I'm working on a game project about a top down car game in 2d. I want to manage all the physics by myself. Im working with this book : http://www.amazon.fr/Game-Physics-Engine-Development-Commercial-Grade/dp/0123819768 to implement the physics.
From now my physic engine can handle force on the different cardinal axes. But I have some issues to implement a correct simulation of rotation. Im trying to implement some torque to find angular acceleration. So I implemented an inertia tensor matrix :
setMass(400.f);
Matrix3 it;
it.setBlockInertiaTensor(Vector3(2, 1, 1), 400);
setInertiaTensor(it);
void setBlockInertiaTensor(const Vector3 &halfSizes, float mass)
{
Vector3 squares = halfSizes.componentProduct(halfSizes);
setInertiaTensorCoeffs(0.3f*mass*(squares.y + squares.z),
0.3f*mass*(squares.x + squares.z),
0.3f*mass*(squares.x + squares.y));
}
To apply torque I apply a force on a body point of my car and I find the torque by a cross product :
The meaning of this is to simulate the steering :
player->addForceAtBodyPoint(Vector3(-2000, 1000, 0), Vector3(0, 100, 0));
void AObject::addForceAtBodyPoint(const Vector3 &force, const Vector3 &point)
{
Vector3 pt = getPointInWorldSpace(point);
addForceAtPoint(force, pt);
}
void AObject::addForceAtPoint(const Vector3 &force,
const Vector3 &point)
{
// Convert to coordinates relative to center of mass.
Vector3 pt = point;
pt -= _position;
_forceAccumulate += force;
_torqueAccumulate += pt % force;
//std::cout << "torque x " << pt.x << " y " << pt.y << " z "<< pt.z << std::endl;
}
Vector3 Vector3::operator%(const Vector3 &vector) const
{
return Vector3(y*vector.z - z*vector.y,
z*vector.x - x*vector.z,
x*vector.y - y*vector.x);
}
The overload of modulo is the cross product
And finally I do the integration of all the physics data (forces and torques)
void Player::integrate(float deltaTime)
{
addForce(_velocity * -150.0f);
// Calculate linear acceleration from force inputs.
_lastFrameAcceleration = _acceleration;
_lastFrameAcceleration.addScaledVector(_forceAccumulate, _inverseMass);
// Calculate angular acceleration from torque inputs.
Vector3 angularAcceleration = _inverseInertiaTensorWorld.transform(_torqueAccumulate);
// Update linear velocity from acceleration .
_velocity.addScaledVector(_lastFrameAcceleration, deltaTime);
// Update angular velocity from acceleration .
_rotation.addScaledVector(angularAcceleration, deltaTime);
// Impose drag.
_velocity *= pow(_linearDamping, deltaTime);
_rotation *= pow(_angularDamping, deltaTime);
// Update linear position.
_position.addScaledVector(_velocity, deltaTime);
_position.z = 0;
// Update angular position
_orientation.addScaledVector(_rotation, deltaTime);
// Normalise the orientation, and update the matrice
calculateWorldLocalData();
// Clear accumulators.
clearAccumulator();
}
And the orientation is not working at all. Im not that good with physics stuff, so I think that im misunderstanding the physic implementation of torque with inertia tensor...
Thank you for your help.
