private void GetBodyPositionVelocityForce(out Vector2 position, out Vector2 velocity, out Vector2 force)
{
float inverse_count = 1.0f / count;
position.X = 0;
position.Y = 0;
velocity.X = 0;
velocity.Y = 0;
force.X = 0;
force.Y = 0;
for (int i = 0; i < count; i++)
{
position.X += pointmass_list[i].position.X * inverse_count;
position.Y += pointmass_list[i].position.Y * inverse_count;
velocity.X += pointmass_list[i].velocity.X * inverse_count;
velocity.Y += pointmass_list[i].velocity.Y * inverse_count;
force.X += pointmass_list[i].force.X * inverse_count;
force.Y += pointmass_list[i].force.Y * inverse_count;
}
}