b2MouseJoint.cpp
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上传日期:2022-01-07
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- /*
- * 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 <Box2D/Dynamics/Joints/b2MouseJoint.h>
- #include <Box2D/Dynamics/b2Body.h>
- #include <Box2D/Dynamics/b2TimeStep.h>
- // p = attached point, m = mouse point
- // C = p - m
- // Cdot = v
- // = v + cross(w, r)
- // J = [I r_skew]
- // Identity used:
- // w k % (rx i + ry j) = w * (-ry i + rx j)
- b2MouseJoint::b2MouseJoint(const b2MouseJointDef* def)
- : b2Joint(def)
- {
- b2Assert(def->target.IsValid());
- b2Assert(b2IsValid(def->maxForce) && def->maxForce >= 0.0f);
- b2Assert(b2IsValid(def->frequencyHz) && def->frequencyHz >= 0.0f);
- b2Assert(b2IsValid(def->dampingRatio) && def->dampingRatio >= 0.0f);
- m_target = def->target;
- m_localAnchor = b2MulT(m_bodyB->GetTransform(), m_target);
- m_maxForce = def->maxForce;
- m_impulse.SetZero();
- m_frequencyHz = def->frequencyHz;
- m_dampingRatio = def->dampingRatio;
- m_beta = 0.0f;
- m_gamma = 0.0f;
- }
- void b2MouseJoint::SetTarget(const b2Vec2& target)
- {
- if (m_bodyB->IsAwake() == false)
- {
- m_bodyB->SetAwake(true);
- }
- m_target = target;
- }
- const b2Vec2& b2MouseJoint::GetTarget() const
- {
- return m_target;
- }
- void b2MouseJoint::SetMaxForce(float32 force)
- {
- m_maxForce = force;
- }
- float32 b2MouseJoint::GetMaxForce() const
- {
- return m_maxForce;
- }
- void b2MouseJoint::SetFrequency(float32 hz)
- {
- m_frequencyHz = hz;
- }
- float32 b2MouseJoint::GetFrequency() const
- {
- return m_frequencyHz;
- }
- void b2MouseJoint::SetDampingRatio(float32 ratio)
- {
- m_dampingRatio = ratio;
- }
- float32 b2MouseJoint::GetDampingRatio() const
- {
- return m_dampingRatio;
- }
- void b2MouseJoint::InitVelocityConstraints(const b2TimeStep& step)
- {
- b2Body* b = m_bodyB;
- float32 mass = b->GetMass();
- // Frequency
- float32 omega = 2.0f * b2_pi * m_frequencyHz;
- // Damping coefficient
- float32 d = 2.0f * mass * m_dampingRatio * omega;
- // Spring stiffness
- float32 k = mass * (omega * omega);
- // magic formulas
- // gamma has units of inverse mass.
- // beta has units of inverse time.
- b2Assert(d + step.dt * k > b2_epsilon);
- m_gamma = step.dt * (d + step.dt * k);
- if (m_gamma != 0.0f)
- {
- m_gamma = 1.0f / m_gamma;
- }
- m_beta = step.dt * k * m_gamma;
- // Compute the effective mass matrix.
- b2Vec2 r = b2Mul(b->GetTransform().R, m_localAnchor - b->GetLocalCenter());
- // K = [(1/m1 + 1/m2) * eye(2) - skew(r1) * invI1 * skew(r1) - skew(r2) * invI2 * skew(r2)]
- // = [1/m1+1/m2 0 ] + invI1 * [r1.y*r1.y -r1.x*r1.y] + invI2 * [r1.y*r1.y -r1.x*r1.y]
- // [ 0 1/m1+1/m2] [-r1.x*r1.y r1.x*r1.x] [-r1.x*r1.y r1.x*r1.x]
- float32 invMass = b->m_invMass;
- float32 invI = b->m_invI;
- b2Mat22 K1;
- K1.col1.x = invMass; K1.col2.x = 0.0f;
- K1.col1.y = 0.0f; K1.col2.y = invMass;
- b2Mat22 K2;
- K2.col1.x = invI * r.y * r.y; K2.col2.x = -invI * r.x * r.y;
- K2.col1.y = -invI * r.x * r.y; K2.col2.y = invI * r.x * r.x;
- b2Mat22 K = K1 + K2;
- K.col1.x += m_gamma;
- K.col2.y += m_gamma;
- m_mass = K.GetInverse();
- m_C = b->m_sweep.c + r - m_target;
- // Cheat with some damping
- b->m_angularVelocity *= 0.98f;
- // Warm starting.
- m_impulse *= step.dtRatio;
- b->m_linearVelocity += invMass * m_impulse;
- b->m_angularVelocity += invI * b2Cross(r, m_impulse);
- }
- void b2MouseJoint::SolveVelocityConstraints(const b2TimeStep& step)
- {
- b2Body* b = m_bodyB;
- b2Vec2 r = b2Mul(b->GetTransform().R, m_localAnchor - b->GetLocalCenter());
- // Cdot = v + cross(w, r)
- b2Vec2 Cdot = b->m_linearVelocity + b2Cross(b->m_angularVelocity, r);
- b2Vec2 impulse = b2Mul(m_mass, -(Cdot + m_beta * m_C + m_gamma * m_impulse));
- b2Vec2 oldImpulse = m_impulse;
- m_impulse += impulse;
- float32 maxImpulse = step.dt * m_maxForce;
- if (m_impulse.LengthSquared() > maxImpulse * maxImpulse)
- {
- m_impulse *= maxImpulse / m_impulse.Length();
- }
- impulse = m_impulse - oldImpulse;
- b->m_linearVelocity += b->m_invMass * impulse;
- b->m_angularVelocity += b->m_invI * b2Cross(r, impulse);
- }
- b2Vec2 b2MouseJoint::GetAnchorA() const
- {
- return m_target;
- }
- b2Vec2 b2MouseJoint::GetAnchorB() const
- {
- return m_bodyB->GetWorldPoint(m_localAnchor);
- }
- b2Vec2 b2MouseJoint::GetReactionForce(float32 inv_dt) const
- {
- return inv_dt * m_impulse;
- }
- float32 b2MouseJoint::GetReactionTorque(float32 inv_dt) const
- {
- return inv_dt * 0.0f;
- }