--- /dev/null
+/*
+* Copyright (c) 2006-2007 Erin Catto http://www.gphysics.com
+*
+* 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.
+*/
+
+#include "b2DistanceJoint.h"
+#include "../b2Body.h"
+#include "../b2World.h"
+
+// 1-D constrained system
+// m (v2 - v1) = lambda
+// v2 + (beta/h) * x1 + gamma * lambda = 0, gamma has units of inverse mass.
+// x2 = x1 + h * v2
+
+// 1-D mass-damper-spring system
+// m (v2 - v1) + h * d * v2 + h * k *
+
+// 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
+
+void b2DistanceJointDef::Initialize(b2Body* b1, b2Body* b2,
+ const b2Vec2& anchor1, const b2Vec2& anchor2)
+{
+ body1 = b1;
+ body2 = b2;
+ localAnchor1 = body1->GetLocalPoint(anchor1);
+ localAnchor2 = body2->GetLocalPoint(anchor2);
+ b2Vec2 d = anchor2 - anchor1;
+ length = d.Length();
+}
+
+
+b2DistanceJoint::b2DistanceJoint(const b2DistanceJointDef* def)
+: b2Joint(def)
+{
+ m_localAnchor1 = def->localAnchor1;
+ m_localAnchor2 = def->localAnchor2;
+ m_length = def->length;
+ m_frequencyHz = def->frequencyHz;
+ m_dampingRatio = def->dampingRatio;
+ m_impulse = 0.0f;
+ m_gamma = 0.0f;
+ m_bias = 0.0f;
+ m_inv_dt = 0.0f;
+}
+
+void b2DistanceJoint::InitVelocityConstraints(const b2TimeStep& step)
+{
+ m_inv_dt = step.inv_dt;
+
+ b2Body* b1 = m_body1;
+ b2Body* b2 = m_body2;
+
+ // Compute the effective mass matrix.
+ b2Vec2 r1 = b2Mul(b1->GetXForm().R, m_localAnchor1 - b1->GetLocalCenter());
+ b2Vec2 r2 = b2Mul(b2->GetXForm().R, m_localAnchor2 - b2->GetLocalCenter());
+ m_u = b2->m_sweep.c + r2 - b1->m_sweep.c - r1;
+
+ // Handle singularity.
+ float32 length = m_u.Length();
+ if (length > b2_linearSlop)
+ {
+ m_u *= 1.0f / length;
+ }
+ else
+ {
+ m_u.Set(0.0f, 0.0f);
+ }
+
+ float32 cr1u = b2Cross(r1, m_u);
+ float32 cr2u = b2Cross(r2, m_u);
+ float32 invMass = b1->m_invMass + b1->m_invI * cr1u * cr1u + b2->m_invMass + b2->m_invI * cr2u * cr2u;
+ b2Assert(invMass > B2_FLT_EPSILON);
+ m_mass = 1.0f / invMass;
+
+ if (m_frequencyHz > 0.0f)
+ {
+ float32 C = length - m_length;
+
+ // Frequency
+ float32 omega = 2.0f * b2_pi * m_frequencyHz;
+
+ // Damping coefficient
+ float32 d = 2.0f * m_mass * m_dampingRatio * omega;
+
+ // Spring stiffness
+ float32 k = m_mass * omega * omega;
+
+ // magic formulas
+ m_gamma = 1.0f / (step.dt * (d + step.dt * k));
+ m_bias = C * step.dt * k * m_gamma;
+
+ m_mass = 1.0f / (invMass + m_gamma);
+ }
+
+ if (step.warmStarting)
+ {
+ m_impulse *= step.dtRatio;
+ b2Vec2 P = m_impulse * m_u;
+ b1->m_linearVelocity -= b1->m_invMass * P;
+ b1->m_angularVelocity -= b1->m_invI * b2Cross(r1, P);
+ b2->m_linearVelocity += b2->m_invMass * P;
+ b2->m_angularVelocity += b2->m_invI * b2Cross(r2, P);
+ }
+ else
+ {
+ m_impulse = 0.0f;
+ }
+}
+
+void b2DistanceJoint::SolveVelocityConstraints(const b2TimeStep& step)
+{
+ B2_NOT_USED(step);
+
+ b2Body* b1 = m_body1;
+ b2Body* b2 = m_body2;
+
+ b2Vec2 r1 = b2Mul(b1->GetXForm().R, m_localAnchor1 - b1->GetLocalCenter());
+ b2Vec2 r2 = b2Mul(b2->GetXForm().R, m_localAnchor2 - b2->GetLocalCenter());
+
+ // Cdot = dot(u, v + cross(w, r))
+ b2Vec2 v1 = b1->m_linearVelocity + b2Cross(b1->m_angularVelocity, r1);
+ b2Vec2 v2 = b2->m_linearVelocity + b2Cross(b2->m_angularVelocity, r2);
+ float32 Cdot = b2Dot(m_u, v2 - v1);
+
+ float32 impulse = -m_mass * (Cdot + m_bias + m_gamma * m_impulse);
+ m_impulse += impulse;
+
+ b2Vec2 P = impulse * m_u;
+ b1->m_linearVelocity -= b1->m_invMass * P;
+ b1->m_angularVelocity -= b1->m_invI * b2Cross(r1, P);
+ b2->m_linearVelocity += b2->m_invMass * P;
+ b2->m_angularVelocity += b2->m_invI * b2Cross(r2, P);
+}
+
+bool b2DistanceJoint::SolvePositionConstraints()
+{
+ if (m_frequencyHz > 0.0f)
+ {
+ return true;
+ }
+
+ b2Body* b1 = m_body1;
+ b2Body* b2 = m_body2;
+
+ b2Vec2 r1 = b2Mul(b1->GetXForm().R, m_localAnchor1 - b1->GetLocalCenter());
+ b2Vec2 r2 = b2Mul(b2->GetXForm().R, m_localAnchor2 - b2->GetLocalCenter());
+
+ b2Vec2 d = b2->m_sweep.c + r2 - b1->m_sweep.c - r1;
+
+ float32 length = d.Normalize();
+ float32 C = length - m_length;
+ C = b2Clamp(C, -b2_maxLinearCorrection, b2_maxLinearCorrection);
+
+ float32 impulse = -m_mass * C;
+ m_u = d;
+ b2Vec2 P = impulse * m_u;
+
+ b1->m_sweep.c -= b1->m_invMass * P;
+ b1->m_sweep.a -= b1->m_invI * b2Cross(r1, P);
+ b2->m_sweep.c += b2->m_invMass * P;
+ b2->m_sweep.a += b2->m_invI * b2Cross(r2, P);
+
+ b1->SynchronizeTransform();
+ b2->SynchronizeTransform();
+
+ return b2Abs(C) < b2_linearSlop;
+}
+
+b2Vec2 b2DistanceJoint::GetAnchor1() const
+{
+ return m_body1->GetWorldPoint(m_localAnchor1);
+}
+
+b2Vec2 b2DistanceJoint::GetAnchor2() const
+{
+ return m_body2->GetWorldPoint(m_localAnchor2);
+}
+
+b2Vec2 b2DistanceJoint::GetReactionForce() const
+{
+ b2Vec2 F = (m_inv_dt * m_impulse) * m_u;
+ return F;
+}
+
+float32 b2DistanceJoint::GetReactionTorque() const
+{
+ return 0.0f;
+}
projects / blok / blobdiff