physics_particle_get_damping()
返回： Real（实数）
With this function you can find out what the current linear
damping is for particles in the physics simulation (you can set
this value using physics_particle_set_damping()).
if physics_particle_get_damping() < 1
{
physics_particle_set_damping(physics_particle_get_damping() + 0.01);
}
The above code will check the current damping value for all particles in the system and if it is less than 1 then it will add 0.01 to it.