void Body::ResetMassData()
{
// Compute mass data from shapes. Each shape has its own density.
m_mass = 0.0f;
m_invMass = 0.0f;
m_I = 0.0f;
m_invI = 0.0f;
m_sweep.localCenter = glm::vec2(0.0f,0.0f);
// Static and kinematic bodies have zero mass.
if (m_type == staticBody || m_type == kinematicBody)
{
m_sweep.c0 = m_xf.p;
m_sweep.c = m_xf.p;
m_sweep.a0 = m_sweep.a;
return;
}
assert(m_type == dynamicBody);
// Accumulate mass over all fixtures.
glm::vec2 localCenter = glm::vec2(0.0f,0.0f);
for (Fixture* f = m_fixtureList; f; f = f->m_next)
{
if (f->m_density == 0.0f)
{
continue;
}
MassData massData;
f->GetMassData(&massData);
m_mass += massData.mass;
localCenter += massData.mass * massData.center;
m_I += massData.I;
}
// Compute center of mass.
if (m_mass > 0.0f)
{
m_invMass = 1.0f / m_mass;
localCenter *= m_invMass;
}
else
{
// Force all dynamic bodies to have a positive mass.
m_mass = 1.0f;
m_invMass = 1.0f;
}
if (m_I > 0.0f && (m_flags & fixedRotationFlag) == 0)
{
// Center the inertia about the center of mass.
m_I -= m_mass * glm::dot(localCenter, localCenter);
assert(m_I > 0.0f);
m_invI = 1.0f / m_I;
}
else
{
m_I = 0.0f;
m_invI = 0.0f;
}
// Move center of mass.
glm::vec2 oldCenter = m_sweep.c;
m_sweep.localCenter = localCenter;
m_sweep.c0 = m_sweep.c = Physics::Transform2D::Mul(m_xf, m_sweep.localCenter);
// Update center of mass velocity.
m_linearVelocity += MathUtils::Cross2(m_angularVelocity, m_sweep.c - oldCenter);
}
