physics_particle_get_max_count()
返回： Real（实数）
With this function you can find out what the current cap value
is on particles permitted in the physics simulation (you can set
this value using physics_particle_set_max_count()).
if physics_particle_count() < physics_particle_get_max_count()
{
physics_particle_create(0, x, y, 0, 0, c_white, 1, 1)
}
The above code will check to see if there are less than the maximum number of permitted particles in the room, and if so create one more.