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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 "b2MouseJoint.h"
#include "../b2Body.h"
#include "../b2World.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)
{
m_target = def->target;
m_localAnchor = b2MulT(m_body2->GetXForm(), 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_body2->IsSleeping())
{
m_body2->WakeUp();
}
m_target = target;
}
void b2MouseJoint::InitVelocityConstraints(const b2TimeStep& step)
{
b2Body* b = m_body2;
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_FLT_EPSILON);
m_gamma = 1.0f / (step.dt * (d + step.dt * k));
m_beta = step.dt * k * m_gamma;
// Compute the effective mass matrix.
b2Vec2 r = b2Mul(b->GetXForm().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_body2;
b2Vec2 r = b2Mul(b->GetXForm().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::GetAnchor1() const
{
return m_target;
}
b2Vec2 b2MouseJoint::GetAnchor2() const
{
return m_body2->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;
}
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