch (pc->type) + { + case b2Manifold::e_circles: + { + b2Vec2 pointA = b2Mul(xfA, pc->localPoint); + b2Vec2 pointB = b2Mul(xfB, pc->localPoints[0]); + normal = pointB - pointA; + normal.Normalize(); + point = 0.5f * (pointA + pointB); + separation = b2Dot(pointB - pointA, normal) - pc->radiusA - pc->radiusB; + } + break; + + case b2Manifold::e_faceA: + { + normal = b2Mul(xfA.q, pc->localNormal); + b2Vec2 planePoint = b2Mul(xfA, pc->localPoint); + + b2Vec2 clipPoint = b2Mul(xfB, pc->localPoints[index]); + separation = b2Dot(clipPoint - planePoint, normal) - pc->radiusA - pc->radiusB; + point = clipPoint; + } + break; + + case b2Manifold::e_faceB: + { + normal = b2Mul(xfB.q, pc->localNormal); + b2Vec2 planePoint = b2Mul(xfB, pc->localPoint); + + b2Vec2 clipPoint = b2Mul(xfA, pc->localPoints[index]); + separation = b2Dot(clipPoint - planePoint, normal) - pc->radiusA - pc->radiusB; + point = clipPoint; + + // Ensure normal points from A to B + normal = -normal; + } + break; + } + } + + b2Vec2 normal; + b2Vec2 point; + float separation; +}; + +// Sequential solver. +bool b2ContactSolver::SolvePositionConstraints() +{ + float minSeparation = 0.0f; + + for (int32 i = 0; i < m_count; ++i) + { + b2ContactPositionConstraint* pc = m_positionConstraints + i; + + int32 indexA = pc->indexA; + int32 indexB = pc->indexB; + b2Vec2 localCenterA = pc->localCenterA; + float mA = pc->invMassA; + float iA = pc->invIA; + b2Vec2 localCenterB = pc->localCenterB; + float mB = pc->invMassB; + float iB = pc->invIB; + int32 pointCount = pc->pointCount; + + 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 (int32 j = 0; j < pointCount; ++j) + { + b2Transform xfA, xfB; + xfA.q.Set(aA); + xfB.q.Set(aB); + xfA.p = cA - b2Mul(xfA.q, localCenterA); + xfB.p = cB - b2Mul(xfB.q, localCenterB); + + b2PositionSolverManifold psm; + psm.Initialize(pc, xfA, xfB, j); + b2Vec2 normal = psm.normal; + + b2Vec2 point = psm.point; + float separation = psm.separation; + + b2Vec2 rA = point - cA; + b2Vec2 rB = point - cB; + + // Track max constraint error. + minSeparation = b2Min(minSeparation, separation); + + // Prevent large corrections and allow slop. + float C = b2Clamp(b2_baumgarte * (separation + b2_linearSlop), -b2_maxLinearCorrection, 0.0f); + + // Compute the effective mass. + float rnA = b2Cross(rA, normal); + float rnB = 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 * b2Cross(rA, P); + + cB += mB * P; + aB += iB * 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 >= -3.0f * b2_linearSlop; +} + +// Sequential position solver for position constraints. +bool b2ContactSolver::SolveTOIPositionConstraints(int32 toiIndexA, int32 toiIndexB) +{ + float minSeparation = 0.0f; + + for (int32 i = 0; i < m_count; ++i) + { + b2ContactPositionConstraint* pc = m_positionConstraints + i; + + int32 indexA = pc->indexA; + int32 indexB = pc->indexB; + b2Vec2 localCenterA = pc->localCenterA; + b2Vec2 localCenterB = pc->localCenterB; + int32 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.; + 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 (int32 j = 0; j < pointCount; ++j) + { + b2Transform xfA, xfB; + xfA.q.Set(aA); + xfB.q.Set(aB); + xfA.p = cA - b2Mul(xfA.q, localCenterA); + xfB.p = cB - b2Mul(xfB.q, localCenterB); + + b2PositionSolverManifold psm; + psm.Initialize(pc, xfA, xfB, j); + b2Vec2 normal = psm.normal; + + b2Vec2 point = psm.point; + float separation = psm.separation; + + b2Vec2 rA = point - cA; + b2Vec2 rB = point - cB; + + // Track max constraint error. + minSeparation = b2Min(minSeparation, separation); + + // Prevent large corrections and allow slop. + float C = b2Clamp(b2_toiBaumgarte * (separation + b2_linearSlop), -b2_maxLinearCorrection, 0.0f); + + // Compute the effective mass. + float rnA = b2Cross(rA, normal); + float rnB = 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 * b2Cross(rA, P); + + cB += mB * P; + aB += iB * 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 * b2_linearSlop; +} |